JPH01173618A - Method for forming mask membrane for x-ray lithography - Google Patents

Abstract

PURPOSE:To avoid any defects such as pin holes and increase the resistance against a silicon corrosive agent, by forming such a film as to avoid reflection of visible rays and to obtain protection from a silicon corrosive agent on both sides of a heat-treated polycrystalline silicon film. CONSTITUTION:On both sides of a heat-treated polycrystalline silicon film 3, nitride silicon films 1a-1c or carbide silicon films are formed which serves as a film to avoid reflection of visible rays and also serves as a protective film having a high resistance against a silicon corrosive agent. This protective film avoids reflection of visible rays and improve the transmission factor to visible rays. Since the protection film itself has a tension stress, it reduces the stress of a membrane together with the compression stress of the plycrystalline silicon film. By this method, a good membrane that has a high resistance against a silicon corrosive agent and has few pin holes is gained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a lithography technique in semiconductor manufacturing technology, and particularly to an improvement in a method for forming a mask membrane for X-ray lithography using X-rays.

<Prior art> 64 Mb with a pattern with a minimum line width of 174/'m
X-ray lithography is considered the most promising lithography technology for mass-producing DRAM-class LSIs. In X-ray lithography, since there is no X-ray lens, the mask pattern y is projected onto the wafer at i:i using the proximity method. At this time, visible light is used to align the mask and the sea urchin, so the membrane needs to be transparent to visible light. In addition, in order to maintain the flatness and strength of the membrane, it is necessary to have a low tensile stress on the order of 10" dyn/am2.

FIG. 2 is a sectional view showing the structure of a conventional mask membrane for X-ray lithography. In FIG. 2, reference numeral 11 denotes an X-ray transparent membrane, and this X-ray transparent membrane 11 is held by an outer frame 12. Specifically, the membrane 11 is made of single crystal silicon (Si), hydrogenated silicon nitride (S
iNH), boron hydrogenated nitride (BNH), and polyimide. These light elements do not absorb X-rays, and the membrane 11 has a thin film thickness of approximately 2 μm, so the transmittance of the membrane to X-rays is sufficiently high.

<Problems to be Solved by the Invention> Since the X-ray transparent film is exposed to radiation every time it is exposed to X-rays, its radiation resistance becomes a problem. In this respect, silicon hydronitride (SiNH), boron hydronitride (BNH), polyimide, etc. are unsuitable. For example, in a hydrogenated boron nitride film, IK
It is known that irradiation with soft X-rays of about J/cm' causes desorption of hydrogen, which reduces the visible light transmittance and changes the internal stress to the compressive stress side.

Single crystal silicon (Si) has high radiation resistance, but requires a special mask manufacturing process. That is, when the substrate silicon in a predetermined region is dissolved from the back side using a corrosive solution to form a membrane in the mask manufacturing process, it is necessary to add boron (B) to make the membrane part corrosion resistant. On the other hand, when boron is added, internal stress becomes tensile stress, and in order to alleviate this, it is necessary to add germanium (Ge) and apply compressive stress to control the stress. Therefore, the formation of the boron- and germanium-doped single-crystal silicon described above requires a dedicated CVD apparatus and also requires precise control of the epitaxy process.

In view of the above points, the present inventors first decided on December 1, 1988.
Patent application dated 8th “Mask membrane for X-ray lithography”
We have proposed a membrane with a novel structure using a polycrystalline silicon film as an X-ray transparent film.

When polycrystalline silicon is used as an X-ray transmitting film as previously proposed by the inventor, there are problems with visible light reflection, stress control, and resistance to silicon corrosive agents. By forming a silicon carbide film, reflection of visible light can be prevented and visible light transmittance can be increased. Furthermore, since the polycrystalline silicon film has compressive stress and the stress can be easily controlled by heat treatment, it is possible to provide the membrane with a weak tensile stress with good controllability, in combination with the tensile stress of a silicon nitride film or the like.

However, if a heat treatment is applied to control stress after forming a protective film resistant to silicon corrosive agents, such as a silicon nitride film, on both the front and back surfaces of a polycrystalline silicon film, many pinholes will occur in the protective film, resulting in silicon corrosion. It was later discovered that the problem was that the agent penetrated and created holes in the polycrystalline silicon membrane.

The present invention has been devised in view of the above points, and eliminates the above-mentioned conventional problems. It uses relatively versatile equipment, has high radiation resistance, and transmits visible light with low stress. An object of the present invention is to provide a method for producing a mask membrane for X-ray lithography that is highly resistant to silicon corrosive agents.

Means and Effects for Solving the Problems with Problems> In order to achieve the above object, the present invention provides an X-ray transmissive membrane having a high transmittance to X-rays, and a membrane that uses this X-ray transmissive membrane. A method for forming a mask membrane for X-ray lithography, which includes a support frame for holding the film, includes the step of forming a polycrystalline silicon film as the A process of heat-treating the polycrystalline silicon film, and then providing protection that provides an anti-reflection film against visible light on both the front and back sides of the heat-treated polycrystalline silicon film and has high resistance to silicon corrosive agents. The protective film is formed of either a silicon nitride film or a silicon carbide film.

That is, in the present invention, a polycrystalline silicon film is used when forming an X-ray transparent film, and after the compressive stress of the polycrystalline silicon film is relieved by heat treatment, a silicon nitride film is formed on the surface of the polycrystalline silicon film. Alternatively, by forming a protective film such as a silicon carbide film, it is possible to prevent pinholes from forming in the protective film due to deterioration of polycrystalline silicon due to heat treatment.

In addition, this protective film prevents reflection of visible light and increases visible light transmittance, and since it itself has tensile stress, it reduces the stress of the membrane in combination with the compressive stress of polycrystalline silicon.

In addition, it is possible to provide a high resistance to silicon corrosive agents and obtain a good membrane with few pinholes.

<Example> Hereinafter, as an example of the present invention, a method for forming a mask membrane for X-ray lithography in which silicon nitride is formed on both the front and back surfaces of polycrystalline silicon will be described with reference to the drawings.

FIG. 3 shows that by the method of forming a membrane according to the present invention,
This is a graph showing the theoretical values of film thickness and reflectance at the wavelength of helium-neon laser (633 nm) when silicon nitride films of the same thickness are formed on both the front and back surfaces of polycrystalline silicon with a film thickness of 1 fim using a low pressure CVD method. . As you can see from this @3 figure, 750
The reflectance is the lowest when a silicon nitride film is formed, making it suitable for positioning the master sea urchin.

Next, the manufacturing process of the mask membrane for X-ray lithography according to the present invention will be explained according to FIGS. 1(a) to 1(d).

First, referring to Figure 1 (a),
A silicon nitride film (S i3N< ) with a film thickness of 750^ is deposited on both sides of the silicon substrate 2, which serves as a support body, by low pressure CVD method.
1a and 1b are formed.

Next, referring to FIG. 1Cb), a polycrystalline silicon film 3 having a thickness of about 1 mm is formed on one silicon nitride film lc located on the surface side of the silicon substrate 2 by a low pressure CVD method.
Heat treatment at 0° C. for 60 minutes relieves the compressive stress of polycrystalline silicon. This polycrystalline silicon film 3 becomes an X-ray transparent film in a mask for X-ray lithography.

Next, referring to FIG. 1(c), a silicon nitride film (Si3
N4) form lc. This is the addition of the film loss when the substrate silicon is dissolved in a sodium hydroxide aqueous solution in the post-process, and the film thickness of the silicon nitride film (Si3N4) lc on the polycrystalline silicon film 3 after all processes is 750X.
becomes.

Next, referring to FIG. 1(d), the other silicon nitride film (S13N4) 1b formed on the back side of the silicon substrate 2.
by reactive ion etching to remove a predetermined area of the
Furthermore, the silicon substrate 2 is dissolved in a 25% hydroxide solution at 80°C. In this way, window 4 is formed,
Complete the X-ray mask membrane.

For comparison, a membrane manufactured using the above-mentioned formation method without performing any heat treatment had a shadow of polycrystalline silicon.
The average of the three layers has a compressive stress of about 2 x 10'dyn/cm', but the membrane formed by heat treatment according to the present invention has a tensile stress of about 2 x 10''dyn/an', which is This value is sufficient for a mask membrane for X-ray lithography.

In addition, silicon nitride (Si sNa) is added to the polycrystalline silicon upper layer.
) When heat treatment was applied to control stress after the film was deposited, a large number of pinholes were generated and the formation of a 10 mm square mask was the limit, whereas when formed using the method of the present invention, Almost no pinholes were observed, and 2
A 0 mm square mask membrane could be easily formed.

Using the mask membrane for X-ray lithography manufactured as described above, an accelerated X-ray resistance test was conducted using an electron beam. Irradiation conditions are current density 3.571m/am
2. The electron energy was 10 KeV and the temperature was kept below 100°C. As shown in Figure 4, hydrogenated silicon nitride (Si
NH) has a stress of 2.7x10 at I M J /cm'
``dyn/cm2'', whereas in polycrystalline silicon the stress changes by 100MJ/am' (even with D irradiation, the stress hardly changes.If the sensitivity of the resist used for X-ray exposure is 100 mJ/cm2, IMJ/cm2) cm'
corresponds to the amount of X-rays absorbed by the membrane through approximately 10' exposures, so the conventional membrane
In contrast, in the polycrystalline silicon membrane according to the present invention, pattern position distortion due to stress changes in the membrane does not occur even after 10' or more X-ray exposures, whereas stress changes occur and pattern position distortion occurs after multiple exposures.

In addition, the wavelength of helium neon gas laser (633 nm)
The transmittance of the membrane prepared according to this example was 55.
%, and this value is sufficient for alignment between wafer masks.

In this example, 5is was used as a corrosion-resistant antireflection film.
Although N4 was used, a silicon carbide film (Si
C) can also be used.

<Effects of the Invention> As described above, in the present invention, by using polycrystalline silicon, which is conventionally used in semiconductor processes, as a membrane material, it is possible to easily create an X-ray lithography mask with high X-ray resistance using highly versatile equipment. Membranes can be made. Furthermore, by forming a protective film such as a silicon nitride film or a silicon carbide film on both the front and back surfaces of polycrystalline silicon, reflection of visible light can be prevented and a membrane with low stress can be manufactured.

Furthermore, after forming polycrystalline silicon, heat treatment is performed to relieve stress and then a protective film such as a silicon nitride film or silicon carbide film is formed on the surface of polycrystalline silicon to prevent defects such as sibin holes. A good protective film with high resistance to corrosive agents can be formed.

As is clear from the above, this invention is indispensable in the development and production of X-ray masks, and has a great indirect effect on society through the practical application of X-ray lithography. Its industrial value is extremely high.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(d) are process diagrams for explaining a method of forming a mask membrane for lithography as an embodiment of the present invention, and FIG. 1(a) is a sectional view showing a conventional mask membrane for X-ray lithography. , FIG. 3 is a diagram showing the relationship between the film thickness of the silicon nitride film on both the front and back surfaces and the reflectance at a wavelength of 633 nm in the membrane according to the present invention, and FIG. 4 is a diagram showing the relationship between the electron beam irradiation amount and stress change. It is a diagram. 1 a, l be 1 c=silicon nitride film, 2...
Silicon substrate, 3... Polycrystalline silicon film, 4
···window. Agent Patent attorney Hiroshi Sugiyama (and 1 other person) $1 Figure 2

Claims (1)

[Claims] 1. An X-ray transparent membrane having high transmittance to X-rays and the X-ray
A method for forming a mask membrane for X-ray lithography equipped with a support frame for holding a radiation-transparent film, comprising the steps of forming a polycrystalline silicon film as the X-ray transmission film; A step of heat-treating the polycrystalline silicon film, and then forming a protective film on both the front and back surfaces of the heat-treated polycrystalline silicon film that serves as an anti-reflection film against visible light and has high resistance to silicon corrosive agents. A method for forming a mask membrane for X-ray lithography, comprising the steps of: 2. The method for forming a mask membrane for X-ray lithography according to claim 1, wherein the protective film is made of either a silicon nitride film or a silicon carbide film.