JPS6153871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure sensitive element used, for example, in a semiconductor pressure transducer for measuring fluid pressure.

This type of element is composed of a semiconductor substrate having a thin strain diaphragm portion, a reverse conductivity type diffused resistance layer, and a metal electrode for output extraction. Specifically, it is configured as shown in FIG. That is, 10 is a (100) plane n-type silicon semiconductor substrate, and a thin strain diaphragm portion 11 is formed in a circular shape in the center thereof. Further, on this substrate 10, P-type band-shaped resistance layers 12, 13, 14, and 15 formed by diffusing impurities such as boron are provided. Each layer 12, 13, 14, 1
5 are arranged at the ends of the diaphragm 11 at different positions by 90 degrees. In addition, each layer 12, 1
3, 14, and 15 each face the <110> direction, and each position is a position where stress is maximum when the diaphragm portion 11 receives pressure. That is, the diffused resistance layers 12 and 14 are located in the radial direction of the diaphragm portion 11, and the other layers 13 and 15 are located in the tangential direction. Therefore, when stress is generated due to the principle of the piezoresistive effect, resistance changes occur in opposite directions. Also, 16...... is,
A metal electrode made of aluminum or the like, one end of which is in contact with the diffusion resistance layer 12, 13, 14, 15, extends to the thick part that comes off the diaphragm surface 11 of the substrate 10, and the other end is connected to the outside. It consists of a bonding pet.

A bridge circuit is then constructed using the respective diffused resistance layers 12, 13, 14, and 15 via the metal electrodes 16, and the stress is measured, but this method has the following drawbacks.

First, extremely large thermal stress is generated at the interface between the silicon diaphragm surface and the aluminum wiring during aluminum evaporation, so even when no pressure is applied to the diaphragm 11, this thermal stress can be sensed. This causes the bridge to lose its balance. Generally, the magnitude of thermal stress is
It can be considered using the following equation.

ε _T = A (α _Si − α _Ae ) △T ε _T ; Strain A due to temperature change; Coefficient due to cross-sectional shape of wiring α _Si ; Linear expansion coefficient of silicon α _Ae ; Linear expansion coefficient of aluminum △T; Temperature change Since the generated thermal stress also changes depending on the ambient temperature, the temperature characteristics at the zero point tend to be extremely unstable. Further, the diffusion resistance layers 12, 13, 1 in the radial direction and tangential direction of the diaphragm 11
Because the distance between 4 and 15 is long, the silicon substrate 10
Due to variations in specific resistance, variations in impurity concentration during impurity diffusion, variations in temperature distribution, etc., variations in resistance value or temperature coefficient increase, which also worsens zero point temperature characteristics.

The present invention aims to eliminate these drawbacks, and provides a pressure-sensitive element with excellent zero-point temperature characteristics by forming the diffused resistance layer in a concentrated manner at one end of the diaphragm and minimizing the influence of the metal electrode. This is what we are trying to provide.

An embodiment of the present invention will be described below with reference to FIGS. 2a and 2b. Reference numeral 20 denotes a semiconductor substrate made of n-type silicon and having a circular thin diaphragm portion 21 . At one end of the diaphragm portion 21 of the substrate 20, P-type diffused resistance layers 22, 23, and 24 are formed in a concentrated manner. Each layer 22, 23,
24 is formed by diffusing impurities such as boron, and the diffused resistance layer 22 is located in the <110> direction, and the other layers 23 and 24 are arranged symmetrically with respect to the layer 22. In addition, the longitudinal direction thereof is arranged in a direction perpendicular to the longitudinal direction of the layer 22. Moreover, 25a, 25b...... each layer 22,
23 and 24, which are arranged symmetrically with respect to the diffusion resistance layer 22. especially,
Two electrodes 25a and 25g are formed symmetrically at one end of the resistance layer 22. These electrodes 25a, 25b...... are connected to each layer 22, 23,
After a conductive metal such as aluminum is vacuum-deposited on the entire surface of the substrate 20 on which the metal layer 24 is formed, unnecessary portions of the metal layer are etched with hot acid or the like using a photo-etching technique. Moreover, these electrodes 25a, 25b...
are formed to have a width comparable to that of the diffusion resistance layers 22, 23, and 24 in order to minimize the influence on thermal stress. And electrodes 25a, 25
b...After wiring, perform silittering at 500℃. Further, 26 is an insulating layer of silicon dioxide film.

For example, one diffused resistance layer 22 arranged in the radial direction of the diaphragm part 21 and one diffused resistance layer 23 arranged in the tangential direction, configured in this way,
Furthermore, a bridge circuit is constructed with two dummy resistors (not shown) to detect stress. That is, if pressure is applied from the direction of arrow C in FIG. Output proportional to pressure is extracted.

By the way, when the applied pressure is zero, the bridge circuit output has very little variation in concentration or temperature distribution during impurity diffusion because each resistance layer 22, 23, 24 is concentrated at one end of the diaphragm section 21. The resistance values are similar and therefore close to zero. Similarly, the temperature coefficient at the zero point is also very small.

Next, each resistance layer 22, 23, 24 and the electrode 25
The temperature coefficients of a, 25b, etc. will be considered from the perspective of thermal stress. That is, since the substrate 20 and the insulating layer 26 have different coefficients of linear expansion, stress is concentrated in the holes opened for forming the resistance layers 22, 23, and 24 in the planar structure. This means that the temperature when forming the insulating layer 26 is 1100°C.
This is natural, given the atmosphere. In addition, the substrate 20
The same can be said of the metal electrodes 25a, 25b, etc., and the generated thermal stress affects the temperature characteristics at the zero point.

Therefore, in this embodiment, the insulating layer 2 is first
The minimum number of holes necessary for forming each of the resistance layers 22, 23, and 24 is formed symmetrically in 6, so that the internal stress is balanced when the applied pressure is zero. Further, the electrodes 25a, 25b, . . . are made to the minimum necessary number, extend from each layer 22, 23, 24 through the shortest distance on the substrate 20 outside the diaphragm portion 21, and are arranged symmetrically. In addition,
The electrodes 25a, 25b... are formed to have a narrow width and a small thickness.

In this way, the output of the bridge circuit when the applied pressure is zero and the temperature coefficient at the zero point are reduced, and the temperature characteristics are made stable. In addition, in the conventional example, the zero point of the bridge circuit draws a hysteresis loop during the temperature cycle test as shown in Figure 3, and the bridge zero point error is 4% (FS) at the maximum value.
Occurs to some extent. On the other hand, according to this embodiment, as shown in FIG. 4, it is about 1/10 of the conventional example, so small that it can be ignored, and its performance is significantly improved.

Note that in this embodiment, the n-type semiconductor substrate 2
Although the explanation has been made using a P-type semiconductor substrate, the same implementation is possible using a P-type semiconductor substrate. Furthermore, the directions of the diffusion resistance layers 22, 23, and 24 are not limited to this example. That is, as shown in FIG. 5, the tangentially arranged diffused resistance layers 23 and 24 are arranged in the <110> direction, and the radial layer 22 is arranged in the direction orthogonal to the diffused resistance layers 23 and 24. It can also be implemented in the same way. Furthermore, if the longitudinal direction of at least one of the layers 22, 23, and 24 arranged in the tangential or radial direction is arranged in a direction that has piezoresistive sensitivity that can be used sufficiently near the <110> direction, It is not necessarily necessary to arrange it completely in the <110> direction.

Further, in this embodiment, the diffused resistance layers 22, 2
3 and 24 are arranged centrally at one end of the diaphragm portion 21, for example, a similar group of diffused resistance layers may be provided at the other end, or each layer 22, 23, and 24 may be provided at two or more locations. good. Further, the same effect can be obtained even if two radial diffusion resistance layers and one tangential layer are provided.

Since the present invention is configured in this way, it is possible to reduce the influence of thermal stress and to make the resistance values of the respective diffused resistance layers substantially similar. Therefore, when a bridge circuit is constructed using each resistance layer, the output when the applied pressure is zero can be brought close to zero, and the temperature characteristics at the zero point can be made good.

[Brief explanation of the drawing]

FIG. 1 is a plan view for explaining a conventional pressure-sensitive element, and FIGS. 2 a and 2 b are for explaining an embodiment of the present invention. FIG. 3 and 4 are for explaining the characteristics of the present invention, and FIG. 3 is a characteristic diagram of the conventional example, FIG. 4 is a characteristic diagram of one embodiment, and FIG. 5 is a plan view for explaining another embodiment. In addition, in the figure, 20 is a semiconductor substrate, 21 is a diaphragm part, 22, 23, 24 are diffused resistance layers, and 25
a, 25b... are metal electrodes.

Claims (1)

[Claims] 1. A semiconductor substrate having a strain diaphragm portion;
In a pressure sensitive element having a plurality of diffused resistance layers of opposite conductivity type formed on the diaphragm portion of this substrate and a metal electrode for external connection connected to the resistance layer, the diffused resistance layer is connected to one end of the diaphragm. What is claimed is: 1. A pressure-sensitive element, characterized in that other diffusion resistance layers are arranged symmetrically with respect to at least one diffusion resistance layer, and metal electrodes are arranged symmetrically with respect to the reference. 2. The pressure-sensitive element according to claim 1, wherein the width of the metal electrode is equal to or less than the width of the diffused resistance layer.