JPH09186067A - Transmission mask for charged beam gang exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission mask wherein the number of forming processes is small, influence due to thermal distortion is little, and transfer precision by a charged beam is high. SOLUTION: This transmission mask is formed by using a laminated substrate composed of an upper Si substrate 1a, a lower substrate 2a holding the upper substrate 1a, and a silicon dioxide film 3a as an adhesive layer. The face orientation of the main surface of the upper Si substrate 1a is constituted of a <111> face. The face orientation of the main surface of the lower Si substrate 2a is constituted of a <100> face. In this case, the thickness of the silicon dioxide film 3a as the adhesive layer of the upper Si layer 1a and the lower Si layer 2a is set in the range from 200Å to 1000Å.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission mask for collective exposure of a charged beam (hereinafter referred to as a transmission mask), and more specifically, it can be manufactured by a smaller number of steps than before, and is less affected by thermal strain. The present invention relates to a transmission mask with high transfer accuracy by a beam.

[0002]

2. Description of the Related Art In order to explain the structure of a conventional transmission mask, a typical manufacturing process of a conventional transmission mask will be described with reference to FIG. First, a lower silicon (hereinafter referred to as Si) substrate 12 on which a silicon dioxide film 13 is formed by thermal oxidation and an upper Si substrate 11 are bonded by thermal bonding to prepare a substrate (see FIG. 3A). A bonded substrate having such a thermally oxidized silicon dioxide film 13 as an adhesive layer is generally S.
It is called an OI (Siliconon insulator) substrate and is generally used as a substrate for producing sensors. (For example, Makoto Ishida, Rie Yi Tai: Applied Physics 7, p. 700 (1995)). When used as a transmission mask, the lower Si substrate usually has a thickness of about 500 μm,
The thickness of the upper Si substrate is about 20 μm.

Next, the upper Si substrate 11 is etched by dry etching or the like using a resist pattern consisting of a single layer or multiple layers as a mask, and then the resist pattern is peeled off to produce a patterned upper Si substrate 11a, which is charged beam transparent. The holes 19 are formed (see FIG. 3B).
Note that it is difficult to etch Si to a depth of 20 μm with a single-layer resist, and when using a multi-layer resist method, it is desirable that the material of the lower layer be a conductive film that does not peel off after completion of the transmission mask. . Next, a silicon dioxide film 16 having the same thickness as the silicon dioxide film 13 serving as the adhesive layer is formed on the back surface of the bonded Si substrate, that is, on the lower Si substrate 12 side. The reason for this is that the deposition of the back-etching protective film 15 in the next step is usually a high-temperature thermal step, so that the internal stress change of the silicon dioxide film 13 causes the entire substrate to warp.
Therefore, a film of the same type as the adhesive layer is also attached to the back surface so as to reduce the warp.

Next, a back etching protective film 15 for depositing an opening 18 in a later step (hereinafter, this step is referred to as back etching) is deposited on the back surface side and the front surface side of the bonded Si substrate (FIG. 3). (See (c)). The reason for depositing on the surface side here is that the entire substrate is often exposed to the back etching solution, especially near the end of the back etching. Further, such back etching protection film 15 can be deposited in one step by a low pressure CVD method or the like capable of simultaneously forming the front and back surfaces. After that, the back etching protection film 15 and the silicon dioxide film 16 are etched by dry etching or the like using the photoresist pattern as a mask to form a back etching protection film pattern serving as a mask when forming the opening 18 (back etching). 15a, a patterned silicon dioxide film 16a is formed (see FIG. 3D).

Next, the back etching protection film pattern 15
The lower Si substrate 12 is exposed to K at 80 to 90 ° C. using a as a mask.
After back-etching with an OH aqueous solution or the like to form the opening 18, the silicon dioxide film 13 on the surface of the opening, which is an adhesive layer, is formed.
Are removed to form a patterned silicon dioxide film 13a. Further, the back etching protection film pattern 15a and the patterned silicon dioxide film 16a are peeled off to form a basic form of a transmission mask having a penetrating charged beam transmission hole 19. Then, in order to enhance the electric conductivity of the transmission mask, both the front and back surfaces are covered with a conductive film 17 such as gold which is hard to be oxidized, and the transmission mask having the conventional structure is completed (see FIG. 3E).

[0006]

In the transmission mask having the conventional structure described with reference to FIG. 3, both the lower Si substrate and the upper Si substrate have principal planes of <100.
> A bonded substrate consisting of a surface was used. Therefore,
Only the silicon dioxide film, which is the adhesive layer of the bonded substrate, has an etching stop function when back-etching the lower Si substrate to form the opening.

In the etching of Si by a KOH aqueous solution using the silicon dioxide film as an etching stop layer as described above, silicon dioxide is etched very quickly (reference (a); "Si micromachining advanced technology" (Science Forum)). Company), Chapter 2, p.115), and in order to avoid shape defects caused by in-plane non-uniformity of etching due to the temperature distribution of the etching solution, etc., the thickness of the silicon dioxide film as an adhesive layer is conventionally 2 μm. It was considered necessary.

Since the back etching protection film must have sufficient resistance to the back etching solution, a silicon nitride film or the like formed by the low pressure CVD method is usually used. The low pressure CVD method is usually a high temperature process of around 800 ° C. Therefore, what becomes a problem is that the internal stress of the silicon dioxide film, which is the adhesive layer, changes due to the high temperature process, and the substrate warps and deforms. In order to alleviate this phenomenon, conventionally, a step of forming a silicon dioxide film having the same thickness as the adhesive layer on the back surface of the substrate is required.

Further, the energy lost by the charged particles incident on the transmission mask in the transmission mask is converted into almost 100% thermal energy, so that the temperature of the transmission mask rises.
Therefore, if the transmission mask is made of a material having a large coefficient of thermal expansion, the thermal strain becomes large and the transfer accuracy deteriorates. Comparing the thermal expansion coefficients of Si and silicon dioxide, it is desirable that the silicon dioxide film as the adhesive layer is as thin as possible, as can be seen from the fact that Si is larger by about one digit, although it depends on the temperature.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide a transmission mask which has a small number of manufacturing steps, is less affected by thermal strain, and has a high transfer accuracy by a charged beam. Especially.

[0011]

In order to achieve the above object in the present invention, first, in claim 1, an upper Si substrate in which a charged beam transmission hole is formed and a lower Si substrate holding the upper Si substrate are provided. In a transmission mask produced by using a bonded substrate having a silicon dioxide film as an adhesive layer, the main surface of the upper Si substrate has a <111> surface orientation, and the main surface of the lower Si substrate has a surface orientation. Is a <100> plane.

Further, in a second aspect of the present invention, the thickness of the silicon dioxide film which is the adhesion layer between the upper Si substrate and the lower Si substrate is in the range of 200 angstroms to 1000 angstroms. It is a transparent mask.

[0013]

1 is a sectional view of a transmission mask of the present invention, and FIG. 2 is a process sectional view showing a manufacturing process of the transmission mask of the present invention. A bonded substrate having the main surface of the upper Si substrate 1 made of the <111> plane and the main surface of the lower Si substrate 2 made of the <100> plane and using the silicon dioxide film 3 as an adhesive layer is used. It is made by. FIG. 1 (a)
1B shows the basic structure of the transmission mask of the present invention, FIG. 1B is a transmission mask having a conductive layer on the upper surface of the transmission mask of the basic structure of FIG. 1A, and FIG. 1) is further added to the transparent mask of 1), a conductive film is formed on the lower surface of the transparent mask, and the conductive mask has conductive layers on both front and back surfaces.

Next, in order to explain the mutual relations of claims 1 and 2 of the present invention, among the transmission masks of the present invention, the manufacturing process of the transmission mask of FIG. 2 will be described. First, the principal plane of the upper Si substrate 1 has a <111> plane orientation, and the principal plane of the lower Si substrate 2 has a <111> plane orientation.
A bonded substrate having the silicon dioxide film 3 of 100> surface as an adhesive layer is prepared. Here, the thickness of the silicon dioxide film 3, which is the adhesive layer, is in the range of 200 angstroms to 1000 angstroms.

Here, from 200 angstroms to 100
The reason for limiting the range to 0 Å will be described. As described above, it is desirable that the thickness of the silicon dioxide film 3 as the adhesive layer is thin, but a certain thickness is necessary to realize a good bonded state. The lower limit is estimated to be about 200 Å from the literature (Takao Abe, Kiyoshi Mitani, Yasuaki Nakazato: Applied Physics 1
1, p. 1080 (1994)). Also, as is well known, the magnitude of the warp of the substrate due to the change of the internal stress of the thin film is proportional to the thickness of the thin film. Therefore, if the thickness of the silicon dioxide film 3, which was 2 μm in the past, is set to 1000 angstrom, the warp becomes 1/20, which is a problem-free region for producing a transmission mask with good pattern accuracy.

Next, a conductive layer 4 is formed on the surface of the upper Si substrate 1 by a known sputtering method or the like so as to serve as a mask during dry etching of the upper Si substrate 1 for forming the charged beam transmitting holes 9. (See FIG. 2A). This conductive layer 4 becomes a lower layer resist in the multi-layer resist method.

Next, an upper layer resist is applied on the conductive layer 4, and the charged beam transmission hole 9 of the transmission mask is formed by means of ordinary photolithography or electron beam lithography.
A resist pattern for forming the conductive layer 4 is formed, and the conductive layer 4 is etched by a known method such as reactive ion etching using the resist pattern as a mask to form a patterned conductive layer 4a. After this, the upper layer resist pattern may be left, but it is usually peeled off with an organic solvent or the like.

Next, using the patterned conductive layer 4a as a mask, the upper Si substrate 1 is etched by means such as known reactive ion etching to form a charged beam transmission hole 9 on the surface of the upper Si substrate 1. Upper S
The i substrate 1a is formed (see FIG. 2B).

After that, the conductive layer pattern 4a is not peeled off,
By leaving it as it is, it can be used as a conductive layer on the upper surface of the completed transmission mask.

Next, the upper and lower surfaces of the bonded substrate on which the charged beam transmission holes 9 are formed and the side surfaces of the charged beam transmission holes 9 are covered with a back-etching protective film 5 resistant to a KOH aqueous solution (FIG. 2C). reference). Thereafter, the back etching protection film 5 is etched using the photoresist pattern as a mask to form a back etching protection film pattern 5a for forming the opening 8 in the lower Si substrate 2 (see FIG. 2D).

Next, the back etching protection film pattern 5a
Using the as a mask, the lower Si substrate 2 is back-etched with a KOH aqueous solution to form an opening 8. Here, in the transmission mask of the present invention, the silicon dioxide film 3 which is the first back etching stop layer is formed from 200 angstroms to 10 angstroms.
It is as thin as 00 angstrom. Therefore, in the manufacturing process of the transmission mask of the present invention, the <111> plane which is the main surface of the upper Si substrate is used as the second back etching stop layer.

According to the literature ((a) p.114-115), the etching rate of the <111> plane of Si by the KOH aqueous solution is much smaller than that of the <100> plane, and <10>.
It is about 1/400 of the 0> plane. Therefore, even if the back etching of the lower Si substrate 2 progresses unevenly due to the temperature distribution or the like and a part of the silicon dioxide film 3 disappears first, the upper Si substrate 1 functions as an etching stop layer together with the silicon dioxide film 3. Therefore, there is no problem of defective etching shape. After forming the opening 8, the silicon dioxide film 3 in the portion where the lower Si substrate 2 is back-etched is removed by a buffer hydrofluoric acid treatment or the like to form a patterned silicon dioxide film 3a (FIG. 2).
(E)).

Further, after the back etching protection film pattern 5a is peeled off, the patterned conductive layer 4a is left as it is, the conductive film 7 is formed on the lower surface of the transparent mask, and the conductive layer is formed on the front and back surfaces of the transparent mask. A transmission mask is completed (see FIG. 2 (f)).

[0024]

EXAMPLES The present invention will be described in more detail below with reference to FIG. 2 by showing Examples.

The main surface has a plane orientation of <111> and a thickness of 20 μm.
m having an upper Si substrate 1 and a main surface having a plane orientation of <100>,
A substrate was prepared by laminating a lower Si substrate 2 having a thickness of 500 μm on the surface of the lower Si substrate via a silicon dioxide film 3 having a thickness of 700 angstrom formed by thermal oxidation.

Next, C for forming the conductive layer 4 of the completed transmission mask on the surface of the bonded substrate on the upper Si substrate 1 side.
The r film was formed into a film having a thickness of 1500 angstrom by the sputtering method (see FIG. 2A). The Cr film was selected because it is a conductive film having a thermal expansion coefficient close to that of Si.

Next, an electron beam resist was applied as an upper layer resist on the conductive layer 4, and a resist pattern was formed by a usual electron beam lithography process.

Next, using the resist pattern as a mask, the lower conductive layer 4 is etched by dry etching using a chlorine-based gas to form a patterned conductive layer 4a.
Was formed. After this, the upper layer resist pattern was stripped with an organic solvent.

Next, by using the patterned conductive layer 4a as a mask, the upper Si substrate 1 is etched by dry etching using SF6 gas as a main gas to form a charged beam transmission hole 9 (see FIG. 2B). ). At this time, the film thickness of the conductive layer 4a patterned by dry etching was reduced, but as is well known, since the Cr film is difficult to be etched by the fluorine-based gas, a Cr film of about 1000 angstrom is still formed even after the dry etching is completed. It was left. The patterned conductive layer 4a is not peeled off, and is used as it is as a part of the conductive layer on the upper surface of the completed transmission mask.

Next, the entire mask substrate in which the charged beam transmission holes 9 were formed was covered with a silicon nitride film to be the back etching protection film 5 (see FIG. 2 (c)). A low pressure CVD method was used as the film forming method, and the thickness was 700 angstrom. At this time, the low pressure CVD was carried out at 800 ° C., but since the silicon dioxide film 3 as the adhesive layer was as thin as 700 angstrom, the warp of the substrate which would be a problem in the subsequent process did not occur.

After that, a resist pattern is formed on the silicon nitride film on the lower surface of the lower Si substrate 2 by an ordinary photolithography method, and the silicon nitride film is etched by an ordinary dry etching using this resist pattern as a mask to form an opening. A back etching protection film pattern 5a for forming the portion was formed (see FIG. 2D).

Next, the back etching protection film pattern 5a
Using the as a mask, the lower Si substrate was back-etched with a 30 wt% KOH aqueous solution to form the opening 8. At this time, until the end of back etching is near, liquid pressure is applied only to the lower Si substrate side of the silicon dioxide film 3 at a liquid temperature of 90 ° C. so as to increase the etch rate, and thereafter, the entire transparent mask is processed. Was immersed in a liquid at 60 ° C. until the end. As a result of this back etching,
The back surface of the upper Si substrate, which is the end point of the back etching, and the upper S exposed to the back etching solution near the end.
No problematic etching shape defect occurred on the upper surface of the i substrate and the side surface of the charged beam transmission hole.

After that, the silicon dioxide film 3 in the back-etched portion of the lower Si substrate was completely removed by buffered hydrofluoric acid to form a patterned silicon dioxide film 3a (see FIG. 2 (e)). Further, the back etching protection film pattern 5a formed of the silicon nitride film is removed by a hot phosphoric acid solution at 100 ° C., and the conductive film 7 is formed on the lower surface of the transmission mask by an electron beam heating vapor deposition method using an Au film having a thickness of 300 Å. Then, the transmission mask of the present invention having conductive layers on the front and back surfaces of the transmission mask was completed.

[0034]

As described above in detail, according to the transmission mask of the present invention, the upper Si substrate has a main surface whose plane orientation is the <111> plane, and the lower Si substrate is also the <100> plane. Since the substrate is used, a silicon dioxide film having a thickness of 200 angstroms, which causes warpage due to a thermal process during manufacturing of a transmission mask, heat generation during collective exposure of a charged beam, and thermal strain due to a difference in thermal expansion coefficient with Si, is used. To as thin as 1000 angstroms. For this reason, the step of forming a silicon dioxide film on the back surface of the lower Si substrate becomes unnecessary, and the thermal strain at the time of collective exposure of the charged beam is reduced, so that the transfer accuracy is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the structure of a transmission mask according to the present invention.

FIG. 2 is an explanatory view showing an example of a manufacturing process of a transmission mask according to the present invention in process order.

FIG. 3 is an explanatory view showing a structure of a conventional transmission mask and a manufacturing process of the conventional transmission mask in process order.

[Explanation of symbols]

1, 11 ... Upper Si substrate 1a, 11a ... Patterned upper Si substrate 2, 12 ... Lower Si substrate 2a, 12a .. Patterned lower Si substrate 3, 13 ... Silicon dioxide film 3a, 13a ... Patterned silicon dioxide film 4 ... Lower resist or conductive layer 4a ... Patterned lower resist or conductive layer 5, 15 ... Back etching protective film 5a, 15a ... Back etching protective film pattern 7, 17 ... Conductive film 8, 18 ... Opening 9, 19 ... Charge beam transmission hole 16 ... Silicon dioxide film 16a ... Patterned Silicon dioxide film

Claims (2)

[Claims] 1. A charged beam produced by using a bonded substrate in which an upper silicon substrate having a charged beam transmission hole formed therein and a lower silicon substrate holding the upper silicon substrate are adhered with a silicon dioxide film. In the collective exposure transmissive mask, the plane orientation of the main surface of the upper silicon substrate is <111.
> Plane, and the plane orientation of the main surface of the lower silicon substrate is <
A transmission mask for collective exposure of a charged beam, comprising a 100> surface. 2. The charge beam collective exposure according to claim 1, wherein the thickness of the silicon dioxide film, which is an adhesive layer between the upper silicon substrate and the lower silicon substrate, is in the range of 200 angstroms to 1000 angstroms. Transparent mask.