JPS63291425A - Etching - Google Patents

Abstract

PURPOSE:To facilitate etching the rear surface of an X-ray mask supporter without influence upon the X-ray mask part by a method wherein, after a silicon nitride film is formed on a silicon substrate, a predetermined part is dripped in pottasium hydroxide solution doped with silicon powder to each the silicon film and the silicon substrate of the predetermined part. CONSTITUTION:After an X-ray mask part is formed on the surface of an Si wafer 1, which is an x-ray mask supporter, an SiN film 2a is built up on the upper layer as a protective film and an SiN film 2b is built up on the rear surface of the silicon wafer 1. Then a cylinder 6 made of material which is not corroded by KOH solution is placed at the center of the Si wafer 1 and the cylinder 6 is filled with KOH solution 7, to which silicon powder 8 is added. By this process, the region of the SiN film 2 in the cylinder is etched. Then the whole wafer is dipped in KOH solution to obtain an X-ray mask.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an etching method used in the manufacture of X-ray masks.

BACKGROUND OF THE INVENTION With the increasing density of semiconductor devices and the miniaturization of patterns, it is desired to establish submicron pattern exposure technology. With conventionally used light exposure, it is difficult to form submicron patterns due to the influence of diffraction. Therefore,
Exposure techniques using electron beams, ion beams, and X-rays are attracting attention.

Among these, electron beam and ion beam exposure have low productivity, but X-ray exposure is practical because it allows batch exposure. In X-ray exposure, manufacturing an X-ray mask is important.

2(a) to 2(d), an X-ray mask will be explained in the order of manufacturing steps based on a conventional example. As shown in Figure 2(a),
After forming the X-ray transmitting body 9 on the X-ray mask support Si wafer 1, forming the X-ray absorbing body pattern 10 thereon,
Create a mask part. As shown in FIG. 2(b), after forming a mask protective film 11 on the upper layer, a silicon nitride film 2 is formed on the back surface of the X-ray mask support Si wafer 1, and a resist 12 is applied on the upper layer. After exposure and development, a predetermined portion is opened and the silicon nitride film 2 directly under the resist opening is dry etched, thereby transferring the resist opening to the silicon nitride film as shown in FIG. 2(C). Also,
No. 211 (C) can be similarly obtained by masking a predetermined portion and forming a film.

Next, using this silicon nitride film 2 as a mask, the X-ray support Si wafer 1 is wet-etched with an aqueous potassium hydroxide solution, leaving an outer peripheral frame to obtain an X-ray mask as shown in FIG. 2(d). .

Problems to be Solved by the Invention When manufacturing an X-ray mask, a problem is the film stress of the X-ray transmitting body and X-ray absorbing body. Therefore, it is necessary to strictly control stress. Even if a film is formed under film formation conditions for optimizing film stress, the stress changes depending on the steps after film formation, so it is desirable to reduce the number of steps after film formation.

In the conventional example, when etching the back surface of an X-ray mask support Si wafer, a silicon nitride film is formed on the back surface of the X-ray mask support Si wafer, and then a resist is applied.
A predetermined portion is opened by exposure and development, and the silicon nitride film directly under the opening is dry etched, and Si is etched using the silicon nitride film as a mask. Therefore, the process is complicated even after the mask portion is formed on the surface of the X-ray mask support, and the resist must be baked, so it is necessary to carefully examine the effect of heat treatment on the formed film. Furthermore, when a silicon nitride film is formed in a desired area by masking, there is a problem in that the film wraps around and forms in areas other than the desired area, resulting in poor etching shape in subsequent Si etching. .

Means for Solving the Problem In order to solve this problem, the present invention provides a method for etching only a predetermined portion of the silicon nitride film using hydroxide with silicon powder added when etching the back surface of the Si wafer that is the X-ray mask support. After the silicon nitride film is etched by immersing it in a potassium aqueous solution, Si is etched using the silicon nitride film as a mask.

Function: By using the present invention, after forming an X-ray mask portion on the surface of a Si X-ray mask support wafer, it becomes possible to etch the back surface of the Si X-ray mask support in a very simple process.

Embodiment FIGS. 1A to 1A are cross-sectional views in the order of steps for explaining an embodiment of the method for manufacturing an X-ray mask according to the present invention.
The present invention will be explained with reference to this drawing.

As shown in FIG. 1(a), an X-ray transmitting material, for example, a silicon nitride film (SiN film) 2 is deposited to a thickness of 1.5 um on a 3-inch Si wafer 1 by plasma CVD. Here, the SiN film 2 was formed using 95%N215%SiH4 gas as a reaction gas at a gas flow rate of 250cc/min and a substrate temperature of 3.
Deposition was carried out for 25 minutes under the conditions of 00° C. and 200 W of high frequency power. A tungsten film (W film) 3 is deposited on top of this by sputtering to a thickness of 0.6 μm. The sputtering conditions at this time are: argon (Ar) is used as the discharge gas, the discharge gas pressure is 3 QmTorr, and the high frequency amount cuff is 00W.

Next, as shown in FIG. 1(b), a dry etching-resistant electron beam resist 4, such as chloromethylated polystyrene, is applied to a thickness of 0.5 um on the tungsten film 3.
After prebaking at 120°C for 25 minutes, a pattern was drawn using an electron beam 5 and developed for 1 minute with a developer containing isoamyl acetate: ethyl cellosolve = 1:4, as shown in Figure 1 (C). A desired resist pattern is formed. Next, using this resist pattern as a mask, the tungsten film 3 is etched by reactive ion etching.
By etching for a minute, a tungsten pattern as shown in FIG. 1(d) is obtained. The etching conditions at this time were: sulfur hexafluoride (SFs)/carbon tetrachloride (CCe4) was used as the reaction gas, gas flow rate was 10 cc/min, gas pressure was 1 QmTorr, and high frequency power was 100 W. According to the etching process under these conditions, the etching rates of the tungsten film 3 and the electron beam resist 4 are 600 A/min and 500 A/min, respectively.

Thereafter, as shown in FIG. 1(e), a 1 μm thick SiN film 2a is deposited as a protective film on top of the silicon wafer 1.
A SiN film 2b is deposited to a thickness of 0.3 pm on the back surface of the substrate. Here, the SiN films 2a and 2b were manufactured by the same method as the SiN film 2. Next, as shown in FIG. 1(f), the Si wafer 1
A cylinder 6 made of a material that is not attacked by potassium hydroxide (KOH) and having an inner diameter of 30 mm is erected in the center and filled with a KOH aqueous solution 7, into which silicon powder 8 having a particle size of 1 mm or less is added. SiN film 2 in a cylinder area with a diameter of 30w11 in 30 minutes
is easily etched, resulting in the result shown in FIG. 1(g).

SiN films are inherently etching resistant to KOH aqueous solutions, but by adding fine Si powder, KOH
It is thought that the etching rate of the SiN film increases due to the reaction between the silicon powder and Si. Note that the silicon powder preferably has a particle size of 1w11 or less in order to promote reactivity.

Next, by immersing the entire wafer in a KOH aqueous solution, an X-ray mask as shown in FIG. 1(h) is obtained.

Effects of the Invention As detailed above, by using the present invention, after forming the X-ray mask portion, when etching the back surface of the X-ray mask support Si wafer, the silicon nitride film mask can be removed through the resist process and dry etching process. It can be formed in a very simple way without using any
Etching of the back side of the X-ray mask support becomes possible.

[Brief explanation of the drawing]

Figures 1(a) to 1(a) are cross-sectional views of an X-ray mask manufactured by the manufacturing method of the present invention in the order of steps, and Figures 2(a) to (d) are cross-sectional views of the X-ray mask manufactured by the conventional manufacturing method in the order of steps. Yes. 1...Si wafer, 2.2a, 2b...
・SiN film, 3...W film, 4...electron beam resist, 5...electron beam, 6...
・Cylinder, 7...KOH aqueous solution, 8...
Si powder, 9... X-ray transparent material, 10...
・X-ray absorber pattern, 11... Protective film, 12
・・・・・・Resist. Name of agent: Patent attorney Toshio Nakao 1 person 3 ---
Z no Haskyo 1

Claims (1)

[Claims] An etching method in which, after a silicon nitride film is formed on a silicon substrate, a predetermined portion is immersed in an aqueous potassium hydroxide solution containing silicon powder, and the predetermined portion of the silicon nitride film and the silicon substrate are etched.