JPH04342113A - Manufacture of x-ray mask; x-ray mask - Google Patents

Abstract

PURPOSE:To simplify a process by a method wherein the shape of an X-ray transmitting window is worked with high accuracy and the number of replacement operations of an etchant is reduced to one CONSTITUTION:An X-ray transmitting thin film 3 is formed on one face of a silicon substrate 1; an X-ray absorbing pattern 6 is formed on the X-ray transmitting thin film 3 on a side opposite to the silicon substrate 1; the silicon substrate 1 in parts, including an X-ray exposure region, in which the X-ray absorbing pattern 6 has been formed is etched and removed. Thereby, an X-ray transmitting window including the X-ray exposure region is formed. At this time, a protective film 2 with which a part other than the X-ray exposure region is covered is formed on a face opposite to the X-ray transmitting thin film 3 on the silicon substrate 1; the part, of the silicon substrate 1, which is not covered with the protective film 2 is removed [Fig. (e)] down to a halfway depth by an anisotropic etching operation; after that, its remaining depth part is removed [Fig. (f)] by an isotropic etching operation; the X-ray transmitting window including the X-ray exposure region is formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an X-ray mask used in an X-ray exposure apparatus to transfer a fine pattern of a VLSI or the like with high precision, and an X-ray mask manufactured by the method.

0002

2. Description of the Related Art The X-ray exposure method is known as a technique capable of transferring fine patterns of submicron size or less by using soft X-rays with a wavelength of 0.4 to 5 nm. Conventionally,
As a method for manufacturing an X-ray mask using a carbon film as an X-ray transparent thin film, for example, Windischmann [He
nry Windischmann, “A75mm
diamond x-ray
membrane”, Proceedings
of SPIE 1263, 241 (1990)]
reported that a carbon film is formed on a silicon substrate, and a mixed solution of hydrofluoric acid, nitric acid, and acetic acid (HF:HNO3 :CH3 COOH=
2:2:1), a portion of the silicon substrate was removed to form an opening, thereby forming an X-ray transparent window including the X-ray exposure area.

[0003] By the way, anisotropic wet etching of silicon substrates using an alkaline solution enables high-precision processing and causes less liquid fatigue during etching. , compared to isotropic wet etching using a mixed solution of nitric acid and acetic acid.
Although it has the advantage of being simple, carbon films have poor alkali resistance, so anisotropic wet etching of silicon substrates using an alkaline solution has not been employed in the past.

0004

However, in the above-mentioned isotropic wet etching, etching progresses not only in the depth direction of the silicon substrate but also in its lateral direction, resulting in poor dimensional processing accuracy of the opening and Not only is it not possible to form an X-ray transmitting window with the desired size and shape with high precision, but the above-mentioned etching solution deteriorates quickly, so it is necessary to replace the solution several times during etching, which is inconvenient.

[0005] The present invention was made in view of the above situation, and its purpose is to improve the processing precision of the X-ray transmitting window shape and to facilitate the exchange of etching liquids through two-stage etching treatment using different types of etching liquids. An object of the present invention is to provide an X-ray mask manufacturing method that can simplify the process by reducing the number of times to one, and an X-ray mask manufactured by the method.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing an X-ray mask of the present invention includes anisotropic etching using an alkaline solution in a wet etching process for forming an X-ray transparent window. The method is characterized in that two-stage etching is performed as a first stage, followed by isotropic etching using a mixed solution of hydrofluoric acid, nitric acid, and acetic acid as a second stage.

That is, the method for manufacturing an X-ray mask of the present invention involves forming an X-ray transparent thin film on one side of a silicon substrate;
An X-ray absorbing pattern is formed on the X-ray transparent thin film surface opposite to the silicon substrate, and the X-ray absorbing pattern is formed and
In a method for manufacturing an X-ray mask, in which an X-ray transparent window including an X-ray exposure area is formed by etching away a portion of the silicon substrate including the radiation exposure area, the surface of the silicon substrate opposite to the X-ray transparent thin film; A protective film is formed on top to cover most of the area other than the X-ray exposure area, and after removing the silicon substrate portion not covered by the protective film to a midway depth by anisotropic etching, the remaining portion is removed by isotropic etching. This method is characterized in that a deep portion is removed to form an X-ray transparent window that includes an X-ray exposure area.

In this case, it is desirable to use a carbon film as the X-ray transparent thin film. Note that the present invention includes an X-ray mask manufactured by such a manufacturing method.

[0009]

[Operation] In the method for manufacturing an X-ray mask of the present invention,
In the process of forming a line-transmitting window, first, most of the thickness of the silicon substrate is removed by anisotropic etching using an alkaline solution, etc., and then the remaining thickness of the silicon substrate is removed using hydrofluoric acid, nitric acid, and acetic acid. Since removal is performed by isotropic etching using a mixed solution or the like, most of the X-ray transmitting window formed on the silicon substrate is formed by anisotropic etching, and its size and shape are highly accurate. In addition, the etching solution only needs to be replaced once, from an anisotropic etching solution such as an alkaline solution to an isotropic etching solution such as a hydrofluoric acid mixed solution, reducing the number of steps. .

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the method of manufacturing an X-ray mask of the present invention will be described below with reference to the drawings. Figures 1(a)-(g
) is a schematic cross-sectional view showing the manufacturing process of one embodiment of the method for manufacturing an X-ray mask according to the present invention.

[0011] First, mirror-polished thickness 0.3 to 6.4
A protective film of S with a thickness of 0.4 to 4 μm is coated on the entire surface of one side of a silicon substrate 1 with a thickness of 0.4 to 4 μm by CVD or sputtering.
Form an iN film. Next, a photoresist is coated on this SiN film, and a resist pattern is formed by normal photolithography to leave a protective film in areas other than the X-ray transparent window, and then dry etching is performed using a gas such as CF4. The protective film 2 is formed by etching away the SiN film portion corresponding to the X-ray transmission window, and then removing the remaining resist pattern by plasma etching using oxygen gas. It goes without saying that this protective film 2 may be formed after the formation of the X-ray transparent thin film 3 in the next step.

Next, as disclosed in the document by Windischmann mentioned in the explanation of the prior art, an X-ray transparent thin film was formed by microwave plasma CVD using a mixed gas of methane and hydrogen. , thickness 0.8-40μm
, tensile stress 5 x 108 ~ 2.2 x 109 dyn
As shown in FIG. 1(a), a carbon film 3 having a thickness of /cm2 is formed on the entire surface of the silicon substrate 1 opposite to the surface to which the protective film 2 is attached.

Next, as shown in FIG. 1(b), a 0.2 to 1 μm thick X film made of tantalum, tungsten, or an alloy mainly composed of these is deposited on the carbon film 3 by sputtering or CVD. A line-absorbing material layer 4 is formed.

Next, as shown in FIG. 1(c), a desired resist pattern 5 is formed by a conventional electron beam exposure method or the like. Next, using the resist pattern 5 as a mask, CF4
After etching the X-ray absorbing material layer 4 to form the X-ray absorbing pattern 6 by reactive ion etching using a gas such as , Cl2 + O2, etc., the remaining resist pattern 5 is subjected to plasma etching using oxygen gas. is removed to form an X-ray absorbing pattern 6 as shown in FIG. 1(d).

Next, the portion of the silicon substrate 1 that is not protected by the protective film 2 is removed from the back side by anisotropic wet etching using an alkaline solution to remove most of the total thickness of the silicon substrate, as shown in FIG. 1(e). ), it is possible to form a silicon substrate 7 having a high-precision window with a desired trapezoidal cross section. During this etching, in order to protect the carbon film 3 and the X-ray absorbing pattern 6, a jig consisting of an O-ring or the like is used, and the etching solution is
By using an aqueous solution of 0 to 40% KOH, NaOH, etc., good high-precision etching is possible.

Next, a mixed solution of hydrofluoric acid, nitric acid and acetic acid (HF:HNO3:CH3COOH=1:2~
3:1) as an etching solution, the remaining silicon substrate thickness is removed, and the final X-ray including the X-ray exposed area as shown in Figure 1(f) is A transmission window and a silicon frame 8 are formed. Since the thickness removed by this etching is extremely small, the highly precise shape of the window formed by the first stage anisotropic etching is hardly deformed and remains highly precise.

Finally, as shown in FIG. 1(g), the protective film 2 is bonded to a reinforcing frame 10 made of borosilicate glass or the like with a thickness of 2 to 10 mm via an epoxy adhesive layer 9. The X-ray mask is completed.

[0018]

As is clear from the above description, according to the method for manufacturing an X-ray mask of the present invention, in the step of forming an X-ray transmitting window, most of the thickness of the silicon substrate is first removed using an alkaline solution or the like. Then, the remaining silicon substrate thickness is removed by isotropic etching using a mixed solution of hydrofluoric acid, nitric acid, and acetic acid.
Most of the X-ray transmitting windows formed in the silicon substrate are formed by anisotropic etching, and their dimensions and shapes are highly accurate. In addition, when replacing the etching solution,
It is only necessary to switch from an anisotropic etching solution such as an alkaline solution to an isotropic etching solution such as a hydrofluoric acid mixed solution once, and the number of steps can be shortened.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the steps of one embodiment of the method for manufacturing an X-ray mask according to the present invention.

[Explanation of symbols]

1...Silicon substrate 2...Protective film 3...X-ray transparent thin film (carbon film) 4...X-ray absorbing material layer 5...Resist pattern 6...X-ray absorption pattern 7...Silicon substrate with window 8...Silicone frame 9...Adhesive layer 10...Reinforcement frame

Claims (3)

[Claims] Claim 1: An X-ray transparent thin film is formed on one side of a silicon substrate, an X-ray absorbing pattern is formed on the side of the X-ray transparent thin film opposite to the silicon substrate, and the X-ray absorbing pattern is formed. In the method for manufacturing an X-ray mask, the side of the silicon substrate opposite to the X-ray transparent thin film is formed by etching away a portion of the silicon substrate that includes the X-ray exposure area to form an X-ray transparent window that includes the X-ray exposure area. A protective film is formed on the surface of the silicon substrate that covers most of the area other than the X-ray exposed area, and the portion of the silicon substrate that is not covered by the protective film is removed to an intermediate depth by anisotropic etching. A method for manufacturing an X-ray mask, the method comprising: removing the remaining depth to form an X-ray transmission window including an X-ray exposure area. 2. The method of manufacturing an X-ray mask according to claim 1, wherein the X-ray transparent thin film is a carbon film. 3. An X-ray mask manufactured by the manufacturing method according to claim 1 or 2.