JPS6035819B2 - Method for manufacturing an X-ray exposure mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an X-ray exposure mask used in the X-ray exposure method, which is attracting attention as a high-precision transfer technique for fine patterns.

The X-ray exposure method is considered to be most effective when applied to the transfer process of extremely fine patterns including line widths of around 1 Am or less.
Therefore, the X-ray exposure mask used in the X-ray exposure method is required to have various conditions such as high contrast against soft x-rays, high flatness, low coefficient of thermal expansion, chemical resistance, and dimensional stability. Furthermore, transparency to visible light is also required for mask alignment. Silicon nitride film has characteristics such as high transparency to soft x-rays and visible light, low thermal bloat rate similar to Si, excellent chemical resistance, and low moisture absorption. It is suitable for use as a mask substrate material for exposure. For this reason, prototype X-ray exposure masks using a silicon nitride film as a supporting film for the transfer pattern have been manufactured, for example, as described in the book "Solid Stit Technology" written by Mr. Burrows et al. in 1978 (
E. Bag ssous pond SOLm STATETEC
HNOLOGY. September 1976).

These conventional typical X-ray exposure masks have a thickness of several 1
A silicon nitride pus with a thickness of 1000A to 2000A is formed on a silicon substrate with a thickness of 0.00 mm by a vapor phase growth method using a thermal decomposition reaction of a gas such as NH3/SiH4/N2, and a desired amount is deposited on the surface of the silicon nitride pus. This pattern is formed by forming a pattern using a heavy metal such as Au, and then selectively etching away a predetermined region of the silicon substrate to expose the surface of the silicon nitride film. However, in the above method, the silicon nitride film formed on the silicon substrate by the thermal decomposition reaction of NH3/SiH4/N2 gas is approximately 0.5
Because it has a very large tensile stress on the order of ×1 and 1.0 to 1 and 100 Hz/, it remains supported by the frame of the silicon substrate when the silicon substrate is selectively etched away. In many cases, the silicon nitrided pus was damaged by its own tensile stress. For this reason, attempts have been made to reduce the tensile stress of the silicon nitride film by appropriately selecting the flow rate ratio of the reaction gas system in the vapor phase growth method to increase the composition ratio of silicon in the silicon nitride film. However, even in this case, the tensile internal stress of the silicon nitride film formed on the silicon substrate can only be reduced to the extent of about 2 × 1 dynes/. Silicon grains tend to form in the film, making it difficult to form a silicon nitride film with a smooth surface. For this reason, the dimensions of the silicon nitride film that remains supported by the silicon frame are limited to a few elevation angles at most, making it difficult to put it into practical use as an X-ray exposure mask. On the other hand, in order to supplement the mechanical strength of the silicon nitride film, Si
02/Si3N4, SIC/Si8N4, Si02/S
i3N4/Si2, Si3N4/Si02/Si3N4
, etc. are also known in the past, using composite membranes having a two- or three-layer structure.

In the case of a composite film like the one mentioned above, the mechanical strength is certainly improved compared to the case of a single conventional silicon nitride film, but it has the disadvantage of requiring multiple manufacturing steps and low productivity. .
As mentioned above, the present invention is capable of producing silicon nitride by forming silicon nitridation, which was conventionally formed by a vapor phase growth method using high-temperature heating, under specific conditions using a plasma CVD method using RF plasma excitation. The present invention provides a method for manufacturing an X-ray exposure mask that improves mechanical strength, which is a drawback of X-ray exposure masks using nitride films, and has excellent productivity.

The internal stress of the silicon nitride film formed by the plasma CVD method varies depending on the flow rate of the reaction gas, the RF power, and the temperature of the deposition atmosphere, as shown in FIGS. 1 and 2, for example. In order to use a silicon nitride flag as an X-ray exposure mask substrate, it is necessary to have a tensile stress of about 1×1 dynes/ground to 1×1 dynes/ground, and SjA/NH3/N2 Plasma CVD conditions that satisfy this condition when using the above-mentioned gases fall within the range shown by diagonal lines in FIG. The present invention is the third
This embodiment is characterized in that a silicon nitride film formed under plasma CVD conditions indicated by diagonal lines in the figure is used as a mask substrate for X-ray exposure. Hereinafter, details of the present invention will be clarified by explaining the manufacture of an X-ray exposure mask according to an embodiment of the present invention. Each diagram from a to e in FIG. 4 shows the X-ray exposure mask manufacturing process according to an embodiment of the present invention.
FIG. 3 schematically shows a cross-sectional view of a line exposure mask.

First, as shown in FIG. 4a, on the surface of a silicon single crystal substrate 1 having a {100} plane and a thickness of about several hundred French meters, a film is deposited to a thickness of several hundred to several hundred meters by a normal thermal phase growth method. Silicon nitride pus 2 of approximately several thousand amperes is formed. Next, a resist is patterned on the surface of the silicon nitride film 2 using a normal optical exposure method, and a predetermined area of the silicon nitride film 2 is etched using the resist pattern as a protective film using a plasma etching method using CF4 gas or the like. The resist pattern is removed to form a pattern 2' formed of a portion of the silicon nitrided pus 2, as shown in Figure b.

During this etching process, the other surface of the silicon single crystal substrate is protected with a resist to prevent it from being etched. Next, the resist was removed and SiH4/NH diluted to a concentration of about 3% with Ar was applied to the exposed surface of the silicon single crystal substrate.
A nitride film 3 is deposited to a thickness of several thousand to lAm by RF plasma CVD using a 3/N2 gas mixture.

This state is shown in FIG. 4c. At this time Sj Fan;NH3;N
It is convenient to set the flow rate ratio of 2 to about 1:2:16 and the pressure inside the RF plasma discharge chamber to about ITord room temperature, but this need not be so limited. However, S
It has been found that three factors, the flow rate of i, the temperature of the silicon single crystal substrate 1, and the RF power, have a large effect. It is desirable that these conditions fall within the range shown by diagonal lines in FIG. The silicon nitride pus formed under these conditions is approximately 1×1 p~1×1
It has a tensile stress on the order of P. dynes/, which is about an order of magnitude smaller than the stress of silicon nitride pus formed by conventional vapor phase growth. As a result, the tensile strength has been significantly improved, and it has become possible to easily form a film with a large area of several skin angles, which was impossible to form with silicon nitride films formed by conventional vapor phase growth methods. Next, as shown in FIG. 4d, a desired transfer pattern 4 is formed on a predetermined area of the surface of the silicon nitride pus 3 using a technique such as a selective plating method or an IJ foot-off method. It is formed of heavy metals such as Au, Pt, and W with a film thickness of .

Finally, while protecting the metal pattern 4 with an arbitrary jig using an O-ring or the like, a predetermined region of the Si single crystal substrate 1 is heated, for example, using the silicon nitride pus 2 as a protective film. The silicon nitride pus 3 is etched away using an aqueous solution of potassium hydroxide or the like until the surface thereof is exposed, and a reinforcing support beam 1' shaped like a window frame is formed to form an X-ray exposure mask as shown in FIG. 4e. Complete.

[Brief explanation of the drawing]

FIGS. 1 and 2 show the relationship between the stress of a silicon nitride film formed by plasma CVD, RF output, and Si gas flow rate, respectively. FIG. 3 shows the range of plasma CVD conditions for a silicon nitride film in the manufacturing process of an X-ray exposure mask according to the present invention. Each figure from a to e in FIG. 4 is a schematic cross-sectional view of an X-ray exposure mask showing the manufacturing process according to an embodiment of the method of manufacturing an X-ray exposure mask according to the present invention. be. In the figure, each symbol indicates the following. 1...Silicon single crystal substrate, 2...Silicon nitride layer, 2'...Etching protective film formed from a part of silicon nitride pus 2, 3...Silicon nitride film ,
4...Transfer pattern, 1'...Reinforcement support beam formed from a part of the silicon single crystal substrate 1. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. Depositing a silicon nitride layer on one surface of the silicon single crystal substrate by CVD or plasma CVD, etching the silicon nitride layer into a desired shape, and etching the other surface of the silicon single crystal substrate. The SiH_4 flow rate is 2SCCM to 8SCCM, the substrate temperature is 150℃ to 350℃, and the RF
Depositing a second silicon nitride layer at a power output of 0.2 W/cm^2 to 0.8 W/cm^2, and applying both X-rays and visible light onto the second silicon nitride layer. a step of forming and arranging a layer that absorbs water into a desired pattern; and using the first silicon nitride layer patterned by etching into a predetermined shape in the step as a protective film to form a part of the silicon single crystal substrate. A method for manufacturing an X-ray exposure mask, comprising the step of: exposing the second silicon nitride layer by etching and removing the second silicon nitride layer.