TWI659263B - Photomask inspection method, photomask manufacturing method and photomask inspecting device - Google Patents

Abstract

According to the present invention, it is possible to directly and directly measure the phase shift amount of the phase shift portion included in the transfer pattern of the photomask. The present invention is a method for inspecting a photomask, which measures the phase characteristics of a phase shift portion included in a transfer pattern of the photomask, and has the following steps: setting the photomask to a projection optical system Inspection device steps; optical image data acquisition step, which is to obtain optical image data by exposing a set mask and projecting an optical image of a phase shift portion onto an imaging surface; and a calculation step, which is Use the obtained optical image data to obtain the phase shift amount of the phase shift portion; and in the optical image data acquisition step, make at least a part of the mask, the projection optical system, and the imaging surface along the optical axis direction Move to obtain the optical image data in each state of the plurality of focus states, and in the calculation step, use the obtained optical image data of the plurality of focus states to obtain the phase shift amount.

Description

Photomask inspection method, photomask manufacturing method, and photomask inspection device

The present invention relates to an inspection of a photomask used to manufacture electronic devices, and more particularly to an inspection of a photomask suitable for manufacturing display devices. In particular, the present invention relates to a method and apparatus for measuring a phase shift amount of a photomask (phase shift mask) having a pattern for transfer using a phase shift effect.

Phase shift masks are mainly used as photomasks for semiconductor device manufacturing because of their superior transfer performance, especially depth of focus or contrast, compared to binary masks. In addition, there is proposed an inspection method for inspecting the phase shift amount of the patterns of the phase shift masks.

Patent Document 1 describes a phase inspection method that measures a phase deviation caused by a translucent phase shift film formed on an exposure mask. The phase inspection method includes the steps of using the first pattern group and the second pattern group to form an optical image of each pattern group on a measurement surface through a projection exposure optical system. The first pattern group is formed on a light-shielding film and includes a line / Gap, the second pattern group is formed on a translucent phase shift film and includes a line / gap; the measurement surface is moved along the optical axis (Z) direction to obtain a plurality of the optical images; and the plurality of optical images obtained according to the above , Calculating the difference between the focus position of the first pattern group and the focus position of the second pattern group; and calculating the phase difference caused by the translucent phase shift film based on the calculated focus position difference.

Patent Literature 2 describes a measurement method for simultaneously measuring a phase shift amount and a transmittance of a phase shifter formed in a halftone phase shift mask using a Shearing Interferometer. The measuring method includes the steps of projecting an illumination beam toward a monitoring pattern including a light transmitting portion formed as a half-tone film or a monitoring pattern including a half-tone film forming a light transmitting portion, and adjusting a shear amount of a shear interferometer, A horizontally staggered interference image including the first and second interference images and the third interference image is formed on a two-dimensional imaging device. The first and second interference images are formed by transmitted light transmitted through a monitoring pattern and transmitted monitoring. The third interference image is formed by the transmitted light passing through the peripheral area of the monitor pattern. The horizontally staggered interference image including the first to third interference images is formed. Phase modulation of each cycle amount, and phase modulation data representing the relationship between the phase modulation variable and the brightness value are obtained for the first to third interference images respectively; the phase modulation data of the first and second interference images are used Calculate the phase shift amount between the first interference image and the second interference image and output it as the phase shift amount of the phase shifter; and calculate the amplitude and the first phase modulation data of the first interference image. 3 The square of the amplitude ratio of the phase modulation data of the interference image is output as the transmittance of the phase shifter. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 3431411 [Patent Document 2] Japanese Patent No. 5660514

[Problems to be solved by the invention]

For display devices including liquid crystal display (Liquid Crystal Display) or organic EL (Organic Electro Luminescence) display devices, it is expected to be brighter and save power, and to improve display performance such as high definition, high speed display, and wide viewing angle .

For example, a thin film transistor (TFT) used in the above display device will be described. If the contact holes formed in the interlayer insulating film among the plurality of patterns constituting the TFT do not ensure that the upper and lower patterns are reliably connected Effect, there is no guarantee of correct action. On the other hand, for example, in order to make the display ratio of the liquid crystal display device as large as possible and to make a bright and power-saving display device, the diameter of the contact hole is required to be sufficiently small. With the demand for higher density of these display devices, it is also desirable Refine the diameter of the hole pattern (for example, less than 3 μm). For example, it is considered that a hole pattern having a diameter of 0.8 μm or more and 2.5 μm or less, and further a diameter of 2.0 μm or less is desired. Specifically, it is also desirable to form a hole pattern having a diameter of 0.8 to 1.8 μm.

On the other hand, the NA (Numerical Aperture, numerical aperture) of the optical system of the exposure device used in this field is about 0.08 to 0.15, and the exposure light source also uses i-line, h-line, or g-line. It mainly includes such wide-wavelength light sources, and has a strong tendency to obtain a large amount of light for irradiating a large area, so as to attach importance to production efficiency or cost.

However, it is well known that the half-tone phase shift mask used in semiconductor device manufacturing has used a semi-transparent film (also known as a translucent film that shifts the phase of the exposed light by approximately 180 degrees and has a specific transmittance). It is a photomask having a pattern for transfer) and a photomask that improves resolution by utilizing interference of light. Specifically, it can be said that it has the effect of improving Depth of Focus (DOF) or contrast. In addition, this type of mask (Attenuated Phase Shift Mask) is different from other types (Alternating Phase-Shift Mask) and has fewer restrictions on pattern design. It is advantageously applied to a hole pattern, especially to an isolated hole pattern, and the effect is improved.

In recent years, in the manufacture of display devices, due to the ever-increasing demand for pattern miniaturization as described above, research and application have been used as halftone phase shift masks for semiconductor device manufacturing technologies.

In the manufacturing steps of the photomask, various inspections are performed on the coordinates of the formed transfer pattern or the presence or absence of defects. Regarding the phase shift mask, if the phase shift amount deviates from the design value, the transferability is lowered. Therefore, an inspection step for measuring the phase shift amount is required.

However, according to the methods of Patent Documents 1 and 2, it is necessary to form a monitoring pattern, which is determined in advance for measuring the phase difference, outside a region of the transfer pattern of the photomask, or the like. Therefore, regarding a mask without a specific monitoring pattern, the phase difference of the phase shift portion cannot be measured.

In addition, the measured result is a phase shift amount of the monitor pattern portion, and is not a direct measurement result of the pattern for transfer. Here, the transfer pattern refers to a pattern that is transferred to a transfer target based on a design of an electronic device to be obtained. If it is a mask for manufacturing a semiconductor device with a side of about 6 inches, the phase shift amount of the monitor pattern portion and the phase shift amount of the transfer pattern portion can be considered to be substantially the same without any particular problem. On the other hand, the substrate size of a photomask for display device manufacturing is large (for example, a quadrangle having a main surface of the substrate of 300 to 2000 mm), and it is difficult to make the deviation of the in-plane film thickness zero when forming a phase shift film. . Therefore, there may be a case where the phase shift amount of the monitor pattern portion provided near the outer edge of the substrate deviates from the phase shift amount inside the transfer pattern, and the phase shift generated when the pattern is transferred cannot be accurately grasped. The disadvantages of the shift effect.

Therefore, a main object of the present invention is to provide a method and an apparatus for easily and directly measuring a phase shift amount of a phase shift portion included in a transfer pattern. [Technical means to solve the problem]

(1st aspect) The 1st aspect of this invention is a mask inspection method which measures the phase characteristic of the phase shift part contained in the transfer pattern of a mask, and has the following steps : The step of setting the above-mentioned photomask to an inspection device provided with a projection optical system; the step of obtaining optical image data by exposing the set of the above photomask and using the above-mentioned projection optical system to expose the phase shift portion The optical image is projected onto the imaging surface to obtain the optical image data; and the calculation step is to use the obtained optical image data to obtain a phase shift amount of the phase shift section; and based on the optical image data In the obtaining step, at least a part of the mask, the projection optical system, and the imaging surface is moved in the direction of the optical axis, and the optical image data in each state of a plurality of focused states is obtained, and in the calculating step, , Using the obtained optical image data of the plurality of focus states to obtain the phase shift amount. (Second aspect) The second aspect of the present invention is the inspection method of the photomask according to the first aspect described above, wherein in the above-mentioned calculation step, for each of the plurality of focused states obtained, according to the optical A CD (Critical Dimension, critical dimension) value is obtained from the image data, and the phase shift amount is obtained based on the CD value of the optical image. (Third aspect) The third aspect of the present invention is the inspection method of the photomask according to the second aspect, wherein in the calculation step, based on the focus state and the phase deviation when the CD value reaches a maximum value, The above-mentioned phase shift amount is obtained by correlating the shift amount. (Fourth aspect) The fourth aspect of the present invention is the inspection method of the photomask according to the second or third aspect described above, wherein there is a previous step before the above calculation step, and the previous step is directed to the above-mentioned transfer pattern To grasp the correlation between the focus state when the CD value of the optical image formed by the projection optical system becomes the maximum value and the phase shift amount of the phase shift section. (Fifth aspect) The fifth aspect of the present invention is the inspection method of the photomask according to the fourth aspect described above, wherein the preceding step includes the following steps: for the transfer pattern, grasping the image obtained by the projection optical system. The focus state of the formed optical image is related to the change in the CD value of the optical image caused by the focus state. (Sixth aspect) The sixth aspect of the present invention is a method for inspecting a photomask according to any one of the first to fifth aspects, wherein the transfer pattern includes an isolated pattern. (Seventh aspect) The seventh aspect of the present invention is the inspection method of the photomask according to any one of the first to sixth aspects, wherein the pattern for transfer includes a hole pattern. (Eighth aspect) The eighth aspect of the present invention is the inspection method of the photomask according to any one of the first to seventh aspects, wherein the phase shifting portion is a light transmittance T for exposure of 2 to 10%, phase offset A phase shift film of 170 to 190 degrees is formed on a transparent substrate constituting the photomask. (Ninth aspect) A ninth aspect of the present invention is a method for manufacturing a photomask, which includes a method for inspecting a photomask according to any one of the first to eighth aspects. (Tenth aspect) The tenth aspect of the present invention is a mask inspection device for measuring the phase characteristics of a phase shift portion included in a pattern for transferring a mask, and has: A mask holding member that holds a mask serving as a subject; a light source that emits light; an illumination optical system that guides the light emitted by the light source to irradiate the mask held by the mask holding member; projection An optical system that receives the light beam that has passed through the photomask and guides it to the imaging surface; an optical image acquisition unit that is formed by including an imaging member on the imaging surface; a driving unit that makes the photomask and the projection optical The system and at least a part of the imaging surface are moved in the direction of the optical axis to change the focus state on the imaging surface. A measurement unit measures at least a part of the photomask, the projection optical system, and the imaging surface. A moving distance when moving by the driving unit; and a computing unit that calculates the distance on the imaging surface based on the optical image data acquired by the optical image acquiring unit. Studies of the value of the video CD, and by a moving distance based on the CD and said measured value of the above-described measuring unit for calculating a phase shift amount of the phase shift unit. (Eleventh aspect) The eleventh aspect of the present invention is the mask inspection apparatus according to the tenth aspect, wherein the projection optical system includes an objective lens, and the driving unit moves the objective lens along an optical axis direction. (Twelfth aspect) The twelfth aspect of the present invention is the mask inspection device according to the tenth or eleventh aspect, wherein the computing unit has a memory unit that stores the phase shift amount and the CD in advance. Correlation of the above-mentioned moving distance when the value becomes the maximum value. (Thirteenth aspect) The thirteenth aspect of the present invention is the mask inspection device according to any one of the tenth to twelfth aspects, wherein the projection optical system has an automatic focusing mechanism. [Effect of the invention]

According to the present invention, it is possible to directly and directly measure the phase shift amount of the phase shift portion included in the transfer pattern of the photomask.

<Phase Offset Mask> Generally, in the manufacturing step of the phase offset mask, the phase offset amount of the phase offset portion becomes approximately 180 degrees with respect to the wavelength included in the exposed light (for example, 170 degrees to 190 degrees), select the composition or film thickness of the phase shift film to be used. However, it is preferable to measure the phase shift amount during or after the manufacturing process to confirm whether there is a change in the phase shift amount or to confirm whether the intended phase shift amount has been achieved.

FIG. 1 illustrates a photomask (also referred to as a test mask) serving as a subject. Fig. 1 (a) shows a plan view, and Fig. 1 (b) shows a cross section. The inspected mask 1 is a so-called halftone-type phase shift mask. The inspection mask (phase shift mask) 1 is formed with a phase shift portion 3 that surrounds a hole pattern including the light transmitting portion 2 and inverts the phase of the exposed light. The phase shift section 3 is formed by forming a phase shift film 5 on a transparent substrate 4 such as a glass substrate. The phase shifting section 3 may set the light transmittance T (%) of the exposure (for example, when the i-line is used as the representative wavelength in the light included in the exposed light, the transmittance for the i-line) is set to 2 ≦ T ≦ 10. This transmittance is based on the transmittance of the transparent substrate 4. If it is within this range, the influence caused by the generation of side lobes in the optical image is small, and the following calculation can be performed more accurately, which is ideal. In this embodiment, a phase shift film 5 having a transmittance of 5.2% is used.

If the phase shift mask 1 is exposed by an exposure device, a transfer image (optical image) represented by the optical image data shown in FIG. 1 (c) can be formed on the object to be transferred. The exposure device is, for example, a projection exposure device of equal magnification, and can be applied as an optical condition with NA of about 0.08 to 0.20 and homology factor σ of about 0.5 to 1.0.

Consider the case where the CD (Critical Dimension, critical dimension, here used as the meaning of the pattern width) of the hole pattern on the photomask is set to 4 μm or less (for example, 1.5 to 4.0 μm) and transferred A hole pattern having a CD of 4 μm or less (for example, 0.5 to 3.5 μm, more preferably 1.0 to 2.5 μm) is formed on the body. For such a fine hole pattern, the effect of a phase shift mask can be favorably exerted. In this embodiment, as an example, the CD of the hole pattern on the mask is set to 2.5 μm, and the target CD of the hole pattern formed on the transferred body is set to 2.0 μm. That is, a case is considered in which the CD of the hole pattern formed on the object to be transferred is smaller than the CD of the hole pattern on the mask and the transfer is performed.

If the above-mentioned photomask 1 is set in an exposure device and irradiated with the exposed light, a transfer image can be formed on the object to be transferred. The light to be exposed may be light including any of i-line, h-line, and g-line, or may be wide-wavelength light including all of i-line, h-line, and g-line. However, in the inspection method / apparatus of the present embodiment described below, a single wavelength is used as the inspection using a representative wavelength included in the exposed light. Furthermore, it is preferable that the inspection device of this embodiment has a member (optical filter, etc.) capable of using light of a plurality of wavelengths, such as i-line, h-line, and g-line, as a single wavelength, respectively.

In a state where the photomask 1 of FIG. 1 is set on an exposure device, any one of the photomask 1, the optical system of the exposure device, and the transferred surface is along the optical axis direction (hereinafter, also referred to as the Z direction). The relative movement can change the focus state including the state of just focus, or the state of defocus after a certain distance from its position. At this time, the optical image formed on the object to be transferred changes.

In this embodiment, as described in detail later, a changing optical image is acquired by the imaging member, and the phase of the phase shift portion 3 of the mask 1 that becomes the subject is checked based on the obtained information. The characteristics, specifically, the amount of phase shift.

<Mask inspection apparatus> FIG. 2 illustrates a mask inspection apparatus (hereinafter, also referred to as this apparatus) 10 according to this embodiment.

This device 10 is used to check the phase characteristics of the phase shift section 3 (FIG. 1) included in the transfer pattern of the photomask 1, and specifically measures the phase shift section 3 for a specific exposure light The phase offset.

In order to measure the amount of phase shift, the apparatus 10 is configured as follows. The light source 11, the illumination optical system 13, and the projection optical system 14 included in the device 10 are preferably the same as the exposure device having the same configuration as the exposure device to be used as the mask 1 of the subject.

(Light source) For example, the light source 11 provided in the apparatus 10 can be set to have the same wavelength as the light source of the exposure apparatus. Specifically, if the light source of the exposure device is a wavelength including an i-line, an h-line, and a g-line, it is preferable to have any one of them as the light source 11. If the exposure device includes a light source having a wide wavelength including all of the i-line, the h-line, and the g-line, the light source 11 may be a light source 11 that emits a representative wavelength (for example, i-line).

(Holding member) In addition, the device 10 includes a mask holding member (hereinafter, also simply referred to as a holding member) 12 that holds the photomask 1 serving as a subject. The photomask 1 serving as a subject can be a so-called phase shift mask including a pattern for transfer including a phase shift portion on a transparent substrate. For example, the phase shift film formed on a transparent substrate is patterned to have a phase shift mask having a light transmitting portion and a phase shift portion; or a phase shift film and a light shield are formed on the transparent substrate. The film was patterned and each of them had a phase shift mask of a light transmitting portion, a light shielding portion, and a phase shift portion. Furthermore, it can also be applied to a phase shift mask (a so-called Levenson mask, a chrome-free mask, etc.) having a phase shift portion in which a transparent substrate surface is etched to a specific depth.

(Illuminating Optical System) Further, the device 10 includes an illuminating optical system 13. The illumination optical system 13 includes, for example, an illumination lens and a diaphragm, and guides a light beam emitted from the light source 11 to the surface of the mask 1 held on the holding member 12.

(Projection Optical System) In addition, the device 10 includes a projection optical system 14 that guides the transmitted light of the mask 1 to the imaging surface 15. The projection optical system 14 may include an objective lens and a magnification adjustment lens. As a result, an optical image of the transfer pattern included in the photomask 1 is formed on the imaging surface 15 described below at a specific magnification.

(Optical image acquisition section) The light emitted from the projection optical system 14 reaches the imaging surface 15, and an imaging member (an imaging element, here CCD: Charge-Coupled Device) is provided on the imaging surface 15, Obtain optical image data (specifically, two-dimensional optical image data). That is, the part that acquires the optical image data is the optical image acquisition section 16 of the device 10.

(Driver) In this device 10, at least a part of the mask 1, the projection optical system 14, and the imaging surface 15 of the optical image acquisition section 16 can be in the Z direction as a whole or in part (one or more). Movement (hereinafter, also referred to as Z movement). Preferably, any one of the projection optical system 14 (especially the objective lens) or the reticle 1 performs Z-movement, which is better in device design. Here, the Z direction refers to the optical axis direction of the projection optical system 14. Therefore, the present device 10 includes a driving unit 17 for moving them.

Furthermore, in this device 10, the objective lens which is a part of the projection optical system 14 performs Z-movement. The amount of movement is precisely controlled, for example, the position can be controlled in units of 5 μm. The driving unit 17 that performs precise Z-movement in this manner can be configured using, for example, a known driving source (for example, a servo motor, a piezoelectric element, or the like).

(Measurement Section) The apparatus 10 includes a measurement section 18 for measuring a movement amount during Z movement (hereinafter, also referred to as Z measurement). The measurement unit 18 uses a member such as a laser interferometer to grasp the position of the object to be Z-moved, and measures the movement distance. The measurement unit 18 may measure the movement distance by grasping the position before and after the movement, or may grasp the position of the object by measuring the movement distance. In this embodiment, both the grasp of the position and the measurement of the moving distance are included in the measurement of the moving distance.

The above-mentioned Z movement can change the focus state of the transfer pattern of the photomask 1 on the imaging surface 15 to form a positive focus and a plurality of different levels of defocus. Therefore, it is preferable that the driving section 17 has an automatic focusing mechanism for determining the positive focus position, and it is preferable that the measurement section 18 and the driving section 17 can easily form a specific amount of defocused state from the positive focus position. Structure of collaboration. In addition, the auto-focusing mechanism described herein refers to a mechanism that can move at least a part of the mask 1, the projection optical system 14, and the imaging surface 15 as a whole or partly in the Z direction, and can Measure the position in the Z direction directly and adjust to the positive focus position.

(Calculation Section) The device 10 includes a driving section 17 that is responsible for the above-mentioned driving, and a calculation section 19 for calculating a phase shift amount. In addition, the computing unit 19 may include a memory unit that stores and stores useful information for calculation in advance. Such a calculation unit 19 can be configured using, for example, a computer device that executes a specific program. In addition, the details of these functions implemented by the arithmetic unit 19 will be described later.

<Principle of Mask Inspection Method> Hereinafter, the principle of the mask inspection method according to the embodiment of the present invention will be described using optical simulation.

For example, consider the following case: a phase shift film 5 having a phase shift amount of 180 degrees is used to form the photomask 1 of FIG. 1, which is exposed and transferred to the transfer surface of the transfer target (generally, it is A resist film formed on the film surface to be etched). If the photomask of FIG. 1 is set on the device 10 and exposed, an optical image of a transfer pattern is generated on the imaging surface 15 of the device 10 corresponding to the transferred surface, and a two-dimensional optical image can be obtained by the imaging member. data. Regarding the two-dimensional data of the optical image, if the position is taken on the horizontal axis and the light intensity is taken on the vertical axis, it will behave as shown in Fig. 1 (c).

Here, for example, two-dimensional data of the optical image is acquired while the focus state is changed while the objective lens is Z-moved. If every 5 μm of Z movement, two-dimensional data of the optical image of the focal position and the defocus position of ± 5 to 30 μm relative to the focal position are obtained, and the CD values of the images obtained everywhere are plotted separately, then A mountain-shaped curve (a curve of a thick solid line) shown in FIG. 3 is obtained. In addition, here, the light amount of the target CD (2.0 μm) obtained at the positive focal position is set as a threshold value, and the CD value under the light amount is obtained in each of the defocused states described above, and plotted.

Here, the following exposure conditions are assumed and an optical simulation is performed. Optical conditions of the exposure device: NA = 0.085 of the projection optical system, coherence factor σ = 0.65, photo-i-line resist conditions of the exposure light: Di700 substrate material: SiO ₂ pattern: isolated hole pattern, CD on the mask = 2.5 μm , The target CD of the transferred image = 2.0 μm

As a result, the CD value of the above-mentioned hole pattern becomes maximum when the focus is positive, and the CD value decreases when the lens is defocused to the + side or the-side (refer to the solid line at 180 degrees in FIG. 3). The "Resist CD" in FIG. 3 means a CD (μm) of a transferred image formed on a transfer target.

Next, when the phase shift amount of the phase shift section 3 of the photomask 1 is changed, the CD values in each focus state are plotted in the same manner as described above. The graph drawn for each phase offset is superimposed on the solid line curve of FIG. 3 (refer to the lines of 170 degrees, 175 degrees, etc. in FIG. 3).

As a result, it can be seen that if the phase shift amount is changed by 5 degrees each time, and the curve for the phase shift amount of 170 to 190 degrees is plotted, the position of the mountain curve is shifted to the left and right, and the peak position The X coordinate also moves.

That is, it can be understood that there is a correlation between the phase shift amount of the phase shift section 3 and the focus state (defocus amount) having the maximum value of the CD. Therefore, as long as the correlation is grasped in advance, the phase shift amount can be accurately obtained by measuring the defocus amount of the maximum value of the CD of the subject 1 having an unknown phase shift amount. That is, for each of the plurality of focus states, a CD value can be obtained from the optical image data, and a phase shift amount of the mask can be obtained based on the CD value of the optical image. Here, the "CD value based on an optical image" may refer to obtaining a defocus amount having a CD maximum value as described above, and may also refer to obtaining a CD maximum value itself as described below.

Since this association can be considered to be inherent to an exposure device having a specific optical system, it is preferable to use an optical system having the same specifications as the exposure device used for the exposure of the mask 1 to prepare the mask inspection of this embodiment.装置 10。 Device 10.

<Specific Example of Mask Inspection Method> Then, using the mask inspection device 10 of this embodiment is described in detail in the form of an embodiment of the present invention (hereinafter, also referred to as this embodiment) based on the principle described above. Implementation of mask inspection method.

The inspection flow of the phase shift amount of the mask inspection method of this embodiment is illustrated in FIG. 4.

The inspection processes exemplified here include (1) a process for grasping the association (previous steps), and (2) a process for measuring the mask 1 to be inspected.

(1) Understanding of the correlation In the present embodiment, first, the correlation between the amount of phase shift included in the phase shift section 3 and the amount of defocus that shows the maximum value of CD when the phase is exposed is grasped. Specifically, a calibration curve serving as a reference is obtained.

To grasp the correlation, first, five types of phase shift masks (hereinafter, also referred to as reference masks) having different phase shift amounts are prepared.

A reference mask is illustrated in FIG. 5. The five reference masks 20 are formed by forming a phase shift film on a 6-inch square transparent substrate and patterning the same according to the monitoring pattern 21 illustrated in FIG. 5. Here, the phase shift amount of each reference mask 20 is set to 170 degrees, 175 degrees, 180 degrees, 185 degrees, and 190 degrees.

In addition, the reference masks 20 are performed by using a phase difference measuring machine (for example, MPM series manufactured by Lasertec, etc.) used for manufacturing a photomask for a semiconductor device (LSI: Large-Scale Integration). Measurement, and accurately grasp the amount of phase shift. Regarding the reference mask 20 shown in FIG. 5, as the monitoring pattern 21, four light-transmitting portions arranged radially are formed. The size of these light-transmitting portions is based on the designation of the measuring machine (for example, W1 ≧ 20 μm). , W2 ≧ 40 μm, d ≧ 15 μm), and the center of gravity of the pattern (see the X mark in the figure) is the measurement part of the measuring machine. With such a monitoring pattern 21, the phase shift amount can be accurately measured using the measuring machine (see above, refer to step (i) in FIG. 4).

On the other hand, a square hole pattern 22 is formed near the center of the reference mask 20, and the hole pattern 22 is formed based on the pattern of the mask 1 to be measured as a phase shift amount of the subject. It is assumed that the subject has a hole pattern having a CD of 2.5 μm in the same manner as the photomask 1 described above, thereby forming a hole pattern having a CD of 2.0 μm on the transfer object.

After the above-mentioned five types of reference masks 20 are prepared, the prepared reference masks 20 are sequentially set on the device 10. Then, the two-dimensional data of the optical image is obtained at the focal position of the reference mask 20 including the hole pattern 22. Furthermore, by moving the objective lens from the prefocus position to Z-focus, it is defocused by a specific distance to form a plurality of defocus states, and two-dimensional data of the optical image in each defocus state are acquired. Here, as an example, 6 kinds of defocusing states of ± 5 μm, ± 10 μm, and ± 15 μm with respect to the positive focal position are formed, and two-dimensional data of the optical image are acquired. In addition, here, the exposure conditions are also set to NA = 0.085 and σ = 0.065 in the optical system, and the light source is i-line (365 nm).

The results are shown in Figs. 6 (a) to (e). Here, the light intensity at which a hole pattern having a CD with a diameter of 2 μm is formed at the time of normal focus is used as a threshold value, and the CD is plotted against the defocus amount at this time as shown in FIGS. 7 (a) to (e).

According to the focus-CD curves shown in Figs. 7 (a) to (e), it can be seen that the behavior of CD changes relative to the focus state is significantly different due to the difference in the amount of phase shift. For example, in phase offset for In the case of <180 degrees, the defocus amount (apex X coordinate) showing the maximum value of the CD curve is on the negative side. When it is> 180 degrees, the vertex X coordinate is leaned to the positive side (above, refer to step (ii) in FIG. 4).

According to the research conducted by the inventor of the present application, it can be known that the correlation between the phase offset and the vertex X coordinate can be approximated by a linear formula, and the correlation between the phase offset and the vertex Y coordinate can be approximated by a quadratic formula. This is shown in FIG. 8.

That is, from the above, it is possible to grasp the correlation between the phase shift amount of the phase shift section and the CD maximum value obtained when the exposure is performed or the defocus amount showing the CD maximum value. In more detail, based on the measurement result of the phase shift amount of each reference mask 20 (that is, the result of (i) in FIG. 4) and the change in the maximum value of CD relative to the defocus when it is exposed (Ie, the result of (ii) in FIG. 4), to grasp the correlation between the phase shift amount and the maximum value of the CD or the defocus amount showing the maximum value of the CD, and a reference calibration curve can be obtained (see above, refer to Step (iii)). Here, it is assumed as follows: A calibration curve showing the correlation between the phase shift amount and the defocus amount (apex X coordinate) showing the maximum value of CD is made into a calibration curve, and the calibration curve based on the linear equation is used to check It becomes the phase shift amount of the mask 1 of a subject.

Moreover, the correlation between the phase offset and the vertex coordinates is preferably stored in advance in a memory section attached to the calculation section 19 of the device 10 as calibration curve data to be used in the measurement of the mask to be inspected in the subsequent stage.

(2) Inspection of the phase offset (measurement of the inspected mask) If the correlation between the phase offset and the vertex coordinates is obtained to obtain a calibration curve, the above-mentioned correlation can be used to measure and check the unknown phase Phase shift amount of the mask 1 to be shifted.

When measuring the phase shift amount, first, a photomask (subject mask) 1 having a phase shift portion 3 as a subject is prepared. Here, it is assumed that a halftone phase shift mask for manufacturing a display device is such that a phase shift film 5 is formed on a transparent substrate 4 including glass, and FIG. 1 (a) is formed on the phase shift film 5 The pattern shown. The material of the phase shift film 5 may be a chromium (Cr) compound (oxide, nitrogen carbide, oxynitride, carbon oxynitride, etc.) or a metal silicide (such as MoSi). As a main component, a film having a transmittance of 2 to 10% (more preferably 3 to 8%) is obtained by sputtering.

After the inspection mask 1 is prepared, the inspection mask 1 is set in the apparatus 10 and exposed under the same conditions as the actual exposure conditions. At this time, a plurality of focusing states are formed by the Z movement of the objective lens, and two-dimensional data of the optical image are acquired in each focusing state. This is shown in Fig. 9 (a).

Based on the two-dimensional data of the optical image obtained in this way, the defocus amount that becomes the maximum CD value is obtained and plotted, and the obtained is the focus-CD curve shown in FIG. 9 (b). Here, the X coordinate of the vertex of the curve is shifted to the negative side from the positive focus, and -3,323 μm is displayed (above, refer to step (iv) in FIG. 4).

Here, assuming that the focus state showing the largest CD value is 0 (ie, positive focus), it can be seen that the phase shift amount of the phase shift section 3 in the mask 1 to be inspected is 180 degrees. On the other hand, when the focused state showing the largest CD value is the defocused state on the positive or negative side, it is possible to grasp that the phase shift amount of the phase shift section 3 in the inspection mask 1 deviates from 180 degrees. , And we can know the amount of deviation.

Therefore, the above-mentioned defocus amount is substituted into the linear equation of the calibration curve obtained in FIG. 8 to calculate the phase shift amount. Here, for example, the above-mentioned -3.323 is substituted into the value of y = 0.4746198962x-85.4321961555, and the phase shift amount x is obtained. As a result, as shown in FIG. 9 (c), the phase difference is 173 degrees (for the above, refer to step (v) in FIG. 4).

<Functions and Effects of This Embodiment> According to the above-mentioned mask inspection apparatus 10 and the mask inspection method using the same, even when the inspected mask 1 does not have a monitoring pattern having a specific measurement area, it is possible to address the problem. The phase shift portion 3 included in the transfer pattern of the test mask 1 measures the phase shift amount. That is, the phase shift amount of the phase shift portion 3 included in the transfer pattern of the mask 1 to be inspected can be directly and easily measured. This case is particularly advantageous when the present invention is applied to an inspection of a photomask for manufacturing a display device.

In addition, according to the above-mentioned mask inspection apparatus 10 and a mask inspection method using the same, the coordinates and phase shift amounts representing the maximum value of the CD (that is, the maximum value of the CD value of the optical image) in a plurality of focused states are grasped. After the correlation, a phase shift amount of the mask 1 to be inspected is measured based on a calibration curve indicating the correlation. Therefore, the measurement result of the phase shift amount is made very accurate and highly reliable by using an optical system having the same specifications as the exposure device used for the exposure of the mask 1 to be inspected. Furthermore, if the correlation is grasped in advance, when measuring the amount of phase shift, only the mask 1 to be inspected needs to be provided, and thus the measurement can be easily performed.

Furthermore, regarding the grasp of the relationship described in (1) above, it is assumed that a mask having a hole pattern with a CD having a diameter of 2.5 μm is used, thereby forming a CD having a 2.0 μm on the transfer object. Hole pattern. On the other hand, the inspection method of the present invention is not limited to this pattern, and can also be applied to patterns of different designs.

For example, FIG. 10 shows a case in which hole patterns of different sizes are to be formed. That is, in the case where a hole pattern of a CD larger than the above-mentioned case or a hole pattern of a CD smaller than the above-mentioned case is formed on the object to be transferred, the phase shift amount is verified and the maximum value of the CD is displayed when exposed. Correlation of focus. The curve of the single-dot chain line indicates the use of a mask with a hole pattern with a CD of 2.3 μm on the mask and the formation of a hole pattern with a CD of 1.8 μm on the transferee. The dashed curve indicates the use of a mask with a mask. A mask with a CD pattern of 2.7 μm holes on the mask, and a 2.2 μm pattern of CD holes on the transferee. R2 is the determination coefficient.

It can be seen that in these cases, the approximation using the linear equation can be performed in the same manner as described above. In addition, it is preferable to grasp the above-mentioned correlation and prepare various calibration curves according to the design of the target pattern to be obtained. In addition, it is preferable that various prepared calibration curves are used as reference data and stored in advance in a memory section included in the device 10.

The use of the photomask applied to the above-mentioned photomask inspection apparatus 10 and the photomask inspection method using the same is not particularly limited. As long as it is a photomask having a phase shift portion, the above-mentioned effects can be obtained.

The above-mentioned mask inspection apparatus 10 and a mask inspection method using the same are particularly advantageous when applied to inspection of a mask for manufacturing a display device as described above, but can also be applied to a mask for manufacturing a semiconductor device. In the above description, the hole pattern has been described as an example of the pattern for transfer, but it is not limited to this, and other patterns (for example, line and gap patterns) may be used.

However, regarding transfer patterns, there are cases where they are called Dense patterns and Iso patterns separately. The above-mentioned dense patterns are generated by arranging a plurality of patterns with a certain regularity, and these patterns are mutually generated. For optical influencers, the above-mentioned isolated patterns are those that do not constitute such a regular arrangement.

The photomask 1 to be the subject may be either a case where a dense pattern is formed on the object to be transferred, or a case where an isolated pattern is formed. However, the NA of the exposure device for semiconductor device manufacturing (for LSI) exceeds 0.20, and the NA of the exposure device for display device manufacturing (for FPD) is approximately 0.085 to 0.20. That is, when a photomask for manufacturing a display device is used as a subject, a relatively low NA is applied. If an isolated line pattern is used, the change in CD due to a change in focus state is relatively small. Therefore, in order to reliably grasp the above-mentioned correlation, it is necessary to form a wide range of defocused states. Therefore, regarding the efficiency of inspection, when a hole pattern (dense or isolated) or a line and gap pattern (especially a fine line and gap pattern with a pitch of 2.5 μm or less) is taken as an object, the above-mentioned effect of the present invention changes. To be significant.

That is, the above-mentioned mask inspection device 10 and a mask inspection method using the same can be applied not only to the case of forming a dense pattern, but also to the case of forming an isolated pattern. Moreover, regarding the isolated pattern, the isolated pattern is a hole pattern (Ie, isolated hole patterns).

<Modifications> As long as the mask inspection method and the mask inspection device of the present invention do not lose the above-mentioned effects, they are not limited to the aspects disclosed in the above embodiments.

For example, the use of the photomask used in the present invention is not particularly limited, and a photomask for manufacturing a semiconductor device may be used as a test mask. According to the mask inspection method of the present invention, since the monitoring pattern provided outside the transfer area is not measured, but the phase shift amount of the transfer pattern can be directly measured, the larger the size (therefore (Possibility of deviation of phase shift amount) is particularly useful for a mask for manufacturing a display device.

As an example of a photomask used for manufacturing a display device of the present invention, a fine pattern having a pattern with a CD of 4 μm or less (for example, 1.5 to 4.0 μm) can be mentioned. The improvement in transferability obtained by these photomasks by the phase shift effect is remarkable. In addition, it is preferable to perform transfer using an equal magnification projection exposure apparatus.

In addition, according to the present invention, it is known that the phase shift amount exhibited by the mask under test with respect to each of the exposure wavelengths (for example, i-line, h-line, and g-line), and thus it is possible to grasp the wavelength dependency of the phase shift amount.

Furthermore, the photomask applied to the present invention may include other optical films or functional films as part of the phase shift film or light shielding film, or may include other optical films or functional films in addition to the phase shift film or light shielding film.

(Manufacturing method of photomask) The present invention includes a method of manufacturing a photomask, which uses the above-mentioned photomask inspection method. That is, the manufacturing method of the photomask of the present invention has the following steps: preparing a photomask substrate on which at least a phase shift film is formed on a transparent substrate, and further forming a resist film; A drawing device such as a jet plotter to draw a desired transfer pattern; developing the resist film to form a resist pattern; and patterning the phase shift film using the resist pattern; and after the patterning The inspection of the phase shift amount can be performed by the mask inspection method of the present invention. Furthermore, the above-mentioned photomask substrate may be a photomask base or a photomask intermediate in a photomask manufacturing process.

1 Photomask 2 Light transmitting section 3 Phase shift section 4 Transparent substrate 5 Phase shift film 10 Mask inspection device 11 Light source 12 Mask holding member 13 Illumination optical system 14 Projection optical system 15 Imaging surface 16 Optical image acquisition section 17 Drive Section 18 Measurement section 19 Calculation section 20 Reference mask 21 Monitoring pattern 22 Hole pattern

FIG. 1 is a diagram illustrating a pattern for transfer of a photomask serving as a subject, (a) is a plan view showing a constitution example, (b) is a diagram showing a cross-section of the constitution example, and (c) is a diagram obtained An example of optical image data. FIG. 2 is a schematic diagram showing a configuration example of a mask inspection apparatus according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of a change in CD of an optical image due to a defocus amount for phase shift films having different phase shift amounts. FIG. 4 is a flowchart showing a procedure for inspecting a phase shift amount of a mask inspection method to be implemented in the embodiment of the present invention. FIG. 5 is a plan view illustrating a configuration example of a reference mask used to prepare a calibration curve. Fig. 6 is a diagram showing a specific example of optical image data used to make a calibration curve, (a) is a diagram showing an example of optical image data of a reference mask with a phase difference of 170 degrees, and (b) is a diagram showing a phase difference of 175 degrees (C) is a diagram showing an example of an optical image data of a reference mask with a phase difference of 180 degrees, and (d) is a diagram showing an example of an optical image data of a reference mask with a phase difference of 180 degrees (E) is a diagram showing an example of optical image data of a reference mask with a phase difference of 190 degrees. FIG. 7 is a diagram showing a specific example of the behavior of CD change with respect to defocus, (a) is a diagram showing an example of CD change due to a reference mask with a phase difference of 170 degrees, and (b) is a diagram showing the change due to (C) is a diagram showing an example of the change in CD due to a reference mask with a phase difference of 180 degrees, and (d) is a diagram showing an example of the change in CD due to a reference mask with a phase difference of 180 degrees (E) is a diagram showing an example of CD change caused by a reference mask having a phase difference of 190 degrees. FIG. 8 is a diagram showing an example of the relationship between the phase shift amount of the mask and the vertex X coordinate of the CD change with respect to the defocus. FIG. 9 is a diagram showing a specific example of measurement of a phase shift amount for a mask serving as a subject, (a) is a diagram showing an example of optical image data, and (b) is a diagram showing a focus-CD curve (C) is a diagram showing an example of calculating a phase difference (phase shift amount) from a calibration curve. FIG. 10 is a diagram showing an example of a correlation (calibration curve) when a hole pattern of different sizes is to be formed.

Claims (13)

A method for inspecting a photomask, which measures a phase characteristic of a phase shift portion included in a pattern for transferring a photomask, and has the following steps: The above-mentioned photomask is set in an inspection device having a projection optical system Steps of obtaining optical image data, which are to obtain the optical image data by exposing the provided photomask and using the projection optical system to project the optical image of the phase shift portion onto the imaging surface; And calculation steps, which use the obtained optical image data to obtain a phase offset amount of the phase shift section; and in the optical image data acquisition step, the mask, the projection optical system, And at least a part of the imaging surface is moved along the optical axis direction to obtain the optical image data in each state of a plurality of focused states, and in the calculation step, the acquired optical images of the plurality of focused states are used The data is used to determine the above-mentioned phase shift amount. For example, the inspection method of the photomask of claim 1, wherein in the above calculation steps, for each of the plurality of the obtained focus states, a CD value is obtained based on the optical image data, and based on the CD value of the optical image, The above-mentioned phase shift amount is obtained. For example, in the inspection method of claim 2, the phase shift amount is obtained based on the correlation between the focus state when the CD value becomes the maximum value and the phase shift amount in the calculation step. For example, the inspection method of the photomask of claim 2 or 3, which has a pre-step before the above-mentioned calculation step. The pre-step is to grasp the change of the CD value of the optical image formed by the projection optical system for the transfer pattern. The focus state at the maximum value is related to the phase shift amount of the phase shift section. For example, the inspection method of the reticle according to claim 4, wherein the foregoing steps include the following steps: for the transfer pattern, grasping the focus state of the optical image formed by the projection optical system, and the state caused by the focus state Correlation of the change in the CD value of the optical image. The inspection method of a photomask according to any one of claims 1 to 3, wherein the pattern for transfer includes an isolated pattern. The inspection method of a photomask according to any one of claims 1 to 3, wherein the pattern for transfer includes a hole pattern. The inspection method of the photomask according to any one of claims 1 to 3, wherein the above-mentioned phase shifting section sets the light transmittance T of the exposure to 2 to 10% and the phase shift amount. A phase shift film of 170 to 190 degrees is formed on a transparent substrate constituting the photomask. A method for manufacturing a photomask, which includes the method for inspecting a photomask according to any one of claims 1 to 8. A mask inspection device for measuring a phase characteristic of a phase shifting portion included in a pattern for transferring a mask, and includes a mask holding member that holds a mask serving as a subject A light source that emits light; an illumination optical system that guides the light emitted by the light source to irradiate a mask held by the mask holding member; a projection optical system that receives the light beam that passed through the mask and It is guided to the imaging surface; an optical image acquisition section is formed by including an imaging member on the imaging surface; and a driving section is configured to cause at least a part of the photomask, the projection optical system, and the imaging surface to follow the light Moving in the axial direction to change the focusing state on the imaging surface; a measuring unit that measures a moving distance when at least a part of the photomask, the projection optical system, and the imaging surface is moved by the driving unit; and A computing unit that obtains the CD value of the optical image on the imaging surface based on the optical image data acquired by the optical image acquisition unit, and By moving to a distance and said measured CD value of the above-described measuring unit for calculating a phase shift amount of the phase shift unit. The mask inspection device according to claim 10, wherein the projection optical system includes an objective lens, and the driving unit moves the objective lens in an optical axis direction. For example, the mask inspection device of claim 10 or 11, wherein the computing unit has a memory unit that stores in advance a correlation between the phase shift amount and the moving distance when the CD value becomes a maximum value. The mask inspection device according to claim 10 or 11, wherein the above-mentioned projection optical system has an automatic focusing mechanism.