JPH07209121A - Pressure sensor and its production method - Google Patents

Abstract

PURPOSE:To provide a pressure sensor superior in mechanical strength and able to be easily produced. CONSTITUTION:A diaphragm 3 is placed nearly at the center of a square shape frame 2, and in its center, a mesa part 5 of a reverse octagonal trimcaled pyramid with nearly equal sides of which side surfaces 5a are constituted of silicone wafer {411} planes, is provided. A nearly square mask 11 is applied to a silicon wafer 10 at {100} plane so that the four sides of the mask 11 are parallel to <110> azimuth and the frame 2, the diaphragm 3 and the mesa part 5 are formed in one with anisotropic etching. By this, the stress concentration generating in the diaphragm 3 is lessened and mechanical strength can be improved. Furthermore, the mesa part 5 can be easily made with a simple mask pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor and its manufacturing method. Specifically, it relates to the shape of the mesa portion of the pressure sensor.

[0002]

2. Description of the Related Art A sectional view of a conventional pressure sensor 1 is shown in FIG. In the pressure sensor 1, a thin-film diaphragm 3 is arranged in the center of a frame 2 having a rectangular frame shape, and a cover 6 is placed on the frame 2. A recess 4 is formed on the inner surface of the cover 6 so as to be swingable in the thickness direction of the diaphragm 3. Further, in order to improve the linearity of the sensitivity of the pressure sensor 1, a truncated pyramid-shaped mesa portion 5 is formed on the lower surface of the diaphragm 3. The diaphragm 3, the mesa portion 5, and the frame 2 are integrally formed by anisotropically etching a silicon wafer. As shown in FIG. 2, the {111} plane having the slowest etching rate is usually the mesa portion 5. The mesa portion 5 having a rectangular bottom surface 5b was formed by etching so as to form the side surface 5a.

[0003]

However, in the conventional pressure sensor 1, since the four side surfaces 5a of the mesa portion 5 are formed by using the {111} planes of the {100} plane silicon wafer, the etching rate is reduced. Fast crystal plane, eg {4
11} surface 5c (hatched area in the figure) appeared at the four corners of the mesa portion 5 and a corner drop 9 as shown in FIG. 3 occurred. In order to prevent the corner drop 9, when the pressure sensor 1 is produced, correction is performed so that smaller rectangular patterns are overlapped at each of the four corners of the rectangular pattern shown in FIG. 4 on the {100} surface of the silicon wafer 8. The mask 7 must be applied, and the manufacturing process of the pressure sensor 1 is complicated.

Further, since the shape of the mesa portion 5 is rectangular, when the diaphragm 3 is displaced, the mesa portion 4 of
There is also a problem that stress concentration occurs in the corners and mechanical properties deteriorate.

The present invention has been made in view of the above-mentioned drawbacks of the conventional examples, and an object thereof is to make the shape of the mesa portion into an octagonal shape or a hexagonal shape by utilizing the {411} plane having a high etching rate. The purpose is to solve the above-mentioned problems by using a rectangular shape.

[0006]

A first pressure sensor of the present invention is a pressure sensor in which a detection part having a rigid part in a thin film elastic part is supported on a detection substrate, and the planar structure of the rigid part is It is an octagon, and is characterized in that the rigid portion is surrounded by eight side surfaces made of the {411} plane of silicon.

A first method of manufacturing a pressure sensor of the present invention is a method for manufacturing the pressure sensor,
Anisotropic etching is performed on a {100} plane silicon wafer having a rectangular mask having four sides parallel to the <110> direction, and a rigid portion surrounded by only eight side surfaces consisting of {411} planes. Is formed.

A second pressure sensor of the present invention is a pressure sensor in which a detection portion having a thin film elastic portion provided with a rigid portion is supported on a detection substrate, and the rigid portion has a dodecagonal planar structure, It is characterized in that the rigid portion is surrounded by eight side surfaces composed of silicon {411} planes and four side surfaces composed of silicon {111} planes.

A second pressure sensor manufacturing method of the present invention is a method for manufacturing the above second pressure sensor, which is a rectangular shape having four sides parallel to the <110> direction. Anisotropic etching is performed on a mask-formed {100} plane silicon wafer to form a rigid portion surrounded by eight side surfaces formed of {411} planes and side surfaces formed of {111} planes.

[0010]

In the pressure sensor of the present invention, since the side surface of the rigid portion is formed by using the {411} face of silicon, the rigid portion having an octagonal or dodecagonal planar structure is supported on the thin film portion. Can be made. In this way, the planar structure supports the octagonal or dodecagonal rigid part,
It is possible to alleviate the stress concentration that occurs with the displacement of the thin film portion, and improve the mechanical strength of the thin film portion.

Further, since the rigid portion is surrounded by eight side surfaces of the {411} plane of silicon or eight side surfaces of the {411} plane and four side surfaces of the {111} plane, side surfaces of the rigid portion. It is possible to accurately create the rigid portion without any corner drop.

For this purpose, a {100} plane silicon wafer having a rectangular mask having four sides parallel to the <110> direction is anisotropically etched until the {111} plane does not appear. It is possible to easily create a rigid portion surrounded by eight side surfaces composed of {411} planes. If etching is stopped in the state where the {111} plane appears, eight side surfaces composed of {411} planes and {111} planes are formed.
The rigid portion surrounded by the four side surfaces can be easily formed. Further, at this time, since the rigid portion is formed by using the {411} surface of the silicon wafer having the highest etching rate, it is not necessary to apply the correction pattern, and the manufacturing process can be simplified.

[0013]

FIG. 5 is a bottom view of a pressure sensor according to the present invention. The pressure sensor 21 has the same structure as the pressure sensor 1 shown in FIG. 1, in which a rectangular diaphragm 3 is arranged substantially in the center of a frame 2 having a square frame shape, and a lower surface of the diaphragm 3 is substantially centered. A mesa portion 5 having an octagonal bottom surface 5b and a substantially octagonal inverted octagonal truncated pyramid is provided. The diaphragm 3, the mesa portion 5 and the frame 2 are integrally formed from a {100} plane silicon wafer, and the eight side surfaces 5a of the mesa portion 5 are {411} planes, respectively.

Next, a method of forming the octagonal mesa portion 5 will be described. First, the {100} plane silicon wafer 1
A mask 11 having a square rectangular pattern as shown in FIG. 6 is formed in a region where the 0 mesa portion 5 is formed so that four sides of the mask 11 are parallel to the <110> direction, Anisotropic etching is performed using a 45 wt% potassium hydroxide solution. At this time, since the etching rate of the {111} plane of the silicon wafer 10 is slow,
As shown in FIG. 7, in each of the four corners 11a of the mask 11 made of the {110} plane of the silicon wafer 10, the {411} plane is etched at an angle of 30.96 ° with respect to the {110} plane. , 1 on the four sides of the mask 11
11} plane appears. In the {100} plane silicon wafer 10 thus masked in a rectangular shape, the corners 39 due to the {411} plane gradually appear at each corner 11a as shown by the broken line a → broken line b → broken line c in FIG. The initially appearing {111} plane becomes smaller gradually, and finally the {111} plane does not appear. In this manner, the mesa portion 5 is formed in the order of the solid line A → the solid line B → the solid line C, and the mesa portion 5 surrounded by only the eight side surfaces 5a of the {411} plane is formed. Therefore, when the mask 11 having a predetermined size is applied in consideration of the size of the diaphragm 3 to be formed, and etching is performed for a predetermined time until the size becomes a desired size, the bottom surface 5b as shown in FIG. 5 has an octagonal mesa shape. The part 5 can be formed and its eight sides 5
Each a can be composed of {411} planes. Incidentally, when the etching rates of the {100} plane and the {411} plane were measured, the etching rate of the {411} plane was {1
It was about 1.2 times the etching rate of the {00} plane.

The pressure sensor 21 produced in this way
In this case, since the mesa portion 5 has an octagonal truncated pyramid shape, stress concentration generated due to the displacement of the diaphragm 3 is relaxed as compared with the case where the square pyramidal truncated mesa portion 5 is provided. The mechanical strength can be improved. Further, the mesa portion 5 and the diaphragm 3 can be easily formed by using the mask 11 having a simple rectangular shape instead of the mask 7 having the corrected pattern as in the conventional example.

Further, if the mask 11 is formed in a square shape as in this embodiment, the mesa portion 5 having a substantially equilateral octagonal pyramid is formed, and the mesa portion 5 can be made closer to a circular shape, so that the stress concentration can be reduced. 5 will be evenly distributed around the periphery.

FIG. 8 shows a bottom view of a pressure sensor 31 which is another embodiment of the present invention. The mesa portion 5 of the pressure sensor 31 is formed into a dodecagonal bottom surface 5b in the shape of an inverted dodecagonal pyramid with approximately equal sides, and its side surface 5a has eight {41.
It is composed of a 1} plane and four {111} planes (hatched areas in the figure). Similar to the first embodiment, the mesa portion 5 is also masked using the silicon wafer 10 having the {100} plane so that the four sides of the substantially square mask 11 are parallel to the <110> orientation. It can be created by anisotropic etching. At this time, for example, as shown by the solid line A in FIG. 6, if the etching is stopped in the state where the {111} plane remains, the dodecagonal pyramid-shaped mesa portion 5 can be formed. Therefore, if the size of the diaphragm 3 is taken into consideration and the mask 11 having a predetermined size is applied and anisotropic etching is performed, the mesa portion 5 having a desired size can be easily formed. Further, as can be seen from FIG. 6, when the mesa portion 5 having substantially the same size as that of the first embodiment is formed, a mask smaller than the mask 11 shown in FIG. 6 may be applied.

Thus, by forming the mesa portion 5 having a dodecagonal bottom surface 5b, the stress concentration generated by the displacement of the diaphragm 3 is further alleviated, and the mechanical strength of the diaphragm 3 can be further enhanced. Further, if the square mask 11 is applied as in the present embodiment, the mesa portion 5 can be made into a dodecagonal pyramid having substantially equal sides, and the mesa portion 5 can be made even more circular. Further, as in the first embodiment, since it is sufficient to apply a mask having a simple shape (rectangular shape), the manufacturing process does not become complicated.

[0019]

In the pressure sensor of the present invention, since the side surface of the rigid portion is formed by using the silicon {411} plane, it is possible to form the rigid portion whose planar structure is octagonal or dodecagonal. it can. Therefore, the stress concentration generated by the displacement of the thin film portion can be relaxed, and the mechanical strength can be improved. Further, there is no corner drop in the rigid portion, and the rigid portion can be formed accurately.

In these rigid portions, the four sides are <1 of silicon.
The rigid portion can be easily formed by anisotropically etching a {100} plane silicon wafer on which a rectangular mask having sides parallel to the 10> direction is formed. Further, at this time, since it is not necessary to apply a complicated correction pattern to the mask, the manufacturing process can be simplified.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a conventional pressure sensor.

FIG. 2 is a bottom view showing the pressure sensor of the above.

FIG. 3 is an enlarged view in which the mesa portion of the above is partially broken.

FIG. 4 is a diagram showing a mask pattern used for producing the pressure sensor of the above.

FIG. 5 is a bottom view showing a pressure sensor according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a state in which a mesa portion of the above pressure sensor is formed.

FIG. 7 is an explanatory diagram showing how {411} planes appear on a {100} plane silicon wafer by anisotropic etching.

FIG. 8 is a bottom view showing a pressure sensor according to another embodiment of the present invention.

[Explanation of symbols]

 2 frame 3 diaphragm 5a side surface of mesa 5b bottom surface of mesa 11 mask

Claims (4)

[Claims] 1. A pressure sensor in which a detection part having a thin film elastic part provided with a rigid part is supported on a detection substrate, wherein the planar structure of the rigid part is octagonal, and the rigid part is made of silicon {411} plane. A pressure sensor characterized in that it is surrounded by eight side faces. 2. A pressure sensor in which a detection part having a thin film elastic part provided with a rigid part is supported on a detection substrate, wherein the rigid part has a dodecagonal planar structure and the rigid part is made of silicon {411}. A pressure sensor characterized in that it is surrounded by eight side surfaces composed of planes and four side surfaces composed of {111} planes of silicon. 3. The method for manufacturing the pressure sensor according to claim 1, wherein a {100} plane silicon wafer having a rectangular mask formed by four sides having sides parallel to a <110> direction is formed. A method of manufacturing a pressure sensor, characterized by performing anisotropic etching to form a rigid portion surrounded by only eight side surfaces of {411} planes. 4. The method for manufacturing the pressure sensor according to claim 2, wherein the {100} plane silicon wafer is provided with a rectangular mask in which four sides are parallel to the <110> direction. A method of manufacturing a pressure sensor, characterized by performing anisotropic etching to form a rigid portion surrounded by eight side surfaces of {411} planes and four side surfaces of {111} planes.