JP3222531B2 - Method for manufacturing photomask having phase shift layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reticle used for manufacturing high-density integrated circuits such as LSIs and VLSIs and a method for manufacturing the reticle, and more particularly, to a reticle used for forming a fine pattern with high precision. The present invention relates to a method for manufacturing a photomask having a shift layer.

[0002]

2. Description of the Related Art A semiconductor integrated circuit such as an IC, an LSI, and a super LSI is coated with a resist on a substrate to be processed such as a silicon wafer, exposed to a desired pattern by a stepper or the like, and then developed, etched, doped, and CVD. And the like, that is, by repeating a so-called lithography process.

[0003] A photomask called a reticle used in such a lithography process tends to be required to be more and more accurate as the performance and integration of a semiconductor integrated circuit are increased. Taking a DRAM which is a typical LSI as an example, the dimensional deviation in a 5-fold reticle for a 1-Mbit DRAM, that is, a reticle having a size five times as large as the pattern to be exposed, is an average value ± 3σ.
(Σ is the standard deviation).
m is required. Similarly, a quintuple reticle for a 4M bit DRAM has a dimensional accuracy of 0.1 to 0.15 μm,
5x reticle for 6Mbit DRAM is 0.05-0.1
The dimensional accuracy of μm is required for a 5 × reticle for a 64-Mbit DRAM having a dimensional accuracy of 0.03 to 0.07 μm.

Furthermore, the line width of a device pattern formed using these reticles is 1 Mbit DRAM.
1.2 μm, 0.8 μm for 4 Mbit DRAM, 1 μm
0.6 μm for 6 Mbit DRAM, 64 Mbit DR
AM requires 0.35 μm more and more miniaturization, and various exposure methods have been studied to meet such a demand.

However, in the case of the next-generation device pattern of, for example, a 64-Mbit DRAM class, the stepper exposure method using a reticle reaches the resolution limit of a resist pattern. As shown in JP-A-58-173744 and JP-B-62-59296,
A reticle based on a new concept called a phase shift reticle has been proposed. Phase shift lithography using a phase shift reticle is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light passing through the reticle.

[0006] Phase shift lithography will be briefly described with reference to the drawings. FIG. 2 is a diagram showing the principle of the phase shift method,
FIG. 3 is a diagram showing a conventional method, and FIG. 2 (a) and FIG.
(A) is a cross-sectional view of the reticle, FIG. 2 (b) and FIG. 3 (b)
2 (c) and 3 (c) show the light amplitude on the wafer, FIGS. 2 (d) and 3 (d) show the light intensity on the wafer, respectively, and 1 denotes the light intensity on the wafer. A substrate 2, a light shielding film 3, a phase shifter 3, and an incident light 4 are shown.

In the conventional method, as shown in FIG. 3A, only a light-shielding film 2 made of chrome or the like is formed on a substrate 1 made of glass or the like, and a light transmitting portion of a predetermined pattern is formed. However, in phase shift lithography,
As shown in FIG. 2A, a phase shifter 3 made of a transmission film for inverting the phase (a phase difference of 180 °) is provided on one of the adjacent light transmission portions on the reticle. Therefore, in the conventional method, the amplitude of light on the reticle is in phase as shown in FIG. 3 (b), and the amplitude of light on the wafer is also in phase as shown in FIG. 3 (c). While the pattern on the wafer cannot be separated as shown in FIG. 3D, in phase shift lithography, the light transmitted through the phase shifter
As shown in FIG. 2B, since the phases are made opposite to each other between the adjacent patterns, the light intensity becomes zero at the boundary of the patterns, and the adjacent patterns are clearly separated as shown in FIG. 2D. be able to. As described above, in the phase shift lithography, a pattern that cannot be separated conventionally can be separated and the resolution can be improved.

Next, an example of a conventional method for manufacturing the above phase shift reticle will be described with reference to the drawings. FIG.
FIG. 3 is a cross-sectional view showing a manufacturing process of the phase shift reticle,
In the figure, 31 is a substrate, 32 is a light-shielding film pattern of chrome or the like,
33 is an alignment mark, 34 is a phase shifter layer, 3
5 is a resist layer, 36 is an etching stopper layer, 37
Denotes ionizing radiation such as laser light or electron beam, 38 denotes an exposed portion, 39 denotes etching gas plasma, and 40 denotes oxygen plasma.

First, an SiO ₂ film is formed as a phase shifter layer 34 on the reticle having the light-shielding film pattern 32 formed thereon by spin-on-glass (SOG), sputtering, CVD, or the like (FIG. 1A). Subsequently, a resist is uniformly applied on the phase shifter layer 34 by a conventional method such as spin coating, and is subjected to a heat-drying treatment to form a resist layer 35 having a thickness of about 0.1 to 2.0 μm (see FIG. Figure (b). The heating and drying treatment is usually performed at 80 to 200 ° C. for about 5 to 60 minutes, depending on the type of resist used. Next, as shown in FIG.
In 5, alignment is performed using an exposure apparatus such as an electron beam lithography apparatus according to a conventional method, and a desired pattern is drawn to form an exposed portion 38. Subsequently, the resist pattern is developed with a predetermined developing solution and rinsed with a predetermined rinsing liquid to form a resist pattern 38 as shown in FIG.

Next, after performing a heat-drying process and a descum process as required, the transparent film 34 exposed from the opening of the resist pattern 38 is etched by an etching gas plasma 39 as shown in FIG. Dry etching is performed to form a phase shifter pattern 34 (FIG. 3E). It is obvious to those skilled in the art that the formation of the phase shifter pattern 34 may be performed by wet etching instead of dry etching by the etching gas plasma 39.

Next, the remaining resist 38 is ashed and removed by oxygen plasma 40 as shown in FIG.

Through the above steps, a phase shift reticle having a phase shifter 34 as shown in FIG.

In the above-described conventional method of manufacturing a phase shift reticle, a drawing apparatus for drawing a pattern on a resist layer for forming a phase shifter has recently been a general electron beam drawing apparatus as a reticle drawing apparatus. For example, MEBES manufactured by ETEC, JEOL Ltd.
JBX-6AIII, JBX-7000MV, Co., Ltd.
Pattern drawing is performed using HL-700 manufactured by Hitachi, Ltd. or the like.

[0014]

However, in the above-mentioned conventional method for manufacturing a phase shift reticle, in order to form a phase shifter, alignment is performed by an electron beam exposure apparatus or the like, and a pattern is drawn on a resist layer. Since the phase shifter layer is a non-conductive layer, the resist layer is charged and a charge-up phenomenon occurs, which causes a problem that the pattern drawing accuracy by ionizing radiation such as an electron beam is reduced. In particular, in the manufacture of a phase shift photomask, there is a problem that a charge-up phenomenon is remarkably exhibited as compared with a normal photomask, and solving this problem has been the mission of researchers.

The present invention has been made in view of such a situation, and an object of the present invention is to efficiently prevent a charge-up phenomenon when forming a phase shifter of a phase shift reticle using an electron beam lithography apparatus or the like. It is another object of the present invention to provide a more practical manufacturing method capable of manufacturing a highly accurate phase shift reticle.

[0016]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention has developed a method for stably manufacturing a high-precision phase-shift reticle without greatly changing the conventional phase-shift reticle manufacturing process. As a result of investigations, it was found that by providing ground points at multiple points around the substrate surrounding the drawing area when drawing the phase shifter pattern, it is possible to efficiently prevent the charge-up phenomenon and manufacture a highly accurate phase shift reticle. And completed the present invention based on such findings.

Hereinafter, a method for manufacturing a photomask having a phase shift layer according to the present invention will be described with reference to the drawings. The entire manufacturing process is, for example, as shown in FIG. 4. However, the resist layer is formed on the resist layer by ionizing radiation such as an electron beam that causes charge-up of an electron beam lithography apparatus or the like, as shown in FIG. When writing the phase shifter pattern, the resist layer is grounded at a plurality of positions around the substrate surrounding the pattern drawing area from a plurality of directions around the pattern shift area.

Referring to the drawings, a more detailed description will be given.
FIG. 5 shows a top view and a cross-sectional view of a conventional substrate cassette 12 for holding the photomask substrate 11 during manufacturing.
The ground pin 13 for grounding the upper resist layer is
It was provided so as to contact only a single position around one. Therefore, the charge-up phenomenon cannot be prevented particularly in the drawing area opposite to the ground position. In contrast, in the present invention, FIG.
(A) and (b), as shown in the same drawing, the substrate 11
The ground pins 13 may be arranged at a plurality of positions surrounding the surroundings from a plurality of directions so as to make contact with the periphery of the substrate 11 at a plurality of points (FIG. 9A), or conductive from the upper part of the periphery of the substrate holding opening of the substrate cassette 12. The eaves member 14 is protruded inward, and the eaves member 14 is brought into surface contact with the periphery of the substrate 11 (FIG. 2B), so that the eaves member 14 is close to any side near the drawing area. Since it is grounded, the charge-up phenomenon can be prevented over the entire drawing area, and a highly accurate phase shift reticle can be manufactured.

If the ground positions are provided at a plurality of positions around the substrate as described above, and a conductive resin is applied to the surface of the resist layer for phase shifter before drawing, the charge-up phenomenon is more efficient. Can be prevented.

The manufacturing method according to the present invention is not limited to the spatial frequency type phase shift photomask as shown in FIG. It can also be applied to a method for manufacturing a high-precision photomask. Further, the lamination relationship between the light-shielding film layer and the phase shifter layer can be applied regardless of which one is on the top.

As is apparent from the above, the method of manufacturing a photomask having a phase shift layer according to the present invention comprises forming a resist thin film on a substrate having a phase shifter layer formed thereon, and patterning the resist thin film with ionizing radiation. Drawing, developing a resist thin film after pattern drawing to form a resist pattern, etching the exposed phase shifter layer using this resist pattern as a mask, and having a phase shift layer for removing the remaining resist after etching is completed In the method for manufacturing a photomask, at least at each one of the four sides of the substrate surrounding the pattern drawing area from a plurality of directions around the pattern drawing area at least at the time of pattern drawing.
This method is characterized in that the resist thin film is grounded.

In this case, grounding may be performed by contact with a ground pin, or may be performed by surface contact with a ground member. Before forming the resist thin film, a grounding conductive pattern may be provided around the drawing area of the phase shifter layer. By applying a conductive resin to the surface after the formation of the resist thin film, the charge-up phenomenon can be more efficiently prevented.

[0023]

In the present invention, the resist thin film is grounded at least at each one of the four sides of the substrate surrounding the pattern drawing area from a plurality of directions around the pattern drawing area at least at the time of drawing the phase shifter pattern. Since the grounding is performed at the closest distance between the four sides, the charge-up phenomenon can be prevented over the entire drawing area, and a highly accurate phase shift reticle can be manufactured.

[0024]

EXAMPLES Examples and comparative examples of the method of manufacturing a photomask having a phase shift layer according to the present invention will be described below.

Example 1 An etching stopper layer made of an alumina thin film having a thickness of about 100 nm and a phase shifter made of SOG (spin-on-glass) having a thickness of about 400 nm on an optically polished 5-inch square ultra-high purity synthetic quartz glass substrate. About 100 nm
An electron beam resist (EBR-9, manufactured by Toray Industries, Inc.) is applied by spin coating on a phase shift photomask substrate having a three-layer structure formed with a thick light-shielding thin film mainly composed of chromium. By heating for 30 minutes, a uniform resist thin film having a thickness of 0.5 μm was obtained.

Next, the substrate is applied with an electron beam exposure apparatus at an accelerating voltage of 20 kV to about 10 μC / cm.
^A pattern was drawn with an exposure amount of ² .

Subsequently, the resist was developed with an organic solvent containing methyl isobutyl ketone as a main component and rinsed with isopropyl alcohol to form a resist pattern.

Subsequently, the chromium layer exposed from the opening of the resist pattern was etched for 60 seconds with an etching solution containing a ceric ammonium nitrate aqueous solution as a main component, and the remaining resist was ashed and removed by oxygen plasma.

Subsequently, the photomask was inspected, the pattern was corrected if necessary, and the photomask was washed to complete a chromium pattern.

Next, an electron beam resist (ZEP-520, manufactured by Zeon Corporation) is applied on the chromium pattern by spin coating, and heated and dried at 90 ° C. for 30 minutes to form a 0.6 μm-thick film. A uniform resist thin film was obtained.

An antistatic film (TQV manufactured by Nitto Chemical Co., Ltd.) was applied on the resist thin film by a spin coating method, and dried by heating at 70 ° C. for 10 minutes to obtain a uniform film having a thickness of 50 nm. .

A substrate cassette of a type in which this substrate can be grounded by surface contact with a width of about 5 mm from its end (FIG. 1 (b)
), And writing was performed while performing alignment using a normal electron beam exposure apparatus. The exposure amount at this time was 16 μC / cm ² at an acceleration voltage of 20 kV.

Subsequently, the resist was developed with an organic solvent composed of a mixed solution of methyl isobutyl ketone and methyl ethyl ketone, and rinsed with isopropyl alcohol to form a resist pattern.

Subsequently, a short-time oxygen plasma treatment (descum treatment) is performed, if necessary, and then the phase shifter layer exposed from the opening of the resist pattern is etched with a carbon fluoride-based gas as a main component. , And the remaining resist was ashed and removed by oxygen plasma to complete a reticle having a phase shift layer.

The completed phase shift reticle is
The position shift of the phase shifter was as high as 0.043 μm at the maximum.

Example 2 An etching stopper layer comprising an alumina thin film having a thickness of about 100 nm, a low-reflection chromium thin film having a thickness of about 40 nm and a thin film having a thickness of about 60 nm were formed on an optically polished 5-inch square ultra-high purity synthetic quartz glass substrate. An electron beam resist (manufactured by Tosoh Corporation) is formed on a phase shift photomask substrate on which a four-layer structure of a chromium thin film having a thickness of about 40 nm and a low reflection chromium thin film having a thickness of about 40 nm is formed
CMS-EX (S)) is applied by a spin coating method, and is heated at 120 ° C. for 30 minutes to have a thickness of 0.6 μm.
Was obtained.

Next, a pattern was drawn on the substrate by an electron beam exposure apparatus according to a conventional method. At this time, the exposure was performed at an acceleration voltage of 10 kV and an exposure amount of ² μC / cm ² .

Subsequently, the resist was developed with an organic solvent containing ethyl cellosolve and isoamyl acetate as main components, and rinsed with isopropyl alcohol to form a resist pattern.

Subsequently, after post-baking at 150 ° C. for 30 minutes and descum treatment with oxygen plasma for 3 minutes, the chromium layer exposed from the opening of the resist pattern is etched with an aqueous solution of ceric ammonium nitrate as a main component. , And the remaining resist was ashed and removed by oxygen plasma to complete a chrome reticle.

Subsequently, the photomask is inspected, a pattern is corrected if necessary, and after cleaning, SOG is applied on the chromium pattern by spin coating.
A heat drying treatment was performed to form a 0.4 μm thick SOG phase shifter layer. The heat drying treatment was performed at 90 ° C. for 30 minutes, 150 ° C. for 30 minutes, and 400 ° C. for 60 minutes.

An electron beam resist (manufactured by Shipley Co., Ltd.) is placed on the mask substrate on which the phase shifter layer made of SOG is formed.
SAL-601) was applied by a spin coating method, and dried by heating at 90 ° C. for 30 minutes to obtain a uniform resist thin film having a thickness of 0.6 μm.

Subsequently, an antistatic resin (Espacer-100 manufactured by Showa Denko KK) was applied on the resist thin film for 50 hours.
It was applied in a thickness of nm.

Next, a substrate cassette of a type in which the substrate can be grounded by surface contact with a width of about 5 mm from the end (FIG. 1)
(See (b)), drawing was performed while performing alignment using a normal electron beam exposure apparatus. The exposure amount at this time was 10 μC / cm ² at an acceleration voltage of 20 kV.

Subsequently, development is performed with an alkaline aqueous solution mainly containing tetramethylammonium hydroxide,
The resist pattern was formed by rinsing with pure water.

Subsequently, the phase shifter layer exposed from the opening of the resist pattern is dry-etched for about 20 minutes with an etching gas containing carbon fluoride as a main component, and the remaining resist is stripped of a resist containing ethanolamine as a main component. It was removed with a liquid to complete a reticle having a phase shift layer.

The completed phase shift reticle is
The position accuracy of the phase shifter was as high as 0.05 μm at the maximum.

COMPARATIVE EXAMPLE An etching stopper layer comprising an alumina thin film having a thickness of about 100 nm, a low-reflection chromium thin film having a thickness of about 40 nm, and a thin chromium film having a thickness of about 60 nm were formed on an optically polished 5-inch square ultra-high purity synthetic quartz glass substrate. An electron beam resist (manufactured by Tosoh Corporation) is formed on a phase shift photomask substrate having a four-layer structure of a chromium thin film and a low reflection chromium thin film having a thickness of about 40 nm.
CMS-EX (S)) is applied by a spin coating method, and is heat-treated at 120 ° C. for 30 minutes to have a thickness of 0.6 μm.
Was obtained.

Next, a pattern was drawn on this substrate by an electron beam exposure apparatus according to a conventional method. At this time, the exposure was performed at an acceleration voltage of 10 kV and an exposure amount of ² μC / cm ² .

Subsequently, the resist was developed with an organic solvent containing ethyl cellosolve and isoamyl acetate as main components, and rinsed with isopropyl alcohol to form a resist pattern.

Subsequently, after post-baking at 150 ° C. for 30 minutes and descum treatment with oxygen plasma for 3 minutes, the chromium layer exposed from the opening of the resist pattern is etched with an aqueous solution of ceric ammonium nitrate as a main component. , And the remaining resist was ashed and removed by oxygen plasma to complete a chrome reticle.

Subsequently, the photomask is inspected, a pattern is corrected if necessary, and after cleaning, SOG is applied on the chromium pattern by spin coating.
A heat drying treatment was performed to form a 0.4 μm thick SOG phase shifter layer. The heat drying treatment was performed at 90 ° C. for 30 minutes, 150 ° C. for 30 minutes, and 400 ° C. for 60 minutes.

An electron beam resist (manufactured by Shipley Co., Ltd.) is placed on the mask substrate on which the phase shifter layer made of SOG is formed.
SAL-601) was applied by a spin coating method, and dried by heating at 90 ° C. for 30 minutes to obtain a uniform resist thin film having a thickness of 0.6 μm.

Subsequently, an antistatic resin (Espacer-100 manufactured by Showa Denko KK) was applied on the resist thin film for 50 hours.
It was applied in a thickness of nm.

Next, using two substrate cassettes (see FIG. 5) in which a normal ground pin was brought close to the substrate, drawing was performed while performing alignment using a normal electron beam exposure apparatus. The exposure amount at this time is 10 at an acceleration voltage of 20 kV.
μC / cm ² .

When ten substrates were drawn under these conditions, troubles in which the drawing apparatus was aborted (emergency stop) due to poor grounding continued.

[0056]

As is apparent from the above description, according to the method for manufacturing a photomask having a phase shift layer of the present invention, at least at the time of drawing a phase shifter pattern, the four sides of the substrate surrounding the pattern drawing area from a plurality of directions around the pattern drawing area. The resist thin film is grounded at least at each one point, and grounded at the closest distance of the four sides around the drawing area, so that the charge-up phenomenon can be prevented over the entire drawing area, and the phase shift can be performed with high precision. Reticles can be manufactured.

[Brief description of the drawings]

1A and 1B are a top view and a cross-sectional view of two examples of a substrate cassette used in a method for manufacturing a photomask having a phase shift layer according to the present invention.

FIG. 2 is a diagram illustrating the principle of the phase shift method.

FIG. 3 is a diagram showing a conventional method.

FIG. 4 is a cross-sectional view showing a manufacturing step of one method for manufacturing a phase shift reticle.

FIG. 5 is a top view and a sectional view of a conventional substrate cassette.

[Explanation of symbols]

 11 photomask substrate 12 substrate cassette 13 ground pin 14 conductive eaves member

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-142636 (JP, A) JP-A-60-57624 (JP, A) JP-A-60-90452 (JP, U) JP-A 57- 54154 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (5)

(57) [Claims] 1. A resist thin film is formed on a substrate on which a phase shifter layer is formed, a pattern is drawn on the resist thin film by ionizing radiation, and the resist thin film after pattern drawing is developed to form a resist pattern. The method for manufacturing a photomask having a phase shift layer for removing the remaining resist after etching is completed by etching the exposed phase shifter layer using the resist pattern as a mask, wherein at least the pattern drawing area is formed around the phase shift layer at the time of pattern drawing. Each of the four sides of the substrate surrounding from the direction
A method of manufacturing a photomask having a phase shift layer, wherein a resist thin film is grounded at each one point . 2. The method for manufacturing a photomask having a phase shift layer according to claim 1, wherein the grounding is performed by contacting a ground pin. 3. The method for manufacturing a photomask having a phase shift layer according to claim 1, wherein the grounding is performed by surface contact with a grounding member. 4. The phase shift layer according to claim 1, wherein a ground conductive pattern is provided around a drawing area of the phase shifter layer before the resist thin film is formed. Photomask manufacturing method. 5. The method according to claim 1, wherein after forming the resist thin film, a conductive resin is applied to the surface of the resist thin film.
A method for manufacturing a photomask having the phase shift layer according to any one of the above.