JP2010061020A - Method for manufacturing multi-tone photomask, and multi-tone photomask - Google Patents

Abstract

The thickness of a semi-transparent film in a semi-translucent portion is made constant, and the gradation change at the boundary between the semi-transparent film and the light shielding film is made steep.
[Means for Solving the Problems]
A multi-tone photomask including a light-shielding portion that blocks exposure light, a light-transmitting portion that transmits exposure light, and a semi-light-transmitting portion that transmits part of the exposure light is prepared on a transparent substrate. Next, a transmission band having a width less than the resolution limit of the exposure apparatus is formed at the boundary between the light shielding portion and the semi-transparent portion. The step of forming the transmission band is to form a transmission band having a width equal to or less than the resolution limit of the exposure apparatus at the boundary between the light shielding film and the semi-transparent film by zapping after forming the light shielding part, the light transmitting part, and the semi-transparent part. Form.
[Selection] Figure 2

Description

The present invention relates to a multi-tone photomask using a semi-transparent film, and more particularly to a technique for improving contrast (light intensity ratio) at a boundary portion between a light-shielding portion and a semi-transparent portion.

Since multi-tone photomasks can form resist patterns with different film thicknesses by one exposure, they are attracting attention because of various advantages such as a reduction in the number of mask processes (see Patent Documents 1 to 3, etc.).

However, in the conventional multi-tone photomask, the contrast (light intensity ratio) tends to decrease at the boundary between the light-shielding portion and the semi-translucent portion, that is, in the projection exposure using the multi-tone photomask. The change in the resist film thickness obtained by developing the photoresist in the portion corresponding to the boundary portion was likely to be gradual.

In order to solve this problem, for example, in Patent Document 4, a so-called “bottom half type” multi-tone photomask in which a light shielding film and a semi-transparent film are laminated in this order on a transparent substrate is referred to as “light shielding region”. A configuration in which “a transmittance adjusting region where a transparent substrate is exposed” is formed between the “semi-transparent region” (19th to 22nd paragraphs, FIG. 1 and the like) is disclosed.
JP 2002-196474 A JP 2007-233350 A JP 2008-058943 A JP 2008-065138 A

In addition to the “bottom half type” multi-tone photomask, a so-called “top half type” multi-tone photomask in which a light-shielding film and a semi-transparent film are laminated in this order on a transparent substrate is also known. .

Even when a top half type photomask is used, there is a problem that the contrast is lowered at the boundary between the translucent part and the semitranslucent part, but the mechanism is slightly different. That is, in the case of the top half type, since the semi-transparent film is formed so as to cover the pattern of the light shielding film, the decrease in contrast causes the step of the semi-transparent film at the edge of the light shielding film to scatter the exposure light. Due to that.

For example, FIGS. 4A and 4B show a conventional so-called top half type multi-tone photomask 101 (a plan view and a cross-sectional view, respectively). As shown in these drawings, the conventional multi-tone photomask includes a light-shielding portion A, a semi-transparent portion B, and a translucent portion C, and the pattern of the light-shielding film 111 constituting the light-shielding portion is the semi-transparent film 112. 4B, as is clear from the cross-sectional view shown in FIG. 4B, the light shielding part of the pattern of the light shielding film 111 and the boundary part (edge part) of the pattern of the semi-transparent film 112 are A step S of the semi-transparent film 112 formed when the semi-transparent film 112 covers the pattern of the light shielding film 111 is formed.

FIG. 4C is a cross-sectional view of a resist pattern completed by irradiating the multi-tone photomask 101 shown in FIG. 4B with exposure light I from an exposure apparatus (not shown), and then developing and the like. Shape. A resist pattern 305 having a film thickness changed according to an exposure site is formed on the exposure target substrate 300, but the resist film thickness in the semi-translucent portion is thick and uneven at both ends, and the light shielding portion It can be seen that the resist film thickness changes gently at the boundary with the semi-transparent portion. It can be seen that this is a shape far from the ideal resist pattern shape R indicated by the broken line in the figure.

FIG. 5 shows how the exposure light I is scattered at the step S. FIG. As shown in this figure, at the step S, the film thickness is locally larger than the film thickness of the adjacent semi-transparent film 112, and the surface shape is a gently curved cross section. For this reason, the exposure light passing through the step S cannot travel straight and is scattered in various directions.

As a result, the shape of the resist pattern corresponding to the projection-exposed semi-transparent portion becomes gentle at the portion corresponding to the step S, and the contrast (light intensity ratio) is lowered, so that the change in gradation is caused. There is a problem that it becomes difficult to distinguish and the process margin of the process is insufficient.

The present invention has been made in view of the above-described problems. The thickness of the semi-transparent film in the semi-transparent portion is made constant, and the gradation corresponding to the boundary portion between the semi-transparent film and the light-shielding film is obtained. The technical problem is to increase the process margin of the process by making the change steep.

The multi-tone photomask manufacturing method according to the present invention is used to form a resist pattern on an exposure target substrate on which a resist film is formed by irradiating exposure light from an exposure apparatus.
For a multi-tone photomask including a light-shielding part that blocks the exposure light, a translucent part that transmits the exposure light, and a semi-transparent part that transmits part of the exposure light on a transparent substrate,
A method for producing a multi-tone photomask, comprising a step of forming a transmission band having a width equal to or less than a resolution limit of the exposure apparatus at a boundary between the light shielding part and the semi-transparent part,
In the step of forming the transmission band, after forming the light-shielding portion, the light-transmitting portion, and the semi-light-transmitting portion, a width less than a resolution limit of the exposure apparatus is formed at a boundary portion between the light-shielding film and the semi-light-transmitting film by zapping. It is characterized by forming a transmission band.

Zapping is usually used to correct a defective portion of a pattern after forming a multi-tone photomask. One of the technical features of the present invention is not only a defective portion of a pattern in the zapping process. Then, zapping is also performed on the boundary portion between the light-shielding portion and the semi-transparent portion where the contrast tends to decrease, thereby forming a transmission band afterwards. By such a method, when the half-transparent film is provided on the upper side of the light-shielding film in the structure of the multi-tone photomask, that is, the light-shielding portion, the semi-transparent film is provided on the lower side of the light-shielding film. Regardless of the bottom half type, the contrast at the boundary between the light shielding portion and the semi-translucent portion can be increased afterwards.

In addition, since the width of the transmission band in the above configuration is set to a width equal to or smaller than the resolution limit of the exposure apparatus, the transmission band is not resolved during development. Further, since the transmission band is formed afterwards, there is an advantage that it can be formed only in a specific pattern having insufficient contrast after actual exposure and development.

In the above configuration, a light shielding film is formed on the transparent substrate, and a first photoresist film is formed on the light shielding film, and exposure light is irradiated from the exposure apparatus and developed to form a light shielding film pattern. A first pattern forming step, a step of forming a semi-transparent film so as to cover the pattern of the light-shielding film, and a second photoresist film formed on the semi-transparent film and exposing from an exposure apparatus And a second pattern forming step of forming a pattern of the semi-translucent film by irradiating and developing light.

In the case of including such a configuration, the multi-tone photomask has a so-called top half type structure. As described above, as described above, the multi-tone photomask manufacturing method according to the present invention can be applied regardless of the structure of the photomask. Since a step portion is easily formed at the edge portion, it is considered that this portion is more effective in that this portion can be effectively removed by a width less than the resolution limit of the exposure apparatus.

The zapping in the configuration of the present invention is preferably a laser transpiration method or a focused ion beam method. These are examples of means used in the process of correcting defects, and remove a semi-transparent film or a laminated film of a semi-transparent film and a light-shielding film (regardless of the order of lamination) formed on a transparent substrate. This is because a transmission band having a width less than the resolution limit of the exposure apparatus can be formed.

The multi-tone photomask according to the present invention is used to form a resist pattern on an exposure target substrate on which a resist film is formed by irradiating exposure light from an exposure apparatus.
A multi-tone photomask comprising a light shielding part that blocks the exposure light on a transparent substrate, a translucent part that transmits the exposure light, and a semi-transparent part that transmits part of the exposure light,
A transmission band having a width less than the resolution limit of the exposure apparatus is provided at the boundary between the light shielding part and the semi-translucent part, and local film thickness variation parts are formed at both ends of the transmission band. It is characterized by.

Note that the film thickness variation portion as described above is formed when zapping is performed by a laser evaporation method (also referred to as “laser zapping”), and the film thickness variation portion is below the resolution limit of the exposure apparatus. Needless to say, it is necessary to be of a size.

In the method of manufacturing a multi-tone photomask according to the present invention, a transmission band is formed afterwards by zapping at a boundary portion where the light shielding portion and the semi-transparent portion are adjacent to each other. An advantage of this method is that a transmission band can be provided afterwards in a conventional multi-tone photomask that has already been completed (where no transmission band is formed). The target multi-tone photomask may be a top half type or a bottom half type. When a resist pattern is formed using a photomask obtained by the photomask manufacturing method according to the present invention, the contrast (light intensity ratio) between the light-shielding portion and the semi-transparent portion is improved, so that the change in gradation Can be easily determined, and the process margin of the process can be increased.

In the first embodiment, an example of a method for manufacturing a multi-tone photomask according to the present invention and a photomask obtained thereby will be described.

(First embodiment)
As described above, FIGS. 4A and 4B show a conventional so-called top-half type multi-tone photomask 101. As shown in these drawings, the conventional multi-tone photomask includes a light-shielding portion A, a semi-transparent portion B, and a translucent portion C. 4B, as is clear from the cross-sectional view shown in FIG. 4B, the light shielding part of the pattern of the light shielding film 111 and the boundary part (edge part) of the pattern of the semi-transparent film 112 are A step S of the semi-transparent film 112 formed when the semi-transparent film 112 covers the pattern of the light shielding film 111 is formed. When exposure is performed as it is using the conventional photomask 101, the contrast is lowered at the boundary between the light shielding portion and the semi-transparent portion due to the step S as shown in FIG.

In the present invention, the transmission band is formed afterwards by performing zapping on necessary portions on the pattern of the conventional photomask 101. That is, the multi-tone photomask may be formed by a conventional manufacturing method. A pattern for improving the contrast is formed afterwards only in a necessary portion. Specifically, a transmission band having a width equal to or smaller than the resolution limit of the exposure apparatus may be formed in the step S portion that causes the contrast to decrease.

FIG. 1 is a diagram showing a procedure for explaining a method of manufacturing a multi-tone photomask according to the first embodiment of the present invention.

Step S1 is a step of forming a conventional multi-tone photomask according to a conventional method. Taking the method of manufacturing a multi-tone photomask having a top half type structure as an example, step S1 is a step of forming a light-shielding film on a transparent substrate, and a first photoresist film is formed on the light-shielding film and exposed. A first pattern forming step of forming a light-shielding film pattern by irradiating exposure light from the apparatus and developing; a step of forming a semi-transparent film so as to cover the pattern of the light-shielding film; And a second pattern forming step of forming a pattern of the semi-translucent film by forming the photoresist film 2 and irradiating with exposure light from the exposure apparatus and developing.

Step S2 is a step of performing exposure and development using the multi-tone photomask obtained in step S1. By this step, the presence or absence of a defective exposure portion such as a pattern defect and a low contrast portion is confirmed. In the case of a large-sized photomask or the like, predetermined equipment or the like is required for exposure and development. Therefore, if exposure failure data indicating the relationship between the failure pattern and the exposure failure is accumulated, step S2 may be omitted. .

Step S3 is a step of identifying a defect or a low-contrast pattern on the multi-tone photomask using an optical microscope or the like based on the exposure failure position data.

Step S4 is a step of zapping the exposure failure position. By this step, the translucent film and the semi-transparent film in the pattern defect portion are removed. In addition, when the process of correcting the pattern defect of the semi-transparent film is necessary, a process of forming the semi-transparent film with a predetermined film forming apparatus is required after that. For this zapping, means such as a laser transpiration method (so-called laser zapping) or a focused ion beam method of irradiating gallium ions or the like can be used. Thereby, by forming a transmission band having a width less than the resolution limit of the exposure apparatus in the step S portion, the thickness of the semi-transparent film in the semi-transparent portion becomes constant, and the light shielding portion and the semi-transparent portion The contrast after exposure / development corresponding to the boundary of the image becomes clear.

FIG. 2A is a plan view showing a part of the pattern of the multi-tone photomask according to the first embodiment of the present invention. Moreover, FIG.2 (b) is sectional drawing of the X2-X2 line | wire shown to Fig.2 (a). As shown in these drawings, the multi-tone photomask 1 has a light shielding film pattern 11 formed on the surface of a transparent substrate 10 and a semi-transparent film pattern 12 formed thereon.

This multi-tone photomask 1 is provided with a light-shielding portion A, a light-transmitting portion B, and a semi-light-transmitting portion C on a transparent substrate 10 so that the exposure light intensity is changed by a single exposure. It can express gradation.

The light shielding portion A is configured by a portion where the pattern of the light shielding film 11 is formed, and this includes a portion where the semi-transparent film 12 is laminated on the light shielding film. The semi-translucent portion B is composed of a portion where twelve patterns of the semi-transparent film are formed, and this includes a band-like transmissive region provided at the end of the semi-transparent film (this is referred to as “transmission band 20 ”). The light transmitting portion C is a portion other than the light shielding portion and the semi-light transmitting portion in the exposure pattern forming region, and is a portion where a film that greatly changes the transmittance is not formed on the transparent substrate 10.

The transmission band 20 is a band-shaped pattern formed in step S4, and its width d is set to be less than the resolution limit of the exposure apparatus. For this reason, the pattern of the transmission band is not transferred onto the photoresist. When the zapping is laser zapping in step S4, as shown in FIG. 1B, a local film thickness variation portion 26 is likely to be formed at the edge portion of the semi-transparent film. The size of the film thickness variation portion varies depending on the laser beam conditions, but it is always formed along the trajectory through which the laser beam passes as long as laser zapping is performed. The reason why the film thickness variation portion 26 is formed is thought to be that the thin film at the end is peeled off and rounded by the thermal energy of the laser beam. For this reason, if the energy of the laser beam is too large, the film thickness tends to be thicker than the surroundings, and if it is small, the film thickness tends to be thin. It is necessary to examine the conditions of the laser beam in advance and make adjustments so as not to adversely affect the exposure.

In any case, the fact that the multi-tone photomask according to the present invention is manufactured by applying laser zapping to zapping can be verified by observing the presence or absence of the film thickness variation portion 26 described above.

When the transmission band 20 is provided in the semi-transmission part B, the amount of exposure light passing through the semi-transmission part is increased. Therefore, it is preferable to adjust the width of the transmission band by zapping to the minimum necessary. It is preferable to set the transmittance of the semi-transparent film in advance in the pattern design stage so as to reduce the transmittance. Specifically, when the area where the transmission band is to be formed is known in advance, the film thickness of the semi-translucent film is set larger than when the transmission band is not provided, or the composition of the semi-translucent film is adjusted. Then, the composition ratio of metal atoms (for example, chromium) constituting the translucent film is increased. In this way, it is possible to adjust so that the overall light quantity does not change when the exposure is performed by subtracting the increase in the light quantity due to the transmission band 20.

As described above, the width of the transmission band 20 needs to be selected in consideration of both the size of the semi-transparent portion, particularly the distance between the opposing light shielding portions and the resolution of the projection exposure apparatus. For example, when the width of the semi-transmission part (distance between the light shielding parts opposite to each other) is 4 μm and the resolution of the projection exposure apparatus is about 2 μm, according to the results of various experiments, the width of the transmission band is about 0. It has been found that a range of 0.5 to 1.5 μm, particularly about 1.0 μm, is preferable.

FIG. 2C shows a resist pattern completed by irradiating the multi-tone photomask 1 shown in FIG. 2B with exposure light I from a projection exposure apparatus (not shown), and then developing and the like. Cross-sectional shape. A multi-tone resist pattern 35 having a film thickness changed according to the exposed part is formed on the substrate 30 to be exposed, but the resist film thickness corresponding to the semi-translucent part is uniform, and the light-shielding part and the semi-transparent part are provided. It can be seen that the resist film thickness changes sharply at the boundary with the optical part.

That is, according to the multi-tone photomask according to the first embodiment of the present invention, it approaches the ideal resist pattern shape R indicated by the broken line in the figure, and the contrast at the boundary between the light shielding portion and the semi-transparent portion. The process margin can be increased by increasing the light intensity ratio.

(Second Embodiment)
3A to 3C show variations in the shape of the transmission band. FIG. 3A shows a case where a region sandwiched between two light-shielding films configured in an L shape is a semi-transparent part, and constitutes a semi-transparent part with the light-shielding film 11a constituting the light-shielding part. A transmission band 20a is provided at the boundary with the semi-transparent film 12a. FIG. 3B shows a case where a region sandwiched between two light-shielding films configured in an I-shape is a semi-transparent portion, and constitutes a semi-transparent portion with the light-shielding film 11b constituting the light-shielding portion. A transmission band 20b is provided at the boundary with the semi-transparent film 12b. FIG. 3C shows a case where a region inside the light shielding film formed in a hole shape such as a regular polyhedron (including a circle) becomes a semi-translucent portion, and the light shielding film 11c constituting the light shielding portion and the semi-transparent portion. A transmission band 20c is provided at the boundary with the semi-transparent film 12c constituting the light part.

In any case, by providing the transmission bands 20a to 20c, the change in the resist film thickness corresponding to the boundary portion between the light shielding portion and the semi-transparent portion after the formation of the photoresist pattern becomes steep, and the process margin of the process Increased.

(Third embodiment)
In the first and second embodiments, an embodiment using a multi-tone photomask having a so-called “top half type” structure in which a light-shielding film pattern is formed and then a semi-transparent film is formed will be described. However, the present invention can also be applied to a multi-tone photomask having a structure called “bottom half type” in which a semi-transparent film is provided below the light-shielding film.

As is well known, the bottom half-type multi-tone photomask is composed of an upper light shielding film and a lower semitransparent film with respect to a mask blank in which a semitransparent film and a light shielding film are laminated in this order on a transparent substrate. Can be obtained by sequentially patterning, but can be easily manufactured by forming a transmission band pattern in the pattern forming process of the semi-transparent film. As described above, in the bottom half type multi-tone photomask, the step S as shown in FIG. 4 hardly occurs, but even in this case, if a transmission band is provided, the film of the semi-transparent film in the semi-transparent portion is provided. The process margin of the process can be increased by making the thickness constant and making the change in gradation corresponding to the boundary between the semi-transparent film and the light shielding film steep.

The multi-tone photomask according to the present invention has a great industrial applicability as it increases the process margin in the resist pattern forming process.

FIG. 1 is a diagram showing a procedure for explaining a method of manufacturing a multi-tone photomask according to the first embodiment of the present invention. FIG. 2A is a plan view showing a part of the pattern of the multi-tone photomask according to the first embodiment of the present invention. FIG. 2B is a cross-sectional view taken along line X2-X2 shown in FIG. FIG. 2C is a cross-sectional view of a resist pattern completed by irradiating the multi-tone photomask 1 shown in FIG. 2B with exposure light I from an exposure apparatus (not shown) and then developing and the like. Shape. Fig.3 (a)-FIG.3 (c) have shown the variation of the shape of a transmission band. FIG. 3A shows a case where a region sandwiched between two light shielding films configured in an L shape is a semi-transparent portion, and FIG. 3B shows two light shielding films configured in an I shape. 3 (c) shows a case where a region inside a light shielding film configured in a hole shape such as a regular polyhedron (including a circle) becomes a semi-transparent portion. It is. FIG. 4A is a plan view showing a part of a pattern of a conventional multi-tone photomask. FIG. 4B is a cross-sectional view taken along line X1-X1 shown in FIG. In FIG. 4C, the multi-tone photomask 101 shown in FIG. 4B is irradiated with exposure light I from a projection exposure apparatus (not shown), and then the resist pattern completed through processes such as development is performed. Cross-sectional shape. FIG. 5 shows how the exposure light is scattered at the step S of the semi-transparent film.

Explanation of symbols

1 Multi-tone photomasks 11 and 111 Light-shielding films 12 and 112 Semi-transparent film 20 Transmission band 26 Thickness variation portion

Claims (4)

Used to form a resist pattern on an exposure target substrate on which a resist film has been formed by irradiating exposure light from an exposure apparatus,
For a multi-tone photomask including a light-shielding part that blocks the exposure light, a translucent part that transmits the exposure light, and a semi-transparent part that transmits part of the exposure light on a transparent substrate,
A method for producing a multi-tone photomask, comprising a step of forming a transmission band having a width equal to or less than a resolution limit of the exposure apparatus at a boundary between the light shielding part and the semi-transparent part,
In the step of forming the transmission band, after forming the light-shielding portion, the light-transmitting portion, and the semi-light-transmitting portion, the width below the resolution limit of the exposure apparatus is formed at the boundary between the light-shielding film and the semi-light-transmitting film by zapping. A method for producing a multi-tone photomask, comprising forming a transmission band having the same. A step of forming a light-shielding film on the transparent substrate; a first photoresist film formed on the light-shielding film; and a pattern of the light-shielding film formed by irradiating exposure light from an exposure apparatus and developing A pattern forming step, a step of forming a semi-transparent film so as to cover the pattern of the light-shielding film, and a second photoresist film is formed on the semi-transparent film, and exposure light is irradiated from an exposure apparatus. The method for producing a multi-tone photomask according to claim 1, further comprising a second pattern forming step of forming a pattern of the semi-translucent film by developing. 2. The method of manufacturing a multi-tone photomask according to claim 1, wherein the zapping is a laser evaporation method or a focused ion beam method. Used to form a resist pattern on an exposure target substrate on which a resist film has been formed by irradiating exposure light from an exposure apparatus,
A multi-tone photomask comprising a light shielding part that blocks the exposure light on a transparent substrate, a translucent part that transmits the exposure light, and a semi-transparent part that transmits part of the exposure light,
A transmission band having a width less than the resolution limit of the exposure apparatus is provided at the boundary between the light shielding part and the semi-translucent part, and local film thickness variation parts are formed at both ends of the transmission band. Multi-tone photomask characterized by

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