JPH04153653A - Production of photomask having phase shift layer - Google Patents

Abstract

PURPOSE:To obviate the generation of defects by inserting a stage for removing the outer peripheral parts of a transparent film used for forming phase shifters by wet etching, etc., after formation of this film during the production process. CONSTITUTION:The stage for removing the outer peripheral parts of the transparent film used for forming the phase shifters is inserted before the stage for forming the phase shifter patterns. The cracks based on the nonuniformity of stresses enter the transparent film of the edge parts of the reticule and dust is generated by contact of the edge parts with a holder, etc., while the reticule undergoes the stage in the process for producing the conventional phase shift reticule, but the generation of the dust from the outer peripheral parts of the transparent film is prevented in such a manner, by which the phase shift mask free from defect is formed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a photomask used for manufacturing high-density integrated circuits such as LSL VLSI, and in particular,
The present invention relates to a method of manufacturing a photomask having a phase shift layer for forming fine patterns with high precision.

[Prior Art] Semiconductor integrated circuits such as ICs, LSIs, and VLSIs are manufactured by applying a resist onto a substrate to be processed such as an S1 wafer, exposing a desired pattern using a stepper, etc., and then developing and etching it. It is manufactured by repeating the lithography process.

Photomasks called reticles used in such lithography processes are used to improve the performance of semiconductor integrated circuits.
With the increase in integration, there is a tendency for higher precision to be required.For example, taking DRAM, a typical LSI, for example, a 5x reticle for DRAM (1M pin),
The dimensional deviation of a reticle that is five times the size of the pattern to be exposed requires an accuracy of 0.15 μm even when the average Hanato 3σ (σ is the standard deviation) is taken.
Similarly, a 5x reticle for 4M pick) DRAM is 0.
16 Mbit DRAM with dimensional accuracy of 1 to 0.15 μm
A 5x reticle is required to have a dimensional accuracy of 0.05 to 0.1 μm.

Furthermore, the line width of device patterns formed using these reticles is 1.2.
um, 0. for 4M bit DRAM. There is a demand for further miniaturization of 8 μm and 0.6 μm for 16 Mbit DRAMs, and various exposure methods are being researched to meet these demands.

However, when it comes to next-generation device patterns in the 64-Mbit DRAM class, for example, the conventional stepper exposure method using a reticle reaches the resolution limit of the resist pattern.
A new type of reticle called a phase shift mask as shown in Japanese Patent Publication No. 62-59296 has been proposed. Phase shift lithography using a phase shift reticle is a technique that improves the resolution and contrast of a projected image by manipulating the phase of light that passes through the reticle.

(Phase Shift) The IJ sogerafy will be briefly explained according to the drawings. Figure 2 is a diagram showing the principle of the phase shift method, and Figure 3 is a diagram showing the conventional method.
) are cross-sectional views of the reticle, Figures 2(b) and 3(b)
is the amplitude of the light on the reticle, Figures 2(c) and 3(c)
) is the amplitude of the light on the wafer, Fig. 2(d) and Fig. 3(
d) shows the light intensity on the wafer, 1 is the substrate,
2 is a light shielding film, 3 is a phase shifter, and 4 is incident light.

In the conventional method, as shown in FIG. 3(a), a light-shielding film 2 made of chromium or the like is formed on a substrate 1 made of glass or the like to form a light-transmitting part in a predetermined pattern. However, in phase shift lithography, Fig. 2 (
As shown in a), a phase shifter 3 made of a transmission film for inverting the phase (phase difference of 180°) is provided on one of the adjacent light transmission parts on the reticle. Therefore, in the conventional method, the amplitude of the light on the reticle is
fl The light on the wafer becomes in phase as shown in (b), and the amplitude of the light on the wafer also becomes in phase as shown in Fig. 3 (c). As a result, the pattern on the wafer becomes as shown in Fig. 3 (d). phase shift) IJ
As shown in Fig. 2(b), in the case of Sogelahui, the light that passes through the phase shifter is made to have opposite phases between adjacent patterns, so the light intensity becomes zero due to the boundary between the patterns. Therefore, adjacent patterns can be clearly separated as shown in FIG. 2(d). In this way, in phase shift lithography-A, patterns that could not be separated in the past can be separated, and the degree of dissolution can be improved.

Next, an example of a conventional manufacturing process for a phase shift reticle will be described with reference to the drawings. FIG. 4 is a cross-sectional view showing the manufacturing process of a phase shift reticle, in which 11 is a substrate, 12
is a chromium film, 13 is a resist layer, 14 is ionizing radiation, 1
5 is a resist pattern, 16 is an etching gas plasma, 17 is a chrome pattern, 18 is an oxygen plasma, 19 is a transparent film, 20 is a resist layer, 21 is an ionizing radiation, 22 is a resist pattern, 23 is an etching gas plasma, 2
4 indicates a phase shift pattern, and 25 indicates an oxygen plasma.

First, as shown in FIG. 4(a), a chromium film 12 is formed on an optically polished substrate 11, and then an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a conventional method such as spin coating. Then, a heat drying process is performed to form a resist layer 13 having a thickness of about 0.1 to 2.0 μm. The heat drying treatment is usually carried out at 80 to 150° C. for about 20 to 60 minutes, although it depends on the type of resist used.

Next, as shown in FIG. 6(b), a pattern is drawn on the resist layer 13 using ionizing radiation 14 using an exposure device such as an electron beam drawing device according to a conventional method, and an organic solvent such as ethyl cellosolve or ester is used as the main component. After development with a developer solution, the resist pattern 15 is rinsed with alcohol to form a resist pattern 15 as shown in FIG.

Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as the resist layer remaining on the edge portions of the resist pattern 15, whiskers, etc. The portion to be processed exposed through the opening of the resist pattern 15, that is, the chromium layer 12, is dry-etched using an etching gas plasma 16 to form a chrome pattern 17. Note that the formation of the chromium pattern 17 is performed using an etching gas plasma. It will be clear to those skilled in the art that wet etching may be used instead of dry etching using No. 16.

After etching in this manner, as shown in FIG.
) Complete the photomask shown in (). Note that this treatment can also be performed by solvent stripping instead of the ashing treatment using the oxygen plasma 18.

Subsequently, this photomask is inspected, pattern corrections are made if necessary, and after cleaning, a transparent mask made of 5i02 etc. is placed on the chrome pattern 17 as shown in the same figure (g).
form 19. Next, as shown in FIG.
9, a 1-inch radiation resist layer 20 of chloromethylated polystyrene or the like is formed in the same manner as above.
), the resist layer 20 is aligned according to a conventional method, a predetermined pattern is drawn using ionizing radiation 21 from an electron beam exposure device, etc., developed and rinsed. , a resist pattern 22 is formed.

Next, after performing a heat treatment and a descum treatment as necessary, the portion of the transparent film 19 exposed from the opening of the resist pattern 22 is dried with an etching gas plasma 23, as shown in the same figure. Etching is performed to form a phase shifter pattern 24. Note that the phase shifter pattern 24 may be formed by wet etching instead of dry etching using the etching gas plasma 23.

Next, the remaining resist is removed as shown in (1) of the same figure.
Ashing is removed by oxygen plasma 25. Through the above steps, a phase shift mask having a phase shifter 24 as shown in ) is completed.

2. Problems to be Solved by the Invention: 2. However, as mentioned above, 1. The production capacity of the conventional holder reticle is eliminated; 2. It is used for forming the holder reticle. A transparent film is formed on the chrome pattern, then an ionizing radiation resist layer such as chloromethylated polystyrene is formed in the same manner as the transparent film, and a resist pattern is formed by drawing a predetermined pattern with ionizing radiation, developing it, and rinsing it. During the process of dry etching with etching gas plasma using this as a mask to form a phase shifter pattern, cracks may appear in the transparent film at the edges of the reticle due to uneven stress, or the edges may Dust is generated by contact with holders, etc. This dust contaminates the photomask, causing defects in the final product.Currently, photomasks have reticles that are reduced by one-fifth. Although it is widely used, if there is one defect on the reticle, the defect is transferred to all chips on the wafer, making the photomask unusable.

The present invention was made in view of this situation, and
The purpose is to provide a more practical method for manufacturing a phase shift photomask that does not cause defects in the photomask due to dust generated from the transparent film at the edge portion of the reticle during the manufacturing process.

[Means for Solving the Problem 2] In view of this problem, the present inventor has developed a defect-free phase shift photomask ( As a result of research to develop a method for stably manufacturing a reticle (reticle), a step was added to remove the outer periphery of the transparent film used to form the phase shifter (5) before the step of forming the phase shift pattern. By doing so,
We have discovered that it is possible to stably manufacture phase shift reticles without defects, and have completed the present invention based on this knowledge.

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 is a cross-sectional view showing the steps of the method for manufacturing a photomask having a phase shift layer according to the present invention, in which 30 is a substrate, 31 is a light shielding layer, 32 is an ionizing radiation resist layer, and 33 is ionizing radiation. , 34 is a resist pattern, 35 is an etching gas plasma, 36 is a light shielding pattern, 37 is an oxygen plasma, 3
8 is a transparent film, 39 is a photoresist layer, 40 is a photoresist layer whose outer periphery has been removed, 41 is wet etching, 42 is ionizing radiation, 43 is an ionizing radiation resist pattern, 44 is a phase shift pattern, 45 is a resist stripping liquid shows.

First, as shown in FIG. 1(a), a light shielding layer 31 with a thickness of 50 to 200 nm is formed on an optically polished substrate 30, and an ionizing radiation resist such as chloromethylated polystyrene is applied by spin coating. A resist layer 32 having a thickness of about 0.1 to 2.0 μm is formed by uniformly coating the resist layer 32 by a conventional method and performing a heat drying process. Here, considering that the phase shift mask is for short wavelengths such as 1-line (365 nm) or excimer laser (248 nm), quartz or high-purity synthetic quartz is preferable as the substrate 307)
However, in addition, low expansion glass, white board, blue board (SL)
, MgF2, CaFx, etc. can be used. The light-shielding layer 31 can be formed by forming a chromium thin film in a single layer5) or in multiple layers, but it can also be formed using chromium nitride, chromium oxide, tungsten, molybdenum, molybdenum silicide, etc. It can be formed by Further, the heat drying treatment is usually performed at 80 to 150° C. for about 20 to 60 minutes, although it depends on the seed jaws of the resist.

Next, as shown in IZ(b), on the resist layer 32,
A predetermined pattern is drawn using an exposure device using ionizing radiation 33 such as an electron beam drawing device according to a conventional method, developed with a developer containing an organic solvent such as ethyl cellosolve or ester, and rinsed with alcohol. A resist pattern 34 as shown in C) is formed.

Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as the resist layer remaining on the 8th edge of the resist pattern 34, whiskers, etc., as shown in FIG.
As shown in d), the portion to be processed exposed through the opening of the resist pattern 34, that is, the light-shielding layer 31, is dry-etched using etching gas plasma 35 to form a light-shielding pattern 36. -=Oh, this light shielding pattern 36
It will be clear to those skilled in the art that the formation of the etching gas plasma 35 may be performed by wet etching instead of dry etching using the etching gas plasma 35.

After 21 minutes in this way, as shown in FIG.
A photomask in which a predetermined light shielding pattern 36 is formed on 0 is created. Note that this treatment is performed using oxygen plasma 37
Instead of the ashing treatment, solvent stripping can also be used.

Next, after inspecting this photomask, making corrections to the pattern if necessary, and cleaning it, a spin-on glass (SO
G) A transparent film 38 of S+Oa or the like is formed by vapor deposition or the like. The material for forming this transparent film 38 is one-line (365 nm) exposed by a stepper or excimer laser.
Any material that has sufficient transmittance to ultraviolet light such as (248 nm) and has a high refractive index may be used.In addition to 5102, S
lsN<, PMMA, PGMA, CMS, etc. are preferably used. The thickness d of the transparent film 38 is the same as that of the transparent film 38.
The refractive index of the material forming 8 is n,! ! If the optical wavelength is λ, then the value is given by d-λ/2(n-1), and 5
102 and one line exposure, the value of d is about 397 nm.

Next, as shown in FIG.
9 is formed, followed by UV irradiation, development, and rinsing to form a resist layer 40 with only the outer periphery removed ((1) in the same figure).
. Next, as shown in FIG. 4J, the outer peripheral portion of the transparent film 38 used to form the phase shifter is removed by wet etching 41 using a buffered hydrofluoric acid solution or the like. After peeling off and cleaning the photoresist 40, as shown in the same figure (supplement), an ionizing radiation resist such as chloromethylated polystyrene is applied uniformly, alignment is performed according to a conventional method, and an electron beam exposure apparatus, etc. After drawing a predetermined pattern 43 for phase shift using the ionizing radiation 42, the resist pattern 43 is developed and rinsed to form a resist pattern 43 as shown in FIG.

Then, as shown in FIG. 4(e), wet etching is performed using a buffered hydrofluoric acid solution or the like to form a phase shift pattern 44.

Next, as shown in (n) of the same figure, the remaining resist is peeled off and removed using a predetermined resist stripping solution 45, and a phase shift photomask without defects as shown in (0) of the same figure is completed. .

[Effect]

In the present invention, after the formation of the transparent film used to form the phase shifter, a step of removing the outer peripheral part by wet etching etc. is inserted into the conventional phase shift photomask manufacturing process. By preventing dust from being generated from the outer periphery of the transparent film during a process such as ionizing radiation drawing when creating a shifter pattern, it becomes possible to create a defective L1 phase shift photomask.

: Example 2 Examples of the present invention will be described below.

Example 1 A chromium thin film with a thickness of 800 nm and a chromium thin film with a thickness of
A resist solution of chloromethylated polystyrene was applied by spin coating onto a mask substrate on which a two-layer structure of a 0 nm thick low-reflection chromium thin film was formed.
Prebaking was performed for 0 minutes to obtain a uniform resist film with a thickness of 0.6 μm.

Next, an electron beam with an accelerating voltage of 20 kV was applied to the
Exposure was performed at a dose of crl to draw a pattern. After exposure, this substrate was developed for 60 seconds with a developer consisting of a mixture of isoamyl acetate and ethyl cellosolve, and then rinsed with isopropyl alcohol for 30 seconds to obtain a resist pattern. Subsequently, this was post-baked at 140°C for 30 minutes, and then IT.

rr, descum with 100W oxygen plasma for 2 minutes and expose the exposed substrate using the resist pattern as a mask.
Dry etching was performed for 8 minutes in a plasma containing carbon tetrachloride and oxygen at an output of 300 W. Next, the remaining resist was removed by ashing with oxygen plasma at 2 Torr and 4° OW to obtain a photomask before phase/lid formation. After confirming the quality of the foot 7 mask manufactured in this way, a SOG (spin-on-glass) solution was applied onto the mask by spin coating, and a heating drying process was performed.
A uniform SOG film with a thickness of 450 nm was obtained. This film was fired at 450° C. for 1 hour in a nitrogen atmosphere.

A resist solution of 0FPR-800 was applied to this substrate by spin coating, and then heated and dried to a thickness of 1 μm.
A resist film with uniform thickness was obtained. After exposing the outer periphery with a width of several mm to 10 mm to ultraviolet rays at a dose of 100 mJ/d, this substrate was treated with a developer of NMD-3 (manufactured by Tokyo Ohka ■) for 6 hours.
The resist pattern was developed for 0 seconds and then rinsed with pure water for 120 seconds to obtain a resist pattern with the outer peripheral portion removed. After post-baking this at 120°C for 30 minutes, the exposed substrate was heated to 20wt using the resist pattern as a mask.
% ammonium fluoride aqueous solution and 50% hydrofluoric acid 10:1
Wet etching was performed using a mixed solution. Resist N
- Stripped with methylpyrrolidone resist stripping solution, rinsed with pure water for 120 seconds, applied chloromethylated polystyrene resist solution to this substrate by spin coating, and heated and dried to form a uniform resist with a thickness of 0.6 μm. A membrane was obtained. Next, pattern exposure was performed at a predetermined position while detecting the alignment marks on the photomask using an electron beam lithography system with an acceleration voltage of 20 kV. After exposure, this substrate was developed and rinsed with the same solvent as above to obtain a resist pattern. Next, heat treatment and descum treatment are performed, and then the exposed SO is removed using the resist pattern as a mask.
The G film was wet-etched using a mixed solution of 20 wt% ammonium fluoride aqueous solution and 50% hydrofluoric acid. Finally, the remaining resist was removed using a resist stripping solution of N-methylpyrrolidone to obtain a photomask having a phase shifter layer made of SOG.

It was confirmed that the phase shift photomask manufactured in this manner had no defects and that a highly accurate phase shift photomask was obtained.

〔Effect of the invention〕

The method for manufacturing a photomask having a phase shift layer of the present invention involves removing the outer periphery of the transparent film by wet etching or the like after forming a transparent film used to form a phase shifter during the conventional phase shift photomask manufacturing process. By inserting a step in the middle of the process such as ionizing radiation drawing when creating a phase shifter pattern, it prevents dust from being generated from the outer periphery of the transparent film, thereby producing a defect-free phase shift photo. It is possible to create masks.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the steps of one embodiment of the method for manufacturing a photomask having a phase shift layer according to the present invention, FIG. 2 is a diagram showing the principle of the phase shift method, and FIG. 3 is a diagram showing the conventional method. 4 are cross-sectional views showing the manufacturing process of the phase/ft photomask. 30... Substrate, 31... Light shielding layer, 32... Ionizing radiation resist layer, 33... Ionizing radiation, 34... Resist pattern, 35... Etching gas plasma, 3
6... Light shielding pattern, 37... Oxygen plasma, 38...
...Transparent film, 39...Photoresist layer, 40...
Photoresist layer with outer peripheral portion removed, 41... Wet etching, 42... Ionizing radiation, 43... Ionizing radiation resist pattern, 44... Phase shift pattern, 45... Resist stripping solution Applicant Dai Nippon Printing Co., Ltd. Agent Patent Attorney Hiroshi Nizawa (7 others)/-44 M4 figure M4 figure

Claims (4)

[Claims] (1) A method for manufacturing a photomask having a phase shifter pattern includes at least a step of forming a transparent thin film that transmits ultraviolet light on a substrate to be processed on which a light-shielding pattern is formed, and removing an outer peripheral portion of the transparent thin film. a step of forming an ionizing radiation resist thin film on the transparent thin film; a step of irradiating a pattern of ionizing radiation at a predetermined position of the resist thin film and developing it to form a resist pattern; and a step of masking the resist pattern. A method for manufacturing a photomask having a phase shift layer, comprising the steps of: etching the exposed transparent thin film; and removing resist remaining after etching. (2) The step of removing the outer periphery of the transparent thin film includes the step of forming a photoresist thin film on the transparent thin film, and irradiating the resist thin film with ultraviolet rays to form a resist pattern that distinguishes the outer periphery from the inside. 2. The method further comprises the steps of: etching the exposed peripheral portion of the transparent thin film on the substrate to be processed using the resist pattern as a mask; and removing the resist remaining after etching. A method of manufacturing a photomask having a phase shift layer. (3) The substrate to be processed is high purity synthetic quartz, quartz, low expansion glass, white plate, blue plate, MgF_2, or CaF_2.
The method for manufacturing a photomask having a phase shift layer according to claim 1 or 2, wherein the photomask has a phase shift layer. (4) The light-shielding pattern is made of a chromium thin film, a chromium nitride thin film, a chromium oxide thin film, a tungsten thin film, a molybdenum thin film, a molybdenum silicide thin film, or the like according to any one of claims 1 to 3. A method for manufacturing a photomask having a phase shift layer.