JPS5938744B2 - Pressure-electricity converter and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure-carrying electrical transducer in which a pressure sensitive element is arranged on a single crystal silicon substrate by diffusion or the like, and in particular has an excellent diaphragm uniformity, and a method for manufacturing the same.

Normally, when a mechanical stress is applied to a semiconductor pressure sensing element made of silicon, germanium, etc., its resistance value changes due to the piezoresistance effect.

Utilizing this physical phenomenon, in a piezoelectric converter made of a single crystal silicon plate, a strain gauge is formed on the semiconductor diaphragm using a diffusion layer, etc., and the strain gauge is deformed by the pressure applied to the diaphragm, and a piezoresistor is created. Pressure is measured by detecting changes in resistance due to effects. In this case, in order to manufacture a highly accurate product with little variation, it is important to precisely manufacture the thickness of the diaphragm. However, when conventionally forming the pressure-receiving part of a diaphragm, the etching rate changes significantly depending on the temperature of the etching solution, stirring conditions, changes in the composition of the etching solution, etc., so accurate control is not only necessary, but also the thickness of the diaphragm. The etching process is repeated after measuring the thickness. The thickness of the diaphragm is a very important factor in making the characteristics of this piezoelectric converter device uniform. However, with the conventional methods described above, it is extremely difficult to accurately control the thickness and parallelism of the diaphragm, resulting in poor yields and increased costs. Also, due to diffusion issues and sensitivity characteristics, elements are usually fabricated by forming a P-type diffusion resistance gauge on an N-type silicon substrate, but when measuring pressure in water etc., the N-type silicon substrate is used as a ground. It is necessary to separate the device itself so that it does not become a potential, which not only increases cost but also causes deterioration in characteristics.

The present invention has been made in view of the above-mentioned drawbacks, and includes a piezoelectric converter and a method for manufacturing the same, which control the parallelism of a semiconductor diaphragm with high accuracy, and reduce variations in characteristics by making the diaphragm thickness uniform between each chip. The purpose is to provide the following.

Next, in order to better understand the present invention, the present invention will be specifically explained using an example shown in the drawings.

FIG. 1 shows a structure in which a thermal oxide film 2 is formed on one main surface of a single crystal silicon substrate 1, which is an N-type or P-type crystal plane having a specific direction, for example, a (110) plane. Continuing on, Fig. 2 shows that P is applied to the opposite main surface on which the thermal oxide film 2 is not formed in order to stop alkaline etching in the later process.
Boron is used as a type impurity, and the impurity concentration is 5 x 1019 pieces/
This shows that an impurity layer 3 is formed in a predetermined region with a concentration of more than .cit. Next, an N-type single crystal silicon layer 4 is epitaxially grown on the surface of the impurity layer 3 of the substrate 1, as shown in FIG. The thickness of this silicon layer 4 can be arbitrarily selected depending on the pressure measurement range of the pressure converter. For example, for a diaphragm with a diameter of 3ER for measuring 1 atm, a diameter of about 50μ is optimal.
Also shown in FIG. 3 is a thermal oxide film 2, which is used as an etching mask for forming a diaphragm, and has holes opened only in predetermined areas. Here, etching for diaphragm formation using a selective etching solution such as potassium hydroxide is a well known method. Perform the following. At this time, the thermal oxide film 2 acts as a mask against the potassium hydroxide solution. Etching progresses sequentially in the removed portions of the thermal oxide film 2, but since the etching rate of single-crystal silicon containing 5 x 1019 or more boron atoms is almost zero, impurities When layer 3 is reached, the etching is automatically stopped, and a diaphragm is formed with a thickness equal to that of impurity layer 3 and epitaxially grown N-type single crystal silicon layer 4. At this time, since the etching solution is anisotropic with respect to the plane orientation of the crystal, the boundary between the diaphragm and the diaphragm support can be defined approximately linearly (at an acute angle). The diaphragm 6 and diaphragm support T formed in this manner are shown in FIG. 5 is an oxide film formed on the silicon layer 4.

FIG. 5 shows a structure in which the P-type impurity is subsequently diffused to form an isolation layer 8 for electrically isolating the element portion. FIG. 6 shows a piezoelectric transducer in which a P-type diffusion layer 9 serving as a strain gauge acting as a pressure-sensitive element is formed, and an electrode 10 is formed of aluminum. FIG. T is a plan view of the apparatus shown in FIG. 6. In this embodiment, the pressure sensitive element portion 9 was formed after forming the diaphragm 6 and the diaphragm support T, but the steps may be reversed. In addition, the isolation layer 8 for electrically isolating the pressure sensitive element portion 9 is formed by performing alkali etching treatment on the PN junction formation portion on the side surface of the semiconductor in FIG. If the insulation between the sidewall portion and the impurity layer 3 is improved, it can be omitted. Furthermore, in the embodiment described above, the P-type diffusion layer 9 was provided as a strain gauge, but it is also possible to detect the strain deformation of the diaphragm made of silicon by using another strain detection element without providing the strain gauge. Of course. As described above, in the present invention, an impurity layer is formed in advance in a single crystal silicon substrate to serve as a predetermined stop for etching, and the silicon substrate is etched to this region, so that the thickness of the diaphragm and Parallelism is determined only by the thickness of the impurity layer and the epitaxially grown layer, and it is not only extremely easy to control, but also because etching automatically stops when the desired diaphragm thickness is reached. It is possible to manufacture a large number of complete piezoelectric converters.

In addition, by using an etching solution that is anisotropic with respect to the plane orientation of the crystal of the silicon substrate, the boundary between the diaphragm and the diaphragm support can be clearly formed as a straight line rather than a curved one. Stress generated by pressure can be used effectively. Furthermore, conventionally, when measuring pressure in water, etc., it is necessary to separate the device itself so that the silicon substrate of the diaphragm does not come into direct contact with water, which increases costs and reduces characteristics.However, according to the present invention, the isolator Electrical isolation is completely achieved by the PN junction formed by the silicon diaphragm, and pressure can be applied directly to the silicon diaphragm, so there is no decrease in response or characteristics, and the device itself can be simplified. As described above, it is possible to provide a large number of pressure car electrical converters with uniform characteristics and electrical isolation performed with high precision, which is an excellent effect.

[Brief explanation of drawings]

1 to 6 are process diagrams used to explain an embodiment of the pressure car electric converter and method for manufacturing the same according to the present invention, and FIG. 7 is a plan view of the device shown in FIG. 6. . 1... N-type single crystal silicon substrate, 3...
... P-type impurity layer, high concentration boron impurity layer, 4...
...N-type epitaxial layer, 8...P-type isolation layer, 9 ...P forming a pressure-sensitive element
Type diffusion layer (strain gauge).

Claims (1)

[Scope of Claims] 1. An impurity layer having a P-type impurity concentration of a predetermined value or more formed on one main surface of a single crystal silicon substrate, and an epitaxial layer having a predetermined thickness formed on the impurity layer; A pressure sensitive element disposed at a predetermined position corresponding to the pressure receiving region of the epitaxial layer, and a pressure sensitive element disposed at a predetermined position corresponding to the pressure receiving region of the epitaxial layer; and a diaphragm portion formed by etching down to the impurity layer using a chemical etching solution. 2. An impurity layer with a P-type impurity concentration of a predetermined value or more formed on one main surface of a single crystal silicon substrate, an epitaxial layer with a predetermined thickness formed on the impurity layer, and a pressure receiving region of the epitaxial layer. An anisotropic etching solution is applied to both crystal orientations of the silicon substrate on a pressure-sensitive element disposed at a predetermined position corresponding to the pressure-sensitive element and on a portion of the other main surface of the silicon substrate corresponding to the pressure-receiving region. and a diaphragm portion formed by etching up to the impurity layer, and an isolation layer in which a P-type impurity is diffused and formed around the pressure sensitive element in the epitaxial layer so as to reach the impurity layer. Characteristic pressure-electricity conversion device. 3. A step of forming an impurity layer on one main surface of a single crystal silicon substrate to stop etching, and a step of forming an epitaxial layer with a predetermined thickness on the impurity layer.
a step of arranging a pressure-sensitive element at a predetermined position corresponding to the pressure-receiving region of the epitaxial layer; and a step of disposing a pressure-sensitive element at a predetermined position corresponding to the pressure-receiving region of the epitaxial layer; A method of manufacturing a pressure-to-electricity converter, comprising the step of etching down to the impurity layer by applying a directional etching solution to form a diaphragm portion.