JPH118179A - Pattern forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a pattern from being deformed by a method wherein a light source is changed in form, and a transparent auxiliary pattern where the phase difference of a transmitted light is equal to that of a transparent region is arranged at a main pattern which is to be projected. SOLUTION: A region 72 semitransparent to an exposure light and a transparent region to become a main pattern 73 are included, the semitransparent region 72 is so regulated as to reverse a phase difference between light which passes through the semitransparent region 72 and another light which passes through the transparent region, and the main pattern 73 is recurrently arranged. The recurrent pitch of the main pattern 73 is set 3.2 or less times as large as the size of the main pattern 73. Furthermore, an auxiliary pattern 74 which is a transparent auxiliary aperture and whose one side is smaller in size than the resolution limit of the projection optical system of a projection aligner is arranged so as to correct the main pattern 73 on form. By this setup, a fine pattern can be prevented from being deformed, and a hole pattern can be arranged high in density with an enough margin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used for manufacturing a semiconductor device or the like, and more particularly to a photomask having a process of changing the phase of illumination light, and more particularly to correcting the shape of a pattern to be transferred.

[0002]

2. Description of the Related Art As one of conventional techniques for improving the resolution of an exposure apparatus for transferring a mask pattern, Japanese Patent Application Laid-Open No.
In 136854, as a means for improving the resolution of a single transparent pattern, the periphery of the single pattern is made translucent, that is, the light shielding portion of the conventional mask is made translucent, and a small amount of light passing through the translucent portion and a transparent pattern are passed. The phase of the light is inverted. That is, light less than the sensitivity of the resist for transferring the pattern is passed through the translucent film, and the phase of this light and the light passing through the transparent pattern are inverted. Since the light that has passed through the translucent film has a phase inverted with respect to the light that has passed through the main pattern, the phase is inverted at the boundary, and the light intensity at the boundary approaches zero. As a result, the ratio of the intensity of light that has passed through the transparent pattern to the intensity of light at the boundary of the pattern becomes relatively large, and a light intensity distribution with higher contrast than that of the conventional method can be obtained. This mask structure can be realized only by changing the conventional light-shielding film to a translucent film having a phase inversion function, and is characterized in that the mask can be easily manufactured.
As a means for improving the depth of focus of a periodically arranged pattern, there is a method of forming a pattern using an exposure apparatus using a special stop having an annular transparent portion as disclosed in Japanese Patent Application Laid-Open No. 61-91662. When this exposure apparatus is used, it is possible to improve the depth of focus of a pattern having periodicity.

[0003]

In the projection image obtained in the above-mentioned prior art, there is a problem that the pattern shape is deformed (for example, a circle becomes an ellipse) when the pitch of the pattern to be formed is small. Due to the deformation of the pattern, there has been a problem that the effective depth of focus is reduced, which becomes an obstacle to formation of a good pattern.

[0004] It is an object of the present invention to prevent pattern deformation.
The purpose is to have a larger lithography process margin.

[0005]

In order to achieve the above object, according to the present invention, a transparent auxiliary pattern having the same phase difference of transmitted light as a transparent region is used as a main pattern for changing a light source shape and projecting. Placed. That is, using the oblique incidence illumination method,
Utilizing the fact that a periodic pattern is easily formed, a mask having an auxiliary transparent pattern arranged in a non-periodic direction is used.

[0006] More specifically, the translucent area includes at least a translucent area for exposure light and a transparent area serving as a main pattern, and the translucent area includes the translucent area and the light passing through the transparent area. The phase difference is adjusted so as to be inverted, the main pattern is repeatedly arranged, and the repetition pitch of the main pattern is different in the horizontal direction and the vertical direction on the main surface of the photomask, and the repetition pitch in any direction is different. Is arranged 3.2 times or less of the size of the main pattern, the size of at least one side to correct the shape of the main pattern transferred to the substrate is not more than the resolution limit of the projection optical system of the projection exposure apparatus And a pattern forming method using the photomask, wherein the transparent auxiliary opening is disposed.

[0007] Here, translucent means that light transmittance is 2
5% or less, preferably 5% or less.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a normal mask when a main pattern is formed of a transparent region will be described with reference to FIG. FIG. 1A is a plan view of a conventional mask, and FIG.
Is a cross-sectional view of the mask. 11 is a glass substrate, 12 is a translucent phase shift film, and 13 is a main pattern formed in a transparent region. The translucent phase shift film 12 is a chromium oxynitride film (CrON
Membrane) was used.

The transmittance of the translucent phase shift film 12 for exposure light is 4%. The thickness of the translucent phase shift film 12 is set to a thickness such that the phases of light transmitted through a region where the film is present and a region where the film is not present are substantially reversed to each other. Although the CrON film is used here as the translucent film, the invention is not limited to this.
Normal translucent phase shift mask structure, as long as the phase of light passing through the translucent part and the transparent part, such as a multilayer film of a transparent film such as CrO, CrN, MoSiO, MoSiON, or SiO2, is almost reversed. Is good.

As shown in FIG. 1C, the amplitude distribution of the light passing through the mask is such that the light passing through the main pattern 13 which is a light transmitting portion has a positive sign, while the translucent phase shift film
The phase of the light passing through 12 is inverted and becomes a negative sign. When this light is projected onto the wafer through a lens, the light is inverted immediately below the boundary between the main pattern 13 and the translucent phase shift film 12, which are light transmitting portions, as shown in FIG. The intensity is almost zero. Therefore, the spread of light intensity is suppressed,
A fine pattern with high contrast can be formed.

A conventional method will be described with reference to FIGS. FIG. 2A is a plan view of a conventional mask, and FIG.
2B is a cross-sectional view of the mask in the discontinuous direction AA ′, and FIG. 2D is a cross-sectional view of the mask in the continuous direction BB ′. 21 is a glass substrate, 22 is a translucent phase shift film, and 23 is a main pattern formed in a transparent region. As the translucent phase shift film 22, a CrON film was used.
The transmissivity of the translucent phase shift film 22 to the exposure light was 4%. In this case, the CrON film is used as the translucent film, but it is not limited to this. Normal translucent phase shift mask structure, as long as the phase of light passing through the translucent part and the transparent part, such as a multilayer film of a transparent film such as CrO, CrN, MoSiO, MoSiON, or SiO2, is almost reversed. Is good. FIG. 2C shows the light intensity distribution in the discontinuous direction AA ′, and FIG. 2E shows the light intensity distribution in the continuous direction BB ′. Since there is no periodicity in the non-continuous direction and it is almost isolated, the effect of the translucent phase shift mask can be sufficiently obtained, and a good light intensity profile can be obtained. However, in the light intensity distribution in the continuous direction shown in FIG. 2D, since the patterns are arranged at a small pitch, the effect of the translucent phase shift mask cannot be sufficiently obtained, and the light intensity profile is deteriorated. It is. FIG. 3 shows the relationship between the pitch P of the main pattern 23 and the non-continuous dimension of the transfer pattern when the transfer pattern size in the continuous direction of the main pattern 23 is 0.24 μm under these conditions. Here, the pattern was transferred by using a stepper having an exposure wavelength λ = 0.248 μm and a numerical aperture NA = 0.55 of the lens, and using the normal illumination of σ0.3 as shown in FIG. 3B. The transmittance of the translucent film is 4% when the transmittance of the transparent portion is 100%, and the phase difference between the transparent portion and the translucent portion is 1%.
80 °, design dimension W of light transmitting portion corresponding to main pattern 23 to be transferred
To 0.30 μm square (because the magnification of the projection exposure optical system is 1/5,
1.5 μm square on a mask). Pitch P of main pattern 23
In the range of approximately P ≧ 0.75 μm, the main patterns are sufficiently separated from each other, so that the difference between the non-continuous direction and the continuous direction of the transfer pattern is sufficiently small. Due to the interference effect between the main patterns, the dimension of the transfer pattern in the discontinuous direction increases when the pitch P of the main pattern 23 is approximately 0.52 <P <0.75 μm, and the pitch P of the main pattern 23 is approximately P <0.52 μm. Thus, the transfer pattern becomes an elliptical shape in which the dimension in the continuous direction becomes large, which is a problem. FIG. 4 shows the focal depth of the transfer pattern when the pitch P of the main pattern 23 is 0.48 μm. The dimension difference between the discontinuous direction and the continuous direction is as large as about 0.03 μm, which is a problem because it is about 13% of the target pattern dimension. Further, when the allowable size variation is set to the target size of 0.24 μm ± 10%, the depth of focus can be obtained only about 0.6 μm in width.

A conventional method for forming patterns arranged at a small pitch in one direction is shown in FIGS. FIG.
The case where the oblique incidence illumination method, which has a periodic pattern and has the effect of improving the depth of focus, is used together will be described. FIG. 5A is a plan view of the mask, and FIG. 5B is a plan view of the mask in the discontinuous direction AA ′.
(D) is a cross-sectional view of the mask in the continuous direction BB '. 51 is a glass substrate, 52 is a translucent phase shift film, and 53 is a main pattern formed in a transparent region. The translucent phase shift film 52
A CrON film was used. The transmissivity of the translucent phase shift film 22 to the exposure light was 4%. In this case, the translucent film
Although a CrON film was used, it is not limited to this. CrO, CrN, MoSi
It is only necessary that the phase of light passing through the translucent portion and the transparent portion, such as a multilayer film of a transparent film such as O, MoSiON, or SiO2, be substantially inverted, and a normal translucent phase shift mask structure may be used. FIG. 5C shows the light intensity distribution in the discontinuous direction AA ′, and FIG. 5E shows the light intensity distribution in the continuous direction BB ′. In the discontinuous direction, since there is no periodicity and the effect of the oblique incidence illumination method cannot be obtained, the light intensity profile is inferior. However, in the light intensity distribution in the continuous direction shown in FIG. 5D, since the patterns are arranged with periodicity, good light intensity contrast can be obtained by the effect of the oblique illumination method.
FIG. 6A shows the depth of focus of the transfer pattern when the pitch P of the main pattern 53 obtained under this condition is 0.48 μm. Even when the annular illumination method, which is one of the oblique incident illumination methods as shown in FIG. 6B, is used, a long pattern is formed in the continuous direction, and the dimensional difference between the continuous direction and the discontinuous direction of the transfer pattern is small. About 0.
It is formed at 01 μm. This dimensional difference is as small as about 1/3 of the case where the normal illumination method is used, but it is a fluctuation of about 4% of the target dimension, which lowers the process margin. When the allowable size variation is set to the target dimension of 0.24 μm ± 10%, the depth of focus is about 1.05 μm in width, and the depth of focus is about 1.8 times as large as that obtained by using the normal illumination method. It should be noted that substantially the same results were obtained when the quadrupole illumination method was used as the light source shape.

FIG. 7 shows the principle of the present invention, and FIGS. 8 and 9 show embodiments thereof. In the present invention, as shown in FIG. 7A, a transparent auxiliary pattern 74 having the same phase difference as the main pattern not transferred onto the wafer is arranged in a discontinuous direction in which the arrangement pitch of the main pattern 73 is large. FIG. 7B is a cross-sectional view of the mask in the discontinuous direction AA ′, and FIG. 7D is a cross-sectional view of the mask in the continuous direction BB ′. 71 is a glass substrate, 72 is a translucent phase shift film, and 73 is a main pattern formed in a transparent region.
As the translucent phase shift film 72, a CrON film was used. The transmissivity of the translucent phase shift film 72 to the exposure light was 4%. In this case, the CrON film is used as the translucent film, but it is not limited to this. CrO, CrN, MoSiO, MoSiON, etc., or SiO
It is sufficient that the phase of light passing through the translucent portion and the transparent portion, such as a multilayer film of a transparent film such as a second, is substantially inverted, and a normal translucent phase shift mask structure may be used. FIG. 7C shows a light intensity distribution in a discontinuous direction, and FIG. 7E shows a light intensity distribution in a continuous direction. By arranging the auxiliary patterns even in the non-continuous direction, the patterns are periodically arranged, the effect of the oblique incidence illumination method is obtained, and a steep light intensity profile is obtained. In the light intensity distribution in the continuous direction shown in FIG. 7D, since the patterns are arranged with a periodicity, a good light intensity contrast can be obtained by the effect of the oblique illumination method. By forming a pattern under these conditions, good contrast can be obtained in both the continuous direction and the discontinuous direction. The effect of the present invention can be obtained when the arrangement pitch of the main pattern is not more than about 3.2 times the transfer pattern dimension where the effect of interference is obtained as shown in FIG.

FIG. 8A shows the relationship between the dimension in the continuous direction and the discontinuous direction and the arrangement position R of the auxiliary pattern when the maximum dimension of the transferred main pattern is 0.24 μm. The arrangement position R of the auxiliary pattern is the distance between the pattern edges of the auxiliary pattern 74 and the main pattern 73. Here, the pattern is transferred by using a stepper having an exposure wavelength λ = 0.248 μm and a numerical aperture NA = 0.55 of the lens, and the illumination condition is an outer diameter σ 0 .0 as shown in FIG.
7. Ring illumination with an inner diameter of σ0.4 was used. The transmittance of the translucent film is 4% when the transmittance of the transparent portion is 100%, the phase difference between the transparent portion and the translucent portion is 180 °, the design dimension W of the light transmitting portion corresponding to the main pattern 73 to be transferred. 0.28 μm square (1.4 μm square on the mask because the magnification of the projection exposure optical system is 1/5), the main pattern
A mask having an arrangement pitch P of 0.48 μm (2.4 μm on the mask because the magnification of the projection exposure optical system is 1/5) was used. The width G of the auxiliary transparent pattern 74 is desirably equal to or less than the resolution limit, and is represented by G = b × λ / NA (where the exposure wavelength is λ, the numerical aperture of the lens is NA, and 0.05 ≦ b ≦ 0.25) Here, G was set to 0.10 μm. As shown in FIG.
The transfer pattern dimension in the continuous direction and the discontinuous direction with a small pitch is reversed with the auxiliary pattern arrangement position R centered at about 0.225 μm. Further, when the arrangement position R of the auxiliary pattern is about 0.28 μm or more or about 0.24 μm or less, the dimensional difference becomes larger than when the auxiliary pattern is not arranged, so that the opposite effect is obtained. When the arrangement position R of the auxiliary pattern 74 is about 0.225 μm, the transfer pattern dimensions in the continuous direction and the discontinuous direction become almost the same. Therefore, the distance R between the center of the auxiliary transparent pattern and the center of the main pattern is determined by R = a × λ / NA (where the exposure wavelength is λ, the numerical aperture of the lens is NA, and 0.53 ≦ a ≦ 0.62) from the effect of dimensional correction. , Can achieve the goal.

FIG. 9 shows the depth of focus of the transfer pattern formed at the auxiliary pattern position R = 0.26 μm. Auxiliary pattern 74
By arranging, the difference in transfer pattern dimension between the continuous direction and the non-continuous direction could be reduced to about 0.001 μm, a value close to a perfect circle. The depth of focus is approximately 1.
35 μm was obtained, and the depth of focus was also improved. Here, the annular illumination method, which is one of the oblique incidence illumination methods as shown in FIG. 8B, is used as the illumination shape. Almost the same results were obtained by arranging the patterns at the optimum positions.

Although the arrangement pitch of the main pattern and the size and coefficient of the auxiliary pattern are limited as described above, the size, shape, and arrangement position of the main pattern and the auxiliary pattern are optimal depending on the transmittance of the translucent region and the light source shape. The values are different. For example, when the transmittance changes, the light intensity passing through the translucent region changes. For example, when the transmittance is changed to 6%, the light intensity passing through the translucent region becomes large. As a result, the dimensions of the main pattern and the dimensions of the auxiliary pattern are changed.
By optimizing each of them, the shape of the pattern can be corrected with almost no problem. As a result, a pattern having a good shape can obtain a larger depth of focus. Further, since the optimum value of the arrangement pitch changes by changing the shape of the light source, the optimum position at which the auxiliary pattern is arranged changes. For example, when quadrupole illumination is used, the optimum value of the pattern pitch changes depending on the opening position of the light source, and the depth of focus is lower than before depending on the pitch. As a result, the size, arrangement position, etc. of the auxiliary pattern are changed, but if each is optimized, the shape of the pattern can be corrected with almost no problem, and as a result, a larger depth of focus can be obtained.
Therefore, it is necessary to optimize the arrangement position of the auxiliary pattern and the like according to the transmittance of the translucent region and the shape of the light source. The shape of the main pattern is not limited to a square hole pattern. Even in the case of a rectangular pattern or the like, the present invention can be applied to the case where they are continuously arranged at a small pitch. The shape of the auxiliary pattern is not limited to a rectangular slit pattern. Even a square pattern or the like can be applied as long as the main pattern is continuously arranged at a small pitch and there is a pattern intended to correct the shape at a portion where the pattern is arranged at a large pitch. The transmissivity of the translucent region is not limited to this embodiment, but can be applied by using a coefficient suitable for the transmissivity. Further, the structure and material of the mask are not limited to the materials used in this embodiment. That is, in the present invention, the structure of the mask used includes a transparent region and a translucent region, and the phase difference of light passing through the transparent region and the translucent region is approximately 180 °, and the main pattern to be projected is at least one direction. Are arranged continuously in
In addition, the object can be achieved if a transparent pattern having the same phase as the main pattern and not resolving is arranged in a portion arranged at a large pitch. In addition, although the annular illumination method is used in the text, the shape of the light source is not limited to this. The oblique incidence illumination method can be applied by changing the position and the like of the auxiliary pattern according to each light source such as a quadrupole.

An example in which the present mask is applied to the formation of an electrode connection hole pattern of a dynamic RAM will be described with reference to FIGS. FIG. 10 is a plan view of a memory cell group in which a plurality of memory cells are arranged. In the figure, word lines WL1 to WL
L4 is arranged in the Y direction, and data lines BL1 to BL3 are arranged in the X direction. The lower electrode 101 of the crown-shaped capacitor is formed above these word lines and data lines. On the active region 102 in the gap between the word lines WL1 to WL4, a plug electrode 103 whose planar shape is in the Y direction is in contact with the active region 102 and extends to a region other than the active region. The plug electrode 103 has a data line B
L1 to BL3 are arranged so as to partially overlap. Further, an opening 104 is formed on the active region 102, and the lower electrode 101 of the capacitor is connected through the opening. Here, FIG. 11 shows the shape of the photomask used to form the opening 104. Reference numeral 111 denotes a main pattern of the opening 104, and an auxiliary pattern 11 for correcting the shape of the main pattern.
2 was arranged. In this case, a stepper having an exposure wavelength λ = 0.248 μm and a numerical aperture NA = 0.55 of the lens is used for pattern transfer, and the illumination condition is an outer diameter σ0.7 which is one of the oblique incident illumination.
Ring illumination with an inner diameter of σ 0.4 was used. The transmittance of the translucent film is 4% when the transmittance of the transparent portion is 100%, the phase difference between the transparent portion and the translucent portion is 180 °, the design size of the main pattern 111 corresponding to the aperture 104 to be transferred. Is 0.28 μm square (1.4 μm square on the mask because the magnification of the projection exposure optical system is ５), the auxiliary pattern 11
A mask having a width of 0.10 μm was used. Depth of focus that satisfies the target dimensional standard is about 0.9 when no auxiliary pattern is used.
However, in the case of applying the present invention, the thickness is about 1.4 μm, and the focus latitude of about 1.5 times can be realized, and the yield of good devices can be improved by about 10%.

[0018]

According to the present invention, the hole pattern can be densely arranged with a sufficient margin without increasing the number of steps such as exposure of the fine pattern twice. Particularly, it is possible to realize a finer pattern and a fine arrangement of an electrode extraction hole pattern of a super LSI, which is difficult to miniaturize, and a sufficient depth of focus can be ensured even with a fine pitch arrangement, thereby realizing the manufacture of the ultra LSI using optical lithography. Things become possible. Further, the defect rate of the VLSI product can be reduced, which is extremely industrially advantageous.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a conventional method.

FIG. 2 is an explanatory diagram of the principle of a conventional method.

FIG. 3 is an explanatory view of a main example of a conventional method.

FIG. 4 is an explanatory view of a main example of a conventional method.

FIG. 5 is an explanatory diagram of the principle of a conventional method.

FIG. 6 is an explanatory view of a main example of a conventional method.

FIG. 7 is an explanatory diagram of the principle of the present invention.

FIG. 8 is an explanatory diagram of a main embodiment of the present invention.

FIG. 9 is an explanatory view of a main embodiment of the present invention.

FIG. 10 is an explanatory diagram of a main embodiment of the present invention.

FIG. 11 is an explanatory view of a main embodiment of the present invention.

[Explanation of symbols]

11, 21, 51, 71: glass substrate, 12, 22, 52, 72: translucent phase shift film, 13, 23, 53, 73: transparent main pattern, 14, 2
4, 54, 75… Transparent main pattern light intensity peak, 15, 25 ……
The second light intensity peak of the transparent main pattern, the so-called sub-peak, 74
… Transparent auxiliary pattern.

Claims (8)

[Claims] 1. A method of transferring a pattern provided on a photomask onto a substrate by using a projection exposure apparatus having an oblique incidence illumination optical system, wherein the photomask has at least a translucent area and a main pattern with respect to exposure light. Including a transparent region, wherein the translucent region is adjusted so that the phase difference of light passing through the translucent region and the transparent region is 180 degrees, the main pattern is repeatedly arranged, The repetition pitch of the main pattern is different in the horizontal direction and the vertical direction on the photomask main surface, and the repetition pitch in any direction is arranged to be 3.2 times or less the size of the main pattern, and is transferred to the substrate. In order to correct the shape of the main pattern, a transparent auxiliary opening having a size of at least one side smaller than the resolution limit of the projection optical system of the projection exposure apparatus is arranged. A pattern forming method. 2. The pattern forming method according to claim 1, wherein said oblique incidence illumination is annular illumination. 3. The pattern forming method according to claim 1, wherein said oblique incidence illumination is quadrupole illumination. 4. The auxiliary opening has at least one side dimension G satisfying the following relationship: G = b × λ / NA
Is the numerical aperture of the projection exposure optical system, λ is the wavelength of the exposure light, b
Is a value in the range of 0.05 ≦ b ≦ 0.25), the pattern forming method according to any one of claims 1 to 3. 5. The distance R between pattern edges of the main pattern comprising the auxiliary aperture and the transparent region satisfies the relationship of R = a × λ / NA (where NA is the numerical aperture of the projection exposure optical system, λ 5. The pattern forming method according to claim 1, wherein a is a wavelength of exposure light, and a is a value in a range of 0.53 ≦ a ≦ 0.62. 6. A translucent area including at least a translucent area and a transparent area serving as a main pattern with respect to exposure light, wherein the translucent area has a phase difference between light passing through the translucent area and the transparent area. The main pattern is adjusted so as to be 180 degrees, the main pattern is repeatedly arranged, and the repetition pitch of the main pattern is different in a horizontal direction and a vertical direction on the main surface of the photomask, and the repetition pitch in any direction is different. Arranged at 3.2 times or less the size of the main pattern, the size of at least one side is equal to or less than the resolution limit of the projection optical system of the projection exposure apparatus to correct the shape of the main pattern transferred to the substrate. A photomask, wherein a transparent auxiliary opening is arranged. 7. The auxiliary opening has at least one side dimension G satisfying the following relationship: G = b × λ / NA
Is the numerical aperture of the projection exposure optical system, λ is the wavelength of the exposure light, b
Is a value in the range of 0.05 ≦ b ≦ 0.25). 8. The distance R between pattern edges of the main pattern comprising the auxiliary aperture and the transparent region satisfies the relationship of R = a × λ / NA (where NA is the numerical aperture of the projection exposure optical system, λ 8. The photomask according to claim 6, wherein a is a wavelength of the exposure light, and a is a value in a range of 0.53 ≦ a ≦ 0.62).