JP2010191009A - Photomask and method for manufacturing the same - Google Patents

Abstract

An ArF excimer laser is used as an exposure light source and is used for projection exposure by modified illumination, and a transfer image with high contrast of the main pattern is formed without resolving the auxiliary pattern while maintaining the effect of expanding the depth of focus as the auxiliary pattern. Provided are a halftone mask having an auxiliary pattern and a method of manufacturing the same.
A photomask is provided with a main pattern transferred onto a transfer target surface by projection exposure and an auxiliary pattern formed in the vicinity of the main pattern and not transferred. It is composed of a translucent film made of the same material, which causes a phase difference of 180 degrees between the light transmitted through the main pattern and the light transmitted through the transparent area of the transparent substrate, and the light transmitted through the auxiliary pattern and the transparent substrate. A predetermined phase difference in the range of 70 to 115 degrees is generated in the light transmitted through the transparent region.
[Selection] Figure 1

Description

  The present invention relates to a photomask for use in a photolithography technique using an exposure light source of a short wavelength, such as an excimer laser exposure apparatus used for pattern formation of a semiconductor element, and a manufacturing method thereof, and in particular, assists in the vicinity of a main pattern. The present invention relates to a halftone photomask having a pattern and a method for manufacturing the same.

  In order to achieve high integration and ultra-miniaturization of semiconductor elements that progress from half-pitch 65 nm to 45 nm and further 32 nm, in photolithography, as a high-resolution technique in an exposure apparatus, the numerical aperture of the projection lens is increased. A high NA technique, an immersion exposure technique in which exposure is performed with a high refractive index medium interposed between the projection lens and the exposure target, a modified illumination-mounted exposure technique, and the like have been put into practical use.

  Resolution measures for photomasks used for photolithography (hereinafter also referred to as masks) include the miniaturization and high accuracy of conventional binary masks composed of light-transmitting parts and light-shielding parts, Levenson-type (also called Shibuya / Levenson-type) phase shift mask that improves resolution by phase shift effect using interference, a halftone phase shift mask composed of a light transmitting part and a semi-transmitting part A phase shift mask such as a chromeless type phase shift mask that is not provided with a light shielding layer such as chrome is used.

  In photolithography technology, the minimum dimension (resolution) that can be transferred by a projection exposure apparatus is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (NA) of the lens of the projection optical system. With the demand for the reduction in wavelength, the exposure light has been shortened and the projection optical system has a higher NA. However, there is a limit to satisfying this requirement only by the shorter wavelength and the higher NA.

Therefore, in order to increase the resolution, a super-resolution technique for miniaturization by reducing the value of process constant k ₁ (k ₁ = resolution line width × numerical aperture of projection optical system / exposure light wavelength) has recently been proposed. Has been. As such a super-resolution technique, a method of optimizing the mask pattern by giving an auxiliary pattern or a line width offset to the mask pattern according to the characteristics of the exposure optical system, or a method using modified illumination (also called a grazing incidence illumination method). ) And so on. For projection exposure using modified illumination, usually, annular illumination using a pupil filter (also referred to as Annular), dipole illumination using a dipole (also referred to as Dipole) pupil filter, and quadrupole. Quadrupole illumination using a pupil filter (also referred to as cross quad: Cquad) is used.

  In the method using the auxiliary pattern, a pattern (hereinafter referred to as an auxiliary pattern) that is not transferred onto the wafer and is below the resolution limit of the projection optical system in the vicinity of a pattern transferred on the wafer (hereinafter referred to as a main pattern). And a lithography method using a photomask having an effect of improving the resolution and depth of focus of the main pattern (see, for example, Patent Document 1). The auxiliary pattern is also called SRAF (Sub Resolution Assist Feature) (hereinafter, the auxiliary pattern is also called SRAF in the present invention).

  However, with the miniaturization of the semiconductor element pattern, the photomask having the auxiliary pattern has been difficult in mask manufacturing. First, it is necessary that the auxiliary pattern does not form an image as described above, and the auxiliary pattern must have a size smaller than that of the main pattern. As a result, with the miniaturization of the main pattern dimension, the line width dimension of the required auxiliary pattern has been miniaturized from several hundred nm to a further minute dimension, and is approaching the limit of production. For example, when a 65 nm line width semiconductor device is formed on a wafer, the line width dimension of the main pattern on the mask (usually a reticle having a tetraploid pattern) is subjected to optical proximity correction (OPC) or the like, and 200 nm. Whereas the auxiliary pattern has a line width dimension of 120 nm or less, it is extremely difficult to manufacture a mask. As described above, under the exposure conditions for transferring a pattern having a half pitch of 65 nm or less, the dimension of the auxiliary pattern is a big problem in mask manufacturing.

  Furthermore, as a transfer characteristic of a mask for transferring a pattern with a half pitch of 65 nm or less, a halftone mask often provides a better transfer image than a binary mask, as will be described later. There is also a strong demand for a halftone mask structure, and halftone masks having auxiliary patterns have also been proposed (see, for example, Patent Document 2, Patent Document 3, and Non-Patent Document 1). However, because of the transfer characteristics of a halftone mask, a negative bias is normally applied to the mask pattern dimension, so the dimension of the auxiliary pattern formed with a semi-transparent film as a halftone mask is a binary mask formed only with a light-shielding film. A value smaller than the dimension of the auxiliary pattern is required. In the generation of semiconductor devices with a half pitch of 45 nm to 32 nm, an auxiliary pattern dimension of 60 nm or less in mask line width is required depending on the semiconductor design and exposure conditions.

  In addition, with the miniaturization of auxiliary patterns, halftone masks provided with conventional auxiliary patterns are used in mask manufacturing processes such as cleaning, or when re-cleaning a mask that has become dirty during use in an exposure apparatus. The aspect ratio (pattern height / pattern width) approaches 1 and a part of the auxiliary pattern is missing, the auxiliary pattern is peeled off from the substrate surface, or the auxiliary pattern falls in the line width direction. Also occurred.

  In Patent Document 2, as a countermeasure for miniaturization of an auxiliary pattern by a halftone mask, a phase difference of 180 degrees is generated between light transmitted through a translucent pattern and light transmitted through a transparent region of a transparent substrate, and translucent. There has been proposed a photomask that causes a predetermined phase difference of less than 50 degrees between light transmitted through the auxiliary pattern and light transmitted through the transparent region of the transparent substrate to flatten the focus characteristics of the translucent pattern. FIG. 24 is a plan view (FIG. 24A) and a longitudinal sectional view (FIG. 24B) of the photomask disclosed in Patent Document 2. The photomask according to Patent Document 2 makes it possible to form an auxiliary pattern provided in the vicinity of a line pattern as a main pattern with the same dimensions as the main pattern.

  As shown in FIG. 24, the halftone mask having the auxiliary pattern described in Patent Document 2 is a line pattern in which the line width of the semitransparent pattern as the main pattern 1 is 0.3 μm on the wafer, and the semitransparent auxiliary pattern 2. Is a mask provided with a line pattern of the same line width on the left and right of the main pattern 1, and the main pattern 1 has a two-layer structure in which a transparent film 304 is further stacked on the semitransparent film 302 to form a two-layer structure. A phase difference of 180 degrees is generated between the light transmitted through the semi-transparent main pattern 1 and the light transmitted through the transparent area of the transparent substrate 301, while the light transmitted through the semi-transparent auxiliary pattern 2 and the transparent area of the transparent substrate 301 are This is a mask in which a predetermined phase difference in a range smaller than 50 degrees is generated in transmitted light, and the focus characteristics of a semitransparent pattern are flattened.

Japanese Patent Laid-Open No. 7-140639 Patent No. 2953406 JP 2003-302739 A

N. V. Laffety, et al. , Proc. of SPIE Vol. 5377, 381-392 (2004)

  However, the halftone mask having the auxiliary pattern described in Patent Document 2 uses a mercury lamp i-line (365 nm) or a KrF excimer laser (248 nm) as an exposure light source, and the numerical aperture NA of the projection optical system is 0.6. It is a generation mask for small, sub-micron semiconductor devices with a pattern size on the wafer of 0.3 to 0.35 μm. The ArF excimer laser, which is currently in practical use, is used as an exposure light source, and NA In order to use it as a mask for a semiconductor element having a pattern size on a wafer of 65 nm or less, and further 45 nm and 32 nm, which is used in an exposure apparatus having a high NA of 1 or more, preferably around 1.3 to 1.35, There were the following problems.

That is, as the process constant k ₁ becomes smaller, modified illumination is used to improve the resolution of the main pattern, but there is a problem that the auxiliary pattern is also easily resolved. Furthermore, the oblique illumination of the modified illumination causes a problem that the auxiliary pattern can be easily resolved on the transfer target surface due to a three-dimensional effect (a three-dimensional effect of the mask) due to the thickness of the mask perpendicular to the mask substrate surface. . In the halftone mask having the auxiliary pattern described in Patent Document 2, the auxiliary pattern is resolved by the three-dimensional effect even if the phase difference of the main pattern is within a predetermined range, and further against defocusing. As a result, the dimensional variation becomes asymmetrical, and the quality of the transferred image is lowered, which is not suitable for practical use.

  Further, the photomasks described in Patent Document 2, Patent Document 3 and Non-Patent Document 1 all have only a main pattern of a translucent film on the lower layer on the transparent substrate side, a light-shielding film on the upper layer, or a translucent material different from the lower layer. In the production of a photomask having an auxiliary pattern of a semi-transparent film, which has a two-layer structure in which films or transparent films are stacked, the main pattern film forming process is required twice, which complicates the manufacturing process. was there. Furthermore, in the manufacture of the photomask described in Patent Document 2, it is difficult to align the first pattern formed on the transparent substrate and the second pattern to be formed next, along with the pattern miniaturization. The space between the auxiliary pattern and the auxiliary pattern must be greater than the value considering the misalignment (usually about 200 nm), and it becomes difficult to make the auxiliary pattern width the same as the main pattern width as the pattern becomes finer. There was a problem.

  As described above, with the miniaturization of semiconductor element patterns, a halftone mask provided with an auxiliary pattern is strongly demanded, but a photomask provided with a conventional auxiliary pattern has a half pitch of 65 nm or less, and further There is a problem that it is not compatible with miniaturization as a mask for semiconductor elements of 45 nm and 32 nm, and its manufacture is difficult.

  Therefore, the present invention has been made in view of the above problems. That is, an object of the present invention is to use an ArF excimer laser as an exposure light source, and as a mask used for projection exposure by modified illumination, while maintaining the effect of expanding the depth of focus as an auxiliary pattern, without resolving the auxiliary pattern, It is an object to provide a halftone mask having an auxiliary pattern capable of suppressing a chipping and falling and forming a transfer image having a high contrast of a main pattern, and a manufacturing method thereof.

  In order to solve the above-described problems, a photomask according to the first aspect of the present invention is a photomask used for projection exposure by modified illumination using an ArF excimer laser as an exposure light source, wherein the photomask is a transparent substrate. A photomask provided on one main surface with a main pattern transferred to the transfer target surface by the projection exposure and an auxiliary pattern formed in the vicinity of the main pattern and not transferred to the transfer target surface, The main pattern and the auxiliary pattern are composed of a translucent film made of the same material, and cause a phase difference of 180 degrees between the light transmitted through the main pattern and the light transmitted through the transparent region of the transparent substrate, and A predetermined phase difference in the range of 70 to 115 degrees is generated between the light transmitted through the auxiliary pattern and the light transmitted through the transparent region of the transparent substrate. It is.

  According to a second aspect of the present invention, there is provided a photomask according to the first aspect, wherein the auxiliary pattern has a thickness smaller than that of the main pattern and a film thickness difference of 24 nm to 40 nm. It is a film thickness difference.

  A photomask according to a third aspect of the present invention is the photomask according to the second aspect, wherein the film thickness difference is formed by dry etching.

  A photomask according to a fourth aspect of the present invention is the photomask according to any one of the first to third aspects, wherein the exposure light transmittance of the auxiliary pattern is within a range of 15% to 29%. It is characterized by the transmittance.

  A photomask according to a fifth aspect of the present invention is the photomask according to any one of the first to fourth aspects, wherein the translucent film made of the same material is a single-layer translucent film or two layers. It consists of a semi-transparent film.

  A photomask according to a sixth aspect of the present invention is the photomask according to any one of the first to fifth aspects, wherein a light shielding region is formed in an outer peripheral portion of the photomask. Is.

  The photomask according to the invention of claim 7 is the photomask according to any one of claims 1 to 6, wherein the single-layer translucent film is a translucent film of molybdenum silicide-based material, The two-layer semi-transparent film is characterized in that a chromium-based material semi-transparent film and a molybdenum silicide-based material semi-transparent film are sequentially provided on the transparent substrate.

  A photomask according to an invention of claim 8 is the photomask according to any one of claims 1 to 7, wherein the main pattern and the auxiliary pattern are both line patterns, and the main pattern is It is an isolated pattern or a periodic pattern.

  According to a ninth aspect of the present invention, there is provided a photomask manufacturing method that uses an ArF excimer laser as an exposure light source, is used for projection exposure by modified illumination, and is transferred onto a surface of a transparent substrate by a projection exposure onto a transfer target surface. And a supplementary pattern that is formed in the vicinity of the main pattern and is not transferred to the transfer target surface, comprising: (a) a translucent film on one main surface of the transparent substrate Forming a light-shielding film in order, and setting the film thickness so that the phase difference between the light transmitted through the translucent film and the light transmitted through the transparent region of the transparent substrate is approximately 180 degrees; and (b) on the light-shielding film Forming a first resist pattern, dry-etching the light-shielding film and the translucent film in order to form a main pattern portion and an auxiliary pattern portion, and (c) peeling off the first resist pattern, Next Forming a second resist pattern on the light shielding film, etching and removing the light shielding film of the auxiliary pattern portion; and (d) removing the second resist pattern, and then forming one of the transparent substrates. The auxiliary pattern portion is dry-etched on the entire main surface, and the auxiliary pattern portion has a film thickness at which the light transmitted through the auxiliary pattern and the light transmitted through the transparent region of the transparent substrate have a predetermined phase difference in the range of 70 to 115 degrees. A step of dry-etching the semi-transparent film to form an auxiliary pattern, and (e) etching and removing the light-shielding film of the main pattern portion to form a main pattern, and the light transmitted through the main pattern and the transparent And a step of producing a phase difference of 180 degrees in the light transmitted through the transparent region of the substrate.

  The photomask manufacturing method according to the invention of claim 10 is the photomask manufacturing method according to claim 9, wherein the dry etching of the semitransparent film in the step (b) is halfway through the film thickness of the semitransparent film. It is the half etching of this.

  The photomask manufacturing method according to the invention of claim 11 is used for projection exposure with ArF excimer laser as an exposure light source, and is transferred to a transfer target surface by projection projection on one main surface of a transparent substrate. And a supplementary pattern that is formed in the vicinity of the main pattern and is not transferred to the transfer target surface, comprising: (a) a translucent film on one main surface of the transparent substrate A light-shielding film is formed in order, the semi-transparent film is composed of two semi-transparent films, and the lower semi-transparent film on the transparent substrate side also serves as an etching stopper layer of the upper semi-transparent film, A step of setting the film thickness so that the phase difference between the light transmitted through the transparent film and the light transmitted through the transparent region of the transparent substrate is approximately 180 degrees, and (b) forming a first resist pattern on the light shielding film, The light shielding film and the two layers. A step of dry-etching the transparent film in order to form a main pattern portion and an auxiliary pattern portion; (c) peeling off the first resist pattern, and then forming a second resist pattern on the light shielding film; (D) removing the second resist pattern, and then dry-etching the entire main surface of the transparent substrate to transmit the auxiliary pattern. The semi-transparent film of the auxiliary pattern portion is dry-etched to form a auxiliary pattern until the film thickness is such that the light to be transmitted and the light transmitted through the transparent region of the transparent substrate have a predetermined phase difference in the range of 70 degrees to 115 degrees. And (e) etching and removing the light shielding film of the main pattern portion to form a main pattern. The light is transmitted through the main pattern and the light transmitted through the transparent region of the transparent substrate. A step of generating a phase difference of, is characterized in that comprises a.

  The photomask manufacturing method according to the invention of claim 12 is the photomask manufacturing method according to any one of claims 9 to 11, wherein a film thickness difference between the auxiliary pattern and the main pattern is different. , And a predetermined film thickness difference in the range of 24 nm to 40 nm.

  The photomask manufacturing method according to the invention of claim 13 is the photomask manufacturing method according to any one of claims 9 to 12, after the step (d) of forming the auxiliary pattern, Forming a resist pattern for a light shielding region, removing the light shielding film on the main pattern by dry etching to form a main pattern, and further forming a light shielding region on the outer periphery of the photomask. It is what.

  According to the photomask of the present invention, in a halftone mask having an auxiliary pattern, it is possible to form a transfer image with high contrast while maintaining the effect of expanding the depth of focus as the auxiliary pattern by thinning only the auxiliary pattern portion. it can. Even if the auxiliary pattern size is increased from 56 nm to 104 nm, the auxiliary pattern portion is not resolved, and there is no adverse effect on the focal depth expansion effect of the main pattern at the repeated end, and the auxiliary pattern size is about twice that of the conventional size. By reducing the aspect ratio of the auxiliary pattern, it is possible to suppress the auxiliary pattern from being chipped or fallen. Further, in the case of the photomask of the present invention, when the translucent film is a single layer, the conventionally used halftone mask blanks can be used as they are, and it is not necessary to change the mask blanks material. Mask blank compatibility can be ensured for a halftone mask that does not use an auxiliary pattern, and mask quality can be maintained and mask cost can be reduced.

  According to the photomask manufacturing method of the present invention, since the main pattern and the auxiliary pattern are composed of a translucent film made of the same material, the process of forming the translucent film is easy, and the translucent film is a single layer. In this case, mask blanks for halftone masks that have been conventionally used can be used as they are, and it is not necessary to change the mask blank material, so that the mask manufacturing cost can be reduced. By making the auxiliary pattern width smaller than the main pattern, the space between the main pattern and the auxiliary pattern is made wider, and the alignment between the first pattern formed on the transparent substrate and the second pattern to be formed next is performed. It is possible to obtain a photomask that can improve the pattern transfer characteristics without increasing the difficulty of mask manufacture, and a manufacturing method that increases the margin of deviation.

It is a partial section schematic diagram showing one embodiment of a halftone mask which has an auxiliary pattern of the present invention. It is a fragmentary sectional schematic diagram which shows other embodiment of the halftone mask which has an auxiliary pattern of this invention. The Cquad pupil filter used for the evaluation of the halftone mask of the present invention, (a) is a schematic plan view of Cquad, and (b) is a schematic perspective view when exposure light is irradiated to the mask using Cquad. It is. It is a figure of the aerial image which shows the relationship between the evaluation pattern used in the halftone mask of this invention, and the position and light intensity of an evaluation pattern. It is a figure which shows the relationship between SRAF film thickness difference and SRAF light intensity / slice level when the SRAF CD is changed. It is a figure which shows the relationship between the line CD of the main pattern edge on a wafer, and defocusing, when CD of SRAF is changed. It is process cross-sectional schematic diagram which shows 1st Embodiment of the manufacturing method of the photomask of this invention. It is process cross-sectional schematic diagram which shows 2nd Embodiment of the manufacturing method of the photomask of this invention. It is process cross-sectional schematic diagram which shows 3rd Embodiment of the manufacturing method of the photomask of this invention. It is process cross-sectional schematic diagram which shows 4th Embodiment of the manufacturing method of the photomask of this invention. It is process cross-sectional schematic diagram which shows one Embodiment of the manufacturing method of the conventional photomask. In the embodiment shown in FIG. 3, it is a figure which shows the relationship between the etching amount (on a mask) of SRAF, and SRAF CD (dimension on a wafer). FIG. 4 is a diagram showing the influence of an SRAF etching amount error on a main pattern CD in the embodiment shown in FIG. 3. In the embodiment shown in FIG. 3, it is a figure which shows the relationship between main pattern CD of the repetition edge on a wafer, and a defocus (Defocus) when SRAF etching amount is changed. In the embodiment shown in FIG. 3, it is a figure which shows the light intensity distribution of the main pattern of the repetition edge on a wafer when SRAF etching amount is changed. FIG. 6 is a schematic plan view (a) of a QUASAR pupil filter used in the simulation, a schematic perspective view (b) when the mask is irradiated with exposure light using QUASAR, and a schematic plan view (c) of the mask pattern 194. In the embodiment shown in FIG. 16, it is a figure which shows the relationship between the etching amount (on a mask) of SRAF, and SRAF CD (dimension on a wafer). FIG. 17 is a diagram illustrating an influence of an SRAF etching amount error on a mask on a main pattern CD error on a wafer in the embodiment illustrated in FIG. 16. FIG. 17 is a diagram showing a relationship between a main pattern CD and defocus when the SRAF etching amount is changed in the embodiment shown in FIG. 16. In the conventional halftone mask and binary mask, the relationship between mask CD and NILS is shown. In the conventional halftone mask and binary mask, the relationship between mask CD and MEEF is shown. It is a figure which shows mask CD and exposure margin in the conventional halftone mask and binary mask. It is a figure which shows ratio of SRAF part light intensity with respect to the slice level of a light intensity threshold value with respect to CD of SRAF on a wafer in the conventional halftone mask and binary mask. It is the top view and longitudinal cross-sectional view of the photomask which has the conventional semi-transparent auxiliary pattern of patent document 2. FIG.

  The photomask of the present invention is a mask used for projection exposure with ArF excimer laser as an exposure light source, preferably for forming fine semiconductor elements with a half pitch on the wafer of 65 nm or less, and further 45 nm and 32 nm. It is a mask intended to be used.

(Transfer characteristics of conventional halftone mask)
Before describing the present invention, first, the transfer characteristics of a halftone mask having an auxiliary pattern which is the subject of the present invention will be described. The inventor investigated the transfer characteristics of a halftone mask having an auxiliary pattern for forming a fine pattern with a half pitch of 45 nm or less on a wafer by simulation while comparing with a binary mask using a conventional halftone mask. .

  Conventionally, the evaluation of the transfer characteristics of a mask pattern has been predicted by a method of expressing the planar characteristics of the mask pattern mainly by transmittance and phase difference. In recent years, indices such as contrast or NILS (Normalized Image Log-Slope) and MEEF (Mask Error Enhancement Factor) are used for evaluation of transfer characteristics of a photomask. . First, the transfer characteristics of the mask were evaluated using NILS and MEEF.

NILS is expressed by the following mathematical formula (1). When the value of NILS is large, the optical image becomes steep and the dimensional controllability of the resist pattern is improved. In general, NILS is preferably 2 or more, but with the miniaturization of semiconductor elements, there is a demand for a resist process that can resolve even about 1.5 or more. Here, W is a desired pattern dimension, I _th is a threshold value of light intensity giving W, and (dI / dx) is a gradient of the aerial image.
NILS = (dI / dx) / (W × I _th ) (1)

MEEF is expressed by the following mathematical formula (2), and is represented by the ratio of the pattern dimension change amount (Δwafer CD) on the wafer to the mask dimension change amount (Δmask CD). CD indicates the critical dimension of the mask or wafer. The numerical value 4 in the formula (2) is a reduction ratio of the mask, and illustrates a case where a general quadruple mask is used. As shown in Equation (2), the smaller the MEEF value (near 1), the mask pattern is faithfully transferred to the wafer pattern. If the MEEF value decreases, the wafer manufacturing yield improves. As a result, the mask manufacturing yield used for wafer manufacturing is also improved.
MEEF = Δwafer CD / Δmask CD / 4 (2)

  In the present invention, EM-Suite (trade name: manufactured by Panoramic Technology) was used as simulation software for estimating the transfer characteristics of the mask pattern. As main simulation conditions, an ArF excimer laser (193 nm) was used as an illumination light source, NA was 1.35, and modified illumination was used with a Cquad pupil filter 31 shown in FIG. FIG. 4A is a schematic plan view of the Cquad 31, and FIG. 4B is a schematic perspective view when the mask 33 is irradiated with exposure light using the Cquad 31. FIG. Cquad 31 had an opening angle of the fan-shaped light transmission part of 35 degrees, an outer diameter of 0.9, and an inner diameter of 0.7 (the radius of the pupil filter is 1). As the mask 33, a conventional half-tone mask of 6% transmittance (denoted as 6% half-tone) at an exposure wavelength of 193 nm of a general molybdenum silicide type and a molybdenum silicide type binary mask for comparison are used. The target line dimension on the wafer was 45 nm, and the pattern was a line / space repetitive pattern with a pitch of 90 nm (half pitch 45 nm).

  20 and 21 are diagrams showing the relationship between the mask bias and transfer characteristics at a transfer target size of 45 nm on the wafer obtained by the above simulation in the conventional halftone mask and binary mask, and FIG. FIG. 21 shows the relationship between MEEF and mask CD.

  In the NILS shown in FIG. 20, in the halftone mask, the NILS shows the maximum value in the masks CD 32 nm to 44 nm (on the wafer) with the mask bias set to the negative side and the line pattern dimension reduced. On the other hand, in the binary mask, the NILS tends to increase as the mask pattern is increased on the positive side and the line pattern size is increased.

  In the MEEF shown in FIG. 21, both the halftone mask and the binary mask have a smaller MEEF as the line pattern size is reduced by reducing the mask bias, but the halftone mask is smaller than the binary mask. Value, more preferred.

  20 and 21, in the halftone mask, the maximum NILS and the minimum MEEF mask CD substantially coincide. On the other hand, in the binary mask, NILS and MEEF are in a contradictory relationship, and it is understood that if one characteristic is improved, the other characteristic is deteriorated. This indicates that a halftone mask is more suitable than a binary mask for pattern formation with a half pitch of 45 nm or less. Therefore, as described in the present invention, it is one of the preferred choices to use a halftone mask as a photomask for pattern formation with a half pitch of 45 nm or less.

  FIG. 22 is a diagram showing a conventional halftone mask and binary mask mask CD and exposure latitude (also referred to as exposure latitude). The exposure margin is a value indicating an exposure margin for obtaining a good resist size / shape. Here, the exposure margin is evaluated under the condition that the error of the wafer transfer CD is ± 3.8 nm or less when the focal plane is shifted within a range of ± 50 nm and the main pattern mask CD is shifted within a range of ± 2.5 nm. did. Here, since the mask CD is converted on the wafer, the mask CD of the main pattern to be transferred is shown. In FIG. 22, the halftone mask (dotted line in the figure) shows the best exposure margin of 8.3% when the mask CD is 32 nm, and the same exposure margin as the binary mask (solid line) when the mask CD is 40 nm. Degree. On the other hand, the binary mask shows the best exposure margin of 7% when the mask CD is 46 nm, but the exposure margin is smaller than that of the halftone mask.

  FIG. 4 is an evaluation pattern (FIG. 4 (a)) used in the present invention and an aerial image diagram (FIG. 4 (b)) showing the light intensity corresponding to the position of the evaluation pattern. The evaluation pattern has nine lines / spaces with a half pitch of 45 nm as the main pattern, and two SRAFs at both ends of the main pattern in order to improve the resolution of the main pattern at the end (the half pitch of SRAF is the same as the main pattern). The same pattern is repeated, with a 400 nm space in between. Both the main pattern and SRAF are the above 6% halftone.

  Next, the transferability of the auxiliary pattern (SRAF) at the end of the line / space pattern in the halftone mask having the auxiliary pattern will be described. In FIG. 4, the horizontal axis shows the position of a pair of patterns of the main pattern and SRAF, and the vertical axis shows the normalized light intensity when the light intensity of the transmission part having no pattern is 1. A slice level indicated by a solid line is a standardized light intensity threshold. The slice level varies depending on the dimensions of the main mask pattern. If the minimum light intensity of the SRAF portion indicated by the arrow in the figure falls below the slice level, it means that the SRAF is resolved on the wafer.

  FIG. 23 shows the slice level of the standardized light intensity threshold for the SRAF CD (horizontal axis) on the wafer in the halftone mask and binary mask when the film thickness is constant based on the prior art. It is a figure which shows ratio (vertical axis) of the light intensity of the SRAF part with respect to. Halftone masks (triangular points in the figure) show the case where there are three main pattern CDs (32 nm; 36 nm; 40 nm on the wafer). If the above ratio is 1 or less, the SRAF is transferred. Therefore, in order to prevent the SRAF from being transferred, the above ratio must be 1 or more. When the main pattern CD of the halftone mask indicated by the dotted line in the figure is 32 nm (128 nm on the mask), the exposure margin shows the best value, but the SRAF CD is not less than 14 nm (56 nm on the mask). SRAF will be resolved, and it will be understood that the mask manufacturing is difficult.

  The above is a simulation result when a conventional 6% halftone mask having SRAF is used. Although it is understood that the mask characteristic is excellent in the simulation, the SRAF dimension becomes extremely small and actual mask manufacture is difficult. It is.

(Photomask of the present invention)
Next, referring to the above results, embodiments of the photomask and the photomask manufacturing method of the present invention will be described in detail with reference to the drawings. In the present invention, except for the case where SRAF is present between main patterns described later, in the following description of the mask pattern transfer characteristics, the Cquad pupil filter 31 shown in FIG. Suite (trade name: manufactured by Panoramic Technology) was used. The main simulation conditions are ArF excimer laser (193 nm) as an illumination light source, and NA is 1.35. As the evaluation pattern, the pattern shown in FIG. 4A is used.

[First Embodiment]
FIG. 1 is a partial cross-sectional schematic view showing a first embodiment of a halftone mask having an auxiliary pattern which is a photomask of the present invention, illustrating a case where a line / space pattern is provided, and a synthetic quartz substrate A main pattern 12 is provided on a transparent substrate 11 such as a single-layer semi-transparent film that transmits exposure light at a predetermined transmittance and changes phase, and a single layer made of the same material as the main pattern 12 is provided in the vicinity of the main pattern 12. This is a halftone mask 10 on which an auxiliary pattern (SRAF) 13 composed of a semi-transparent film is formed. In FIG. 1, only two main patterns 12 and auxiliary patterns 13 and only a part of the mask pattern are illustrated, but the present invention is not limited to this. The main pattern may be an isolated pattern or a periodic pattern.

  The halftone mask 10 having the auxiliary pattern according to the present invention causes a phase difference of 180 degrees between the light transmitted through the main pattern 12 and the light transmitted through the transparent area without the pattern on the transparent substrate 11 and transmitted through the auxiliary pattern 13. And a predetermined phase difference in the range of 70 degrees to 115 degrees is set between the transmitted light and the light transmitted through the transparent region of the transparent substrate 11. By setting the phase difference between the main pattern 12 and the auxiliary pattern 13 as described above, the halftone mask 10 does not resolve the auxiliary pattern 13 while maintaining the focal depth expansion effect as the auxiliary pattern, and the main pattern 12. Transfer images with high contrast can be formed.

  In order to generate the above-described phase difference, the halftone mask 10 having the auxiliary pattern of the present invention has a film thickness of the auxiliary pattern 13 smaller than that of the main pattern 12, and a film thickness difference (hereinafter referred to as SRAF film thickness difference). Is a predetermined film thickness difference in the range of 24 nm to 40 nm. The predetermined film thickness difference can be formed by selectively dry etching the SRAF part.

  As the halftone mask 10 having the auxiliary pattern, for example, if the ArF exposure light transmittance of the main pattern causing a phase difference of 180 degrees is 6%, a predetermined phase difference in the range of 70 degrees to 115 degrees is generated. The ArF exposure light transmittance of the auxiliary pattern to be made becomes a predetermined transmittance in the range of 15% to 29%.

  The translucent film constituting the main pattern 12 and the auxiliary pattern 13 of the halftone mask 10 of the present invention shown in FIG. 1 is not particularly limited as a material. For example, molybdenum silicide oxidation which is a molybdenum silicide material is used. Examples thereof include semitransparent films such as a film (MoSiO), a molybdenum silicide nitride film (MoSiN), and a molybdenum silicide oxynitride film (MoSiON). The molybdenum silicide-based translucent film is practically used as a halftone mask material and is a more preferable material.

  For forming the translucent film 12, a conventionally known method can be applied. For example, in the case of a molybdenum silicide oxide film (MoSiO), a mixed target of molybdenum and silicon (Mo: Si = 1: 2 mol%) is used. It can be formed by a reactive sputtering method in a mixed gas atmosphere with oxygen, and is formed to a thickness of several tens of nm.

When the translucent film constituting the main pattern 12 and the auxiliary pattern 13 is, for example, a translucent film of molybdenum silicide material, fluorine gas such as CF ₄ , CHF ₃ , C ₂ F ₆ , or a mixed gas thereof Alternatively, dry etching can be performed by using a gas in which oxygen is mixed with these gases as an etching gas to form a pattern.

  Here, when the translucent film is a single layer of molybdenum silicide-based material, when the translucent film is dry-etched to form a mask pattern, the surface of the transparent substrate is usually slightly etched and dug (see FIG. 1 (not shown). In the present invention, the digging depth of the surface of the transparent substrate where there is no mask pattern is preferably controlled to a depth in the range of 0 to 10 nm. If the digging depth exceeds 10 nm, the mask characteristics will be adversely affected. Therefore, in the halftone mask of the present invention, the etching depth of the transparent substrate surface is controlled to a predetermined depth in the range of 0 to 10 nm, and the phase difference including this depth is set in advance. In the following embodiments, the digging depth at which any halftone mask is etched is 4 nm, but other etching depths may be used as long as they are in the range of 0 to 10 nm.

  As the halftone mask of this embodiment, for example, when molybdenum silicide having a film thickness of 68 nm is used as a semitransparent film, the main pattern (film thickness 68 nm) has an ArF excimer laser transmittance of 6%, a transparent region of the transparent substrate, and the like. The auxiliary pattern has a predetermined film thickness difference in the range of 24 nm to 40 nm with respect to the main pattern, and the auxiliary pattern has a predetermined level in the range of 70 degrees to 115 degrees with the transparent region of the transparent substrate. A halftone mask that is a phase difference can be shown.

[Second Embodiment]
In order to reduce the digging of the surface of the transparent substrate, another embodiment of the photomask of the present invention is a halftone mask made up of two layers of translucent films shown in FIG. The main pattern and the auxiliary pattern are composed of two semi-transparent films made of the same material, and the lower semi-transparent film 24 on the transparent substrate side is an etching stop layer at the time of dry etching of the upper semi-transparent film 25. It has a function and also has a function as a translucent film. As the upper semi-transparent film 25, the above molybdenum silicide-based material can be exemplified. In this case, the lower semitransparent film 24 is preferably a chromium oxide film (CrO), a chromium nitride film (CrN), or a chromium oxynitride film (CrON), which is a chromium-based material. This is because the thin film of the chromium-based material is translucent to the exposure light and is resistant to the fluorine-based gas used for dry etching of the molybdenum silicide-based material. The chromium-based material is formed by a conventionally known reactive sputtering method, and the unnecessary portion of the chromium-based material thin film can be dry-etched with a chlorine-based gas without damaging the transparent substrate. The upper semitransparent film 25 is formed to a thickness of several tens of nm, and the lower semitransparent film 24 is formed to a thickness of several nm to several tens of nm.

  In the halftone mask of the present invention, in the first and second embodiments described above, a light shielding region may be formed on the outer periphery of the mask. Usually, in the projection exposure onto the semiconductor wafer, the mask outer peripheral portion is subjected to multiple exposure, so a photomask having a light shielding region provided on the mask outer peripheral portion is used. Therefore, also in the present invention, a light-shielding film can be provided on a semi-transparent film in a desired region such as the outer peripheral portion to form a light-shielding region. The light-shielding film is formed as a light-shielding region by forming a light-shielding metal film of chromium or the like to a thickness of about several tens to 200 nm and patterning.

(Transferability of auxiliary pattern)
Next, the effect of thinning the auxiliary pattern (SRAF) of the halftone mask of the present invention shown in FIG. 1 will be described. FIG. 5 shows a difference between SRAF film thickness difference (horizontal axis) and SRAF light intensity / standardized light intensity threshold when the SRAF CD is changed in a halftone mask having a main pattern CD of 32 nm on the wafer. It is a figure which shows the relationship with a slice level (vertical axis). If the SRAF light intensity / slice level is not 1 or more, the SRAF is resolved on the wafer.

  As shown in FIG. 5, when the SRAF CD is as fine as 14 nm (56 nm on the mask), the SRAF is not transferred even if the SRAF film thickness difference is 0, that is, the same as the main pattern film thickness (68 nm). . When the SRAF CD is 22 nm (88 nm on the mask) and the SRAF film thickness difference is 24 nm or more, the SRAF is not resolved and transferred. Similarly, when the SRAF CD is 26 nm (104 nm on the mask), the SRAF film thickness difference is 30 nm or more, and when the SRAF CD is 30 nm (88 nm on the mask), the SRAF film thickness difference is 34 nm or more. SRAF is not transferred.

  As described with reference to FIG. 23 above, in a halftone mask in which the conventional main pattern and auxiliary pattern (SRAF) are made of the same material and the same film thickness, if the main pattern CD is 32 nm, the SRAF CD is 14 nm or less. However, as described above, by using the thin SRAF of the present invention, even if the SRAF CD is increased to 26 nm to 30 nm, which is twice as large as the conventional size, It can be used without being resolved and transferred. SRAF thin film can be easily formed by selectively dry etching the SRAF portion. Since the SRAF dimension can be increased to about twice that of the prior art, it is possible to use a halftone mask having an SRAF made of the same material, which has been difficult to miniaturize and difficult to use.

  FIG. 6 is a diagram showing the relationship between the CD at the end of the main pattern on the wafer and the defocus (Defocus) when the SRAF CD is changed. Each SRAF CD is etched so that the SRAF is not resolved, and has a film thickness of the main pattern and a predetermined film thickness difference (24 nm, 32 nm, 40 nm). As shown in FIG. 6, by increasing the SRAF CD to 22 nm to 30 nm and reducing the SRAF film thickness, there is no CD variation between the SRAF dimensions when the focus is shaken, and shows almost the same tendency. That is, the SRAF thin film does not adversely affect the defocus, and the same dimensional accuracy can be obtained.

  As described above, the photomask of the present invention can form a transfer image with high contrast while maintaining the effect of expanding the depth of focus as the auxiliary pattern by thinning only the auxiliary pattern portion. Furthermore, the dimension of the auxiliary pattern can be increased to about twice the conventional dimension, and by reducing the aspect ratio of the auxiliary pattern, an effect of reducing the chipping and falling of the auxiliary pattern can be obtained. Further, when a molybdenum silicide-based single layer film is used as the photomask of the present invention, halftone mask mask blanks that have been used in the past can be used as they are, mask quality is maintained, and high accuracy is achieved. A mask having a fine pattern can be used.

  Next, the manufacturing method of the photomask of this invention is demonstrated. As described above, the photomask of the present invention is characterized in that a predetermined phase difference in the range of 70 degrees to 115 degrees is generated between the light transmitted through the auxiliary pattern and the light transmitted through the transparent region of the transparent substrate. In order to cause the above-described phase difference in the auxiliary pattern, the film thickness of the auxiliary pattern is thinner than that of the main pattern, and is set to a predetermined film thickness difference in the range of 24 nm to 40 nm. The predetermined film thickness difference includes a method of changing the film thickness according to the pattern when forming the semitransparent film, and a method of etching the semitransparent film according to the pattern after forming the semitransparent film. There is a way to change. The photomask manufacturing method of the present invention is based on the latter etching method that is easy to manufacture and provides a high-accuracy mask.

(Conventional photomask manufacturing method)
Before describing the method of manufacturing the photomask of the present invention, problems in the case of manufacturing the photomask of the present invention using a known general manufacturing method will be described, and then the method of manufacturing the photomask of the present invention will be described. To do.

  FIG. 11 is a process cross-sectional schematic diagram when the photomask of the present invention is manufactured using a known conventional manufacturing method. As shown in FIG. 11, a semi-transparent film 112 is formed on the transparent substrate 111, and the film thickness is such that the phase difference between the light transmitted through the semi-transparent film and the light transmitted through the transparent region of the transparent substrate is 180 degrees. Then, the light shielding film 113 is formed on the translucent film (FIG. 11A). Next, a first resist pattern 114 is formed on the light shielding film 113, and the light shielding film 113 and the translucent film 112 are sequentially dry etched to form a main pattern portion 115 and an auxiliary pattern portion 116 (FIG. 11B). ). Next, the first resist pattern 154 is peeled off, and the light shielding film in the exposed pattern portion is removed by etching (FIG. 11C). Next, the main pattern portion 115 is covered with the second resist pattern 117, and the translucent film of the auxiliary pattern portion is made up to a film thickness at which the light transmitted through the auxiliary pattern portion and the light transmitted through the transparent region of the transparent substrate have a predetermined phase difference. Then, an auxiliary pattern 118 is formed by dry etching (FIG. 11D), and the second resist pattern 117 is peeled to obtain a halftone mask 110 (FIG. 11E).

  However, in the above manufacturing method, the surface of the transparent substrate 111 that is not covered with the second resist pattern 117 is simultaneously etched during the dry etching of the semitransparent film of the auxiliary pattern portion 116, as shown in FIG. As described above, the level difference 121 is generated on the surface of the transparent substrate 111 at the boundary surface of the resist pattern 117, which causes a problem that the mask quality is deteriorated and cannot be used practically. Therefore, the conventional mask manufacturing method described above cannot be applied to the manufacturing of the photomask of the present invention.

(Method for producing photomask of the present invention)
[First Embodiment]
Therefore, the photomask manufacturing method of the present invention is a manufacturing method that solves the above-described problems, and uses ArF excimer laser as an exposure light source, is used for projection exposure by modified illumination, and is transferred onto a transparent substrate by projection exposure. This is a method of manufacturing a photomask provided with a main pattern transferred to a target surface and an auxiliary pattern formed in the vicinity of the main pattern and not transferred to the transfer target surface.

  FIG. 7 is a process cross-sectional schematic diagram showing the first embodiment of the method of manufacturing the photomask of the present invention shown in FIG. As shown in FIG. 7A, a translucent film 72 is formed on a transparent substrate 71 such as a synthetic quartz substrate, and the phase difference between the light transmitted through the translucent film 72 and the light transmitted through the transparent region of the transparent substrate 71. Then, a photomask blank in which a light shielding film 73 is formed on the translucent film 72 is prepared.

  A conventionally known method can be applied to form the semitransparent film 72 and the light shielding film 73. For example, when the semitransparent film 72 is a molybdenum silicide oxide film (MoSiO), a mixed target of molybdenum and silicon (Mo: Si = 1: 2 mol%) and a reactive sputtering method in a mixed gas atmosphere of argon and oxygen. Even when the light shielding film 73 is a metal film such as chromium, it can be formed by forming a predetermined film thickness by sputtering or the like.

  The film thickness of the translucent film 72 is set to a film thickness at which the phase difference of light is approximately 180 degrees for the following reason. When the semitransparent film 72 is dry-etched to form a mask pattern, the surface of the transparent substrate 71 is usually slightly etched. The etching depth is preferably 4 nm, and the upper limit is set to 10 nm in the present invention. If it exceeds 10 nm, the mask characteristics will be adversely affected. Therefore, in the halftone mask of the present invention, the etching depth of the surface of the transparent substrate 71 during the dry etching of the semitransparent film 72 is controlled to a predetermined depth in the range of 0 to 10 nm, and this depth is included in advance. The phase difference is set. Therefore, the thickness of the semi-transparent film at the time of film formation is set to a film thickness in which the phase difference is approximately 180 degrees in consideration of the variation due to the etching of the transparent substrate in advance, and finally the phase difference of 180 degrees after the main pattern is formed. Is what you get. In the following embodiments, the predetermined etching depth is described as 4 nm as an example. In the present invention, an atomic force microscope (AFM) was used for measuring the film thickness, and a phase difference was measured using a phase shift amount measuring device (Lasertec Corporation: MPM193).

  Next, a first resist pattern 74 is formed on the light shielding film 73, and the light shielding film 73 and the semi-transparent film 72 are sequentially dry-etched into a pattern to form a main pattern portion 75 and an auxiliary pattern portion 76 (see FIG. FIG. 7B).

  Next, the first resist pattern 74 is removed, a second resist pattern 77 is formed on the light shielding film, and the light shielding film 73 of the auxiliary pattern portion 76 is removed by etching (FIG. 7C). .

When the translucent film 72 is a translucent film made of, for example, molybdenum silicide, a fluorine-based gas such as CF ₄ , CHF ₃ , or C ₂ F ₆ , a mixed gas thereof, or a mixture of these gases with oxygen By using this gas as an etching gas, dry etching can be performed to form a pattern. Further, when the light shielding film 73 is, for example, chromium, dry etching is performed using a mixed gas of Cl ₂ and oxygen as an etching gas to form a pattern without damaging the translucent film 72 and the transparent substrate 71. it can. In the process shown in FIG. 7C, the light shielding film 73 can be removed by wet etching with an aqueous solution of ceric ammonium nitrate instead of dry etching.

  Next, the second resist pattern 77 is peeled off, and the entire upper surface of the transparent substrate 71 is dry-etched under the etching conditions of the semi-transparent film 72, so that the light transmitted through the auxiliary pattern and the transparent region of the transparent substrate 71 are transmitted. The auxiliary pattern 78 is formed by dry-etching the semi-transparent film of the auxiliary pattern portion until the film thickness reaches a predetermined phase difference in the range of 70 degrees to 115 degrees (FIG. 7D). The etching amount of the auxiliary pattern 78 for obtaining the above phase difference corresponds to a predetermined film thickness difference in the range of 24 nm to 40 nm in terms of the film thickness difference from the semitransparent film of the main pattern portion. Since the main pattern portion is covered with the light shielding film 73, it is not etched and the film thickness at the time of forming the semitransparent film is maintained. In the step of FIG. 7D, by performing dry etching, uniform and highly accurate etching can be performed on the entire mask surface, and the phase difference of the auxiliary pattern 78 can be controlled to a predetermined value with high accuracy.

  Next, the light shielding film of the main pattern portion is removed by etching to form the main pattern 79. The auxiliary pattern has 180 degrees to the light transmitted through the main pattern 79 and the light transmitted through the transparent region of the transparent substrate 71. A halftone mask 70 that produces the phase difference is formed (FIG. 7E). In the step of FIG. 7E, the light shielding film 73 can be removed by either dry etching or wet etching.

According to the photomask manufacturing method of the first embodiment, a high-quality halftone mask 70 having an auxiliary pattern 78 is obtained without causing a step as described in FIG. 11 on the surface of the transparent substrate 71. be able to.
For example, when molybdenum silicide having a film thickness of 68 nm is a semi-transparent film, the main pattern (film thickness 68 nm) has an ArF excimer laser light transmittance of 6% and a phase difference of 180 degrees from the transparent region of the transparent substrate. A high-quality halftone mask having a predetermined film thickness difference in the range of 24 nm to 40 nm with the main pattern and a predetermined phase difference in the range of 70 degrees to 115 degrees with the transparent area of the transparent substrate. It can be manufactured easily.

[Second Embodiment]
FIG. 8 is a process cross-sectional schematic diagram showing a second embodiment of the method of manufacturing the photomask of the present invention shown in FIG. 1, and the semitransparent film 82 is formed on the transparent substrate 81 as in FIG. The film thickness is such that the phase difference between the light transmitted through the translucent film 82 and the light transmitted through the transparent region of the transparent substrate 81 is approximately 180 degrees, and then a light shielding film 83 is formed on the translucent film 82. The formed photomask blanks are prepared (FIG. 8A).

  Next, the first resist pattern 84 is formed on the light shielding film 83, the light shielding film 83 and the semitransparent film 82 are sequentially dry etched, and the etching is stopped in the middle of the half etching of the semitransparent film 82. At this stage, a thin layer of the semitransparent film 82 to be removed remains partially on the transparent substrate 81 in a half-etched state, but the main pattern portion 85 and the auxiliary pattern portion 86 leave a half-etched portion. (FIG. 8B). The film thickness of the half-etched portion of the semi-transparent film 82 that has been half-etched at this stage is set in advance so as to be a film thickness that is removed by etching simultaneously with the etching of the auxiliary pattern in a later step.

  Next, the first resist pattern 84 is removed, a second resist pattern 87 is formed on the light shielding film, and the light shielding film in the auxiliary pattern portion is removed by etching (FIG. 8C). In the step of FIG. 8C, the light shielding film 83 can be removed by either dry etching or wet etching.

  Next, the second resist pattern 87 is peeled off, and the entire main surface of the transparent substrate 81 is dry-etched under the etching conditions of the semitransparent film 82, so that the light transmitted through the auxiliary pattern and the transparent region of the transparent substrate 81 are transmitted. The semi-transparent film of the auxiliary pattern portion is dry-etched until the film thickness reaches a predetermined phase difference in the range of 70 degrees to 115 degrees to form the auxiliary pattern 88 (FIG. 8D). The etching amount of the auxiliary pattern 88 for obtaining the above phase difference corresponds to a predetermined film thickness difference in the range of 24 nm to 40 nm in terms of the film thickness difference from the main pattern. At this time, the half-etched portion of the semi-transparent film 82 that remains after being half-etched is etched simultaneously. Since the main pattern portion is covered with the light shielding film 83, it is not etched.

  Next, the light shielding film in the main pattern portion is removed by etching to form the main pattern 89, and a phase difference of 180 degrees is generated between the light transmitted through the main pattern 89 and the light transmitted through the transparent region of the transparent substrate 81. Then, the halftone mask 80 having the auxiliary pattern 88 is formed (FIG. 8E). In the step of FIG. 8E, the light shielding film 83 can be removed by either dry etching or wet etching.

  According to the photomask manufacturing method of the second embodiment, the high-quality halftone mask 80 having the auxiliary pattern 88 is obtained without causing the step as described in FIG. 11 on the surface of the transparent substrate 81. be able to.

[Third Embodiment]
FIG. 9 is a process cross-sectional schematic diagram showing an embodiment of a method for producing the photomask of the present invention shown in FIG. As shown in FIG. 9A, a semitransparent film 92a and a semitransparent film 92 are sequentially formed on a transparent substrate 91 such as a synthetic quartz substrate to form two layers of semitransparent films. The lower semi-transparent film 92a functions as an etching stopper layer when the upper semi-transparent film 92 is dry-etched, and also functions as a mask material for the semi-transparent film. The phase difference between the light transmitted through the two-layer semi-transparent film and the light transmitted through the transparent region of the transparent substrate 91 is set to a film thickness that is approximately 180 degrees. The formed photomask blanks are prepared.

  For forming the semi-transparent film 92a, the semi-transparent film 92, and the light shielding film 93, a conventionally known method can be applied. For example, as the lower semi-transparent film 92a, a chromium oxide film (CrO), a chromium nitride film (CrN), or a chromium oxynitride film (CrON), which is a chromium-based material, is used. This is because the thin film of the chromium-based material is translucent to the exposure light and is resistant to the fluorine-based gas used for dry etching of the molybdenum silicide-based material. The chromium-based material can be formed by a conventionally known reactive sputtering method. As the upper semi-transparent film 92, the above molybdenum silicide-based material can be exemplified. When the translucent film 92 is a molybdenum silicide oxide film (MoSiO), a reactive sputtering method is performed in a mixed gas atmosphere of argon and oxygen using a mixed target of molybdenum and silicon (Mo: Si = 1: 2 mol%). Can be formed. The light shielding film 93 is made of chromium, and can be formed by forming a predetermined film thickness by sputtering or the like.

  Next, a first resist pattern 94a is formed on the light shielding film 93, and the light shielding film 93, the semi-transparent film 92, and the semi-transparent film 92a are sequentially dry-etched into a pattern, thereby the main pattern portion 95 and the auxiliary pattern portion. 96 is formed (FIG. 9B). During the etching of the semitransparent film 92a, the transparent substrate 91 is not damaged.

In the process of FIG. 9B, when the light shielding film 93 is, for example, chromium, dry etching is performed using a mixed gas of Cl ₂ and oxygen as an etching gas without damaging the translucent film and the transparent substrate. A pattern can be formed. When the translucent film 92 is, for example, a translucent film of molybdenum silicide-based material, fluorine-based gas such as CF ₄ , CHF ₃ , C ₂ F ₆ , a mixed gas thereof, or a mixture of these gases with oxygen By using this gas as an etching gas, dry etching can be performed to form a pattern. When the translucent film 92a is a chromium-based material such as a chromium oxynitride film, for example, dry etching can be performed using a mixed gas of Cl ₂ and oxygen as an etching gas.

  Next, the first resist pattern 94a is peeled off, a second resist pattern 94b is formed on the light shielding film, and the light shielding film 93 of the auxiliary pattern portion 96 is removed by etching (FIG. 9C). . The light-shielding film 93 may be etched by dry etching or by wet etching with an aqueous solution of ceric ammonium nitrate.

  Next, the second resist pattern 94b is peeled off, and the entire main surface of the transparent substrate 91 is dry-etched under the etching conditions of the semi-transparent film 92, so that the light transmitted through the auxiliary pattern and the transparent region of the transparent substrate 91 are transmitted. The auxiliary pattern 98 is formed by dry etching the semi-transparent film of the auxiliary pattern portion until the light reaches a predetermined phase difference in the range of 70 to 115 degrees (FIG. 9D). The etching amount of the auxiliary pattern 98 for obtaining the above phase difference corresponds to a predetermined film thickness difference in the range of 24 nm to 40 nm in terms of film thickness difference from the main pattern. Since the main pattern portion is covered with the light shielding film 93, it is not etched.

  Next, the light shielding film 93 of the main pattern portion is removed by etching to form the main pattern 99, and the auxiliary pattern 98 is provided. The light transmitted through the main pattern 99 and the light transmitted through the transparent region of the transparent substrate 91 are converted into light. A halftone mask 90 that generates a phase difference of 180 degrees is formed (FIG. 9E). In the step of FIG. 9E, the light shielding film 93 can be removed by either dry etching or wet etching.

  According to the manufacturing method of the photomask according to the third embodiment, the transparent substrate 91 has no level difference as described with reference to FIG. Thus, it is possible to obtain a high-quality halftone mask 90 in which the variation of the above is prevented.

[Fourth Embodiment]
FIG. 10 is a process cross-sectional schematic diagram showing a fourth embodiment of a method for producing a photomask of the present invention. The fourth embodiment is a method for manufacturing a photomask in the case where the light-shielding film at a predetermined position required in the first to third embodiments is left.
Usually, in the projection exposure, the outer periphery of the mask is subjected to multiple exposure, so a photomask having a light shielding region provided on the outer periphery of the mask is used. The fourth embodiment is an example in which a light-shielding region is provided on the outer periphery of the photomask. Since the intermediate steps are the same as the steps shown in the first to third embodiments, refer to FIG. 7 below. However, this will be described with reference to FIG. In FIG. 10, the same parts as those in FIG.

  As shown in FIG. 10A, the manufacturing process proceeds to the process shown in FIG. 7D, and the auxiliary pattern portion 108 is formed. At this time, a light shielding film at a predetermined portion necessary as a photomask is left in advance. FIG. 10 illustrates the case where the light shielding film 104 is left as a light shielding region on the outer periphery of the photomask.

  Next, as shown in FIG. 10B, a light-shielding region resist pattern 105 is formed on the light-shielding film 104 at a required predetermined location. The light shielding region resist pattern 105 may cover not only the light shielding film 104 but also the auxiliary pattern 108. Next, the light-shielding film 103 on the main pattern is removed by etching (FIG. 10C), and then the light-shielding region resist pattern 105 is peeled off to form the main pattern 109 and the auxiliary pattern 108. A halftone mask 100 in which a light shielding film 104 as a light shielding region is provided on the outer periphery of the photomask is formed (FIG. 10D).

According to the photomask manufacturing method of the fourth embodiment, the transparent substrate 101 has the auxiliary pattern in which the step as described with reference to FIG. 11 does not occur on the surface of the transparent substrate 101 and the light shielding region is provided on the outer periphery of the mask. A high quality halftone mask can be obtained.
In the second embodiment and the third embodiment, which are the photomask manufacturing methods of the present invention, a light shielding region can be provided in a desired region such as the outer periphery of the mask in the same manner.

(SRAF etching amount and SRAF dimensions on wafer)
Next, the manufacturing method of the present invention will be described in more detail with respect to an embodiment in which the pitch is changed by a line / space pattern.
In order not to transfer the SRAF onto the wafer, it is necessary that the SRAF light intensity / slice level is 1 or more as described above. FIG. 12 shows the SRAF etching amount (on the mask) and SRAF CD (dimension on the wafer) satisfying the SRAF light intensity / slice level = 1.1 with a margin of 10% in the embodiment in the Cquad illumination shown in FIG. It is a figure which shows the relationship. The etching amount of the SRAF corresponds to the phase difference of the SRAF portion, and the SRAF dimension transferred onto the wafer increases as the etching amount of the SRAF portion increases. The etching amount of SRAF indicates a film thickness difference between the SRAF film thickness after etching and the film thickness of the main pattern (the initial film thickness of the semitransparent film: 68 nm).

  In FIG. 12, the region where the SRAF etching amount indicated by the dotted arrow in the drawing is 48 nm or more corresponds to a region where the phase difference of the SRAF portion is 50 degrees or less (the range described in the above-mentioned Patent Document 2). In this case, the SRAF CD on the wafer is 50 nm or more. However, when the SRAF dimension on the wafer is 50 nm (200 nm on a quadruple mask) or more, the space between the main pattern and the SRAF is as narrow as 200 nm or less on the mask, and a severe value that alignment deviation in the mask manufacturing process is hardly allowed. Become. In the current laser exposure apparatus for mask manufacture, since 200 nm or more is required as a space between patterns in consideration of misalignment, mask manufacture becomes difficult even if the SRAF dimension is too large. On the other hand, if the SRAF etching amount is less than 24 nm (the SRAF CD on the wafer is 20 nm), the SRAF dimension cannot be sufficiently increased. Therefore, in FIG. 12, the region indicated by the solid line double arrow is a preferable SRAF etching amount region in consideration of mask manufacturing.

(Effect of SRAF etching amount error on main pattern CD)
Next, the effect on the main pattern CD adjacent to the SRAF when an error occurs in the SRAF etching amount will be described with reference to FIG. FIG. 13 shows the main pattern CD error on the wafer relative to the etching amount error when the SRAF etching amount is 28 nm, 38 nm, and 48 nm in the embodiment in the Cquad illumination shown in FIG. 3, and the larger the SRAF etching amount, It can be seen that the main pattern CD fluctuations in FIG. It is shown that when the SRAF etching amount is 48 nm, a slight etching error greatly affects the size of the main pattern at the repeated end. Therefore, in the present invention, the SRAF etching amount of 48 nm or more (corresponding to the phase difference of 50 degrees or less in Patent Document 2) is an undesirable range in the manufacturing process.

(Effect on SRAF etching amount and repeated edge main pattern)
A description will be given of the repeated edge main pattern CD, the influence on the defocus, and the light intensity distribution when the SRAF etching amount is changed.
FIG. 14 shows the relationship between the main pattern CD at the repetitive edge on the wafer and the defocus when the SRAF etching amount is changed every 4 nm in the range of 24 nm to 48 nm in the embodiment in the Cquad illumination shown in FIG. FIG. For reference, the case where there is no SRAF and the case where there is no SRAF etching is also shown. When the SRAF etching amount is in the range of 24 nm to 40 nm, the fluctuation of the main pattern CD is relatively gradual with respect to the change of the defocus and shows almost the same behavior. However, when the SRAF etching amounts are 44 nm and 48 nm, the main pattern CD shows a large variation with respect to the change of defocus.

  FIG. 15 shows the light intensity distribution of the main pattern at the repeated end on the wafer when the SRAF etching amount is changed every 4 nm in the range of 24 nm to 48 nm in the embodiment in the Cquad illumination shown in FIG. In the SRAF etching amount range of 24 nm to 40 nm, the slope of the light intensity distribution is relatively large and shows almost the same behavior. However, when the SRAF etching amounts are 44 nm and 48 nm, the slope of the light intensity distribution becomes small, indicating that the resolution of the main pattern is low.

  Therefore, from the results shown in FIGS. 12 to 15, the SRAF etching amount of 44 nm or more is an inappropriate range, and in order to improve the depth of focus and form a high resolution pattern, the SRAF etching amount is 24 nm to 40 nm. Is a preferred range. This etching amount corresponds to a phase difference of 115 to 70 degrees. The phase difference was measured with the above-mentioned phase shift amount measuring apparatus (Lasertec Corporation: MPM193).

(Verification by SRAF between main patterns)
Next, as another embodiment, the present invention is verified for a case where there is an auxiliary pattern (SRAF) between main patterns.
As the simulation software, EM-Suite (trade name: manufactured by Panoramic Technology) was used as described above. As main simulation conditions, an ArF excimer laser (193 nm) was used as an illumination light source, NA was 1.35, and a quasar (registered trademark) pupil filter 161 shown in FIG. 16 was used. (A) is a schematic plan view of the QUASAR 161, (B) is a schematic perspective view when the mask 163 is irradiated with exposure light (referred to as QUASAR illumination), and (C) is a mask pattern. 164 is a schematic plan view of 164. FIG. It is. Quasar has an opening angle of the fan-shaped light transmission portion of 30 degrees, an outer diameter of 0.85, and an inner diameter of 0.65 (the radius of the pupil filter is 1). As a mask, a halftone mask (6% halftone) having an auxiliary pattern according to the present invention having a transmittance of 6% at an exposure wavelength of 193 nm of molybdenum silicide was used. The target CD on the wafer is 60 nm, one SRAF 166 is provided between the main patterns 165, the pattern pitch is a through pitch line / space from the minimum pitch of 120 nm, and the SRAF 166 is 250 nm in pitch.

  FIG. 17 is a diagram showing the relationship between the SRAF etching amount (on the mask) and the SRAF CD (dimensions on the wafer) in the embodiment of the QUASAR illumination shown in FIG. In FIG. 17, similarly to FIG. 12, the region where the SRAF etching amount indicated by the dotted arrow in the drawing is 48 nm or more is a region where the phase difference of the SRAF portion is 50 degrees or less (the range described in the invention of Patent Document 2 above). ). In the case of the present embodiment, since the original SRAF dimension is very small as 9 nm on the wafer (36 nm on the mask) compared to the condition of the main pattern of line / space repetition end and Cquad shown in FIG. Even in the region where the SRAF etching amount is 48 nm or more, the problem that the SRAF dimension on the wafer is too large does not occur.

  FIG. 18 is a diagram showing the influence on the main pattern CD on the wafer when an error occurs in the etching amount of the SRAF on the mask in the embodiment of the QUASAR illumination shown in FIG. Similar to FIG. 13, the SRAF etching amounts are 28 nm, 38 nm, and 48 nm. As shown in FIG. 18, the main pattern CD error on the wafer is extremely small with respect to the SRAF etching amount error.

  FIG. 19 shows the relationship between the main pattern CD and the defocus when the SRAF etching amount is changed every 4 nm in the range of 24 nm to 48 nm in the embodiment of the QUASAR illumination shown in FIG. FIG. For reference, the case where there is no SRAF and the case where there is no SRAF etching are also shown.

  As shown in FIG. 19, when there is no SRAF, the depth of focus is expanded by providing the SRAF as shown by the solid arrow in the figure. However, even without SRAF etching, it is asymmetric with respect to defocus. As the SRAF etching amount increases, the defocusing asymmetry increases as the SRAF etching amount increases, and the main pattern CD on the wafer rises on the defocusing minus side. The main pattern CD on the wafer is lowered, and the dimensional variation of the main pattern on the wafer is asymmetric. For example, when the etching amount is increased to 48 nm and the SRAF etching amount is increased, the transferred image characteristics are deteriorated due to asymmetry. From the results shown in FIGS. 17 to 19, in the present invention, the upper limit of the SRAF etching amount was set to 40 nm. Therefore, in the case of SRAF between main patterns (Quasar illumination), the effect of the photomask of the present invention was verified as in the case of the main pattern repetition end SRAF (Cquad illumination).

  As described above, in the photomask manufacturing method of the present invention, the main pattern and the auxiliary pattern are composed of a translucent film made of the same material, and therefore, the process of forming the translucent film is easy. Further, the phase difference between the light transmitted through the auxiliary pattern and the light transmitted through the transparent region of the transparent substrate is set to a predetermined phase difference in the range of 70 degrees to 115 degrees, and the semi-transparent film of the auxiliary pattern is dry-etched, By obtaining the film thickness difference of the auxiliary pattern as a predetermined film thickness difference in the range of 24 nm to 40 nm, that is, as the etching amount of the auxiliary pattern, a desired phase difference of the auxiliary pattern can be easily obtained. In addition, the photomask can improve the pattern transfer characteristics without increasing the difficulty of mask manufacturing, by making the space between the main pattern and the auxiliary pattern wider, making it possible to achieve a manufacturing method with increased margin of misalignment. Can be obtained.

10, 20 Halftone mask 11, 21 Transparent substrate 12, 22 Main pattern 13, 23 Auxiliary pattern 24 Lower semi-transparent film (etching stop layer)
25 Upper-layer translucent films 31, 161 Pupil filters 32, 162 Illumination light 33, 163 Mask 164 Mask pattern 165 Main pattern 166 SRAF
70, 80, 90, 100 Halftone mask 71, 81, 91, 101 Transparent substrate 72, 82, 102 Translucent film 73, 83, 93, 103 Light shielding film 74, 84 First resist pattern 75, 85, 95 Main Pattern part 76, 86, 96 Auxiliary pattern part 77, 87 Second resist pattern 78, 88, 98 Auxiliary pattern 79, 89, 99 Main pattern 92a Semi-transparent film (etching stop layer) under layer
92 Upper-layer translucent film 94a First resist pattern 94b Second resist pattern 94c Third resist pattern 104 Light-shielding film 105 Light-shielding area resist pattern 110 Halftone mask 111 of conventional manufacturing method Transparent substrate 112 Translucent film 113 Light-shielding Film 114 First resist pattern 115 Main pattern part 116 Auxiliary pattern part 117 Second resist pattern 118 Auxiliary pattern 119 Main pattern 121 Step 1 on transparent substrate surface Main pattern 2 Translucent auxiliary pattern 301 Transparent substrate 302 Translucent film 304 Transparent film

Claims (13)

In a photomask used for projection exposure by modified illumination using an ArF excimer laser as an exposure light source, the photomask is transferred onto one main surface of a transparent substrate onto the transfer target surface by the projection exposure, and A photomask provided with an auxiliary pattern formed in the vicinity of the main pattern and not transferred to the transfer target surface,
The main pattern and the auxiliary pattern are composed of a translucent film made of the same material,
A phase difference of 180 degrees is generated between the light transmitted through the main pattern and the light transmitted through the transparent area of the transparent substrate, and the light transmitted through the auxiliary pattern and light transmitted through the transparent area of the transparent substrate is 70 degrees. A photomask characterized by producing a predetermined phase difference in a range of ˜115 degrees.   2. The photomask according to claim 1, wherein the auxiliary pattern is thinner than the main pattern, and the difference in thickness is a predetermined thickness difference in a range of 24 nm to 40 nm.   The photomask according to claim 2, wherein the film thickness difference is formed by dry etching.   The photomask according to any one of claims 1 to 3, wherein the exposure light transmittance of the auxiliary pattern is a predetermined transmittance in a range of 15% to 29%.   The photomask according to any one of claims 1 to 4, wherein the translucent film made of the same material is a single-layer translucent film or a two-layer translucent film.   The photomask according to any one of claims 1 to 5, wherein a light-shielding region is formed on an outer peripheral portion of the photomask.   The single-layer semi-transparent film is a molybdenum-silicide-based material semi-transparent film, and the two-layer semi-transparent film is a chromium-based material semi-transparent film and a molybdenum-silicide-based material semi-transparent film sequentially on the transparent substrate. The photomask according to any one of claims 1 to 6, wherein the photomask is provided.   The photomask according to any one of claims 1 to 7, wherein the main pattern and the auxiliary pattern are both line patterns, and the main pattern is an isolated pattern or a periodic pattern. An ArF excimer laser is used as an exposure light source, is used for projection exposure by modified illumination, and is formed on one main surface of a transparent substrate, and is formed in the vicinity of the main pattern on the transfer target surface by the projection exposure. A photomask manufacturing method provided with an auxiliary pattern that is not transferred to the transfer target surface,
(A) A semitransparent film and a light-shielding film are sequentially formed on one main surface of the transparent substrate, and a phase difference between light transmitted through the semitransparent film and light transmitted through a transparent region of the transparent substrate is approximately 180 degrees. A film thickness forming step;
(B) forming a first resist pattern on the light shielding film, sequentially dry-etching the light shielding film and the translucent film, and forming a main pattern portion and an auxiliary pattern portion;
(C) removing the first resist pattern, then forming a second resist pattern on the light shielding film, and etching and removing the light shielding film of the auxiliary pattern portion;
(D) The second resist pattern is peeled, and then the entire surface of one main surface of the transparent substrate is dry-etched, so that the light transmitted through the auxiliary pattern and the light transmitted through the transparent region of the transparent substrate are 70 degrees. A step of dry-etching the semi-transparent film of the auxiliary pattern portion to a film thickness having a predetermined phase difference in a range of ˜115 degrees to form an auxiliary pattern;
(E) The light shielding film of the main pattern portion is removed by etching to form a main pattern, and a phase difference of 180 degrees is generated between light transmitted through the main pattern and light transmitted through the transparent region of the transparent substrate. Process,
A method for manufacturing a photomask, comprising:   10. The photomask manufacturing method according to claim 9, wherein the dry etching of the semitransparent film in the step (b) is half etching halfway through the film thickness of the semitransparent film. Method. An ArF excimer laser is used as an exposure light source, is used for projection exposure by modified illumination, and is formed on one main surface of a transparent substrate, and is formed in the vicinity of the main pattern on the transfer target surface by the projection exposure. A photomask manufacturing method provided with an auxiliary pattern that is not transferred to the transfer target surface,
(A) A semi-transparent film and a light-shielding film are sequentially formed on one main surface of the transparent substrate, the semi-transparent film is composed of two semi-transparent films, and the lower semi-transparent film on the transparent substrate side is an upper layer. A step of serving as an etching stop layer for the semitransparent film, and a film thickness in which the phase difference between the light transmitted through the two semitransparent films and the light transmitted through the transparent region of the transparent substrate is approximately 180 degrees;
(B) forming a first resist pattern on the light-shielding film, sequentially dry-etching the light-shielding film and the two semi-transparent films, and forming a main pattern portion and an auxiliary pattern portion;
(C) removing the first resist pattern, then forming a second resist pattern on the light shielding film, and etching and removing the light shielding film of the auxiliary pattern portion;
(D) The second resist pattern is peeled, and then the entire surface of one main surface of the transparent substrate is dry-etched, so that the light transmitted through the auxiliary pattern and the light transmitted through the transparent region of the transparent substrate are 70 degrees. A step of dry-etching the semi-transparent film of the auxiliary pattern portion to a film thickness having a predetermined phase difference in a range of ˜115 degrees to form an auxiliary pattern;
(E) The light shielding film of the main pattern portion is removed by etching to form a main pattern, and a phase difference of 180 degrees is generated between light transmitted through the main pattern and light transmitted through the transparent region of the transparent substrate. Process,
A method for manufacturing a photomask, comprising:   The photomask according to any one of claims 9 to 11, wherein a film thickness difference between the auxiliary pattern and the main pattern is a predetermined film thickness difference in a range of 24 nm to 40 nm. Manufacturing method. The photomask manufacturing method according to any one of claims 9 to 12, wherein after the step (d) of forming the auxiliary pattern, a light-shielding region resist pattern is formed, and the main pattern is formed. Forming a main pattern by removing the light shielding film by dry etching, and forming a light shielding region on the outer periphery of the photomask;
A method for producing a photomask, further comprising:

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