JPH04119672A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To enable a semiconductor pressure sensor to be remarkably enhanced in temperature compensation accuracy by a method wherein the sensor is provided with a strain gauge and a silicon crystal base whose plane orientation is nearly the direction of (110) and a pedestal different from the base in thermal expansion coefficient is jointed to the base. CONSTITUTION:A semiconductor pressure sensor is composed of a substrate 1 of a single-crystal silicon chip diced 3mm square provided with a diaphragm 4 and a pedestal 3 electrostatically jointed to the non-diaphragm part 7 or the peripheral part of the substrate 1, and a pressure to measure is introduced into a recessed side of the diaphragm 4 from outside through a pressure introducing hole 31 provided perforating the pedestal 3, and on the other hand, a constant reference pressure is applied onto the flat side of the diaphragm 4. The plane orientation of the substrate 1 is nearly the direction of (110), and the octagonal diaphragm 4 is engraved at the center of the substrate 1 through anisotropic etching. The diaphragm 4 is demarcated by sides which cross a <100> axis, a <110> axis, and a <111> axis at right angles.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a semiconductor pressure sensor having a diaphragm portion formed by etching a single crystal silicon substrate having an approximately (110) plane orientation.

[Conventional technology] An example of a conventional semiconductor pressure sensor is shown in FIG.

This semiconductor pressure sensor has a diaphragm portion 4a formed by anisotropically etching a single-crystal silicon substrate 1a having a surface orientation of approximately (11O) to form a substantially rectangular recess. When the plane orientation is approximately (110), the strain gauges forming the bridge are provided at the periphery and center of the diaphragm portion 4a.

As shown in FIG. 3, the non-diaphragm portion 7a of the substrate 1a is joined to a pedestal 3 made of, for example, Pyrex glass, and pressure is introduced from the outside into the concave surface of the diaphragm portion 4a through the pressure introduction hole 31 of the pedestal 3. .

The semiconductor pressure sensor disclosed in Japanese Patent Publication No. 60-13314 is
An octagonal diaphragm portion having sides parallel to two different crystal axes on the surface of a semiconductor crystal with a (100) plane orientation is disclosed.

In a semiconductor pressure sensor having this surface orientation, all strain gauges are generally arranged around the diaphragm portion. Further, the above-mentioned publication discloses that by adopting the above-mentioned structure, it is possible to eliminate local stress concentration and increase the maximum value of allowable applied pressure.

[Problems to be Solved by the Invention] In the semiconductor pressure case for bonding the above-mentioned single-crystal silicon substrate to a pedestal whose ultimate coefficient of expansion is different from that of the single-crystal silicon substrate, conventionally, thermal stress is generated in the diaphragm part due to the difference in the coefficient of thermal expansion between the two. It is known that this variation in thermal stress within the diaphragm plane causes an output (hereinafter referred to as a thermal stress fire) to occur in the bridge due to thermal stress. This C thermal stress output includes signal components other than the pressure signal (hereinafter referred to as
It is called offset voltage. ), which will be discussed later, often have nonlinearity with respect to temperature changes, and it is difficult to compensate for this nonlinearity with a simple electronic circuit, which is a major obstacle to improving the accuracy of semiconductor pressure sensors. However, no effective solution has been presented to date.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor pressure sensor that can significantly improve temperature compensation accuracy.

[Means for Solving the Problems] A semiconductor pressure sensor of the present invention includes a strain gauge provided on a diaphragm portion, and a silicon crystal base having a plane orientation of approximately (110>) as a base for the diaphragm. and a pedestal having a coefficient of thermal expansion different from that of the base and joined to the base, wherein the diaphragm part has a <100> axis, a <110> axis,
It is characterized by having an octagonal shape with sides perpendicular to the <111> axis.

Here, when the plane orientation is approximately (110), it means (110
) This means that it may be tilted, for example, by several degrees from the plane. Such a slope is advantageous in reducing defects when performing epitaxial growth on the substrate surface to integrate transistors.

[Operations and Effects of the Invention] The present invention discloses a silicon crystal base having an octagonal diaphragm portion and a plane orientation of approximately (110), and a base having a coefficient of thermal expansion different from that of the base. A semiconductor pressure sensor (hereinafter referred to as a (110) type rectangular semiconductor pressure sensor) includes a silicon crystal base having a substantially rectangular diaphragm portion, and a base having a coefficient of thermal expansion different from that of the base. Calculations using the finite element method and prototype production revealed that the distribution of thermal stress within the plane of the diaphragm part can be changed compared to a conventional semiconductor pressure sensor (hereinafter referred to as a rectangular semiconductor pressure sensor).

As a result, according to the (110) type rectangular semiconductor pressure sensor of the present invention, the output error can be made much smaller than before regardless of temperature fluctuations.

[Example] (Example 1) An example of the semiconductor pressure sensor of the present invention will be described with reference to FIGS. 1 to 4.

As shown in FIG. 3, this semiconductor pressure sensor consists of a substrate 1 made of a single-crystal silicon chip having a diaphragm portion 4 and diced into a square of approximately 3 mm on each side;
It consists of a pedestal 3 made of Pyrex glass (trade name) which is electrostatically bonded to the non-diaphragm part 7, that is, the peripheral edge of the diaphragm part 4. Pressure introduction hole 3 penetrated through pedestal 3]
A pressure to be measured is introduced from the outside to the concave side of the diaphragm portion 4 through the diaphragm portion 4, while a constant reference pressure is applied to the flat side of the diaphragm portion 4.

The thickness of the substrate 1 is approximately 0.3 mm, and the plane orientation is approximately (110).
An octagonal diaphragm portion 4 is recessed in the center of the substrate 1 by anisotropic etching.

The diaphragm portion 4 has a thickness of approximately 40 μm and <1
It is divided by sides perpendicular to the 00>, <110>, and <111> axes. The length of the first side Otsu 1 is approximately 0.54m
m, the length of the second side Otsu 2 is approximately 0.84 mm, and the length of the third side Otsu 3 is approximately 0.48 mm.

Four strain gauges 2 are formed at the periphery and center of the diaphragm part 4 by doping with impurities of the opposite conductivity type to the substrate 1, and these strain gauges 2 are bridge-connected as shown in FIG. .

The manufacturing process of this semiconductor pressure sensor will be explained below.

Strain gauges 2a to 2d are formed using normal semiconductor process technology on a single crystal silicon wafer with approximately (110) plane orientation.
After that, wiring, passivation, contact hole formation, and bonding pad formation are performed. The arrangement of the strain gauges 2a to 2d is the same as when using the normal (110) plane, and the <11
The longitudinal direction of the gauge is set to <11 so that the axis of symmetry is the 0> axis.
0> direction, the strain gauges 2a and 2d are arranged at the periphery of the diaphragm part 4, and the strain gauges 2b and 2C are arranged at the center thereof.

Next, as shown in FIG. 2, an etching mask such as an oxide film is formed on the back surface of the wafer by photolithography, and anisotropic etching is performed using a KOH aqueous solution or the like. In this way, the diaphragm 4 having a helical shape can be formed by straight lines perpendicular to the <100> axis, the <110> axis, and the <111> axis.

Next, this wafer is diced and electrostatically bonded to a pedestal 3 made of Pyrex glass, and bonding pads and input/output pins (not shown) are bonded with gold wire or the like.

Since the structure and manufacturing process of this type of semiconductor pressure sensor are well known, further explanation will be omitted.

Next, the thermal error offset voltage generated at the output end of the bridge (see FIG. 4) will be explained.

This thermal error offset voltage is mainly caused by the pedestal 3 and the substrate 1.
The thermal stress generated due to the difference in thermal expansion coefficient between the substrate 1 and the thermal oxide film, passivation film, etc. deposited thereon varies within the plane of the diaphragm portion.

Figure 5 shows the distribution of thermal stress in the radial direction, which was obtained by analyzing the thermal stress due to the Pyrex pedestal using the finite element method. A shows the radial thermal stress distribution in the semiconductor pressure sensor of this example, and B shows a rectangular semiconductor pressure sensor in which the distance between opposing sides of the diaphragm part is equal to that of the semiconductor pressure sensor of this example (see Fig. 8). ) shows the radial thermal stress distribution.

The analysis conditions are a temperature difference of 100°C and a thermal expansion coefficient difference of 1x10.
−? ['C-''] and the pressure difference was O.

As can be seen from FIG. 5, the semiconductor pressure sensor (A>) of this embodiment has a lower temperature than the conventional semiconductor pressure sensor (B).
It can be seen that the variation in thermal stress within the plane of the diaphragm portion 4 is significantly small. In particular, it has been found that in the semiconductor pressure sensor of this embodiment, the thermal stress is approximately equal between the central portion and the peripheral portion of the diaphragm portion 4, so that almost no thermal error output voltage occurs in the bridge output Vout.

Therefore, the difference in thermal stress between the strain gauges 2b and 2C placed at the center of the diaphragm part 4 and the strain gauges 2a and 2d placed at the periphery can be made extremely small, and as a result, the thermal error offset voltage can be significantly reduced. reduced to

In addition, in the bridge shown in Fig. 4, the total offset voltage vout (p=○) including the thermal error offset voltage is Vout (p=○) = Vin-(Rb-Rc-Ra-Rd)/((Ra + R
b) (Rc+Rd)) However, Ra, Rb, R
C and Rd are strain gauges 2a, 2b, and 2C12d, respectively.
The resistance value is assumed to be , and the pressure difference p applied to the diaphragm 4 is O.

By the way, the resistance values of strain gauges 2a to 2d are determined by thermal stress,
It changes depending on the variation in the temperature coefficient of resistance TCP of each strain gauge itself.

Now, in the range from air temperature to about 150℃, the thermal expansion coefficient αp of Pyrex glass is 3゜2X10 -6
[°C-”], thermal expansion coefficient αS of Si at warm temperature [°C] 4.8x10-9T+2.6X10-6
['C-1], the amount of thermal strain for 6 units is εTl=1. /'T'8 (α low α5) dT≠1-2.
4X10-9・T2 10y6X10-6-T+ε0, and has temperature dependence. However, TB is the temperature when the substrate 1 and the pedestal 3 are joined, and εO is the amount of thermal strain when the temperature T is 0°C.

The quadratic component under temperature in the above equation represents the nonlinear component of the temperature dependence of thermal strain, and as mentioned above, this nonlinear component is more important for temperature compensation than the absolute value of thermal strain itself. This is often a problem.

Each resistance value of these thermal strain amounts 16T1 changes due to temperature fluctuations of each strain gauge 2a to 2d, but in bridge connection, each The variation in the resistance values of the strain gauges 2a to 2d (the difference in thermal strain between the peripheral parts 2a and 2d and the central parts 2b and 2C) is actually used as a thermal error offset voltage (mainly thermal stress output). appear.

Next, test products of the semiconductor pressure sensor of this example were prepared in which the ratio of each side length of the diaphragm portion 4 was varied, and the amount of variation in the thermal error offset voltage with respect to temperature change was measured. As a comparative survey, a rectangular shape with the same distance between sides was also prepared, and the variation amount of the thermal error offset voltage with respect to the temperature change was set as 1, and the relative display is shown in FIG.

The test condition is that the pressure difference between the diaphragm portion 4 is 25 ° C.25 ° C., 120 ° C. Hema Otsu 2
, and the distance between the same first sides B and 1 that are parallel to each other is L-
and L'/L is 1°04 (see Figure 7).

From FIG. 6, it was found that if O/L=0.4, the amount of variation could be reduced to approximately O. However, if the influence of the passivation film and the like is taken into account, the graph shown in FIG. 6 may change somewhat if the scale of the diaphragm thickness, etc. is changed.

Although the modified strain gauges 2a to 2d are fabricated by doping single crystal silicon (110> plane with impurities), they may also be made of polysilicon resistors provided on the diaphragm 4.

Also, if the plane orientation is (100) on the substrate 1 whose plane orientation is (110),
) single crystal silicon substrates are pasted together to form this (100)
A strain gauge resistor may be formed on the substrate.

As the etching method, various conventionally known etching methods can be used in addition to the KOH aqueous solution.

The pedestal 3 can be made of a material other than Pyrex glass.

In this embodiment, there are four strain gauges 2a that constitute the bridge.
Although the strain gauges 2d to 2d are formed on the diaphragm 4, a so-called half-bridge circuit configured with a combination of strain gauges 2a, 2b, or 2C12d on the diaphragm 4 can also have the same effect.

(Effects of Example) As explained above, in this example, a substrate made of single crystal silicon having an octagonal diaphragm portion and a plane orientation of approximately (110), and a pedestal having a coefficient of thermal expansion different from that of this substrate. In the semiconductor pressure sensor, the degree of influence of thermal stress can be adjusted arbitrarily by changing the ratio 1/1 of the length of the first side of the diaphragm part to the distance between the two sides of the two cylinders of the diaphragm part. It can be changed. Therefore, according to this embodiment, not only can the thermal stress output be eliminated, but also the thermal stress output can be changed arbitrarily, so the thermal stress output can be actively used to compensate for the temperature of the pressure sensitivity. This is not a perfect compensation method since the offset voltage and offset voltage are completely different.), and it becomes possible to manufacture a semiconductor pressure sensor with extremely small output fluctuations due to temperature changes.

[Brief explanation of the drawing]

FIG. 1(a) is a plan view showing an embodiment of the substrate used in the semiconductor pressure sensor of the present invention, and FIG. 1(b) is A of FIG. 1(a).
A cross-sectional view, (C) is a CC cross-sectional view of Figure (a), Figure (d) is a BB cross-sectional view of Figure (a), and Figure 2 is a plane showing the etching mask used in its manufacture. 3 is a sectional view of the semiconductor pressure sensor of the above embodiment, FIG. 4 is a bridge connection circuit diagram, and FIG. 5 is a diagram showing the thermal stress distribution in the radial direction.
Fig. 6 is a diagram showing bridge offset voltage fluctuations with respect to temperature changes, Fig. 7 is a diagram showing the dimensions of the sample used in Fig. 6, and Fig. 8 (a) is a plan view of the substrate of a conventional semiconductor pressure sensor. The figure, (b) is the AA sectional view, the same figure (
C) is its BB sectional view. 1... Substrates 2a to 2d... Distortion game 3... Pedestal 4... Diaphragm part

Claims (1)

[Claims] A strain gauge provided on a diaphragm portion, and a silicon crystal base having a plane orientation of approximately (110) as the base of the diaphragm, and having a coefficient of thermal expansion different from that of the base and bonded to the base. In the semiconductor pressure sensor, the diaphragm portion has a diameter of <100>.
A semiconductor pressure sensor characterized by having an octagonal shape with sides orthogonal to an axis, a <110> axis, and a <111> axis.