JPH05100408A - Production of photomask having phase shift layer - Google Patents

Abstract

(57) [Abstract] [Purpose] To make it possible to apply a resist uniformly on the phase shifter layer so that the pattern does not fall off or the cross-sectional shape is abnormal after the resist pattern is formed. [Structure] A resist thin film 21 is applied onto a substrate on which a transparent layer 19 is formed, and the resist thin film 21 is ionized with radiation 22
After the pattern drawing exposure, the resist thin film 21 is developed to form a resist pattern 23, and the exposed transparent layer 19 is etched using the resist pattern 23 as a mask. After the etching is completed, the remaining resist is removed. Then, it is removed to form a phase shift photomask. At this time, the surface of the transparent layer 19 is subjected to a surface treatment 20 for improving the wettability, and then a resist thin film 21 is applied to improve the adhesion.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A semiconductor integrated circuit such as an IC, an LSI, a super LSI and the like is coated with a resist on a substrate to be processed such as a silicon wafer, and after exposing a desired pattern by a stepper or the like, so-called lithography such as development and etching. It is manufactured by repeating the process.

Photomasks called reticles used in such lithography processes tend to be required to have higher precision as semiconductor integrated circuits have higher performance and higher integration. DR that is a simple LSI
Taking AM as an example, when the average value ± 3σ (σ is a standard deviation) is taken as a dimensional deviation in a 5 × reticle for a 1 Mbit DRAM, that is, a reticle having a size 5 × that of a pattern to be exposed. Accuracy of 0.15 μm is also required.
The double reticle has a dimensional accuracy of 0.1 to 0.15 μm of 1
The 5 × reticle for 6 Mbit DRAM is 0.05-0.
A dimensional accuracy of 1 μm is required.

Further, the line width of the device pattern formed by using these reticles is 1 Mbit DRAM.
1.2 μm, 0.8 μm for 4M bit DRAM, 1
For 6 Mbit DRAM, further miniaturization of 0.6 μm is required. Various exposure methods have been actively studied to meet such demands.

However, when a next-generation device pattern of, for example, a 64-Mbit DRAM class, the conventional stepper exposure method using a reticle reaches the resolution limit of the resist pattern. A reticle of a new concept called a phase shift mask has been proposed as disclosed in Japanese Patent Publication No. 58-173744, Japanese Patent Publication No. 62-59296, and the like. 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 conventional method and the phase shift method in FIG. Figure 4
4A to 4D show the principle of the phase shift method, and FIG.
4A to 4D show a conventional method, and FIGS. 4A and 4A are cross-sectional views of the reticle, and FIGS. 4B and 4B.
Is the amplitude of the light on the reticle, and FIGS. 4C and 4C are
Amplitudes of light on the wafer, FIGS. 4D and 4D respectively show light intensities on the wafer, 1 is a substrate, 2 is a light-shielding film, 3 is a phase shifter, and 4 is incident light.

In the conventional method, the photomask is formed as shown in FIG.
As shown in (a), 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 having a predetermined pattern is formed. As shown in FIG. 4A, the phase is inverted to one of the adjacent light transmitting portions on the reticle (with a phase difference of 180 °).
There is provided a phase shifter 3 made of a transparent film for adjusting the degree. Therefore, in the conventional method, the amplitude of the light on the reticle has the same phase between the adjacent light transmitting portions as shown in FIG. 4B, and as a result, as shown in FIG. Whereas the pattern on the wafer cannot be resolved, in phase shift lithography,
As shown in FIG. 4 (B), the light transmitted through the phase shifter has opposite phases to each other between adjacent patterns, so that the light intensity becomes zero at the boundary portion of the patterns, and FIG.
Adjacent patterns can be clearly separated, as shown in FIG. As described above, in phase shift lithography, a pattern that could not be separated by the conventional method can be decomposed, and the resolution can be improved.

Next, one example of the manufacturing process of such a phase shift reticle will be described with reference to FIG. FIG. 5 is a cross-sectional view showing a manufacturing process of a conventional phase shift reticle. As shown in FIG. 5 (a), a chrome reticle having a chrome pattern 6 provided on a substrate 5 is prepared, and then the same figure is used. (B)
As shown in, a transparent film 7 made of SiO ₂ or the like is formed on the chrome pattern 6. Next, as shown in FIG. 6C, an ionizing radiation resist layer 8 such as chloromethylated polystyrene is formed on the transparent film 7, and as shown in FIG. And then
A predetermined pattern is drawn by ionizing radiation 9 such as an electron beam exposure device, developed and rinsed to form a resist pattern 10 as shown in FIG. Next, after performing heat treatment and descum treatment as needed, FIG.
As shown in FIG. 5, the transparent film 7 portion exposed from the opening of the resist pattern 10 is dry-etched by the etching spatterer 11 to form the phase shifter pattern 12. The phase shifter pattern 12 may be formed by wet etching instead of dry etching. Next, the remaining resist is ashed and removed by oxygen plasma 13 as shown in FIG. Through the above steps, the phase shift mask having the phase shifter 12 as shown in FIG.

[0009]

As described above, in manufacturing a phase shift mask, when the phase shifter is processed, the phase shifter pattern is formed mainly by using dry etching. Is desirable.

However, at present, there is a problem that when the resist is applied to the upper layer of the phase shifter layer by the spin coating method, the resist is repelled and cannot be applied uniformly. Further, even if the resist can be applied uniformly, there is a problem that after the resist pattern is formed, the pattern may drop off or the cross-sectional shape may be abnormal. Here, as shown in FIG. 6, the abnormal cross-sectional shape means that a biting portion 15 is formed at the interface between the phase shifter layer 16 and the resist 14, or an inverted trapezoidal shape with a significant dimensional shift during post-processing. belongs to.

The present invention has been made in view of such circumstances, and an object thereof is to make it possible to uniformly apply a resist to be applied onto a phase shifter layer in the manufacture of a phase shift mask, and after forming a resist pattern. It is an object of the present invention to provide a method in which a pattern is not dropped or a sectional shape is not abnormal.

[0012]

In view of the above-mentioned problems, the present invention has been studied to obtain a phase shift mask that enables ultrafine photolithography, and as a result, a resist is applied to the upper layer of the phase shifter layer in the manufacturing process. At that time, by applying a surface treatment to the phase shifter layer, the adhesiveness of the resist is enhanced, the resist can be uniformly applied, and a resist pattern having a vertical cross-sectional shape can be obtained.
It was found that a highly accurate phase shift mask can be manufactured, and the present invention has been completed based on such findings.

FIG. 1 shows a phase shifter pattern forming process according to the present invention. FIG. 1 is a cross-sectional view showing the manufacturing process of the phase shift reticle. As shown in FIG.
A chrome reticle completed by providing a chrome pattern 17 on 8 is prepared, and then, as shown in FIG.
Transparent film 1 made of SiO ₂ or the like on the chrome pattern 17
9 is formed. Next, as shown in FIG. 6C, the surface of the transparent film 19 is subjected to ozone treatment 20 to make the surface hydrophilic, and then an ionizing radiation resist layer 21 is applied as shown in FIG. Then, as shown in FIG. 6E, alignment is performed on the resist layer 21 according to a conventional method, a predetermined pattern is drawn by ionizing radiation 22 such as an electron beam exposure device, and development and rinsing are performed. ), A resist pattern 23 is formed.

Next, after performing heat treatment and descum treatment as needed, the transparent film 19 portion exposed from the opening of the resist pattern 23 is dried by an etching gas plasma 24 as shown in FIG. Etching is performed to form a phase shifter pattern 25 as shown in FIG. Next, the remaining resist is ashed and removed by oxygen plasma, and the phase shift mask having the phase shifter 12 as shown in FIG.

The surface treatment here is mainly to make the phase shifter layer 19 hydrophilic and improve the wettability. In order to improve the wettability, (1) increase the dispersion force interaction, (2) increase the polar force interaction,
There is a method. Here, for example, in order to increase the dispersion force interaction, the density of the surface layer of the phase shifter material may be increased. Further, in order to increase the polar force interaction, the interaction such as hydrogen bond may be increased.

Phase shifter materials to which the method of the present invention can be applied include glass, quartz, spin-on-glass, sputtered SiO ₂ , CaF ₂ , MgF ₂ , SiN and Al _2.
O ₃ , other metal oxides, metal nitrides, fluororesins,
Many phase shifter materials such as synthetic resins having high short-wavelength transparency.

Although the type of resist used in the present invention is not limited, the phenomenon of abnormal cross-sectional shape is often observed in chemically amplified resists. Therefore, the method of the present invention is particularly practical for these resists. It is a technique. The reason why the abnormal cross-sectional shape phenomenon occurs is currently unknown.

The surface treatment used in the present invention will be described. (1) The substrate is immersed in an alkaline solution. Alternatively, the substrate alkaline solution is applied.

(2) The substrate is treated with oxygen plasma, ultraviolet rays, deep ultraviolet rays, ozone, ultraviolet rays and ozone. (3) Treat the substrate with hexamethyldisilazane (HMDS). (4) Immerse the substrate in an organic solvent or apply the organic solvent to the substrate. (5) Reflux the substrate in an organic solvent. (6) Immerse the substrate in the acidic solution or apply the acidic solution to the substrate.

First, the alkali treatment will be described.
Examples of the alkaline liquid include aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alcohol solutions such as methanol, aqueous ammonia, and organic alkalis such as tetramethylammonium oxide.

The treatment method with an alkali can be carried out by an immersion method in an alkaline solution, a coating method using a brush or the like, a spray method and the like. It is suitable that the temperature of the treatment with the alkaline solution is 10 ° C. to 80 ° C. and the treatment time is 10 seconds to 20 minutes.

After the treatment with the alkaline solution, the alkaline solution is removed from the substrate surface by rinsing with pure water, high-pressure cleaning or scrub cleaning.

Oxygen plasma, ultraviolet ray, far ultraviolet ray, ozone, ultraviolet ray and ozone treatment will be described. After cleaning the substrate, it is treated with oxygen plasma, ultraviolet ray, far ultraviolet ray, ozone, or ultraviolet ray and ozone, and the oxide on the substrate surface is treated. And, by decomposing organic matter, it becomes hydrophilic.

Explaining the organic solvent treatment, the substrate is immersed in the organic solvent, the substrate is coated with the organic solvent, or the substrate is refluxed in the organic solvent for cleaning to remove oil and the like adhering to the surface. The method is to make the surface hydrophilic. Examples of the organic solvent used here include ketones such as acetone and MIBK, alcohols such as methanol and ethanol, aromatics such as benzene and xylene, and ethyl cellosolve.

The HMDS treatment method is a method of enhancing the adhesion between the substrate and the resist by cleaning the substrate and then exposing it to an HMDS atmosphere or applying HMDS by spin coating.

Explaining the acid treatment method, the acid solution is, for example, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, formic acid, hydrogen fluoride solution, or a mixed acid thereof.

The treatment method with an acid can be carried out by a dipping method in an acid solution, a coating method using a brush or the like, and a spray method. The temperature of the treatment with the acid solution is 5 ° C. to 80 ° C., and the treatment time is 10 seconds to 30 minutes. This acid treatment may be performed by arranging the acid which is a hydrophilic group on the substrate surface by spin coating or the Langmuir-Blodgett method. After the surface treatment, rinsing cleaning with pure water, high-pressure cleaning or scrub cleaning is performed to remove excess acid solution from the substrate surface.

That is, in the method for producing a photomask having a phase shift layer according to the present invention, a resist thin film is applied onto a substrate having a transparent layer for phase shifter formed thereon, and the resist thin film is subjected to pattern drawing exposure with ionizing radiation or the like. After the pattern drawing exposure, the resist thin film is developed to form a resist pattern, and the exposed transparent layer for the phase shifter is etched by using this resist pattern as a mask. After the etching is completed, the remaining resist is removed to form a phase shift layer. In the method for manufacturing a photomask having the above, the resist thin film is applied after the surface of the transparent layer for phase shifter is subjected to a surface treatment for improving wettability.

In this case, the transparent layer for the phase shifter is made of spin-on glass, SiO ₂ , CaF ₂ , Mg.
It is preferably formed from F ₂ , SiN, Al ₂ O ₃ , other metal oxides, metal nitrides, or fluororesins.

The above-mentioned surface treatment is carried out by immersing the substrate in an alkaline solution or applying an alkaline solution, by treating the substrate with oxygen plasma, ultraviolet rays, far ultraviolet rays, ozone, ultraviolet rays and ozone, or by treating the substrate. Treatment with hexamethyldisilazane or a silicon compound, by dipping or coating the substrate in an organic solvent, by refluxing the substrate in an organic solvent, or by treating the substrate with an acidic solution. Desirably, it is done by dipping in or applying an acidic solution.

[0031]

When the resist is applied on the phase shifter material layer such as spin-on glass, most kinds of resist are repelled, and it is difficult to apply the resist uniformly. Further, when a chemically amplified resist is used as the resist, there are problems such as poor adhesion and abnormal cross-sectional shape. Therefore, according to the present invention, the surface of the transparent layer for phase shifter is subjected to a surface treatment for improving the wettability, and by improving the wettability with respect to the resist, the repellency of the resist is eliminated and the adhesiveness is improved, and the resist is uniformly applied. It is possible to form a resist pattern having a vertical cross-sectional shape with good adhesion and without pattern dropping even after pattern formation. Therefore, a highly accurate phase shift reticle can be efficiently manufactured at low cost.

[0032]

【Example】

Example 1 A photomask substrate having a phase shift layer composed of a chromium layer and SOG (spin on glass) was placed in MF321 manufactured by Shipley Co., which is an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, at a temperature of 21 ° C.
After soaking for 5 minutes, the substrate was washed with pure water and spin-dried to obtain a substrate having a hydrophilic surface.

This phase shift mask substrate was spin-coated with a resist solution of SNR-248 manufactured by Shipley Co., which is a chemically amplified negative resist, and prebaked at 120 ° C. for 30 minutes to form a uniform resist film having a thickness of 0.5 μm. Got

This was pattern-exposed with an irradiation amount of 1.5 μC / cm ² by an electron beam exposure device with an acceleration voltage of 10 kV. After exposure and post-exposure bake, development was performed for 2 minutes with MF321 manufactured by Shipley Co., which is an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, and rinsed with pure water to obtain a resist pattern.

FIG. 2 shows a cross-sectional shape of a resist pattern formed by applying the above-mentioned hydrophilic treatment as observed with a scanning electron microscope. Resist cross section 26 on the substrate that has been subjected to hydrophilic treatment
Was vertical and there was no pattern loss. In the figure, reference numeral 29 is a photomask substrate, 28 is a chrome layer, and 27 is a transparent layer. The resist could not be uniformly applied without such surface treatment.

Example 2 A photomask substrate having a phase shift layer composed of a chromium layer and SOG was treated with ultraviolet rays and ozone for 2 minutes to obtain a substrate having a hydrophilic surface.

First, a resist solution of SNR-248 manufactured by Shipley Co., which is a chemically amplified negative resist, was spin-coated on this photomask substrate and prebaked at 120 ° C. for 30 minutes to form a uniform resist having a thickness of 0.5 μm. A film was obtained.

This was pattern-exposed with an irradiation amount of 1.5 μC / cm ² by an electron beam exposure apparatus with an acceleration voltage of 10 kV. After exposure and post-exposure bake, development was performed for 2 minutes with MF321 manufactured by Shipley Co., which is an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, and rinsed with pure water to obtain a resist pattern.

FIG. 3 shows a cross-sectional shape of a resist pattern formed by applying the above-mentioned hydrophilic treatment, observed with a scanning electron microscope. Resist cross section 30 on the substrate which has been subjected to hydrophilic treatment
Was vertical and there was no pattern loss. In the figure, reference numeral 33 is a photomask substrate, 32 is a chrome layer, and 31 is a transparent layer.

[0040]

As described above, according to the method of manufacturing a photomask having a phase shift layer of the present invention,
When applying the resist thin film for forming the resist pattern, the surface of the transparent layer for phase shifter is subjected to a surface treatment to improve the wettability, and by improving the wettability to the resist, the repellency of the resist is eliminated and the adhesiveness is improved. Therefore, the resist can be evenly applied, and even after the pattern is formed, the resist pattern can be formed with a vertical cross-sectional shape with good adhesion and no pattern falling off. Therefore, a highly accurate phase shift reticle can be efficiently manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of an embodiment of a phase shift reticle according to the present invention.

FIG. 2 is a view showing a cross-sectional shape of a resist pattern formed by applying a hydrophilic treatment of Example 1.

FIG. 3 is a view showing a cross-sectional shape of a resist pattern formed by applying a hydrophilic treatment of Example 2.

FIG. 4 is a comparison diagram with a conventional method for showing the principle of the phase shift method.

FIG. 5 is a cross-sectional view showing a manufacturing process of a conventional phase shift reticle.

FIG. 6 is a cross-sectional view showing an abnormal cross-sectional shape of a resist pattern.

[Explanation of symbols]

 17 ... Chrome pattern 18 ... Substrate 19 ... Transparent film 20 ... Surface treatment 21 ... Resist layer 22 ... Ionizing radiation 23 ... Resist pattern 24 ... Etching gas plasma 25 ... Phase shifter pattern

Claims (8)

[Claims] 1. A resist thin film is applied on a substrate on which a transparent layer for phase shifter is formed, and the resist thin film is subjected to pattern drawing exposure by ionizing radiation or the like. After the pattern drawing exposure, the resist thin film is developed to form a resist pattern. Is formed, the exposed transparent layer for phase shifter is etched using this resist pattern as a mask, and after the etching is completed,
In the method for producing a photomask having a phase shift layer for removing the remaining resist, the surface of the transparent layer for phase shifter is subjected to a surface treatment for improving wettability, and then the resist thin film is applied. And a method for manufacturing a photomask having a phase shift layer. 2. The transparent layer for a phase shifter comprises spin-on-glass, SiO ₂ , CaF ₂ , MgF ₂ , SiN,
Al ₂ O ₃ , other metal oxides, metal nitrides, or
The method of manufacturing a photomask having a phase shift layer according to claim 1, which is made of a fluororesin. 3. The method for producing a photomask having a phase shift layer according to claim 1, wherein the surface treatment is performed by immersing the substrate in an alkaline solution or applying an alkaline solution. 4. The photomask having a phase shift layer according to claim 1, wherein the surface treatment is performed by treating the substrate with oxygen plasma, ultraviolet rays, deep ultraviolet rays, ozone, ultraviolet rays and ozone. Manufacturing method. 5. The method of manufacturing a photomask having a phase shift layer according to claim 1, wherein the surface treatment is performed by treating the substrate with hexamethyldisilazane or a silicon compound. 6. The method of manufacturing a photomask having a phase shift layer according to claim 1, wherein the surface treatment is performed by immersing or coating the substrate in an organic solvent. 7. The method of manufacturing a photomask having a phase shift layer according to claim 1, wherein the surface treatment is performed by refluxing the substrate in an organic solvent. 8. The method for producing a photomask having a phase shift layer according to claim 1, wherein the surface treatment is performed by immersing the substrate in an acidic solution or applying an acidic solution.