JPS61232456A - Photomask blank and photomask - Google Patents

Abstract

PURPOSE:To enhance chemical durability by forming an undercoat made of a Cr film contg. N on a transparent plate and further forming a light shading film contg. N and C or N and B in intimate contact with said undercoat. CONSTITUTION:The undercoat 3 made of a Cr film contg. N on a transparent plate high in adhesion and superior in chemical durability and capable of enhancing etching speed is formed on a transparent plate 1, such as glass plate, and further a light shading film 2 contg. N and C or N and B is formed in intimate contact with said undercoat 3. It is preferred to add N to the film 2 and the undercoat 3 each in an amt. of >=20%. In the case of a low-reflectance photomask or photomask blank, the chemical durability can be also more enhanced by adding N to a low-reflectance Cr film 7 in an amt. of >=20%, thus permitting the obtained photomask or photomask blank to be excellent in each of optical characteristics, mechanical characteristics, and chemical durability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a photomask blank and a photomask used in semiconductor manufacturing and the like.

[Prior art and its problems] In the manufacture of ICs and LSIs, it is necessary to form a single circuit image on a silicone wafer with high precision.

Elements are manufactured using a photomask with a chromium light-shielding film as a high-resolution hard mask plate by lithography using ultraviolet rays. In general, photomask blanks for manufacturing such photomasks include single-layer type photomask blanks in which a single layer of chromium light shielding film is formed on a transparent substrate, or t-type photomask blanks to prevent multiple reflections between the wafer and mask. Chrome light shielding film.

A low-reflection type that combines a chromium oxide-based antireflection film and a chromium oxide-based antireflection film is used.

When such a photomask blank is used as a photomask for semiconductor device manufacturing, a photoresist layer that is sensitive to light is applied onto the light-shielding film of the photomask blank, and then a predetermined pattern is exposed using an exposure device. Then, the resist is developed and the exposed light-shielding film portion is etched to obtain a desired pattern.

Conventionally, as a means to reduce the amount of chromium remaining after etching by increasing the etching rate of the chromium light-shielding film in layers closer to the transparent substrate, the degree of nitridation or oxidation of the layers closer to the transparent substrate is increased. Alternatively, a two-layer photomask blank in which the layer closer to the transparent substrate is a chromium layer containing nitrogen and the layer farther away is a chromium layer containing carbon is disclosed in JP-A-5111-10852 and JP-A-511-9.
It is known from 0853 etc.

On the other hand, for mask materials for photomask blanks, 4LL durability in terms of etching properties and optical properties, especially chemical durability against cleaning solutions such as strong acids, and adhesion between chromium films and glass substrates are important. Chemical durability can be improved by increasing the content compared to pure chromium film.

Strong acid cleaning solutions such as hot concentrated sulfuric acid require a certain content or more. Furthermore, compared to a pure chromium film, increasing the carbon content reduces the etching rate, but the chemical durability is poor, and the adhesion to the glass substrate also decreases, and the light-shielding property decreases. Since it also has the disadvantage that the film thickness must be increased, the method of the prior art patent is insufficient to obtain a mask material that satisfies various performances as a photomask.

[Object of the Invention] The object of the present invention is to provide a photomask blank and a photomask that not only have sufficient optical properties and mechanical properties but also have better chemical durability than conventional chromium light-shielding films. It's something to do. Furthermore, the present invention is a photomask blank that has excellent etching properties as a photomask blank, and *Even if small dust adheres to the resist coating surface, the remaining light shielding film, so-called chromium film, that is caused by it can be extremely reduced. The present invention also aims to provide a photomask with excellent durability.

[Summary of the Invention] The present invention was invented as a result of research based on the above object, and the gist of the first invention is to form a base film made of a thin chromium film containing nitrogen on a transparent substrate, The second invention relates to a photomask blank characterized in that a chromium light-shielding film containing nitrogen and carbon or nitrogen and boron is provided closely thereon, and the gist of the second invention relates to a photomask blank that includes a chromium light-shielding film containing nitrogen and carbon or nitrogen and boron on a transparent substrate. A photomask blank comprising a base film made of a thin chromium film and a chromium light shielding film containing nitrogen and carbon or nitrogen and boron closely formed thereon, characterized in that the base film and the chromium light shielding film are patterned. This relates to photomasks and -.

[Structure of the invention] The present invention will be explained in more detail below.

Fig. 1.2 is a schematic diagram showing the cross-sectional structure of the photomask blank of the present invention, Fig. 3.4 is a schematic diagram showing the cross-sectional structure of the photomask blank of the present invention, and Fig. 5 is a schematic diagram showing the cross-sectional structure of the photomask blank of the present invention. FIG. 6 is a schematic diagram showing the cross-sectional structure of a photomask blank. FIG. 6 is a schematic diagram showing the cross-sectional structure of a conventional photomask.

In the figure, number 1 indicates a transparent substrate such as glass, 3 indicates a base film made of a thin chromium film containing nitrogen, 2 indicates a chromium light-shielding film containing nitrogen and carbon, or nitrogen and boron, 4 indicates a photomask blank, and 5 indicates a photomask blank. Mask 6 shows the removed portions of the patterned photomask base film and chromium light shielding film. During the photomask manufacturing process, depending on the exposure process, it may be necessary to reduce the surface reflectance of the mask blank in the wavelength range used for exposure. A low-reflectivity chromium film 7 containing oxygen and nitrogen can also be provided closely on the light-shielding film 3.

The basic structure of a conventionally used photomask blank is, for example, as shown in FIG. Anti-reflective chromium containing oxygen or oxygen and nitrogen formed in! It consists of i70. Here, the chrome light shielding s20 that is in contact with the glass substrate surface
When patterning is performed by etching, it is necessary to reduce the etching rate to minimize changes in pattern line width that occur during excessive etching, and for this purpose carbon is contained. However, on the other hand, carbon-containing books reduce the adhesion force to the glass substrate, resulting in fine patterns being removed during mechanical cleaning of patterned photomasks, such as ultrasonic cleaning or scrub cleaning using high-pressure water and nylon brushes. Affects omissions. Furthermore, the carbon-containing chromium light-shielding film has poor durability against chemicals used as cleaning solutions, especially when exposed to strong acids such as hot concentrated sulfuric acid. Furthermore, as shown in FIG. 5, the slow etching speed of the chromium light-shielding film in contact with the glass substrate surface makes it difficult to determine the end point of etching.
This is an attempt to eliminate the drawbacks of the conventional films mentioned above.As shown in Figure 2, the adhesive strength of transparent substrates such as glass substrates is strong, the etching speed can be increased, and chemical A nitrogen-containing chromium film with excellent physical durability is provided as the first layer on the transparent substrate surface as a base film 3, and a chromium light-shielding film 2 containing nitrogen and carbon or nitrogen and boron is further closely attached to this base film 3. In the present invention, a more preferable embodiment is that the chromium light shielding 192 and the base film 3 are provided.
The nitrogen content in each film is 20% or more. By setting the nitrogen content to 20% or more, the above-mentioned points can be achieved particularly effectively. Of course, for low-reflection type photomask blanks or low-reflection type photomasks as shown in Figs.
% or more, the chemical durability can be further improved.

The nitrogen content in the chromium film in the present invention will be described below. For the base layer 115I3 in FIG. 1 or 2, the objective of the present invention can be sufficiently achieved with a film composition consisting of nitrogen and chromium, and the nitrogen content at this time is 20% or more in atomic ratio. , preferably 20% to 50%, more preferably 25% to 50%, especially 30 to 50%, in order to fully satisfy the chemical durability. It is sufficient if the nitrogen content is 50%, and nitrogen exceeding that content (i.e. content > 50%) does not participate in bonding with chromium atoms and its importance is not found in a two-element film. Crux composition
Expressed as follows, the nitrogen content of the base 18!3 has an X value of 0.
25-1. O2 preferably 0.33 to 1.0, especially x
It can be said that it is desirable that the value is between 0.42 and 1.0. Chrome light shielding formed on the base film!
For I2, the nitrogen content is 20% or more, preferably 20 to 50%, more preferably 25% to 50% based on the raw material ratio.
In particular, it is desirable that the content be between 30% and 50% in order to fully satisfy the chemical durability.
For a film in which 2 is composed of the three elements nitrogen, carbon, and chromium, the content of not only nitrogen but also carbon is important from the viewpoint of etching performance. The effect of the TR element is such that the etching rate decreases as its content increases, unless it causes a significant change in the structure of the resulting film. However, the etchant in this case is an aqueous solution in which ceric ammonium nitrate, perchloric acid, and pure water, which are usually used in wet etching, are mixed to a predetermined concentration. It has been found that there is an appropriate range for the carbon content in order to satisfy the etching characteristics (etching rate, side etching amount, etc.) of the mask material. That is, the amount of carbon contained in the film is 5 to 40%, preferably 5 to 30%, expressed in atomic ratio. Therefore, the composition ratio that satisfactorily achieves the object of the present invention is 0.25<X<0.25<X<0. i33, and o, os< y
<o, sotea4. However, the minimum values of 0.25 and 0.05 in the ranges of t, Maximum value, i.e. t, X =
o, ss, and Y=0.5, it is possible to form a film with excessive nitrogen or carbon content depending on the film forming conditions, but the particularly important point in terms of performance as a mask material is Since I couldn't find it, I wrote the following example: <X<0.93. Y<0.5
1For example, X −0, i95 or Y =
0.55 nat(7), t: Rani There is no strict restriction for those containing a slight excess amount. 1. Regarding the chromium light-shielding film 2, the chromium film containing carbon and nitrogen has been described. A similar effect can be obtained by introducing boron instead. That is, when the content of boron in the chromium light-shielding film is increased, the etching rate decreases and the chemical durability, especially the durability against strong acids, decreases, similar to the behavior of carbon. Therefore, it has been found that there is an appropriate composition range in which etching properties and chemical durability can be satisfactorily achieved by adding nitrogen in addition to boron.

In the chromium light shielding film 2 containing Or, B, and N, the nitrogen content is 20 to 50% in atomic ratio, preferably 25 to 50%.
In particular, the boron content is preferably 30 to 50%, and the boron content is preferably 1 to 25% in atomic ratio.

In the present invention, the thickness of the above-mentioned chromium light-shielding film is 500 to 150 mm from the viewpoint of light-shielding properties, etching properties, acid resistance, etc.
A range of about 0 people is preferable.

Further, the thickness of the base film is preferably in the range of about 50 Å to about 300 Å from the viewpoint of suppressing the amount of side etching as much as possible or selecting an appropriate etching time.

Note that the above-described chromium light-shielding film and base film may contain 10% or less of other components 1, such as oxygen.

The transparent substrate 1 may be a low-expansion glass such as borosilicate glass, aluminosilicate glass, soda lime silicate glass, quartz glass, or sapphire, which has high light transmittance and a smooth and flat surface. A substrate made of such materials is used. The plate thickness is usually about 11 to 5 mm.

A method for forming a chromium film as a nitrogen-containing base film or a light-shielding film in the present invention is to form a film by sputtering using a target made by mixing metallic chromium and chromium nitride powder and sintering the mixture. Alternatively, a typical example is a method of forming a film by reactive sputtering using a mixture of nitrogen gas and argon gas and a metal chromium target.

In addition, when forming a chromium light-shielding film containing nitrogen and carbon, sputtering is performed using a target made by mixing metallic chromium and chromium nitride powder with chromium carbide powder and sintering the mixture. Typical examples include a method of forming a film, or a method of forming a film by mixing nitrogen gas, methane gas, or carbon dioxide gas with argon gas and performing reactive sputtering using a metal chromium target.

In addition, when forming a chromium light-shielding film containing nitrogen and boron, powders of chromium boride, chromium nitride, chromium oxide, or chromium oxide may be added to powders of metallic chromium and chromium nitride. A method of forming a film by sputtering using a sintered target, or
It can also be formed by mixing diborane and methane gas with argon gas and performing reactive sputtering using a metal chromium target.

Note that the amount of nitrogen introduced into the chromium film, the amount of nitrogen and carbon introduced into the chromium film, or the amount of nitrogen and boron introduced into the chromium film described above depends on the target composition ratio, gas mixture ratio, and It can be adjusted by changing the amount of mixed gas introduced.

E Example J An embodiment of the present invention will be described below.

Example 1 Transparent glass substrate made of precisely polished low-expansion aluminosilicate (dimensions: 5 inch x 5 inch
A base film, a chromium light-shielding film containing nitrogen and carbon, and a low-reflection chromium film were sequentially formed on top of the photomask blank by reactive sputtering under the conditions shown in Table 1. Created. Film composition of the six films of the photomask blank of sample 1 created in this way, M thickness,
Acid resistance and adhesion were as shown in Table 1.

Example 2 Transparent glass substrate made of precisely polished low-expansion aluminosilicate (dimensions: 5 inch x 5 inch)
A base film, a chromium light-shielding film containing nitrogen and boron, and a low-reflection chromium film were sequentially formed on the (3-layer) by reactive sputtering under the conditions shown in Table 1, and a photomask blank was formed. Created. The film compositions of the six films of the photomask blank of Sample 2 created in this way, s, p
, acid resistance and adhesion properties are as shown in Table 1.

Example 3 Precisely polished quartz glass substrate (dimensions: 5 inch
(X 5 inch . The film composition, film thickness, acid resistance, and film adhesion of the six films of this photomask blank were as shown in Table 1.

Comparative Example Transparent glass substrate made of precisely polished low I & 1 tension aluminosilicate (dimensions: 5inch x 5i
A chromium light-shielding film containing nitrogen and carbon and a low-reflection chromium film were sequentially formed on a 3-m-thick film by a reactive sputtering method under the conditions shown in Table 1 to prepare a photomask blank. The film composition, film thickness, acid resistance, and film adhesion of the six films of the photomask blank of Sample 4 prepared in this manner are as shown in Table 1.

The etching rate for the 6th film mentioned above was 185g of ceric ammonium nitrate, which was over J! ! Basic acid (70%) 42 a
Add pure water to fL, make 1000 samples, and add etching solution (
This is the etching speed at 20°C).

In addition, in the above-mentioned embodiment, Ar, N
, 0, CH was used, but NOx gas was used as the N source,
CO2 gas or the like may be used as the C source, and the etching rate, film thickness, composition ratio, etc. can be freely controlled by appropriately changing the gas composition ratio, gas pressure, power, etc. in the table above. can.

[Effect] As described above, according to the present invention, a chromium light-shielding film containing nitrogen and carbon or nitrogen and boron is used as the light-shielding film, and a chromium thin film containing nitrogen is formed between the transparent substrate and the chromium light-shielding film. By interposing the base film, it was possible to obtain a photomask blank and a photomask having excellent optical properties, mechanical properties, and chemical durability. In particular, in the film structure of the 6th theory, the content of 1 nitrogen is 20 to 20 through each layer.
By adjusting the amount to 50%, it was possible to obtain a photomask blank and a photomask having particularly excellent chemical durability. Moreover, by adopting the above structure, it was possible to increase the adhesion force of the chromium light-shielding film to the glass substrate. In particular, conventionally, silica glass had a low adhesion force to a chromium light-shielding film, but according to the present invention, this adhesion force can be significantly increased. In addition, the photomask blank of the present invention can reduce the amount of chromium remaining during etching for patterning, and the final stage of etching is a base film made of a thin chromium film containing nitrogen, which has a high etching rate. At the same time, the etching speed of the earth's membrane becomes faster, and the end point of the etching can be easily determined.

[Brief explanation of the drawing]

1.2 is a schematic partial cross-sectional view of a photomask blank according to a specific example of the present invention, FIGS. 3 and 4 are schematic partial cross-sectional views of a photomask Ω according to a specific example of the present invention, and FIG. FIG. 6 is a schematic partial cross-sectional view of a mask blank, and FIG. 6 is a schematic partial cross-sectional view of a conventional photomask. 1.10; Transparent substrate, 2.20i chrome light shielding film. 3; Base M, 4.40; Photomask blank, 5.
50. Photomask, 6,80; Removal part of film,
7.70. Low reflective chrome film. Part 1, Figure 2, Figure 3. Figure 5 Figure 6

Claims (10)

[Claims] (1) A photosensitive material characterized in that a base film made of a thin chromium film containing nitrogen is formed on a transparent substrate, and a chromium light-shielding film containing nitrogen and carbon or nitrogen and boron is further provided closely thereon. mask blank. (2) The photomask blank according to claim 1, wherein the base film and the chromium light-shielding film each have a nitrogen content of 20% or more in atomic ratio. (3) Carbon in the chromium light-shielding film has an atomic ratio of 5% or more
The photomask blank according to claim 1, characterized in that it contains 30%. (4) The photomask blank according to claim 1, wherein the base film has a thickness of 50 Å to 300 Å. (5) The photomask blank according to claim 1, characterized in that a low-reflectivity chromium film containing nitrogen and oxygen is laminated on the chromium light-shielding film. (6) The base film of a photomask blank in which a base film consisting of a thin chromium film containing nitrogen is formed on a transparent substrate, and a chromium light-shielding film containing nitrogen and carbon or nitrogen and boron is provided closely thereon. A photomask characterized by patterning a chrome light-shielding film. (7) The photomask according to claim 6, wherein the base film and the chromium light-shielding film each have a nitrogen content of 20% or more in atomic ratio. (8) Carbon in the chromium light-shielding film has an atomic ratio of 5% or more
7. The photomask according to claim 6, wherein the photomask contains 30%. (9) The photomask according to claim 8, wherein the base film has a thickness of 50 Å to 300 Å. (10) The photomask according to claim 6, characterized in that a low-reflection chromium film containing nitrogen and oxygen is laminated on the chromium light-shielding film.