JPH07249783A - Production of diaphragm - Google Patents

Abstract

PURPOSE:To make a ring-like U-groove having a vertical side wall and a micro round bottom face corner part in the surface of a silicon substrate. CONSTITUTION:Silicon oxide 2 is deposited by 2mum, as a mask, on the surface of a silicon substrate 1 of 200mum thick and then it is removed using hydrofluoric acid solution to obtain a ring-like exposed part 3. The reaction gas for dry etching is produced by mixing hexafluorosuifric gas and oxygen gas with the ratio of oxygen gas being set in the range of 1-70% and the pressure in a reaction chamber is set at 1-10 Pa. High frequency power is applied between upper and lower electrodes at a rate of 0.3-2.0W/cm<2> to cause physical chemical reaction between the exposed part 3 of the silicon substrate 1 and radicals or reaction gas ions in a plasma produced in a relative space thus effecting dry etching on the exposed part 3. Consequently, a ring-like U-shaped groove of 170mum deep having vertical side wall and micro round corner on the bottom face is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION In order to meet design requirements, the present invention provides a dry etching method for a silicon substrate surface in which side walls are perpendicular to the surface and bottom corners have minute roundness and bottom corners. The present invention relates to a method of manufacturing a diaphragm in which a ring-shaped U-shaped groove having a gentle concave portion is formed near the portion.

[0002]

2. Description of the Related Art Two conventional examples will be described below with reference to the drawings. FIG. 9 is a sectional view of an initial step of one conventional example, and FIG. 10 is a sectional view of an intermediate step thereof. In FIG. 9, a mask composed of a silicon oxide film 31 and a silicon nitride film 32 is deposited on the upper surface of the silicon substrate 1 so as to form an exposed portion 33 of a ring-shaped band region. In the drawing, only the exposed portion 33 on the right side of the ring-shaped region is shown. In this state, when wet etching with a hydrofluoric acid-based solution,
As shown in FIG. 10, a U-shaped groove having a flat bottom surface and large rounded corners is formed. Although not shown here, the mask is removed in the next step.

FIG. 11 is a sectional view showing the initial process of another conventional example.
12 is a sectional view of the same intermediate step. In FIG. 11, on the upper surface of the silicon substrate 1, the exposed portion of the ring-shaped band area is formed.
A mask of silicon nitride film 41 is deposited to form 42. In this state, wet etching with an alkaline solution forms a U-shaped groove having a flat bottom surface and right-angled corners, as shown in FIG. The next mask removing step is omitted.

[0004]

In one conventional example, wet etching with a hydrofluoric acid-based solution proceeds isotropically, so that the bottom surface of the U-shaped groove is flat and the corners have large roundness. Due to the large roundness of the corners, there is a drawback that the sensitivity of the diaphragm is lowered and the miniaturization is hindered. In another conventional example, wet etching with an alkaline solution proceeds according to the plane orientation of the silicon substrate, so by selecting the plane orientation to be perpendicular to the surface, the bottom surface of the U-shaped groove is flat and the corner portion is Can be at a right angle. This right-angled corner is advantageous for increasing the sensitivity of the diaphragm, but stress concentration is likely to occur, which causes destruction.
Further, there is also a drawback that the plane orientation of the silicon substrate becomes a constraint condition for manufacturing the diaphragm.

Further, as a drawback of the wet etching method common to one conventional example and another conventional example, there is a limit to the thickness of the mask to be deposited on the silicon substrate,
There is a limit to the thickness of the usable silicon substrate, the depth of the U-shaped groove that can be formed, and the thickness of the bottom surface of the U-shaped groove. When taking several hundred silicon substrates from a silicon wafer, There is a risk that the thickness of the bottom surface of the U-shaped groove of the silicon substrate will vary, and the yield rate of the product may decrease. Poor workability due to the use of acid or alkali as the etching liquid, and difficult maintenance of the etching liquid. and so on.

The problem to be solved by the present invention is to solve the above problems of the prior art and to meet the design requirements, in which the side wall is vertical to the surface of the silicon substrate and the corner of the bottom surface is formed. It is an object of the present invention to provide a method of manufacturing a diaphragm having a round U-shaped groove having a minute roundness and a gentle recess near the corner of the bottom surface.

[0007]

SUMMARY OF THE INVENTION The present invention comprises a step of depositing a mask of a silicon oxide film or an aluminum film on the surface of a silicon substrate so that only a ring-shaped region is exposed; In the etching device, using a mixed gas of sulfur hexafluoride and oxygen as a reaction gas, the oxygen mixing ratio of the reaction gas is 1 to 70%, the high frequency power per electrode unit area is 0.3 to 2.0 W / cm ² , and the reaction chamber A step of forming a ring-shaped U-shaped groove by dry etching the mask-coated silicon substrate under a pressure of 1 to 10 Pa.

Also, the present invention comprises a step of depositing a mask of a silicon oxide film or an aluminum film on the surface of the silicon substrate so that only the ring-shaped region is exposed; in an anodic bonding type dry etching apparatus, Using a mixed gas of sulfur hexafluoride and oxygen as a reaction gas,
The oxygen mixing ratio of the reaction gas is 1 to 70%, the high frequency power per unit area of the electrode is 2.0 to 6.0 W / cm ² , the pressure in the reaction chamber is 10
A step of forming a ring-shaped U-shaped groove by dry etching the mask-coated silicon substrate under the condition of 120 Pa.

Further, the ring-shaped U-shaped groove can be formed on only one side of the silicon substrate, or can be formed opposite to both sides of the silicon substrate.

[0010]

According to the present invention, a mask of a silicon oxide film or an aluminum film is deposited on the surface of a silicon substrate so that only a ring-shaped region is exposed, and then a hexafluoride film is formed in an anodic bonding type dry etching apparatus. Using a mixed gas of sulfur and oxygen as the reaction gas, the oxygen mixing ratio of the reaction gas is 1 to 70%, and the high frequency power per electrode unit area is 0.3 to
Under the conditions of 2.0 W / cm ² and the pressure in the reaction chamber of 1 to 10 Pa, the silicon substrate on which the mask is deposited is dry-etched to form a ring-shaped U.
Form a groove. That is, sulfur hexafluoride and oxygen are
When dissociated in plasma, fluorine radicals and oxygen radicals are generated. Oxygen radicals in the plasma react with silicon atoms on the silicon substrate to produce silicon oxide as an instantaneous intermediate product. This silicon oxide reacts with fluorine radicals to produce tetrafluorosilicon.
Since this tetrafluorosilicon has a very low boiling point, it naturally becomes a gas and is discharged to the outside of the reaction chamber.

Silicon oxide has a masking effect, that is, an effect of hindering an etching reaction, as described in Japanese Patent Application No. 2-275626 filed by the present applicant. Therefore, silicon oxide is efficiently deposited on the sidewalls of the U-shaped groove formed in the silicon substrate during the etching reaction, and the masking effect makes it possible to etch the sidewalls vertically. It is presumed that in the depth direction of the groove, the masking effect of silicon oxide is blocked by the extremely slight assisting effect of ions due to the small potential gradient existing near the silicon substrate, and the etching reaction is likely to proceed. . Also, the high frequency power per electrode unit area is 0.3 to 2.0 W / cm ² , and R
Since it is smaller than the IE (Reactive Ion Etching) apparatus, the selectivity of dry etching can be greatly improved. As a result, the ring-shaped U formed on the silicon substrate
The groove has a vertical side wall and a minute roundness at the bottom corner.

Further, in the present invention, a mask of a silicon oxide film or an aluminum film is deposited on the surface of the silicon substrate so that only the ring-shaped region is exposed. Using a mixed gas of sulfur fluoride and oxygen as the reaction gas, the oxygen mixing ratio of the reaction gas is 1 to 70%, the high frequency power per unit area of the electrode is 2.0 to 6.0 W / cm ² , and the pressure in the reaction chamber is 10 to 120%. Pa
Under the conditions described above, the silicon substrate on which the mask is deposited is dry-etched to form a ring-shaped U-shaped groove. That is, the ring-shaped U of the silicon substrate is formed by the reaction mechanism as described above.
The side wall of the groove is vertical, and the bottom corners have a small roundness, and the high frequency power per unit area of the electrode and the pressure inside the reaction chamber have been increased, so that the impact of the ions bounced from the side wall As a result, the portion of the bottom surface of the U-shaped groove near the side wall, that is, near the corner, is etched more rapidly than other portions, and a gentle recess is formed near the corner of the bottom surface.

The mask deposited on the surface of the silicon substrate can be a silicon oxide film or an aluminum film. Therefore, depending on the selection of the aluminum film, the depth of the mask is about 1 mm thicker than that of the silicon oxide film. Carving etching becomes possible. Further, since the ring-shaped U-shaped groove can be formed only on one surface of the silicon substrate or can be formed so as to face both surfaces,
The characteristics of the diaphragm can be changed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Three application examples of the method of manufacturing a diaphragm according to the present invention will be described below with reference to the drawings. The first application example will be described with reference to FIGS. 1 and 2. 1 is a sectional view of the initial step, and FIG. 2 is a sectional view of the intermediate step. In FIG. 1, a silicon substrate 1 has a thickness of 200 μm, and a silicon oxide film 2 having a thickness of 2 μm is formed on the upper surface of the silicon substrate 1 by thermal oxidation as a mask.
The silicon oxide film 2 is removed by using a hydrofluoric acid solution to form an exposed portion 3 as a ring-shaped band region. This exposed part 3
Is dry-etched as described below. The mask can be an aluminum film instead of the silicon oxide film, and by selecting the aluminum film in particular, deep etching can be performed on a silicon substrate that is thicker than the silicon oxide film by about 1 mm.

Here, an apparatus for performing dry etching will be described with reference to the configuration diagram of the dry etching apparatus in FIG. This device is called a parallel plate type of anodic coupling type, and a lower electrode 12 also serving as a stage and an upper electrode 13 opposed to this at a distance of 5 to 100 mm are arranged inside a reaction chamber 11. Exhaust pipes 15 are provided in a dispersed manner in the peripheral portion of the bottom plate 14, each of which opens toward the center of the bottom plate 14 and is parallel to this. A high frequency power supply 17 is connected to the upper electrode 13 via a matching tuner 16. A gap 20 between the connector 19 connected to the upper electrode 13 and the top 18 of the reaction chamber 11 is an inlet for the reaction gas 21 whose inflow direction is indicated by an arrow.

The dry etching process will be described. The silicon substrate 1 is placed on the upper surface of the lower electrode 12 which also serves as a stage. Reaction gas 21 introduced into the reaction chamber 11
Is the ratio of oxygen gas to sulfur hexafluoride gas and oxygen gas
It is mixed in the range of 1 to 70%, and 1 to 70% in the reaction chamber 11.
The pressure of 10 Pa is maintained. Lower and upper electrodes 12, 13
High-frequency power of 0.3 to 2.0 W / cm ² per unit area of the electrode was applied between the exposed parts 3 of the silicon substrate 1 (see Fig. 1).
And a physicochemical reaction between radicals and reaction gas ions existing in the plasma 22 formed in the relative space, dry etching is performed from the exposed portion 3, and as shown in FIG. A ring-shaped U-shaped groove 4 with a depth of 170 μm is formed, that is, the thickness of the bottom of the groove 4 is
It becomes 30 μm. Moreover, the side wall 5 of the groove 4 is perpendicular to the surface and has a small roundness at the corner of the bottom surface. By the way, the groove 4 has the vertical side wall 5 so that the requirement of design performance can be met, and the minute roundness at the bottom corner avoids stress concentration and eliminates one of the factors of destruction. The next mask removing step is omitted.

Details of the dry etching mechanism
Explain correctly. Sulfur hexafluoride and oxygen in the plasma
Dissociation produces fluorine radicals and oxygen radicals
It Oxygen radicals in the plasma are
Reacts with the nitrogen atom and forms silicon dioxide as an instantaneous intermediate product.
Are generated. This silicon oxide and fluorine radical
React to produce tetrafluorosilicon. This four
Since silicon has a very low boiling point, it naturally becomes a gas.
Is discharged outside the reaction chamber. Silicon oxide mentioned earlier
Tateyo (Japanese Patent Application No. 2-275626
, The masking effect, that is, the etching reaction
Has an interfering effect. Therefore, during the etching reaction,
On the side wall 5 of the groove 4 formed on the recon substrate, silicon oxide
Is efficiently deposited, and the masking effect of the
It is now possible to etch the wall 5 vertically,
At the same time, in the depth direction of the groove portion 4, the silicon substrate 1
Very small due to small potential gradients in the vicinity
Due to the ion assist effect, silicon oxide mask
The etching effect is blocked and the etching reaction is easy to proceed.
It In addition, high frequency power per electrode unit area is 0.3 to 2.0.
W / cm ² Compared to RIE (Reactive Ion Etching) equipment
Since it is small, the selection ratio of dry etching is greatly improved.
Can be raised. As a result, the silicon substrate 1
The formed ring-shaped groove 4 has vertical side walls 5
A slight roundness occurs at the bottom corner.

The second application example will be described with reference to FIGS. 3 is a sectional view of the initial step, and FIG. 4 is a sectional view of the intermediate step. In FIG. 3, a silicon substrate 1 has a thickness of 200 μm, and a silicon oxide film 2 having a thickness of 2 μm is formed on the upper surface of the silicon substrate by a thermal oxidation process as a mask, and this is removed using a hydrofluoric acid solution to form a ring shape. Make exposed part 3 as a strip-shaped area. The mask may be an aluminum film. The process up to this point is the same as in the first application example.

The dry etching process is carried out in the same apparatus as used in the first application example. That is, the silicon substrate 1 is placed on the upper surface of the lower electrode 12 which also serves as a stage. Reaction gas 21 introduced into the reaction chamber 11
Is the ratio of oxygen gas to sulfur hexafluoride gas and oxygen gas
It is mixed in the range of 1 to 70% and is the same as in the first application example, but the following conditions are different from the first application example. In reaction chamber 11, higher than in the first application example 10
A pressure of ~ 120 Pa is maintained, and the lower and upper electrodes 1
Between 2 and 13, higher than the first application example 2.0-6.0 W / c
High frequency power is applied per unit area of m ² of electrode. As shown in FIG. 4, dry etching is performed from the exposed portion 3 to form a groove portion 4 having a depth of 170 μm. Moreover,
The side wall 5 of the groove 4 is perpendicular to the surface, has a minute roundness at the corner of the bottom surface, and a gentle recess 6 is formed near the corner. By forming the gradual recesses 6 near the corners of the bottom surface, it is possible to obtain a diaphragm having the same high sensitivity as when the bottom surface of the groove 4 is not thinned but is substantially thinned.

The etching mechanism in the case of the second application example is considered as follows. By increasing the high-frequency power per unit area of the electrode and the pressure in the reaction chamber compared to the case of the first application example, the vicinity of the bottom corner of the groove 4 is faster than other parts due to the impact of the rebounded ions from the side wall 4. As a result, along with the formation of the groove portion 4 in the first application example, the gentle concave portion 6 is formed near the corner of the bottom surface. By using an aluminum film as the mask instead of the silicon oxide film, it becomes possible to perform deep etching on a silicon substrate thicker than the silicon oxide film by about 1 mm and to form a deeper recess 6.

A third application example will be described with reference to FIGS. 5, 6 and 7. 5 is a sectional view of the initial process,
6 is a sectional view of the intermediate step, and FIG. 7 is a sectional view of the next step. In FIG. 5, the silicon substrate 1 has a thickness of 200 μ.
m, a silicon oxide film 2 with a thickness of 2 μm is formed on each of the upper and lower surfaces as a mask, and this is removed using a hydrofluoric acid solution, and the exposed portion 3 as a ring-shaped belt-like region is vertically opposed to each other. The production is basically the same as in the first and second application examples. In FIG. 6, a U-shaped groove 7 having a depth of 85 μm is formed by dry etching on the upper side. The side wall 8 of the groove 7 and the recess 9 near the corner of the bottom surface are basically the same as in the first and second application examples. Next, turn over the silicon substrate 1 and, as shown in FIG. 7, perform a U-shaped depth by dry etching on the lower side.
Grooves 7 of 85 μm are formed. Therefore, the thickness between the bottoms of the grooves 7 is 30 μm.

[0022]

According to the present invention, a ring-shaped U of a silicon substrate is used.
The groove has a vertical side wall, and can have a minute roundness at the bottom corner. Further, by increasing the high frequency power per unit area of the electrode and the pressure in the reaction chamber, the groove rebounds from the side wall. By the bombardment of ions, the portion near the sidewall of the groove bottom, that is, near the corner is etched more rapidly than other portions, and a gentle recess can be formed near the corner of the bottom. As a result, the groove has vertical side walls to meet the design performance requirements, and the bottom corner has a minute roundness to avoid stress concentration, and to form a gentle recess near the bottom corner. Thus, it is possible to obtain the same high-sensitivity diaphragm as when the thickness of the bottom surface of the U-shaped groove is not thinned but is substantially thinned. Further, since the mask deposited on the surface of the silicon substrate can be a silicon oxide film or an aluminum film, the selection of the aluminum film makes it possible to form a mask with a depth of about 1 mm thicker than that of the silicon oxide film. Carving etching becomes possible. The ring-shaped U-shaped groove is
It may be formed on only one side of the silicon substrate, or
Since it is also possible to form it on both sides, it is possible to change the characteristics of the diaphragm and flexibly meet the design requirements.

Further, one of the features of the dry etching method is that, when a large number of silicon substrates, such as several hundreds, are taken from a silicon wafer, there is a variation in the thickness of the bottom surface of the U-shaped groove of each silicon substrate. And the uniformity of quality, that is, the yield rate is maintained and improved to improve the productivity, and secondly, the workability is good and the maintenance of the etching medium is relatively easy.

By the way, according to the present invention, since a deeply engraved U-shaped groove is formed in a silicon substrate by dry etching, the side wall thereof is vertical, and a minute roundness for avoiding stress concentration is formed at the corner of the bottom surface. In general, it has a ripple effect that it can be widely used for manufacturing microsensors having complicated shapes and micromachines such as microscanners.

[Brief description of drawings]

FIG. 1 is a sectional view of an initial step of a first application example according to the present invention.

FIG. 2 is a sectional view of the intermediate step of the same.

FIG. 3 is a sectional view of an initial step of a second application example according to the present invention.

FIG. 4 is a sectional view of the same intermediate step.

FIG. 5 is a sectional view of an initial step of a third application example according to the present invention.

FIG. 6 is a sectional view of the same intermediate step.

FIG. 7 is a sectional view of the next process as well.

FIG. 8 is a configuration diagram of a dry etching apparatus used in an application example.

FIG. 9 is a sectional view of an initial step of a conventional example.

[FIG. 10] Similarly, a sectional view of the intermediate step

FIG. 11 is a cross-sectional view of the initial process of another conventional example.

[FIG. 12] Similarly, a sectional view of the intermediate step

[Explanation of symbols]

 1 Silicon Substrate 2 Silicon Oxide Film 3 Exposed Part 4 Groove 5 Sidewall 6 Recess 7 Groove 8 Sidewall 9 Recess 11 Reaction Chamber 12 Lower Electrode 13 Upper Electrode 14 Bottom Plate 15 Exhaust Pipe 16 Matching Tuner 17 High Frequency Power Supply 18 Reaction Chamber Top 19 Connector 20 Gap 21 Reaction gas 22 Plasma

Claims (4)

[Claims] 1. A step of depositing a mask of a silicon oxide film or an aluminum film on a surface of a silicon substrate so as to expose only a ring-shaped region; and sulfur hexafluoride in an anodic bonding dry etching apparatus. A mixed gas with oxygen is used as a reaction gas, and the oxygen mixing ratio of the reaction gas is 1
~ 70%, high frequency power 0.3 ~ 2.0 W /
a step of forming a ring-shaped U-shaped groove by dry etching a mask-coated silicon substrate under conditions of cm ² and a pressure in the reaction chamber of 1 to 10 Pa. 2. A step of depositing a mask of a silicon oxide film or an aluminum film on the surface of a silicon substrate so as to expose only a ring-shaped region; and sulfur hexafluoride in an anodic bonding dry etching apparatus. A mixed gas with oxygen is used as a reaction gas, and the oxygen mixing ratio of the reaction gas is 1
~ 70%, high frequency power per electrode area 2.0 ~ 6.0 W /
a step of forming a ring-shaped U-shaped groove by dry-etching a mask-coated silicon substrate under conditions of cm ² and a pressure in the reaction chamber of 10 to 120 Pa. 3. The method according to claim 1 or 2, wherein
A method of manufacturing a diaphragm, wherein the ring-shaped U-shaped groove is formed on only one surface of the silicon substrate. 4. The method according to claim 1 or 2, wherein
A method of manufacturing a diaphragm, wherein the ring-shaped U-shaped groove is formed so as to face both sides of a silicon substrate.