JPH0580492A - Production of photomask having phase shift layer - Google Patents

Abstract

PURPOSE:To produce the photomask having many stages of phase shifter patterns having high accuracy with a fewer stages at a lower generation rate of defects. CONSTITUTION:After light shielding patterns 32 and phase shifter patterns 33 are formed on a transparent substrate 30, only the peripheral parts 35 of the phase shifter pattern 33 parts existing isolatedly from the light shielding patterns 32 on the transparent substrate are irradiated 34 with ions by using an ion milling method, by which the film thicknesses are decreased and phase differences are generated in the central parts in order to produce the photomask having the light shielding patterns 32 and the phase shifter patterns 33 on the transparent substrate 30 and having the phase shift layers smaller in the film thickness of the peripheral parts 35 of the phase shifter pattern parts existing isolatedly from the light shielding patterns on the transparent substrate 30 than the film thickness of the central parts.

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 particularly to a phase shift layer for forming a fine pattern with high accuracy. And a method for manufacturing a photomask having the above.

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs are formed by applying a resist onto a substrate to be processed such as a Si wafer, exposing a desired pattern with a stepper, and then developing and etching it. It is manufactured by repeating the lithography 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. DRA which is LSI
Taking M as an example, the dimensional deviation of a 5 × reticle for a 1 Mbit DRAM, that is, a reticle having a size 5 × that of a pattern to be exposed is an average value of ± 3σ (σ is a standard deviation). Accuracy of 0.15 μm is required, similarly, the dimensional accuracy of 5 × reticle for 4M bit DRAM is 0.1 to 0.15 μm, and that of 5 × reticle for 16M bit DRAM is 0.05 to 0.1 μm. Dimensional accuracy is required.

Further, the line width of the device pattern formed by using these reticles is 1 Mbit DRAM.
1.2 μm, 4-bit DRAM 0.8 μm, 16
M-bit DRAM is required to be further miniaturized to 0.6 μm, and various exposure methods are being researched in order to meet such demand.

However, for example, in the case of the next-generation device pattern of the 64M DRAM class, the stepper exposure method using the reticle has reached the resolution limit of the resist pattern.
For example, JP-A-58-173744 and JP-B-62.
A reticle of a new concept called a phase shift mask, as shown in Japanese Patent Publication No. 59296, 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. FIG. 3 is a diagram showing the principle of the phase shift method,
FIG. 4 is a diagram showing a conventional method, which is shown in FIGS.
FIG. 3A is a cross-sectional view of the reticle, FIGS. 3B and 4B.
Is the amplitude of the light on the reticle, FIGS. 3 (c) and 4 (c) are the amplitudes of the light on the wafer, and FIGS. 3 (d) and 4 (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. 4 (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 portion having a predetermined pattern. However, in phase shift lithography,
As shown in FIG. 3A, a phase shifter 3 made of a transmissive film for inverting the phase (phase difference 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. 4B, and the amplitude of light on the wafer also becomes in-phase as shown in FIG. 4C. As shown in FIG. 4D, 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. 3 (d). be able to. As described above, in the phase shift lithography, it becomes possible to separate a pattern that could not be separated in the past, and the resolution can be improved.

Next, one example of the conventional manufacturing process of the phase shift reticle will be described with reference to the drawings. FIG. 5 is a cross-sectional view showing a manufacturing process of the phase shift reticle. In the figure, 10 is a substrate, 11 is a conductive layer, 12 is a chrome film, 13 is a resist layer, 14 is ionizing radiation, 15 is a resist pattern, and 16 is a resist pattern.
Is an etching gas plasma, 17 is a chrome pattern, 1
8 is oxygen plasma, 19 is a transparent film, 20 is a resist layer,
21 is ionizing radiation, 22 is a resist pattern, 23 is an etching gas plasma, 24 is a phase shift pattern, 2
Reference numeral 5 represents oxygen plasma.

First, as shown in FIG. 5A, a conductive layer 11 made of a tantalum thin film layer or the like is formed on an optically polished substrate 10 in order to prevent a charge-up phenomenon due to an exposure beam at the time of writing a phase shifter pattern. Is formed, a chromium film 12 is formed thereon, and an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a conventional method such as spin coating, followed by heat-drying treatment to a thickness of 0.1. A resist layer 13 having a thickness of about 2.0 μm is formed. The heating and drying treatment is usually performed at 80 to 150 ° C. for about 20 to 60 minutes, though it depends on the type of resist used.

Next, as shown in FIG. 1B, a pattern is drawn on the resist layer 13 by an ionizing radiation 14 by an exposure apparatus such as an electron beam drawing apparatus according to a conventional method, and an organic solvent such as ethyl cellosolve or ester is drawn. After developing with a developing solution containing the main component, rinsing with alcohol is performed to form a resist pattern 15 as shown in FIG.

Next, if necessary, heat treatment and descum treatment are carried out to remove the resist scraps remaining on the edge portions of the resist pattern 15 and unnecessary resist such as whiskers. As shown, resist pattern 1
The portion to be processed exposed from the opening of 5, that is, the chromium layer 12 is dry-etched by the etching gas plasma 16 to form the chromium pattern 17. It is obvious to those skilled in the art that the chrome pattern 17 may be formed by wet etching instead of dry etching by the etching gas plasma 16.

After etching in this manner, as shown in FIG. 2E, the resist pattern 15, that is, the remaining resist is ashed and removed by oxygen plasma 18, and the photo resist shown in FIG. Complete the mask. Note that this treatment may be performed by solvent stripping instead of the ashing treatment by the oxygen plasma 18.

Subsequently, this photomask is inspected, and if necessary, pattern modification is performed, and after cleaning, SiO 2 is deposited on the chrome pattern 17 as shown in FIG.
_A transparent film 19 made of ₂ or the like is formed. Next, the same figure (h)
As shown in FIG. 2, an ionizing radiation resist layer 2 such as chloromethylated polystyrene is formed on the transparent film 19 in the same manner as described above.
0, and the resist layer 20 is formed as shown in FIG.
Then, an aligning process is performed according to a conventional method, a predetermined pattern is drawn by ionizing radiation 21 such as an electron beam exposure device, developed and rinsed to form a resist pattern 22 as shown in FIG.

Next, after performing a heat treatment and a descum treatment, if necessary, as shown in FIG. 3K, the transparent film 19 portion exposed from the opening of the resist pattern 22 is etched with an etching gas plasma. Dry etching is performed with 23 to form a phase shifter pattern 24. The formation of the phase shifter pattern 24 may be performed by wet etching instead of dry etching by the etching gas plasma 23.

Next, the remaining resist is ashed and removed by oxygen plasma 25, as shown in FIG. Through the above steps, the phase shift mask having the phase shifter 24 as shown in FIG.

[0016]

However, the conventional phase shift mask completed as described above (see FIG. 2).
A sectional view is shown in (a) and a plan view is shown in (b). ) Is used to expose and develop a positive resist, for example, a 180 ° shifter 24 surrounded by a dotted line R in FIG.
The chrome pattern 17 is not accurately exposed at a position isolated on the substrate 10. For example, at the end of the line and space, the end of the originally separated pattern is connected as shown in FIG. The resist pattern remains. This is a problem caused by the fact that the edge portion of the 180 ° shifter 24 suddenly changes the phase by 180 °, and this edge portion acts as a light-shielding layer such as a chrome pattern. This is shown in FIG. As shown, a multistage shifter method in which 90 ° shifters 26 are arranged at the edge portions of 180 ° shifters 24 isolated on the substrate 10 (such a phase shift layer is called a multistage phase shift layer or a multistage shifter). Can be solved by using. This is a matter well known to those skilled in the art.

However, if a phase shift mask having such a multi-stage shifter is manufactured by the conventional process as shown in FIG. 5, the phase shift mask is manufactured by a larger number of processes compared with a normal photomask. In addition, the number of similar processes must be increased, and defects frequently occur, resulting in higher costs, longer manufacturing periods, and the like.

The present invention has been made in view of such circumstances, and an object thereof is a method of manufacturing a photomask having a multi-stage phase shift layer, which is more practical and can reduce the cost and the number of steps. Is to provide.

[0019]

In view of the above problems, the present invention enables reduction of manufacturing period and cost by reducing the number of steps for producing a phase shift mask having a multi-stage shifter, and As a result of research to develop a method for stably manufacturing a highly accurate multi-stage phase shift mask,
In the manufacturing process of the phase shift mask, when the 90 ° shifter pattern is formed on the peripheral portion of the 180 ° shifter isolated on the substrate as described above, it is isolated on the substrate 18
By etching the peripheral portion of the 0 ° shifter pattern by using an ion milling method, the film thickness of the peripheral portion is reduced, thereby changing the phase shift amount from 180 ° (for example, 90 °). At the part where the amount of phase shift spatially changes from 180 ° to 90 °, the amount of ions to be irradiated is continuously changed to create a discontinuous part of the phase difference between the 180 ° shifter and the 90 ° shifter. It was found that a highly accurate multi-stage phase shift layer can be stably manufactured with a small number of steps by continuously changing the amount of phase shift without the need, and the present invention has been completed based on such knowledge. In addition, it is necessary to perform annealing after such ion etching.

The present invention will be described below with reference to the drawings.
FIG. 1 is a diagram for explaining a manufacturing process of a multi-stage phase shift mask according to the present invention. In the figure, 30 is a substrate, 31 is a conductive layer, 32 is a light shielding layer, and 33 is a conventional one as shown in FIG. The 180 ° phase shifter produced by the above method, 34 is a focused ion beam, and 35 is a 90 ° shifter in which the film thickness is reduced and the amount of phase shift is changed by ion irradiation.

As the phase shifter layer 33, a SiO ₂ film by a sputtering method or the like, spin-on-glass (SO
G), organic polymer films, other inorganics transparent in the near ultraviolet region,
Any organic material may be used. Note that SOG is a film obtained by applying an organic solvent solution of an organic silicon compound, drying it, and heating it to change it to silicon oxide. As a starting material for SOG, tetraethoxysilane (Si (OC
A metal alkoxide such as ₂ H ₅ ) ₄ ), an amphoteric solvent such as water or methanol, and hydrochloric acid are used.

First, a shifter pattern 33 of a phase shift mask, which is produced by a conventional method and whose defect is inspected, as shown in the cross section in FIG. 1A, is shown by a dotted line R in the plan view of FIG. 1B. As shown in FIG. 6C, gallium ions 34 are irradiated to the peripheral portion of the isolated portion on the substrate 30 which is surrounded by the ion beam method. The irradiated portion 35 ((d) in the figure) is etched by this ion irradiation, the film thickness of the shifter is reduced, and a difference in the film thickness of the shifter is generated between the unirradiated portion and other portions. By this change in the shifter film thickness, the phase shift amount of the peripheral portion 35 of the isolated portion of the shifter 33 can be set to 90 °, for example, as shown in the plan view of FIG.

By controlling the amount of ions to be irradiated, the amount of ions to be irradiated is continuously changed at a portion where the phase shift amount spatially changes from 180 ° to 90 °, and the shifter film thickness is continuously changed. 180 ° shifter 33
It is also possible to continuously change the phase shift amount without forming a discontinuous portion of the phase difference between the 90 ° shifter 35 and the 90 ° shifter 35.

After forming the 90 ° phase shift layer 35, it is desirable to heat and anneal in order to remove the stress associated with the ion irradiation. In this way, the manufacturing process of the 90 ° phase shift layer 35 can be significantly reduced.

In the above, the 180 ° shifter 3
The phase shift amount of the peripheral portion 35 of the isolated portion of 3 is not limited to 90 °. If the phase difference between adjacent shifter patterns is 90 ° or less, a pseudo pattern is not usually transferred. In addition to gallium, various one or more elements can be used as the ion species to be irradiated by the ion milling method.

As described above, when manufacturing a photomask having a multi-stage phase shift layer, the conventional method has a large number of steps, and thus the substrate is likely to be damaged. , The manufacturing process can be halved,
A high-quality multi-stage phase shift mask can be manufactured by a simpler process as compared with the conventional method.

As described above, the photomask having the phase shift layer of the present invention is provided with the light shielding pattern and the phase shifter pattern on the transparent substrate, and the phase shifter pattern portion which is located on the transparent substrate and is isolated from the light shielding pattern. In a method of manufacturing a photomask having a phase shift layer in which a film thickness of a peripheral portion is smaller than a film thickness of a central portion, a phase shifter pattern which is located on a transparent substrate and is isolated from the light shielding pattern after forming the light shielding pattern and the phase shifter pattern. This is a method characterized in that the film thickness is reduced by irradiating only the peripheral portion of the portion with an ion milling method.

In this case, it is desirable to perform the annealing treatment by heating after the ion irradiation. The phase shifter pattern is a SiO ₂ film formed by sputtering,
It is desirable that it is composed of spin-on-glass or an organic polymer film and is irradiated with gallium ions by an ion milling method.

[0029]

[Function] With the recent high integration of LSIs and VLSIs, the precision of photomasks is required more and more, and accordingly, the frequent occurrence of defects due to dust and the like becomes a problem. Also, the cost is inevitably high.

In the method of manufacturing a photomask having a phase shift layer according to the present invention, a photomask having a multi-stage phase shifter can be manufactured with high accuracy without etching the phase shift layer formed on the light shielding layer at all. It is possible to suppress the occurrence of defects by reducing the number of steps, and at the same time, it is possible to keep the manufacturing cost low.

[0031]

【Example】

Example 1 After inspecting the quality of a phase shift mask having a chrome light-shielding pattern and an SOG phase shifter pattern manufactured according to a conventional method, a region on the mask where a 90 ° shifter pattern is to be provided (for example, a 180 ° shifter on a transparent substrate). Was irradiated with gallium ions at an accelerating voltage of 20 KeV.

Thereafter, this substrate was annealed at 300.degree. The positional shift of the 90 ° shifter portion of the multi-stage phase shift mask manufactured by the process having a small number of steps in this way, when the average value ± 3σ (σ is the standard deviation) is taken,
The value was within ± 0.1 μm, and it was confirmed that a highly accurate phase shift mask was obtained. Further, no pattern distortion or the like was observed in the peripheral portion of the mask.

Even when the thus-prepared multi-stage phase shift mask was exposed to a positive resist and developed, a resist pattern having connected end portions did not remain.

[0034]

As described above, according to the method of manufacturing a photomask having a phase shift layer according to the present invention, a photomask having a multi-stage phase shifter can be formed without etching the phase shift layer formed on the light shielding layer. The mask can be manufactured with high precision, the occurrence of defects can be suppressed by reducing the number of steps, and at the same time, the manufacturing cost can be suppressed low.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a manufacturing process of a multi-stage phase shift photomask according to the present invention.

FIG. 2 is a diagram for explaining a problem of a conventional phase shift mask and a configuration of a multistage phase shift photomask.

FIG. 3 is a diagram showing a principle of a phase shift method.

FIG. 4 is a diagram showing a conventional method.

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

[Explanation of symbols]

 30 ... Substrate 31 ... Conductive layer 32 ... Chrome pattern (light-shielding layer) 33 ... 180 ° phase shifter 34 ... Focused ion beam 35 ... 90 ° phase shifter (ion irradiation unit)

Claims (4)

[Claims] 1. A phase shift having a light-shielding pattern and a phase shifter pattern on a transparent substrate, wherein a film thickness of a peripheral portion of a phase shifter pattern portion located on the transparent substrate and isolated from the light-shielding pattern is smaller than a film thickness of a central portion. In a method for manufacturing a photomask having a layer, after forming a light-shielding pattern and a phase shifter pattern, only a peripheral portion of a phase shifter pattern portion located on the transparent substrate and isolated from the light-shielding pattern is subjected to ion irradiation using an ion milling method. The method for producing a photomask having a phase shift layer, the method comprising: 2. The method of manufacturing a photomask having a phase shift layer according to claim 1, wherein after the ion irradiation, heating is performed to perform the annealing treatment. 3. The method for producing a photomask having a phase shift layer according to claim 1, wherein the phase shifter pattern is made of a SiO ₂ film, a spin-on glass or an organic polymer film by a sputtering method. 4. The method for producing a photomask having a phase shift layer according to claim 1, wherein gallium ions are irradiated by an ion milling method.