JP2003280169A - Photomask and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photomask capable of suppressing blurring of an image projected on work with respect to a gray mask having a transmissivity modulating layer. <P>SOLUTION: In a step 31, a function of blurring due to a photomask and an exposure optical system is obtained, and in a step 32, an original pattern is subjected to reverse convolution with the function of blurring to obtain a mask pattern. Since this mask pattern includes a phase component in addition to an amplitude component, in steps 33 and 34, the objective photomask having a phase shifting layer disposed on a transmissivity modulating layer is produced. A fine structure can be precisely transferred to a resist layer on work by using the photomask, therefore a fine structure can be more precisely produced. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmittance modulation mask capable of transferring an arbitrary three-dimensional shape onto a resist.

[0002]

2. Description of the Related Art There is known a photomask called a transmittance modulation mask, which can transfer a three-dimensional shape to a resist by one exposure by arbitrarily controlling the transmittance at an arbitrary surface position on the photomask. Has been. Many of the transmittance modulation masks have a photosensitive layer, and use a beam of higher energy than the light for exposing the resist, for example, a laser,
By changing the phase of the photosensitive layer by the drawing beam with the energy changed, the photosensitive layer is exposed and fixed, and the transmittance is modulated. Thereby, a layer having a plurality of transmittances is formed on or in the mask. Therefore, when a work having a resist layer formed on the surface is exposed by using the transmittance modulation mask as a photomask, a grayscale image can be projected on the resist layer instead of a binary image. It can be transferred to a layer.
Therefore, if the work body is etched using the resist layer as a mask, it is possible to form a three-dimensional shape having an arbitrary fine structure on the work. It is also possible to mold a microdevice having a fine structure by using a work having a fine structure as a transfer mold. Therefore,
In recent years, the application of diffractive optical elements has been expanding, especially in the field of micro optical elements.

One example of a transmittance modulation mask uses a phenomenon in which, when a dehydrogenated amorphous silicon film is irradiated with a laser, crystallization is induced by heat and the transmittance is increased. VZBotchiyaev et. "High r by al.
esolution optical recording on a-Si films '' (J. Non
-Cryst. Solids, 137 & 138, pp1297-1300 (1991)). HEBS- made by Canyon Materials
Glass contains silver ions, and a gray level mask can be formed by exposing it to a high energy beam.

[0004]

These transmittance modulation masks have a high resolution of the pattern formed on the mask, and can be said to be at a sufficiently practical level in that respect.
However, the thickness of the photosensitive layer is 1 μm to several μm, which is large as compared with the conventional binary mask. Therefore, the image formed on the work tends to be blurred through the exposure optical system that exposes the work. That is, it becomes distorted or has an aberration. In particular, the edge of the edge shape where the depth changes rapidly tends to collapse greatly.

Such a tendency can be controlled by reducing the thickness of the photosensitive layer. However, when the photosensitive layer is made thin, the controllable transmittance range becomes small and the controllable gradation number (gray level) is reduced. ) Is reduced, it becomes difficult to transfer an arbitrary three-dimensional shape to the resist layer.

Therefore, it is an object of the present invention to provide a photomask having a wide range of controllable gray levels and capable of reducing blur of an image projected on a work.

[0007]

In order to eliminate the blur of an image, a method of improving the image forming performance of the exposure optical system is generally adopted. However, aberration due to the factors of the exposure optical system itself,
In addition to deviations such as errors, it is almost impossible for the exposure optical system to correct differences due to the distribution of the photomask in the depth direction. Therefore, in the present invention, the blurring of the image due to the thickness of the photosensitive layer is positively recognized, and the pattern on the mask side is controlled so that a desired image is formed on the work. At that time, focusing on the fact that the photomask originally requires a certain thickness as the photosensitive layer, a phase shift structure is also built in the photomask, and in addition to the correction of the amplitude component by the transmittance modulation, The phase component is corrected by the shift structure so that a predetermined pattern can be imaged on the work with higher accuracy.

That is, in the present invention, the following steps are provided when manufacturing a photomask for modulating light for exposing a work. 1. The blur function that the light modulated by the photomask is modulated before being projected on the work is obtained. 2. The original pattern distribution of the light to be projected onto the work is inversely convolved with the blur function to obtain the mask pattern distribution. 3. The transmittance modulation layer of the photomask is formed based on the intensity component of the mask pattern. 4. A phase shift layer laminated on the transmittance modulation layer is formed based on the phase component of the mask pattern.

An image of a point image on a transmittance-modulating glass projected on a work through an exposure optical system, that is, a blurred image (blurring function) of the point image is represented by a certain pattern m.
The image a obtained on the work through the exposure optical system when is formed on the transmittance modulation mask is a convolution of the pattern m and the blurring function d (a = m * d (* indicates convolution)). Therefore, assuming that the original pattern to be exposed on the work is a, the mask pattern m formed on the transmittance modulation mask is the inverse convolution (m = a *) of the original pattern a with the blur function d.
(1 / d)). At this time, not only the amplitude information but also the phase information can be obtained by the calculation of the inverse convolution, so that the original pattern a can be imaged on the work by reflecting the phase information as a phase shift layer on the photomask. A photomask can be manufactured.

In this manufacturing method, it is possible to correct the blur caused by the differences in the exposure optical system itself on the photomask side, and conversely, obtain the blur function including the differences in the exposure optical system. Is important. Therefore, in the step of obtaining the blur function B, it is desirable to obtain the blur function by projecting the light modulated by the photomask having the sample pattern such as the point image onto the work through the actual exposure optical system.

As described above, in the manufacturing method of the present invention, since it is necessary to form the phase shift layer, the obtained photomask has a transmittance modulation layer capable of modulating the intensity of light for exposure.
It has a phase shift layer laminated on this transmittance modulation layer and capable of modulating the phase of light for exposure.

Most of the transmittance modulation layers are photosensitive layers that change their phase by high-energy light. The mask pattern distribution based on the amplitude obtained by the inverse convolution is converted into high-energy light and projected on the photosensitive layer. By changing the phase, a photomask having a desired pattern formed in the transmittance modulation layer can be manufactured.

On the other hand, the phase shift layer is a layer processed to have an uneven surface to generate a phase difference. In the step of forming this phase shift layer, the surface of the photomask is processed to have an uneven surface to form a phase shift layer. Then, it is possible to employ a method in which a sheet member having a concavo-convex pattern to be a phase shift layer is attached to a substrate provided with a transmittance modulation layer.

Then, using the photomask of the present invention, a work having a resist layer formed on the surface is exposed to light, and a three-dimensional shape is transferred to the resist layer, thereby manufacturing a structure having a highly precise microstructure. It becomes possible to do.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows how a work is exposed using the photomask of the present invention. The exposure apparatus 1 includes a light source 2, a collimator section 3 that converts light from the light source 2 into parallel light, and an exposure optical system 5 that forms an image of the light modulated by the photomask 10 on the work 20. The photomask 10 is a transparent glass (quartz) substrate 1.
1, the transmittance modulation layer 12, and the phase shift layer 13 are laminated. The work 20 includes a substrate 21 and
The resist layer 22 is laminated, and the light modulated by the photomask 10 exposes the resist layer 22 through the exposure optical system 5. As a result, the resist layer 22
Microstructure on the order of micron or submicron 25
Is exposed and the resist layer 22 is developed to transfer the fine structure 25, thereby forming a structure having the fine structure.

FIG. 2 shows a manufacturing process of the photomask 10 of this example. First, in step 31, the photomask 1
A blurring function d that is modulated before the light modulated by 0 is projected on the work 20 is obtained. In this step 31, a transmittance modulation type photomask (sample mask) provided with a sample pattern is prepared, and is projected onto the work 20 by the system shown in FIG. 1 to obtain the blurring function d. The blurring function d reflecting various differences including systematic aberrations, deviations or errors related to the modulation mask, the exposure optical system 5 and the other exposure system 1 can be obtained. The simplest sample pattern is a point image,
That is, the minimum pattern on the mask, and the blurring function d
Is obtained as the amplitude distribution (impulse response) of light through the minimum pattern.

Next, in step 32, the original pattern distribution a of the light to be projected onto the work 20 is inversely convolved with the blur function d to obtain the mask pattern distribution m, and in step 33, the intensity component of the mask pattern m is obtained. Based on the (amplitude), the transmittance modulation layer 1 of the photomask 10
2 is formed, and in step 34, the phase shift layer 13 laminated on the transmittance modulation layer 12 is formed based on the phase component of the mask pattern m. Steps 33 and 34 may be repeated, and it is also possible to proceed with the work at the same time.

FIG. 3 shows the step of obtaining the mask pattern m in more detail. In step 51, the resist shape after development is designed and the pattern (function) h of the fine structure formed on the resist layer 22 of the work 20 is derived. Next, in step 52, this function h is corrected by a function f that corrects the nonlinearity between the exposure amount and the resist development depth, and the pattern i to be actually imaged on the resist layer 22 is obtained. The correction function f of the nonlinear characteristic of the resist can be obtained from the measurement result of the correlation between the exposure amount and the resist development amount.

In step 53, the intensity distribution function i of the light on the resist surface thus obtained is converted into a function a indicating the amplitude distribution of the light on the resist surface. Further, in order to perform inverse convolution with the blurring function d, step 54
Fourier transform of the function a is performed to obtain the function A in the frequency space. Further, in step 55, the function A is divided by the function D obtained by Fourier-transforming the blur function d to obtain the function M in the frequency space in which the blur effect is eliminated. By inverse Fourier transforming it in step 56 and returning it to the real space, it is possible to obtain the function m that is the inverse convolution of the function a indicating the amplitude with the blur function d. This function m indicates the mask pattern formed on the photomask 10 for forming the desired pattern a on the surface of the work 20 by the exposure system 1 shown in FIG.

As can be seen from the function m indicating the mask pattern shown in step 56 of FIG. 3, the obtained mask pattern generally contains a phase component in addition to the amplitude component. Therefore, in step 57, the amplitude component and the phase component are separated, the transmittance modulation layer is formed by the transmittance distribution, and the phase shift layer is formed by the phase component.

FIG. 4 shows how the photomask 10 is manufactured based on the mask pattern m obtained as described above.
First, as shown in FIG. 4A, a photosensitive layer 19 of amorphous silicon is laminated on a quartz substrate 11, heated and dehydrogenated, and then a laser drawing machine 18 is used based on an amplitude component of a mask pattern m. draw. Thereby, the transmittance modulation layer 12 is formed. Next, as shown in FIG. 4B, a transparent resist 17 is formed on the silicon transmittance modulation layer 12.
Is applied, and a plurality of concave portions 15 are formed using the electronic drawing machine 16 based on the phase component of the mask pattern m. Figure 4
As shown in (c), since the difference in the depth of the concave portion becomes the optical path difference in the actual exposure, it becomes the phase shift layer 13 showing the phase information. In this way, the transmittance modulation layer 12 and
The photomask 10 in which the phase shift layer 13 is laminated is completed.

There are several possible methods for forming the phase shift layer 13. When the photosensitive layer to be the transmittance modulation layer is included at a position deeper than the surface of the glass mask to be the substrate 11, the surface of the glass mask 11 is made uneven by machining or the like to form the phase shift layer 13. Is possible.

Further, as shown in FIG. 5 (a), the surface of the transparent resin sheet 14 is processed based on the phase information, and the substrate 11 provided with the transmittance modulation layer 12 and a high-refractive adhesive which are separately prepared. As shown in FIG. 5B, it is possible to manufacture the photomask 10 in which the phase shift layer 13 and the transmittance modulation layer 12 are laminated by accurately laminating them together.

[0024]

As described above, in the present invention, the blurring function resulting from the photomask and the exposure optical system is obtained, and the original pattern is inversely convoluted with the blurring function to obtain the mask pattern. Since this mask pattern contains a phase component in addition to an amplitude component, a photomask in which a phase shift layer is laminated on a transmittance modulation layer is manufactured. In this way, by stacking the phase shift layer on the photomask (gray mask) having the transmittance modulation layer, a microstructure such as a semiconductor wafer or a micro optical element is formed due to the thickness of the transmittance modulation layer and the like. It is possible to solve the phenomenon that the image formed on the work is blurred. Therefore, it is possible to provide a photomask provided with a photosensitive layer having a sufficient thickness, that is, a transmittance modulation layer, and further capable of reducing blurring of an image projected on a work. .

Therefore, a photomask having a wide controllable transmittance range and a sufficiently large controllable gradation number (gray level) can be provided, and an arbitrary three-dimensional shape can be accurately transferred to the resist layer. It will be possible. Therefore, the photomask of the present invention makes it possible to transfer the fine structure to the resist layer on the work with high precision, and thereby to manufacture the fine structure with higher precision.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an exposure system that exposes a work using a photomask.

FIG. 2 is a diagram showing a manufacturing process of a photomask.

FIG. 3 is a diagram showing a process of obtaining a mask pattern.

FIG. 4 is a diagram showing a manner of manufacturing a photomask based on the obtained mask pattern.

FIG. 5 is a diagram showing another example of manufacturing a photomask based on the obtained mask pattern.

[Explanation of symbols]

1 Exposure system 5 Exposure optical system 10 Photomask 11 board 12 Transmittance modulation layer 13 Phase shift layer 20 work 22 Resist layer

Claims (11)

[Claims] 1. A photomask having a transmittance modulation layer capable of modulating the intensity of exposure light and a phase shift layer laminated on the transmittance modulation layer capable of modulating the phase of the exposure light. . 2. The photomask according to claim 1, wherein the transmittance modulation layer is a photosensitive layer that undergoes a phase change by high energy light. 3. The photomask according to claim 1, wherein the phase shift layer is a layer processed to have irregularities. 4. The photomask according to claim 1, wherein the surface of the photomask is roughened to form the phase shift layer. 5. The photomask according to claim 1, wherein the sheet member, which is processed to have the unevenness and serves as the phase shift layer, is attached to a substrate provided with the transmittance modulation layer. 6. A method of manufacturing a photomask for modulating light for exposure, comprising: determining a blur function by which the light modulated by the photomask is projected until it is projected onto a work; A step of inversely convolving the original pattern distribution of the light to be projected with the blur function to obtain a mask pattern distribution; a step of forming a transmittance modulation layer of the photomask based on the intensity component of the mask pattern; A step of forming a phase shift layer to be laminated on the transmittance modulation layer based on a phase component of a mask pattern. 7. The method of manufacturing a photomask according to claim 6, wherein in the step of obtaining the blur function, light modulated by the photomask having a sample pattern is projected onto the work to obtain the blur function. 8. The method of manufacturing a photomask according to claim 6, wherein in the step of forming the transmittance modulation layer, high energy light is projected onto the photosensitive layer to cause a phase change. 9. The method of manufacturing a photomask according to claim 6, wherein in the step of forming the phase shift layer, the surface of the photomask is processed to have an uneven surface to form the phase shift layer. 10. The method of manufacturing a photomask according to claim 6, wherein, in the step of forming the phase shift layer, an uneven sheet member serving as the phase shift layer is attached to a substrate provided with the transmittance modulation layer. . 11. A method for manufacturing a microstructure, comprising the step of exposing a work having a resist layer formed on the surface thereof using the photomask according to claim 1 to transfer a three-dimensional shape to the resist layer.