JPS6222467B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure-electricity conversion element. Normally, when a mechanical stress is applied to a semiconductor pressure transducer element made of silicon, germanium, etc., its resistance value changes due to the piezoresistance effect.
Utilizing this physical phenomenon, in a pressure-to-electricity conversion element made of a single crystal silicon plate, a strain gauge is formed on a semiconductor diaphragm using a diffusion layer, etc., and the strain gauge is deformed by the stress applied to the diaphragm, resulting in resistance due to the piezoresistive effect. Pressure is measured by detecting changes in value.

An example of the conventional structure of such a pressure-electricity conversion element is shown in FIG. In the figure, reference numeral 10 denotes a pressure-to-electricity conversion element consisting of a diaphragm 11 made of a silicon crystal thin plate and a support portion 13 for fixing the diaphragm 11. The diaphragm 11 and the support part 13 are integrally formed from a silicon crystal substrate, and a diffusion layer 12 that serves as a strain gauge is formed on the diaphragm 11. Furthermore, the lower surface of the support part 13 is attached to a mounting base using an adhesive 23. 21. Reference numeral 22 denotes a hole passing through the mounting base 21 and is an inlet for measuring gas (pressure inlet).

What is important in the pressure-to-electrical conversion element having such a configuration is that the diaphragm 11 is not subjected to unnecessary force from surrounding objects, such as the mounting base 21. The diaphragm 11 has a very thin wall thickness. For example, diaphragm 1 with a diameter of 3 mmφ
In order to detect a pressure change of 0 to 1 atmosphere at 1, a thickness of 50μ or less is desired. Diaphragm 1 like this
1 is very thin, so it is easily deformed by forces transmitted from outside, and undesirable stress is likely to act on the strain gauge. In the pressure-electricity conversion element shown in FIG. 1, the diaphragm 11 is fixed on the mounting base 21 via the support part 13 which is thicker than the diaphragm 11, so the force transmitted from the outside is absorbed by the support part 13 and weakened. It will be done.

However, the pressure-to-electricity conversion element of the conventional structure shown in FIG. 1 has a problem. Pressure-electricity conversion element 10
A large number of these are manufactured simultaneously from one silicon crystal substrate. First, as shown in FIG.
form 2. Next, although not shown in the figure, electrodes to be connected to the strain gauge are formed. Finally, a thin diaphragm 11 is formed by selectively etching from the back side. The remaining portion that is not etched becomes a thick supporting portion 13 (FIG. 2b). The one-dot chain line indicates the element separation line.

By the way, the characteristics of the pressure-electricity conversion element strongly depend on the thickness of the diaphragm 11 and its uniformity.
For the same pressure, the strain gauge is diaphragm 11
Since the response is inversely proportional to the square of the wall thickness, if the thickness of the diaphragm 11 varies, the characteristics will vary greatly. Furthermore, if the diaphragm 11 is non-uniform, the strain generated on the surface of the diaphragm 11 will exhibit an abnormal distribution.

However, as shown in FIG. 2b, the diaphragm 11 obtained through the process described above actually varies in thickness depending on each element, and the thickness of the diaphragm of one element is never uniform and uneven etching occurs. Etching sag occurs around the diaphragm 11. Since a strain gauge is normally disposed around the diaphragm 11, this etching sag has a large effect on the characteristics. Therefore, in order to obtain a diaphragm 11 of uniform thickness, various methods have been proposed to perform etching without uneven etching or etching sag. However, no substantial improvement has been achieved. This is because the initial crystal substrate 1 used has a thickness of about 300 .mu.m for handling reasons, but this is selectively etched to create a diaphragm of 50 .mu.m or less. That is,
This is because trenches with a depth of 250μ or more are dug at the same depth without uneven etching or uneven etching. Normally, when etching the crystal substrate 1, the etching solution is agitated in order to create uniform etching conditions at each location within the plane of the crystal substrate. However, if grooves exist within the plane, the flow of the liquid is disturbed, heat is retained within the grooves, causing uneven etching, and etching progresses not only in the depth direction but also in the lateral direction, resulting in etching sag.

As described above, in the conventional pressure-electricity conversion element, the characteristics of each element manufactured from a single crystal substrate vary, resulting in poor yield and high cost. In view of these points, methods have been proposed for providing pressure-to-electricity conversion elements with little variation in characteristics, high yield, and low cost. This method will be described in detail below with reference to Examples.

FIG. 3 shows the structure of one embodiment of a pressure-to-electricity conversion element using this method. In the figure, the same reference numerals as in FIG. 1 indicate the same or corresponding parts. 11 is a silicon diaphragm, and 13' is a cylindrical support body also made of silicon crystal. The silicon diaphragm 11 is attached to the support 1 with adhesive 14.
3' is fixed on top. The force transmitted from the mount 21 to the diaphragm 11 is absorbed and weakened by the support 13'.

Now, the pressure-electricity conversion element 10' according to this method
is formed as follows. As shown in FIG. 4a, a diffusion layer 12 serving as a strain gauge is first formed on a silicon crystal substrate 1 by a well-known diffusion technique, and then an electrode connected to the strain gauge is formed although not shown in the figure. Thereafter, etching is performed from the back side of the silicon crystal substrate 1 to form a diaphragm 11 of a desired thickness (FIG. 4b). The one-dot chain line is an element separation line. Finally, the diaphragm 11 is adhered to the support 13' and the pressure-electricity conversion element 1 is
Complete 0' (Figure 4c).

Incidentally, when the silicon crystal substrate 1 on which the strain gauge 12 is formed is thinned to form the diaphragm 11, etching is performed on the entire back surface of the silicon crystal substrate 1. If etching is performed while sufficiently agitating the etching solution, the etching solution will flow uniformly over the substrate surface and the etching conditions will be uniform over the entire back surface of the silicon crystal substrate 1, unlike when digging a groove as shown in Figure 2. . Therefore, the entire silicon crystal substrate is etched at a constant speed, and since there are no grooves, there is almost no uneven etching, and of course, since no grooves are dug, there are no etching marks.

In this way, the pressure-to-electrical transducer according to this method can have a uniform diaphragm thickness and a uniform diaphragm. In other words, the variation in characteristics is small, the yield is high, and the cost is low. However, the pressure-to-electricity conversion element shown in FIG. 3 has another problem. The diaphragm 11 and the support 13' are both made of the same silicon crystal, but are bonded together with an adhesive 14.
Residual strain stress exists in this bond. This residual strain stress acts on the thin diaphragm 11 and adversely affects the characteristics of the pressure-electricity conversion element 10'. This effect becomes particularly noticeable when the thickness of the diaphragm 11 is made thin. Diaphragm 1
If the thickness of the adhesive part 1 is made thinner, the influence of residual strain stress on the adhesive part can be suppressed by making the thickness of the adhesive part 14 commensurately thinner, but in general, the thinner the adhesive part 14 is, the more the adhesive part 14 becomes thinner. Adhesive strength may weaken, resulting in adhesive peeling or airtight leaks.

As the adhesive 14, resin, low melting point glass, alloy solder, etc. can be used, but even if the thickness of the adhesive part is made sufficiently thin so as not to adversely affect the characteristics of the pressure-electrical conversion element, the adhesive strength As an adhesive that is sufficiently strong and does not cause airtight leakage, a metal such as Au (gold) that causes a eutectic reaction with the silicon crystal constituting the diaphragm 11 and the support 13' is suitable. In fact, we used Au (gold) as the adhesive.
Si constituting the diaphragm 11 and the support 13'
When the diaphragm 11 and the support 13' were bonded together by performing an AuSi eutectic alloy reaction with (silicon), a bond that was sufficiently strong for practical use and without airtight leakage was obtained even if the thickness of the bonded portion 14 was 3 μm. It was possible. Further, in this case, even if the thickness of the diaphragm 11 was reduced to 20 μm, the characteristics of the pressure-electrical transducer were not affected within the normal operating range. However, in order to measure absolute pressure with the conventional pressure-to-electricity conversion element shown in FIG. The pressure to be measured had to be applied through the hole 22 by applying a vacuum to the top of the diaphragm or by some other means. In addition, in FIG. 3, since the support 13' is fixed on the mounting base 21, which generally has a coefficient of thermal expansion different from that of silicon crystal,
At the time of adhesion, the structure was such that the stress from the mounting base directly affected the strain gauge 12 on the diaphragm 11 via the support 13'. SUMMARY OF THE INVENTION In view of the conventional drawbacks, the present invention provides a pressure-to-electricity conversion element that is capable of measuring absolute pressure and has a structure that is less susceptible to strain stress from a mounting base.

FIG. 5 shows another embodiment of the pressure-electric conversion element according to the present invention, which is a pressure-electric conversion element for detecting absolute pressure. In the figure, the same reference numerals as in FIG. 3 indicate the same or corresponding parts. In this embodiment, the silicon diaphragm 11 is glued to a support 13' made of silicon crystal and having a recess 15. The inside of the recess 15 is kept in a vacuum. Therefore, the diaphragm 11 receives pressure only from the side on which the strain gauge 12 is formed, and absolute pressure can be detected. In the figure, the support part 13' is bonded to the mounting base at the center of its lower surface, and the area of the adhesive part 23 is smaller than the area of the lower surface of the support body 13' because the support part 13' is supported from the mounting base 21. This is to weaken the force transmitted to the body 13'.

Although Au (gold) was used as the adhesive 14 in the explanation of the above embodiment, other metals that have a eutectic reaction with Ag (silver), Al (aluminum), and Si (silicon), or with Si (silicon) may also be used. Of course, it may be an alloy containing a metal that undergoes a eutectic reaction.

As described above, according to the present invention, since the adhesive area between the support and the mounting base is reduced, it is possible to provide a pressure-electrical conversion element for absolute pressure detection that is less susceptible to the influence of strain stress from the mounting base. be able to.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional pressure-electric conversion element, FIG. 2 is a diagram for explaining a method of manufacturing a conventional pressure-electric conversion device, and FIG. 3 is a diagram showing a pressure-electric conversion device of the present invention. FIG. 4 is a cross-sectional view showing one embodiment of the present invention, FIG. 4 is a diagram for explaining a method of manufacturing a pressure-to-electricity converter according to the present invention, and FIG. 5 is a cross-sectional view showing another embodiment of the present invention. In the figure, 1 is a silicon crystal substrate, 10' is a pressure-electrical conversion element, 11 is a diaphragm, and 12
13' is a strain gauge, 13' is a support, and 14 is an adhesive. Note that the same reference numerals in the figures indicate the same or corresponding parts. Further, arrows in FIGS. 1, 3, and 5 indicate paths through which strain stress is transmitted from the mounting base 21 to the strain gauge 12.

Claims (1)

[Scope of Claims] 1. A pressure-to-electricity conversion element comprising a diaphragm in which a strain gauge is arranged at a predetermined position of a silicon crystal thin plate, and a support made of silicon crystal that supports the diaphragm, The support has a concave portion on a surface opposite to the diaphragm, and the support and the diaphragm are airtightly fixed so that the inside of the concave is kept in a vacuum, and the side of the support opposite to the side to which the diaphragm is fixed is A surface of the support body is bonded to a mounting base at a central portion of the surface, and the area of the bonded portion between the support body and the mounting base is smaller than the side area of the mounting base of the support body.
Electrical conversion element.