JPH0651489A - Production of halftone phase shift photomask - Google Patents

Abstract

PURPOSE:To produce the halftone phase shift photomask having high accuracy by forming phase shifters so as to have perpendicular edge shapes in the formation thereof. CONSTITUTION:After a halftone light shielding film layer 14 is etched, the resist used for the etching is removed and thereafter, a photoresist layer 20 having etching resistance is formed on the halftone light shielding film 14. The photoresist layer 20 is then back exposed by irradiating the layer with light 21 via the patterned halftone light shielding film 14 from the transparent substrate 11 surface side. The photoresist layer 20 after the exposing is developed and another resist patterns are formed. A phase shifter layer 13 exposed with the another resist patterns and the halftone light shielding film as a mask is etched, by which the halftone phase shift photomask is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a photomask used for manufacturing high density integrated circuits such as LSI and VLSI, and more particularly to a half mask used for forming a fine pattern with high accuracy. The present invention relates to a method for manufacturing a tone phase shift photomask.

[0002]

2. Description of the Related Art In semiconductor integrated circuits such as IC, LSI, and VLSI, a resist is applied on a substrate to be processed such as a silicon wafer, a desired pattern is exposed by a stepper, and then development, etching, doping, CVD are performed. It is manufactured by repeating the so-called lithographic process of performing the above.

Photomasks called reticles used in such lithography processes tend to be required to have higher and higher precision as semiconductor integrated circuits have higher performance and higher integration. Taking a DRAM which is a conventional LSI as an example, the dimensional deviation of a reticle for a 1M bit DRAM, that is, a reticle having a size five times as large as an exposure pattern is an average value ± 3σ.
0.15μ even when (σ is the standard deviation)
An accuracy of 0.1 m is required, and similarly, a quintuple reticle for 4 Mbit 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 to be 0.03 to 0.07 μm for the 5 × reticle for 64 Mbit DRAM.

Further, the line width of the device pattern formed using these reticles is 1 Mbit DRAM.
1.2 μm, 0.8 μm for 4M bit DRAM, 1
0.6 μm for 6 Mbit DRAM, 64 Mbit DR
In AM, further miniaturization of 0.35 μm is required, and various exposure methods are being researched in order to meet such requirements.

However, when a device pattern of the next generation of the 64 Mbit DRAM class, for example, becomes a resolution limit of the resist pattern in the stepper exposure method using the reticle that has been used up to now, and this limit is overcome. As shown in JP-A-58-173744 and JP-B-62-59296,
A reticle of 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.

Phase shift lithography will be briefly described with reference to the drawings. 2 is a diagram showing the principle of the phase shift method,
FIG. 3 is a diagram showing a conventional method, and is shown in FIGS.
(A) is a cross-sectional view of the reticle, FIG. 2 (b) and FIG. 3 (b).
Is the amplitude of light on the reticle, FIGS. 2 (c) and 3 (c) are the amplitudes of light on the wafer, and FIGS. 2 (d) and 3 (d) are the light intensities on the wafer, respectively. Substrate 2, light-shielding film, 3 phase shifter, and 4 incident light.

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

Next, an example of a conventional method of manufacturing the above-mentioned phase shift reticle will be described with reference to the drawings. Figure 4
FIG. 4A is a cross-sectional view showing the manufacturing process of the phase shift reticle,
In the figure, 31 is a substrate, 32 is a light-shielding film pattern such as chromium,
33 is an alignment mark, 34 is a phase shifter layer, 3
5 is a resist layer, 36 is an etching stopper layer, 37
Is ionizing radiation such as laser light or electron beam, 38 is an exposed portion, 39 is etching gas plasma, and 40 is oxygen plasma.

First, a SiO ₂ film is formed as a phase shifter layer 34 on the reticle on which the light-shielding film pattern 32 is formed by spin-on-glass (SOG), a sputtering method, a CVD method, or the like (FIG. 3A). Subsequently, a resist is uniformly applied on the phase shifter layer 34 by a conventional method such as spin coating, and a heat drying treatment is performed to form a resist layer 35 having a thickness of about 0.1 to 2.0 μm (same as above). Figure (b)). The heating and drying treatment is usually performed at 80 to 200 ° C. for about 5 to 60 minutes, though it depends on the type of resist used. Next, as shown in FIG.
5 is aligned by using an exposure apparatus such as an electron beam drawing apparatus according to a conventional method to draw a desired pattern to form an exposed portion 38. Then, it is developed with a predetermined developing solution and rinsed with a predetermined rinsing solution to form a resist pattern 38 as shown in FIG.

Next, after heat-drying treatment and descum treatment, if necessary, as shown in FIG. 3D, the transparent film 34 portion exposed from the opening of the resist pattern 38 is etched by the etching gas plasma 39. Dry etching is performed to form the phase shifter pattern 34 ((e) in the figure). It is obvious to those skilled in the art that the phase shifter pattern 34 may be formed by wet etching instead of dry etching using 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, the phase shift reticle having the phase shifter 34 as shown in FIG. Such a phase shift reticle is the most general type and is called a spatial frequency modulation type.

However, although the phase shift mask as described above has a great phase shift effect, it is difficult to put it into practical use because of its complicated manufacturing method. Taking a bath.

This halftone type phase shift mask will be briefly described with reference to the drawings. FIG. 5 is a diagram showing the principle of the halftone type phase shift method in comparison with the conventional method.
5A is a cross-sectional view of the reticle, FIG. 5B is the amplitude of light transmitted through the reticle, and FIG. 5C is the light intensity on the wafer. Reference numeral 51 is a substrate, 52 is a light-shielding film, and 53 is a half. A tone light shielding film, 54 is a phase shifter, and 55 is incident light.

As shown in FIG. 1A, in the conventional method, a 100% light-shielding film 52 is formed on a substrate 51 and a light transmitting portion having a predetermined pattern is formed.
In the halftone phase shift mask, the light-shielding film is formed of the halftone light-shielding film 53 having a transmittance of several percent, and the light-transmitting film for inverting the phase above or below the halftone light-shielding film 53 (phase difference 180 °). A phase shift layer 54 made of is provided. Therefore, in the conventional method, the amplitude of the light on the reticle becomes in-phase as shown in FIG. 7B, and is distributed outward from the opening of the mask in a skirt spread. As a result, in FIG. As described above, the light intensity distribution on the wafer does not have a shape corresponding to the mask pattern, but has a distribution that spreads outward from the mask opening. On the other hand, in the halftone phase shift mask, the phase shift layer 54 gives a phase difference to the light leaked from the halftone light shielding film 53, and as shown in FIG.
Since the light has a phase opposite to that of the light transmitted through the opening, the light intensity becomes zero at the boundary of the pattern, and as shown in FIG. 7C, the bottom spread of the light intensity distribution can be suppressed. As described above, in the halftone phase shift lithography, it becomes possible to decompose a pattern that could not be conventionally decomposed, and the resolution can be improved.

[0016]

However, in the above-mentioned method of manufacturing the halftone type phase shift reticle, after forming the light shielding film pattern, the phase shifter pattern is formed by etching using the resist having the light shielding pattern as it is as a mask. If this is attempted, there is a problem in that the resist has a tapered cross-section, so that it is not possible to perform high-precision phase shifter processing in which the etching surface is vertical. In particular, in the production of halfton type phase shift reticles, there is a problem that the influence of the shape of the phase shifter edge is more pronounced than in the case of using ordinary phase shift masks, and researchers have been tasked with solving this problem. It was a mission.

The present invention has been made in view of such a situation, and an object thereof is to form a phase shifter of a halftone phase shift photomask with a highly accurate halftone phase shift photo by making its edge shape vertical. It is to provide a more practical manufacturing method capable of manufacturing a mask.

[0018]

In view of the above problems, the present invention is a practical method for stably manufacturing a high-precision halftone phase shift photomask without significantly changing the conventional reticle manufacturing process. As a result of research to develop a new method, by separating the resist used for forming the phase shifter pattern from that for forming the light shielding pattern, the edge shape of the phase shifter becomes vertical and a highly accurate phase shifter pattern is formed. The inventors have found out what is possible and completed the present invention based on such findings.

A method of manufacturing the halftone phase shift photomask of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of the manufacturing process of the present invention, in which 11 is a substrate, 12 is an etching stopper layer, 13 is a phase shifter layer, 14 is a halftone light shielding film layer, and 15 is a light shielding pattern forming resist layer. , 16 is ionizing radiation such as a laser beam or an electron beam, 17 is an exposed portion, 18 is an etching gas plasma, 19 is oxygen plasma, 20 is a photoresist layer for forming a phase shifter pattern, 21 is exposure light, 22 is an exposed portion, 23 is an etching gas plasma and 24 is an oxygen plasma.

First, as shown in FIG. 1A, an etching stopper layer 12, a phase shifter layer 13 and a mercury lamp g are formed on a photomask glass substrate 11 for a photomask.
Line, i-line and excimer laser light transmittance is 8-30%
The light-shielding film layer 14 is formed in this order, and then, in FIG.
As shown in FIG. 3, a light-shielding pattern forming resist thin film 15 is formed on the light-shielding film layer 14, and a laser beam is applied to the resist thin film 15 by using an exposure device such as an electron beam drawing device as shown in FIG. Alternatively, a desired pattern is drawn by ionizing radiation 16 such as an electron beam, the resist thin film after pattern drawing is developed to form a resist pattern 15, and the resist pattern 15 is used as a mask as shown in FIG. , The exposed light-shielding film layer 14 with the etching gas plasma 1
Etching with 8 or the like. The above steps are the same as in the conventional method.

In the present invention, next, as shown in FIG. 1E, the remaining resist 15 is ashed and removed by oxygen plasma 18, and a halftone light-shielding film pattern as shown in FIG. You get 14. After the light-shielding film pattern 14 is inspected and modified, as shown in FIG. 6G, a phase shifter pattern forming photoresist layer 20 having a dry etching resistance is uniformly formed on the light-shielding film pattern 14, and then the same. As shown in FIG. 6H, parallel exposure light 21 is uniformly applied from the substrate 11 side, and the photoresist layer 20 is back-exposed through the opening of the light shielding film pattern 14. The exposed photoresist layer is developed to form a resist pattern 20 having the same pattern as the light-shielding film pattern and a vertical cross section on the light-shielding film 14, and then using the resist pattern 20 and the light-shielding film pattern 14 as a mask. ,
As shown in FIG. 7I, the exposed phase shifter layer 13 is exposed.
Is etched with etching gas plasma 23 or the like,
After that, as shown in FIG.
0 is ashed and removed by the oxygen plasma 24 to complete the halftone phase shift reticle as shown in FIG.

According to the above-described manufacturing method of the present invention, when the phase shifter layer is dry-etched, the vertical resist pattern obtained by the back exposure technique is used.
It enables high-precision vertical phase shifter processing of cross-sectional shape.

According to the method of the present invention, the transmittance is 8
After forming 30% to 30% of the light-shielding film pattern, there is an advantage that the light-shielding film pattern can be inspected and repaired, and defects can be reduced during the process. This will promote the practical application of the existing phase shift photomask. For the correction of the light-shielding film pattern, a correction technique using a current YAG laser and a focused ion beam can be applied.

In the above method, the phase shifter layer was provided on the glass substrate and etched to form the phase shifter pattern. However, the phase shifter layer is not provided and the substrate 11 itself is not provided. You may make it etch a predetermined depth from the surface and use the convex part as a phase shifter pattern. In that case, the etching stopper layer 12 of FIG.
And the phase shifter layer 13 are integrated.

That is, in the method of manufacturing a halftone phase shift photomask of the present invention, a phase shifter layer and a halftone light shielding film layer are formed on a transparent substrate, a resist pattern is formed on the light shielding film layer, and this resist pattern is formed. In the method of manufacturing a halftone phase shift photomask in which the exposed halftone light-shielding film layer is etched using as a mask, and then the phase shifter layer is etched, after etching the halftone light-shielding film layer, the resist used as the mask is removed. After that, a photoresist layer having etching resistance is formed on the halftone light shielding film,
Then, the photoresist layer is back-exposed by irradiating light through the patterned halftone light-shielding film from the transparent substrate surface side, and the exposed photoresist layer is developed to form another resist pattern, The method is characterized in that the exposed phase shifter layer is etched using the resist pattern and the halftone light shielding film as a mask.

In this case, it is desirable that the halftone light-shielding film has a transmittance of 8 to 30% for g-line light, i-line light and excimer laser light.

The surface portion of the transparent substrate may form a phase shifter layer.

[0028]

In the present invention, after etching the halftone light-shielding film layer, the resist used as the mask is removed, and then a photoresist layer having etching resistance is formed on the halftone light-shielding film, and then the transparent substrate is formed. The photoresist layer is back-exposed by irradiating light through the patterned halftone light-shielding film from the surface side, and the exposed photoresist layer is developed to form another resist pattern. Since the exposed phase shifter layer is etched using the halftone light-shielding film as a mask, it is possible to perform vertical phase shifter processing with high precision and cross-sectional shape, and it is possible to manufacture high precision halftone phase shift photomasks. Become. In addition, the inspection and correction can be performed during the manufacturing process after forming the halftone light shielding film pattern, and the defect rate can be reduced.

[0029]

EXAMPLES Examples and comparative examples of the method for manufacturing a halftone phase shift photomask of the present invention will be described below.

EXAMPLE 1 An etching stopper layer made of a tin oxide thin film having a thickness of about 30 nm and a SiO ₂ thin film having a thickness of about 380 nm were formed on an optically polished 5 inch square ultra-high purity synthetic quartz glass substrate.
A positive type electron beam resist (EBR-9 manufactured by Toray Industries, Inc.) was applied by a spin coating method on a mask substrate having a three-layer structure formed with a low reflection chromium thin film having a transmittance of about 15%, and the temperature was set to 190 ° C. Heat treatment for 30 minutes, thickness 0.6
A uniform resist thin film of 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 accelerating voltage was 20 kV and the exposure amount was 10 μC / cm ² .

Then, after post-baking at 120 ° C. for 30 minutes, the resist pattern was formed by developing with an organic solvent containing methyl isobutyl ketone as a main component and rinsing with isopropyl alcohol.

Subsequently, if necessary, an oxygen plasma treatment (descum treatment) is performed for a short time, and then the low reflection chromium thin film exposed from the opening of the resist pattern is changed to an etching solution containing a diammonium cerium ammonium nitrate solution as a main component. For 20 seconds, and the remaining resist is ashed and removed by oxygen plasma to complete a reticle composed of a halftone light-shielding film.

Subsequently, this photomask is inspected, and if necessary, pattern correction is performed, and after cleaning, a photoresist (OF of Tokyo Ohka Co., Ltd.) is formed on the light-shielding film pattern.
PR-800) was applied by spin coating and heat-dried to form a photoresist layer having a thickness of 0.7 μm.

Subsequently, the entire surface of this substrate was back-exposed from the side of the quartz substrate by parallel rays of the g-line of a mercury lamp, developed with an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, and rinsed with pure water. Then, a resist pattern having a vertical cross section was formed.

Subsequently, the phase shifter layer exposed from the opening of the resist pattern is dry-etched for 20 minutes with an etching gas containing a fluorine-based gas as a main component,
The remaining resist was removed by ashing with oxygen plasma to complete a halftone phase shift reticle.

In the halftone phase shift reticle thus completed, the phase shifter edge is vertical, and
The dimensional accuracy of the phase shifter was as high as 0.05 μm at maximum.

Example 2 An etching stopper layer made of an alumina thin film having a thickness of about 100 nm was formed on an optically polished 5 inch square ultra-high purity synthetic quartz glass substrate, and then SOG was formed thereon.
Spin coating (spin on glass), 300
By firing at 0 ° C., an SOG thin film having a thickness of about 400 nm was formed, and a chromium thin film having a transmittance of about 15% was formed thereon.
On this mask substrate, a negative chemically amplified electron beam resist (SAL-601 manufactured by Shipley Co., Ltd.) was applied by a spin coating method and heat-treated at 90 ° C. for 30 minutes to form a uniform resist thin film having a thickness of 0.6 μm. Got

Next, a pattern was drawn on this substrate by an electron beam exposure apparatus according to a conventional method. At this time, the accelerating voltage was 20 kV and the exposure amount was 10 μC / cm ² .

Then, after post-baking at 150 ° C. for 30 minutes, the resist pattern was formed by developing with an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component and rinsing with pure water.

Subsequently, if necessary, an oxygen plasma treatment (descum treatment) is carried out for a short time, and then the chromium thin film exposed from the opening of the resist pattern is dry-etched with a gas containing carbon tetrachloride as a main component for 120 seconds. Then, the chromium thin film was patterned, and the remaining resist was ashed and removed by oxygen plasma to complete a reticle composed of a halftone light-shielding film.

Subsequently, this photomask is inspected, and if necessary, pattern correction is performed, and after cleaning, a photoresist (OF of Tokyo Ohka Co., Ltd.) is formed on the light-shielding film pattern.
PR-800) was applied by spin coating and heat-dried to form a photoresist layer having a thickness of 0.7 μm.

Then, the whole surface of this substrate was back-exposed from the side of the quartz substrate by parallel rays of the g-line of a mercury lamp, developed with an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, and rinsed with pure water. Then, a resist pattern having a vertical cross section was formed.

Subsequently, the phase shifter layer exposed from the opening of the resist pattern is dry-etched for 20 minutes with an etching gas containing a fluorine-based gas as a main component,
The remaining resist was removed by ashing with oxygen plasma to complete a halftone phase shift photomask.

In the halftone phase shift reticle thus completed, the phase shifter edge is vertical, and
The dimensional accuracy of the phase shifter was as high as 0.05 μm at maximum.

Comparative Example An etching stopper layer made of a tin oxide thin film having a thickness of about 30 nm and a SiO ₂ thin film having a thickness of about 400 nm were formed on a 5 inch square ultra-high purity synthetic quartz glass substrate which was optically polished.
Negative electron beam resist (CMS manufactured by Tosoh Corporation) is applied by spin coating on a mask substrate having a three-layer structure formed with a low reflection chromium thin film having a transmittance of about 15%, and heated at 120 ° C for 30 minutes. By processing, a uniform resist thin film having 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 accelerating voltage was 20 kV and the exposure amount was ² μC / cm ² .

Then, after post-baking at 140 ° C. for 30 minutes, the resist pattern was formed by developing with an organic solvent containing ethyl cellosolve as a main component and rinsing with isopropyl alcohol.

Subsequently, if necessary, an oxygen plasma treatment is performed for a short time, and then the chromium low reflection chromium thin film exposed from the opening of the resist pattern is etched for 20 seconds with an etching solution containing a diammonium cerium ammonium nitrate solution as a main component. Etched.

Subsequently, using this resist pattern as it is, the phase shifter layer exposed from the opening is dry-etched for 20 minutes with an etching gas containing a fluorine-based gas as a main component, and the remaining resist is ashed with oxygen plasma. Then, the halftone phase shift photomask was completed.

Although the halftone phase shift reticle thus completed has a simple process, the cross-sectional angle of the phase shifter is about 80 ° and the dimensional accuracy of the phase shifter is 0.15 μm. It was larger than the case of 2.

[0052]

As is apparent from the above description, according to the method of manufacturing a halftone phase shift photomask of the present invention, after etching the halftone light shielding film layer, the resist used as the mask is removed, and thereafter, A photoresist layer having etching resistance is formed on the halftone light-shielding film, and then the photoresist layer is back-exposed by irradiating light from the transparent substrate surface side through the patterned halftone light-shielding film. The photoresist layer is developed to form another resist pattern, and the exposed phase shifter layer is etched using the different resist pattern and the halftone light-shielding film as a mask. Shifter processing is possible,
It is possible to manufacture a highly accurate halftone phase shift photomask. In addition, the inspection and correction can be performed during the manufacturing process after forming the halftone light shielding film pattern, and the defect rate can be reduced. Therefore,
It is possible to promote the practical application of the phase shift photomask.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the steps of a method of manufacturing a halftone phase shift photomask of the present invention.

FIG. 2 is a diagram showing a principle of a phase shift method.

FIG. 3 is a diagram showing a conventional method.

FIG. 4 is a cross-sectional view showing a manufacturing process of a phase shift reticle.

FIG. 5 is a diagram showing the principle of the halftone type phase shift method in comparison with the conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Substrate 12 ... Etching stopper layer 13 ... Phase shifter layer 14 ... Halftone light-shielding film layer 15 ... Light-shielding pattern forming resist layer 16 ... Ionizing radiation such as laser light or electron beam 17 ... Exposed portion 18 ... Etching gas plasma 19 ... Oxygen plasma 20 ... Phase shifter pattern forming photoresist layer 21 ... Exposure light 22 ... Exposure portion 23 ... Etching gas plasma 24 ... Oxygen plasma

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Takahashi 1-1-1 Ichigayakaga-cho, Shinjuku-ku, Tokyo Dai Nippon Printing Co., Ltd.

Claims (3)

[Claims] 1. A phase shifter layer and a halftone light shielding film layer are formed on a transparent substrate, a resist pattern is formed on the light shielding film layer, and the exposed halftone light shielding film layer is etched using the resist pattern as a mask. Then, in the method of manufacturing a halftone phase shift photomask for etching the phase shifter layer, after etching the halftone light-shielding film layer, the resist used as the mask is removed, and then a photoresist layer having etching resistance is half-cut. It is formed on the tone light-shielding film, and then light is irradiated from the transparent substrate surface side through the patterned halftone light-shielding film to back expose the photoresist layer, and the photoresist layer after exposure is developed and separated. Resist pattern is formed, and another resist pattern and halftone light-shielding film are used as a mask to expose. A method for manufacturing a halftone phase shift photomask, characterized in that the exposed phase shifter layer is etched. 2. The g-line light of the halftone light-shielding film, i
Line light and excimer laser light transmittance is 8 to 3
It is 0%, The manufacturing method of the halftone phase shift photomask of Claim 1 characterized by the above-mentioned. 3. The method of manufacturing a halftone phase shift photomask according to claim 1, wherein the transparent substrate surface portion constitutes a phase shifter layer.