JP4574343B2 - Phase shift mask and pattern forming method - Google Patents

Description

  The present invention relates to a phase shift mask and a pattern forming method, and more particularly to a phase shift mask and a pattern forming method capable of reliably forming a fine pattern.

  In order to cope with high integration of semiconductor devices, liquid crystal display devices, and the like, in a lithography process, a pattern to be formed is being miniaturized. For the purpose of pattern miniaturization, for example, technical development has been performed to improve resolution performance, such as shortening the wavelength of an exposure light source and increasing the NA of an exposure lens. However, the required pattern dimensions are much smaller than those obtained by these measures. Therefore, in order to form a highly integrated fine pattern, a process technique for stably forming a fine pattern exceeding the resolution performance of the exposure apparatus is required.

As a technique for forming a fine pattern, there is a method using a phase shift mask. This is a method of providing a pattern for shifting the phase of transmitted light on a transmissive mask substrate, causing a phase difference in exposure light transmitted through the photomask, and improving the contrast of the pattern projection image by mutual interference. (For example, Patent Documents 1 and 2, Non-Patent Documents 1 and 2).
JP 2003-21891 A Japanese Patent Laid-Open No. 5-289308 2002 symposiums on VLSI Technology Digest of Technical papers, "Super-resolution enhancement method with phase-shifting mask available for random patterns", Akio Misaka, Takahiro Matsuo and Masaru Sasago. 2003SPIE (5040-34), "Novel strong resolution enhancement technology with phase-shifting mask for Logic gate pattern Fabrication", Takahiro Matsuo, Akio Misaka and Masaru Sasago

FIG. 19 is a schematic view illustrating the cross-sectional structure of a conventional phase shift mask.
That is, this phase shift mask has a structure in which a phase shift region 101 is provided on the surface of a transmission mask substrate 100 made of quartz or the like, and a light shielding film 201 is provided at an end of the phase shift region 101. The phase shift region 101 has an optical thickness that reverses the phase of transmitted light. Further, by providing the light shielding film 201 at the end portion, the contrast of transmitted light can be increased.

  However, such a conventional phase shift mask has a problem in that the formation of the light shielding film 201 is not easy, and the contrast tends to decrease when a “shift” occurs. That is, in order to form this phase shift mask, after the phase shift region 101 is formed, the light shielding film formed on the phase shift region 101 is patterned and left only at the end of the phase shift region 101. There is a need. For this purpose, a resist film is formed on the light shielding film, the pattern of the light shielding film 201 is exposed to form a resist mask, and then the light shielding film is etched, as shown in FIG. A light shielding film 201 is formed only at the end of the shift region 101.

  That is, in order to form this phase shift mask, two exposure steps are required for the formation of the phase shift region 101 and the patterning of the light shielding film 201. The exposure of the light shielding film pattern must be performed within the resolution range of the exposure apparatus, and the production of the fine light shielding film 201 is difficult. Specifically, in the case of equal magnification (1 time), the lower limit of the size of the light shielding film 201 is about 30 nanometers, and a light shielding film finer than this cannot be formed.

  Furthermore, in order to form the light shielding film 201 at the end of the phase shift region 101, it is necessary to align the mask with high accuracy during exposure of the resist mask for patterning the light shielding film. If the alignment of the mask is shifted during the patterning of the light shielding film, the size of the light shielding film 201 becomes non-uniform as illustrated in FIG. That is, when the mask is misaligned, for example, the width Lc of the light shielding film 201 on the left side of the phase shift region 101 is increased, and the width Lc of the light shielding film 201 on the right side is decreased. When the width Lc of the light shielding film 201 becomes non-uniform in this way, the exposure light pattern also becomes asymmetric.

  FIG. 21 is a graph showing the intensity distribution of the exposure light that has passed through the phase shift mask. Here, the width Ls of the phase shift region is shown for 10, 30, 50, 70, and 80 nanometers. Further, the deviation ΔLc of the width Lc of the light shielding film 201 was set to 30 nanometers.

  FIG. 22 is a graph showing that the intensity distribution of the exposure light that has passed through the phase shift mask becomes asymmetric. That is, here, the deviation ΔLc of the width Lc of the light shielding film 201 represents the intensity distribution of the exposure light for each of minus 5, zero, plus 5, 10, 15, 20, 25, and 30 nanometers. Here, the phase shift region Ls is 70 nanometers.

  From FIG. 21 and FIG. 22, it can be seen that when the width Lc of the light shielding film 201 becomes non-uniform, the exposure light distribution also becomes asymmetric and the exposure pattern is deformed.

  The present invention has been made on the basis of recognition of such a problem, and an object of the present invention is to provide a phase shift mask capable of forming a finer pattern than in the prior art and causing no asymmetry in the intensity of exposure light. It is to provide a pattern forming method.

In order to achieve the above object, according to one aspect of the present invention,
A phase shift mask in which a phase shift region for shifting the phase of exposure light is formed on a transparent substrate,
A light shielding film is provided on a side wall of the phase shift region,
A phase shift mask is provided in which a single dark pattern is formed by the phase shift region and the light shielding film provided on the side wall thereof.

Here, the transmittance of the light shielding film with respect to the exposure light may be 10% or less.
The light shielding film may be provided over the entire side wall of the phase shift region.
Alternatively, the height of the light shielding film may be smaller than the height of the phase shift region.
When the wavelength of the exposure light is λ, the numerical aperture of the reduction projection optical system of the exposure apparatus is NA, and the magnification of the reduction projection optical system is M, the width Ls of the phase shift region is

(0.1 × λ / NA) × M <Ls <(0.4 × λ / NA) × M

It can be in the range.

When the wavelength of the exposure light is λ, the numerical aperture of the reduction projection optical system of the exposure apparatus is NA, and the magnification of the reduction projection optical system is M, the width Lc of the light shielding film is

(0.05 × λ / NA) × M <Lc <(0.2 × λ / NA) × M

It can be in the range.

Further, the phase of the exposure light transmitted through the phase shift region can be reversed from the phase of the exposure light transmitted through the other transparent substrate.
On the other hand, according to another aspect of the present invention,
Forming a layer made of a photoreceptor on a substrate provided with a film to be processed;
Irradiating the photosensitive member with exposure light through any of the phase shift masks;
Developing the photoconductor to form a mask pattern corresponding to the single dark pattern;
Etching the film to be processed through the mask pattern;
A pattern forming method is provided.

  According to the present invention, it is possible to provide a phase shift mask and a pattern forming method capable of forming a finer pattern than before and not causing asymmetry of the intensity of exposure light.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view illustrating the cross-sectional structure of a phase shift mask according to an embodiment of the invention.
The phase shift mask of this embodiment has a structure in which a mesa-type phase shift region 101 is provided on the surface of a transmission mask substrate 100 made of quartz or the like, and a light shielding film 201 is provided on the side wall of the phase shift region 101. The phase shift region 101 has an optical thickness that reverses the phase of transmitted light. Further, by providing the light shielding film 201 on the side wall, the contrast of transmitted light can be increased. As a material of the light shielding film 201, for example, chromium (Cr), silicon oxynitride (SiO _x N _y ), or the like can be used. The light shielding film 201 is desirably formed so that the transmittance for exposure light is 10% or less.

  As will be described in detail later, in the present embodiment, the width Lc of the light shielding film 201 provided on the side wall of the phase shift region 101 can be made substantially equal to the thickness of the film. Therefore, it becomes easy to form the width Lc very small, and a fine pattern can be formed reliably and easily.

2 and 3 are graphs illustrating the intensity distribution of the exposure light transmitted through the phase shift mask of this embodiment.
That is, FIG. 2 shows the intensity distribution of exposure light when the width Lc of the light shielding film 201 is 10 nanometers and the width Ls of the phase shift region 101 is 10, 30, 50, 70, 90 nanometers. FIG. 3 also shows the exposure light intensity distribution when the width Lc of the light shielding film 201 is 10 nanometers and the width Ls of the phase shift region 101 is 100, 120, 140, 160, 180, and 200 nanometers.

As can be seen from FIGS. 2 and 3, when the width Lc of the light shielding film 201 is 10 nanometers, the width Ls of the phase shift region 101 is in the range of 10 nanometers to 70 nanometers. A continuous dark pattern can be formed. If the phase shift region Ls is in the range of 30 nanometers to 70 nanometers, the contrast of the dark pattern can be made very high.
When the width Ls of the phase shift region 101 is larger than 90 nanometers, a light pattern is generated between the light shielding films 201 on both sides instead of a continuous dark pattern immediately below the phase shift region 101.

4 to 6 are graphs illustrating in more detail the change in the intensity distribution of the exposure light when the width Lc of the light shielding film 201 is changed.
That is, FIG. 4 shows the exposure light intensity distribution when the width Lc of the light shielding film 201 is 10 nanometers and the width Ls of the phase shift region 101 is 10, 20, 30, 40, 50, 60, 70, 80 nanometers. Represents. FIG. 5 shows the intensity distribution of exposure light when the width Lc of the light shielding film 201 is 20 nanometers and the width Ls of the phase shift region 101 is 10, 20, 30, 40, 50, 60, 70, 80 nanometers. Represents. FIG. 6 shows the exposure light intensity distribution when the width Lc of the light shielding film 201 is 30 nanometers and the width Ls of the phase shift region 101 is 10, 20, 30, 40, 50, 60, 70, 80 nanometers. Represents.

When the width Lc of the light shielding film 201 is 10 nanometers, as shown in FIG. 4, when the width Ls of the phase shift region 101 is 10 nanometers, the contrast is slightly low, but the contrast increases when the width Ls is larger than that. . The light intensity immediately below the phase shift region 101 is lowest when the width Ls is approximately 50 nanometers. It can be seen that the contrast decreases when the width Ls is 80 nanometers.
When the width Lc of the light shielding film 201 is 20 nanometers, as shown in FIG. 5, the contrast is high when the width Ls of the phase shift region 101 is in the range of about 10 nanometers to 50 nanometers and the width Ls is 60 nanometers or more. There is a tendency to decrease. When the width Lc of the light shielding film 201 is 30 nanometers, as shown in FIG. 6, the contrast is high when the width Ls of the phase shift region 101 is in the range of about 10 nanometers to 40 nanometers, and the width Ls is 50 nanometers or more. There is a tendency for the contrast to decrease.
Including the results illustrated in FIGS. 2 to 6, as a result of studies by the present inventor, when the width Ls of the phase shift region 101 is set within the range represented by the following equation, darkness with high contrast immediately below the phase shift region 101. It turns out that a pattern is obtained.

(0.1 × λ / NA) × M <Ls <(0.4 × λ / NA) × M

Here, λ is the wavelength of the exposure light, NA is the numerical aperture of the reduction projection optical system of the exposure apparatus, and M is the magnification of the reduction projection optical system.

Similarly, it has been found that when the width Lc of the light shielding film 201 is within the range represented by the following equation, a dark pattern with high contrast is obtained directly below the phase shift region 101.

(0.05 × λ / NA) × M <Lc <(0.2 × λ / NA) × M

As described above with reference to FIGS. 2 to 6, according to the present embodiment, by adjusting the width Lc of the light shielding film 201 and the width Ls of the phase shift region 101 as appropriate, 10 nanometers or more. High contrast dark patterns can be formed in the range of 70 nanometers. That is, a fine pattern of about 10 to 70 nanometers can be precisely formed.

  Furthermore, according to this embodiment, the width Lc of the light shielding film 201 can be defined as the film thickness. Therefore, it is not necessary to adjust the alignment of the mask as described above with reference to FIG. 20, and problems such as pattern asymmetry due to fluctuations in the width Lc can be solved. Hereinafter, this point will be described with reference to a method of manufacturing a phase shift mask.

7 and 8 are process cross-sectional views showing the main part of the manufacturing process of the phase shift mask of this embodiment.
First, as shown in FIGS. 7A and 7B, a resist layer 300 is applied on a mask substrate 100 such as quartz. Further, exposure / development processing is performed using a predetermined mask, and the resist layer 300 is patterned as shown in FIG.

Thereafter, as shown in FIG. 7D, the phase shift region 101 is formed by etching the mask substrate 100 using the resist layer 300 as a mask.
After removing the resist layer 300 (FIG. 8A), a light-shielding film material 200 is deposited on the entire surface. At this time, the light shielding film material 200 is also deposited on the side wall of the phase shift region 101. That is, the light shielding film material 200 is deposited on the side wall of the phase shift region 101 with the same thickness as the flat portion.

  After that, the light shielding film material 200 is etched from above by anisotropic etching. As anisotropic etching, for example, a method such as RIE (reactive ion etching) or ion milling can be used. By this etching, the material 200 of the flat portion is removed, and the light shielding film 201 is formed only on the side wall 101 of the phase shift region 101.

  As described above, according to the present embodiment, lithography is not required when forming the light shielding film 201. That is, mask alignment is unnecessary, and the problem of “shift” as described above with reference to FIG. 20 can be solved. Furthermore, since the width Lc of the light shielding film 201 can be defined by the film thickness, an extremely fine width Lc of about 10 nanometers below the resolution limit of the exposure apparatus can be realized easily and stably.

FIG. 9 is a schematic view illustrating the cross-sectional structure of a phase shift mask according to a modification of this embodiment.
In this modification, a trench type phase shift region 101 is provided on the mask substrate 100. That is, the mask substrate 100 made of quartz or the like is provided with a concave phase shift region 101 having a thickness for inverting the phase of exposure light. A light shielding film 201 is provided on the sidewalls on both sides of the trench type phase shift region 101.

  Also in this modified example, the same effect as described above with reference to FIGS. 1 to 6 can be obtained. That is, by adjusting the width Lc of the light shielding film 201 and the width Ls of the phase shift region 101 as appropriate, a dark pattern with high contrast can be formed in the range of 10 nanometers to 70 nanometers. That is, a fine pattern of about 10 to 70 nanometers can be precisely formed.

  Furthermore, also in this modification, the width Lc of the light shielding film 201 can be defined as the film thickness.

10 and 11 are process cross-sectional views illustrating the main part of the manufacturing process of the phase shift mask of this modification. In these drawings, the same elements as those described above with reference to FIGS. 7 and 8 are denoted by the same reference numerals, and detailed description thereof is omitted.
Also in this modified example, after forming the trench type phase shift region 101 as shown in FIG. 11A, the light shielding film material 200 is deposited on the entire surface of the mask substrate 100 (FIG. 11B). By performing anisotropic etching in the vertical direction, the light shielding film 201 can be formed (FIG. 11C).

  Thus, also in this modification, lithography is not required when forming the light shielding film 201. That is, mask alignment is unnecessary, and the problem of “shift” as described above with reference to FIG. 20 can be solved. Furthermore, since the width Lc of the light shielding film 201 can be defined by the film thickness, an extremely fine width Lc of about 10 nanometers below the resolution limit of the exposure apparatus can be realized easily and stably.

Next, a second embodiment of the present invention will be described.
FIG. 12 is a schematic view illustrating the cross-sectional structure of the phase shift mask according to the second embodiment of the invention. In the figure, the same elements as those described above with reference to FIGS. 1 to 11 are denoted by the same reference numerals, and detailed description thereof is omitted.
Also in this embodiment, the light shielding film 201 is provided on the side wall of the phase shift region 101. However, the height d1 is set lower than the height d2 of the phase shift region 101. In this way, the contrast can be further increased.
FIG. 13 is a cross-sectional view illustrating a phase shift mask in which a light shielding film 201 is formed on the entire side wall of the phase shift region 101. In this way, as described above with reference to the first embodiment of the present invention, it is possible to reliably and easily carry out extremely fine patterning that is below the resolution limit of the exposure apparatus.

  However, as indicated by an arrow S in FIG. 13, the exposure light may be reflected or scattered by the side wall of the light shielding film 201 to cause a phase shift. For example, when the mesa-type phase shift region 101 is formed using quartz (refractive index n = 1.47), when i-line (wavelength λ = 0.356 micrometers) is used as exposure light, the height d2 = λ / 2 (n−1) = 0.389 micrometers. That is, the height d2 of the phase shift region 101 is 389 nanometers. As described above, since the side wall of the phase shift region 101 is high, when the light shielding film 201 is formed on the entire side wall, reflected light or scattered light represented by the arrow S may be generated.

  When such reflected light or scattered light is generated, the phase shift effect is weakened and the contrast of the exposure light may be lowered.

On the other hand, according to the present embodiment, as illustrated in FIG. 12, by reducing the height d <b> 1 of the light shielding film 201, light reflection and scattering on the side surface of the light shielding film 201 can be suppressed. As a result, it is possible to suppress a decrease in the phase shift effect due to reflected light or scattered light, suppress a decrease in contrast of exposure light, and form a fine pattern more precisely.
In addition, the height d1 of the light shielding film 201 in this embodiment should just be more than the thickness which can shield exposure light. Therefore, the relationship between the height d1 of the light shielding film 201 and the height d2 of the phase shift region 101 is not limited to that illustrated in FIG. 12, and for example, the height d1 is higher as illustrated in FIG. Alternatively, the height d1 may be low as illustrated in FIG. In short, if the transmittance of the light shielding film 201 with respect to the exposure light is 10% or less, the light shielding effect of the light shielding film 201 can be sufficiently obtained.

  16 and 17 are process cross-sectional views illustrating the method for manufacturing the phase shift mask of this embodiment. In these drawings, the same steps as those described above with reference to FIGS. 7 and 8 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, as shown in FIG. 17C, when the light shielding film material 200 is anisotropically etched in the vertical direction, the etching is continued even after the flat portion material 200 is removed. As shown in FIG. 17D, the etching is finished when the height d1 of the light shielding film 201 reaches a predetermined value. That is, the height d1 of the light shielding film 201 can be adjusted by adjusting the anisotropic etching time.

FIG. 18 is a schematic diagram showing a cross-sectional structure of a phase shift mask according to a modification of the present embodiment.
That is, this modification is a specific example in which the present embodiment is applied to a trench type phase shift mask. Also in this modified example, by reducing the height d1 of the light shielding film 201, light reflection and scattering on the side surface of the light shielding film 201 can be suppressed. As a result, it is possible to suppress a decrease in the phase shift effect due to reflected light or scattered light, suppress a decrease in contrast of exposure light, and form a fine pattern more precisely.
The embodiments of the present invention have been described above with reference to specific examples.
However, the present invention is not limited to these specific examples. For example, the materials and dimensions employed in the phase shift mask according to the present invention, the wavelength of exposure light employed in the pattern formation process performed using this phase shift mask, the material of the resist, other chemicals, the structure of the semiconductor, Regarding the processing conditions and the like, those appropriately selected from a known range by those skilled in the art are also included in the scope of the present invention.

It is a schematic diagram which illustrates the cross-section of the phase shift mask concerning embodiment of this invention. It is a graph which illustrates intensity distribution of exposure light which permeate | transmitted the phase shift mask of embodiment of this invention. It is a graph which illustrates intensity distribution of exposure light which permeate | transmitted the phase shift mask of embodiment of this invention. 6 is a graph illustrating in more detail the change in the intensity distribution of exposure light when the width Lc of the light shielding film 201 is changed. FIG. 6 is a graph illustrating in more detail the change in the intensity distribution of exposure light when the width Lc of the light shielding film 201 is changed. FIG. 6 is a graph illustrating in more detail the change in the intensity distribution of exposure light when the width Lc of the light shielding film 201 is changed. FIG. It is process sectional drawing showing the principal part of the manufacturing process of the phase shift mask of embodiment of this invention. It is process sectional drawing showing the principal part of the manufacturing process of the phase shift mask of embodiment of this invention. It is a schematic diagram which illustrates the cross-section of the phase shift mask concerning the modification of embodiment of this invention. It is process sectional drawing which illustrates the principal part of the manufacturing process of the phase shift mask of the modification of 1st Embodiment. It is process sectional drawing which illustrates the principal part of the manufacturing process of the phase shift mask of the modification of 1st Embodiment. It is a schematic diagram which illustrates the cross-section of the phase shift mask concerning the 2nd Embodiment of this invention. 4 is a cross-sectional view illustrating a phase shift mask in which a light shielding film 201 is formed on the entire side wall of the phase shift region 101. FIG. It is a schematic diagram which illustrates a phase shift mask with high height d1. It is a schematic diagram which illustrates the phase shift mask with low height d1. It is process sectional drawing which illustrates the manufacturing method of the phase shift mask of 2nd Embodiment. It is process sectional drawing which illustrates the manufacturing method of the phase shift mask of 2nd Embodiment. It is a schematic diagram showing the cross-section of the phase shift mask concerning the modification of 2nd Embodiment. It is a schematic diagram which illustrates the cross-section of the conventional phase shift mask. It is a schematic diagram showing the phase shift mask in which the size of the light shielding film 201 is not uniform. It is a graph showing the intensity distribution of the exposure light that has passed through the phase shift mask. It is a graph showing that the intensity distribution of the exposure light that has passed through the phase shift mask becomes asymmetric.

Explanation of symbols

100 mask substrate 101 phase shift region 200 light shielding film 201 light shielding film 300 resist layer

Claims (6)

A phase shift mask in which a phase shift region for shifting the phase of exposure light is formed on a transparent substrate,
A light shielding film is provided on a side wall of the phase shift region,
A single dark pattern is formed by the phase shift region and the light shielding film provided on the sidewall thereof ,
The phase shift mask according to claim 1, wherein a height of the light shielding film is smaller than a height of the phase shift region .   2. The phase shift mask according to claim 1, wherein a transmittance of the light shielding film with respect to the exposure light is 10% or less. When the wavelength of the exposure light is λ, the numerical aperture of the reduction projection optical system of the exposure apparatus is NA, and the magnification of the reduction projection optical system is M, the width Ls of the phase shift region is expressed by the following equation (0.1 × λ / NA) × M <Ls <(0.4 × λ / NA) × M
3. The phase shift mask according to claim 1, wherein the phase shift mask is within the range. When the wavelength of the exposure light is λ, the numerical aperture of the reduction projection optical system of the exposure apparatus is NA, and the magnification of the reduction projection optical system is M, the width Lc of the light shielding film is expressed by the following formula (0.05 × λ / NA). ) × M <Lc <(0.2 × λ / NA) × M
The phase shift mask according to any one of claims 1 to 3 , wherein the phase shift mask is in a range of. The exposure light phase passing through the phase shift region, according to any one of claims 1 to 4, characterized in that inverted from the exposure light phase passing through the transparent substrate otherwise Phase shift mask. Forming a layer made of a photoreceptor on a substrate provided with a film to be processed;
Irradiating the photosensitive member with exposure light through the phase shift mask according to any one of claims 1 to 5 ,
Developing the photoconductor to form a mask pattern corresponding to the single dark pattern;
Etching the film to be processed through the mask pattern;
A pattern forming method comprising:

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