JPS61198156A - Improved photomask blank - Google Patents

Abstract

PURPOSE:To enable a residual chromium film to be extremely reduced by controlling the speed of a light interrupting film to be etched with an etchant in the film thickness direction lower in the lower side than the upper side. CONSTITUTION:A photomask blank 1 is composed of a transparent base plate 2, the light interrupting film 3, and reflection preventing films 4, 4'. As the base plate 2, a plate high in light transmittance, smooth and flat on the surface, such as a plate of borosilicate type glass, quartz glass, or sapphire, is used. The light interrupting film 3 formed between the films 4, 4' is increased in the speed of the film 3 to be etched with the etchant in the film thickness direction in the side of the upper layer higher than in the side of the lower layer, and it is made of a chromium compd. contg. one of N, O, C, and B or metallic Cr, or its alloy.

Description

[Detailed Description of the Invention] [Technical Field 1] The present invention relates to an IC or an LSI'-I? This invention relates to an improvement of a photomask blank for manufacturing a photomask used in step 1 of semiconductor device manufacturing.

[Prior art and its problems] In the manufacture of ICs and LSIs, circuit images are formed on silicone wafers 1 with high precision.

Elements are manufactured using a chrome mask as a high-resolution hard mask plate using the phosphorography method using ultraviolet light. Generally, photomask blanks for manufacturing such chrome masks are of the intermediate layer type with a transparent base and a single layer of chromium formed on the north side, or in order to prevent multiple reflections between the wafer and the mask.
A low reflection type that combines a chromium film and a chromium oxide film is used.

When such a photomask blank is used for manufacturing a chrome mask for manufacturing semiconductor devices, as shown in FIG. After a photoresist layer 5 that is sensitive to light is coated on the photoresist layer 4, a predetermined pattern is exposed to light using an exposure device, the resist is developed, and the exposed light-shielding film portion is etched to obtain a desired pattern. However, in this -4 process, if minute dust adheres to the resist layer after resist coating in the area where the light shielding film is etched,
The part to which this dust adheres becomes the part that is not exposed to light during exposure, and if the resist used is a positive type, there will be a light-shielding film residue (so-called chromium residue), and if the resist is coated on a cloth surface, the light-shielding film will be missing (so-called chromium deficiency). It causes For example, as shown in FIG. 5, a positive photoresist layer 5 is coated on the light shielding film 3 surface of a photomask blank l in which a light shielding film 3 containing chromium (film thickness of approximately 600 mm) is formed on a transparent substrate 2. When opaque dust 6 with a diameter of about 1 μm adheres to the top, when the photoresist is exposed and developed, a remaining photoresist layer 5a with a diameter of about 0.8 μm is left as shown in FIG. 5(b). was observed. When the light-shielding film 3 was further etched, a remaining light-shielding film 3a having a diameter of about 0.5 μm was observed as shown in FIG. 5(C). A remaining light-shielding film (remaining chromium film) of this size does not pose a problem when forming patterns with not very high definition, but it becomes an important drawback when forming circuit patterns that handle line widths of about 1 μm.

Generally, the above process is carried out in a clean room, but even in a highly clean room, dust of about 1 μm may adhere to the surface of the resist-coated cloth, resulting in residual light-shielding film as described above, light-shielding defects, etc. There is a problem that occurs. In the following, the case of a positive resist will be described in the present invention.

[Object 1 of the present invention] The present invention provides a photomask blank that can minimize the amount of remaining light shielding film, so-called chromium film remaining, even if such minute dust adheres to the resist coating surface. The purpose is to

[Structure of the present invention] The present invention was invented as a result of research based on the above object, and includes a photomask blank in which a light shielding film containing chromium is formed on the surface of the transparent substrate. This invention relates to a photomask blank characterized in that the etching rate in the film thickness direction is higher on the L layer side and lower on the lower layer side than on the upper layer side.

According to the present invention, the 1st layer side of the light shielding film is 1st layer side with respect to the lower layer side.
- Since the structure is such that etching is performed quickly, even if there is a residual resist layer caused by attached dust when etching the light shielding film, the light shielding film under the remaining resist layer will be removed from the upper layer. It is possible to prevent the light shielding film from being left behind due to being gouged out from the side.

The present invention will be explained in more detail below.

Figures 1 to 3 are schematic diagrams showing the cross-sectional structure of the photomask blank of the present invention. Figure 1 is a single-layer type, Figure 2 is a two-layer type with low surface reflection, and Figure 3 is a three-layer type. In Figure 0, which shows the double-sided low reflection type of the system, 1 is a photomask blank, 2 is a transparent substrate, 3 is a light shielding film, and 4.4' is an antireflection film.

In the present invention, the transparent substrate 2 is made of low-expansion glass such as borosilicate glass, aluminosilicate glass, or aluminoborosilicate glass, which has high light transmittance and a smooth and flat surface, or soda lime. A substrate made of silicate glass, quartz glass, sapphire, or the like is used.

In the present invention, the light shielding film 3 formed on the surface of the transparent substrate 2 has a high etching rate in the film thickness direction with respect to the etchant on the upper layer side A, and a higher etching rate on the lower layer side B. , and is smaller than that on the layer side A. The etching rate may be set to increase continuously from the lower layer side B to the upper layer side A with a constant slope or with a gradually changing slope, or from the lower layer side B to the upper layer side. The etching speed may be increased in two or several steps toward A, or the etching speed may be increased stepwise and continuously from the lower layer side B to the L layer side A. You can also do it like this.

The light shielding film 3 is preferably a film made of a chromium compound containing at least one of nitrogen, oxygen, carbon, and boron, metallic chromium, or a chromium alloy.

A layer of metallic chromium containing nitrogen and/or oxygen has a faster etching rate than a layer of only metallic chromium, and in particular, the higher the nitrogen content of the chromium film, the faster the knee etching speed per degree.
J tends to be faster.

On the other hand, the etching rate of a layer of metallic chromium containing carbon or boron is slower than that of a layer of only metallic chromium, and the higher the carbon content of the chromium film, or the higher the boron content of the chromium film, the slower the etching rate. tends to be slower.

Therefore, the lower layer of the light-shielding film is a metal chromium layer, the soil layer side is a chromium layer containing oxygen and/or nitrogen, or the upper layer of the light-shielding film is a chromium layer with high nitrogen content, and the lower layer is a chromium layer containing high nitrogen content. A chromium layer with a low carbon or boron content is used on the upper layer of the light shielding film, and a chromium layer with a low carbon or boron content is used on the lower layer, or a chromium layer with a low carbon or boron content is used on the upper layer of the light shielding film. Alternatively, the etching rate of the upper layer of the light-shielding film can be made faster than that of the lower layer by using a chromium layer containing less boron and a layer containing less nitrogen on the lower layer side.

In the present invention, the thickness of the above-mentioned light shielding film is as follows.

500~ in terms of light blocking properties, etching properties, acid resistance, etc.
A range of about 1,500 people is preferable.

In addition, since the single layer type photomask blank has a high surface reflectance, there is a problem in that multimodal reflection occurs between the silicon wafer and the mask, resulting in poor resolution during patterning. In order to improve such defects, antireflection films 4 and 4' can be provided at J- or below t of the light-shielding film 3. This antireflection 1194.4' should preferably have a surface reflectance of 10 to 15% or less at a light wavelength of 436 nm, and should also have sufficient acid resistance and etching properties. In II, the typical antireflection coatings 4, 4' are chromium films containing oxygen and nitrogen, and the thickness thereof is usually in the range of 200 to 500.

In the photomask blank of the present invention, a transparent conductive film made of indium oxide, tin oxide, or the like may be formed on the transparent substrate for antistatic purposes, if necessary.

[Example of the present invention] Examples of the present invention will be described below.

[Example 1] A chromium film containing nitrogen was formed on a transparent glass substrate made of precisely polished low-expansion aluminosilicate under the following sputtering conditions.

RF power: 2.5kW Sputtering gas: Ar/N2 = 85/15 Sputtering gas pressure: 4. OX 1O-3Torr.

Add this light-shielding film to 1B5g of ceric ammonium nitrate and perchloric acid (70%), and add pure water to 100%.
When etching was carried out using an etching solution (20° C.) that had been mixed with 0.0° C., the just etching time was 35 seconds.

(Etching speed: 23 people/s).

On the other hand, 200 people formed a chromium film containing nitrogen and oxygen on the above chromium film under the following sputtering conditions.

FR power: 2.5 Sputter gas: Ar/N7/02=45/5
0/5 sputtering gas pressure: 5. OX 1O-3To
When 1000 people formed this film on different glass substrates and etched it with the same etching solution, the just etching time was 5 seconds (etching speed:
200 people/s).

As shown in -1- below, the film composition was made such that the etching rate was extremely different on the upper and lower sides of the light-shielding film, and a positive resist (0FPR-800 manufactured by Tokyo Ohka Co., Ltd.) was coated by 5,000 people, and pre-baked at 130°C. 30m1n), C1ass 10
The samples were left in an atmosphere of 0.00 for one week, developed, etched, and the remaining light-shielding film (remaining chromium film) was compared.

As a result, as shown in Table 1, it was found that the shielding rate and film residue (chromium residue) were extremely small compared to the pure chromium single layer film (8008) exposed to the same atmosphere.

[Example 2] Similar to Example 1, by sputtering on a transparent substrate,
A pure chromium film was formed by 500 people, and 300 people formed a chromium nitride film thereon by reactive sputtering (under the conditions shown in Table 2).

In the same manner as in Example 1, a positive type resist was applied, prebaking was performed, and the resist film was exposed to an atmosphere of C1ass 1000 for one week, and then the resist film was developed and the chromium film was etched. As a result, as shown in Table 3, the amount of chromium film remaining was smaller than that of a pure chromium film exposed to a similar atmosphere, and it was found that the effect was large.

Table 3 Chromium removal method after etching 1 □ [Example 3] Form 500 chromium carbide films on a transparent substrate by reactive sputtering (conditions in Table 4), then chromium nitride by reactive sputtering (conditions in Table 4) 300 people formed a membrane.

In the same manner as in Example 1, the resist film was subjected to pre-beta after coating with a positive type and exposed to an atmosphere of C1ass 1000 for one week, and then the resist film was developed and the chromium film was etched. As a result, as shown in Table 5, the amount of chromium film remaining is smaller than that of pure chromium film exposed to the same atmosphere.
It turned out to be highly effective.

[Example 4] On a transparent substrate, chromium and chromium boride targetera) (
9: A chromium boride film was heated to 500% using
Formation followed by reactive sputtering (conditions in Table 6)
300 people formed a chromium nitride film.

Table 6 Sputtering conditions As in Example 1, after applying a positive resist, pre-baking was performed, and after being exposed to an atmosphere of C1ass 1000 for one week, the resist film was subjected to a prescribed development process and the chromium film was etched. . As a result, the remaining chromium film is shown in Table 7.
As shown in Figure 3, it was found that the effect was smaller than that of a pure chromium film exposed to a similar atmosphere.

In addition, the kitchen time is 5 times the just etching time.
I added seconds.

[Operations and Effects of the Present Invention] As described above, according to the present invention, since the upper layer side of the light shielding film is etched sufficiently faster than the lower layer side, when etching the light shielding film, Even if there is a residual resist layer caused by attached dust, it is possible to prevent the light-shielding film from being removed from the upper layer side under the residual resist layer, thereby preventing the remaining light-shielding film from being generated.

Therefore, it is possible to provide a high-quality photomask blank that can be used to manufacture photomasks that require high-precision patterns.

[Brief explanation of the drawing]

Figures 1 to 3 show cross-sectional views of the photomask blank of the present invention, Figure 4 is an explanatory diagram showing an example of how the photomask blank is used, and Figure 5 shows photoresist coating and exposure phenomena using the photomask blank. Cross-sectional views of each step of photoresist stripping are shown. 1: Photomask blank, 2: Transparent substrate. 3: Light-shielding film, 4.4″: Anti-reflection film. 5: Photoresist layer, 8: Dust. A: Upper layer side, B: Lower layer side. Figure 1 Dormitory 2 Figure 31! 1 4121 (C) 5 Figure

Claims (4)

[Claims] (1) In a photomask blank in which a light-shielding film containing chromium is formed on the surface of a transparent substrate, the etching rate of the light-shielding film in the film thickness direction with respect to the etchant is increased on the upper layer side, while A photomask blank characterized by being smaller than the sides. (2) The light-shielding film is made of a chromium compound, metallic chromium, or chromium alloy containing at least one of nitrogen, oxygen, carbon, and boron. mask blank. (3) A patent characterized in that the upper layer side of the light-shielding film has a higher degree of nitridation or oxidation than the lower layer side closer to the transparent substrate, thereby making the etching rate of the upper layer faster than that of the lower layer side. A photomask blank according to claim 1. (4) The upper layer side of the light-shielding film has a lower degree of carbonization or boration than the lower layer side closer to the transparent substrate, thereby making the etching rate of the surface layer faster than that of the lower layer side. A photomask blank according to claim 1.