JPH0158673B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in semiconductor diaphragms used as detection elements in devices that measure pressure, differential pressure, absolute pressure, and the like. Measuring instruments for pressure, differential pressure, absolute pressure, etc. that use a piezoresistive element formed on a semiconductor diaphragm as a detection element are becoming more common this year, but there are particular difficulties in achieving their performance. , a temperature change in the measurement span due to a temperature change in the piezoresistance coefficient, and a temperature drift at the zero point due to strain stress applied to the semiconductor diaphragm due to a change in ambient temperature. The present invention relates to improving the temperature drift at the zero point described above, and the heat applied to the thin film diaphragm due to the difference in thermal expansion coefficient between the semiconductor diaphragm and the mount to which it is attached and the bonding layer for attachment. The purpose is to reduce the effects of distortion.

As a conventional proposal to achieve the above purpose,
There is a disclosure in Japanese Patent Application Laid-open No. 54-99585. This uses a mounting base with a special structure to reduce the strain stress applied from the members that make up the pressure receiving part of pressure, differential pressure, and absolute pressure gauges to the semiconductor diaphragm that is the detection element. It has a complicated structure, which makes it difficult to manufacture, and it also has drawbacks such as the fact that it cannot completely eliminate the transmission of strain stress. In addition, as another conventional proposal,
There is a method disclosed in Publication No. 143275, which aims to prevent the occurrence of thermal strain stress due to the difference in thermal expansion coefficient between the mounting base and the semiconductor diaphragm by using a mounting base made of the same material as the semiconductor diaphragm. , by forming a groove in the mounting base,
It seeks to achieve this objective more fully. However, in any of the above proposals, the semiconductor diaphragm itself does not have any means to absorb strain, and the bonding layer for integrating the semiconductor diaphragm and the mounting base absorbs the strain stress generated as a strain-generating part. The problem is that it cannot be done. Methods for integrating the semiconductor diaphragm and the mounting base include bonding with synthetic resin, bonding with low melting point glass, bonding with gold-silicon eutectic alloy,
Various methods have already been proposed and put into practical use, such as anodic bonding and bonding using a metal solder layer, but no matter which method is used, the strain stress generated during bonding remains in the bonding layer, and the semiconductor diaphragm and Since the thermal expansion coefficients of the bonding layer and the mounting base cannot be made to match perfectly, it is inevitable that thermal strain stress will be applied to the thin film diaphragm.

The present invention eliminates this adverse effect and operates stably against changes in ambient temperature. In other words, it provides a semiconductor diaphragm in which thermal strain stress is not applied to the thin film diaphragm, and it is capable of handling pressure, differential pressure,
Suitable for use in absolute pressure gauges, etc.

That is, the semiconductor diaphragm of this invention is
The central part of the lower surface of a semiconductor single crystal plate chip is recessed toward the upper surface, the central part is made thin, and the central part is used as a thin film diaphragm, and the relatively thick part around it is used as a peripheral fixing part, Further, a narrow and deep groove for absorbing stress is formed in the peripheral fixing portion so as to surround the thin film diaphragm. This semiconductor diaphragm can prevent the strain stress applied to the peripheral fixing part of the semiconductor diaphragm from being transmitted from the mounting base through the bonding layer or from the bonding layer itself to the thin film diaphragm by providing a narrow and deep groove. , does not require a special mount that takes into consideration the matching of the coefficient of thermal expansion with the semiconductor diaphragm and the prevention of transmission of strain stress, and the method of joining the semiconductor diaphragm and mount is easy and operates stably over a wide temperature range. It is possible.

Hereinafter, this invention will be explained in detail based on embodiments shown in the drawings.

Reference numeral 1 shown in FIG. 1 is a silicon diaphragm which is an embodiment of the semiconductor diaphragm of the present invention.

This silicon diaphragm 1 is made of a silicon single crystal with 110 planes, and is made by removing the center part 2 of the lower surface of a square plate-shaped chip approximately 7 mm x 7 mm x 200 μm by electrolytic etching, etc., and adding a thickness of several μm to the center. The thin film diaphragm 3 is formed into a circular shape. The diameter of the circle is 2-3 mm.

A 200 μm thick portion around the thin film diaphragm 3 is a peripheral fixing portion 4 .

The groove formed in the peripheral fixing part 4 so as to surround the thin film diaphragm 3 is a narrow and deep groove 6 for absorbing strain stress, and is opened in the lower surface 5 of the peripheral fixing part 4, and these openings 6a, 6b, 6c and 6d form a quadrilateral. The longitudinal directions of the openings forming the sides of the quadrilateral are all oriented in the <112> axis direction. The width of the opening is from several μm to several tens of μm, and the depth of the groove is approximately 80 to 90% of the thickness of the peripheral fixing portion 4, or approximately 160 to 180 μm.

The grooves 6 for absorbing strain and stress are formed by forming a thin film of SiO ₂ , Si ₃ N ₄ , etc. on the lower surface 5 of the peripheral fixing part 4, and then forming a rectangular pattern corresponding to the openings 6a, 6b, 6c, and 6d. After hollowing out using photolithography technology, APW (Amine
It can be shaped very well by etching (Pyocatechol Water). That is, according to APW etching, surface 111 is hardly etched. Therefore, if APW etching is performed on silicon that has an etching window with the longitudinal direction along the 112 axis on the 110 plane, etching will occur only in the depth direction, and lateral etching, that is, underetching will occur on the 111 plane. Because it appears, there is almost no progress. As a result, the lower surface 5 is etched only in the depth direction of the quadrilateral pattern, and the grooves 6 for absorbing strain and stress, which have groove walls 7a, 7b, 7c, and 7d perpendicular to the lower surface 5, have a narrow and deep cross section that is approximately U-shaped. This is because it will be formed in The depth of the groove 6 for absorbing strain stress can be controlled by the etching time, and the width can be controlled by the width of the sides of the quadrilateral pattern formed in the etching mask by the photolithography technique.

As shown in FIG. 4, the silicon diaphragm 1 in which the groove 6 for absorbing strain and stress, which has a substantially U-shaped cross section and opens in the lower surface 5 of the peripheral fixing part 4, is formed has a photo-conductor on its upper surface. A strain gauge part 9 made of, for example, a piezoresistive element is formed by a lithography method, and is attached to a mounting base 10 at a part of the mounting surface 5a of the peripheral fixing lower surface 5 outside the groove 6 for absorbing strain stress. - Used as a detection element 11 for differential pressure, absolute pressure, etc.

Since the silicon diaphragm 1 itself has the groove 6 for absorbing strain stress as described above, the thin film diaphragm 3 is connected to the peripheral fixing part 4.
There is almost no transmission of strain stress to the Therefore, there is very little temperature drift at the zero point due to strain stress, and the device can operate extremely stably. In addition, mounting base 1
There is no need for 0 to have a special structure, and any material such as glass, silicon, alumina, or metal can be used. Furthermore, attachment to the mounting base 10 can be carried out by any method such as using low melting point glass, synthetic resin adhesive, or gold-silicon eutectic. In addition, since the groove 6 for absorbing strain stress is narrow and deep and has a U-shaped cross section, the differential pressure between both sides of the diaphragm 1 causes the bridge portion 12 to
The stress generated in this case becomes shear stress, but silicon is strong against shear stress, so it can be used even under large differential pressures without any problems in terms of strength.

Other examples include one in which the groove for strain stress absorption is a groove that opens on the top surface of the diaphragm, or one in which the groove is a double groove with a groove that opens on the bottom surface and a groove that opens on the top surface. . Further, grooves for absorbing strain stress may be formed using other anisotropic etching such as alkali etching.

In addition, sputtering, plasma etching,
Grooves for absorbing strain stress may be formed using electron beam machining or the like. In this case, since it is not necessary to form grooves in a quadrilateral pattern with sides in the <112> axis direction, it is possible to form grooves in any pattern such as a circular pattern. Further, examples include those using germanium as the semiconductor.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the semiconductor diaphragm of the present invention in FIG. 2, FIG. 2 is a bottom view of the semiconductor diaphragm shown in FIG. 1, and FIG. 3 is a perspective view of the same bottom surface. FIG. 4 is a longitudinal end view of the pressure sensing element using the semiconductor diaphragm shown in FIG. 1. DESCRIPTION OF SYMBOLS 1...Silicon diaphragm, 3...Thin film diaphragm, 4...Peripheral fixing part, 5...Bottom surface, 5a...Mounting surface, 6...Groove for strain stress absorption, 6a, 6b, 6
c, 6d...Opening, 7a, 7b, 7c, 7d...Groove wall, 9...Piezo resistance element, 10...Mounting base, 11...
Pressure detection element.

Claims (1)

[Scope of Claims] 1. A thin film diaphragm is formed by recessing the central part of the lower surface of a semiconductor single crystal plate chip toward the upper surface, and a relatively thick part around the thin film diaphragm is used as a peripheral fixing part to be attached to a mounting base. A semiconductor diaphragm to be mounted, in which a narrow and deep groove is formed in the peripheral fixing part so as to surround the thin film diaphragm, and the lower surface of the peripheral fixing part outside the groove serves as the mounting surface of the mounting base. 2 The semiconductor is silicon, and the top of the plate-shaped chip
The bottom surface is 110, and <112 on the bottom 110 surface.
2. The semiconductor diaphragm according to claim 1, wherein the semiconductor diaphragm is formed by performing anisotropic etching along each side of a quadrilateral having sides in the axial direction to form a narrow and deep groove opening at the lower surface of the peripheral fixation. 3 Anidirectional etching is APW (Amine
3. The semiconductor diaphragm according to claim 2, wherein the semiconductor diaphragm is etched using pyrocatechol water. 4. The semiconductor diaphragm according to any one of claims 1 to 3, wherein a piezoresistive element is formed on the upper surface of the thin film diaphragm.