JPH0727643A - Piezo resistance type semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To obtain an inexpensive and accurate pressure sensor by providing a recess having a flat bottom part on one main surface side of Si single-crystal substrate for forming a diaphragm with a rim and then forming a piezo resistor strain gauge in the bottom part. CONSTITUTION:Oxide film is formed on Si single-crystal substrate 21 by thermal oxidation and then a window is opened on its upper surface by etching. Further, etching is performed from the window and then a recess with a flat bottom part and a diaphragm 22 with a rim are formed on the substrate 21. After the surface of the diaphragm 22 is thermally oxidized, etched, and then cleaned, oxide film 23 is formed and then polycrystalline Si layer of impurity dope is formed on it. and then patterning is performed and a piezo resistor 24 is formed on the oxide film 23. Then, oxide film 28 is formed on the entire surface, a hole Is opened in the oxide film 28 on the resistor 24 by etching and a conductive material is deposited, and further an inner electrode 25, an outer electric wire 26, and a wiring 27 are formed by etching. Then, passivation film 29 is deposited on an entire surface and a lead wire is connected to an electrode 26, thus accurately manufacturing the sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel structure of a piezoresistive semiconductor pressure sensor element used in fields such as industrial measurement and automobiles.

[0002]

2. Description of the Related Art In a conventional piezoresistive semiconductor pressure sensor element, as shown in FIG. 2, a rim-equipped diaphragm 2 is formed by forming an indentation having a flat bottom on the lower surface side of a Si single crystal substrate 1. An oxide film 3 is provided on the upper surface side of the substrate 1, and non-doped polycrystalline S is provided on the oxide film 3.
An i layer 4 is provided, a strain resistor 5 is formed in the non-doped polycrystalline Si layer 4, an electrode 6 is provided on the strain resistor 5, and a wiring portion of the electrode 6 and the polycrystalline Si layer are provided. An insulating film 7 is interposed between the piezoresistive strain gauges 4 and the piezoresistive strain gauges 4 and 4. In this device structure, a strain gauge is first formed on the Si substrate surface,
Finally, it is obtained by etching the rear surface of the substrate, leaving the peripheral edge portion, to form a recess, and forming the diaphragm 2 with a rim. The peripheral portion becomes the rim of the diaphragm.

The diaphragm 2 is usually 10 to 100 μm.
The thickness of the diaphragm 2 is about m, and when the external pressure 8 or 9 is applied to the diaphragm 2, the diaphragm 2 is deformed, and the resistivity of the strain resistor 5 above the diaphragm 2 is changed by the piezo effect. The amount of change in the resistivity depends on the crystal orientation of the substrate and can be detected by converting it into an electric signal related to the applied force, which can be used for detecting the pressure. In FIG. 2, two strain gauges on the left and right are shown, but these are arranged in the lateral direction,
Further, a pressure change can be detected as a bridge output by forming a bridge circuit with four strain gauges in combination with two strain gauges arranged in the vertical direction.

[0004]

By the way, it is general that a large number of such element structures are formed on one Si single crystal substrate, and finally dicing is performed to separate the elements. In the conventional element, it is necessary to form a diaphragm on the back surface of the Si substrate in accordance with the position of the strain gauge manufactured on the front surface of the Si single crystal substrate. With the miniaturization of the element, the position of the front surface strain gauge and the back surface diaphragm The matching requires sufficient accuracy. In order to obtain this accuracy, a commonly used mask alignment apparatus is not sufficient, and an expensive apparatus capable of performing double-sided mask alignment is required, which has a drawback of high cost. In addition, alignment of both surfaces takes time, which is disadvantageous in terms of production efficiency. Furthermore, a process of applying resist to the substrate to form the diaphragm, exposing, developing, etching, and peeling the resist is necessary, but damages or contaminates the strain gauge already formed in this process. There is a fear.
If the strain gauge is damaged or contaminated, the device performance will be significantly deteriorated.

An object of the present invention is to reduce damage and contamination of the strain gauge and the diaphragm which are caused by forming the diaphragm on different surfaces of the Si substrate, and further to provide an expensive mask alignment device for the strain gauge and the diaphragm. Another object of the present invention is to provide a structure of a piezoresistive semiconductor pressure sensor that can be accurately arranged without using and can be manufactured at low cost and with high accuracy.

[0006]

In order to achieve the above object, the sensor of the present invention is provided with a rimed diaphragm in which a recess having a flat bottom is provided on one main surface side of a Si single crystal substrate. It is characterized in that at least one piezoresistor strain gauge is formed on the diaphragm at the bottom of the recess.

[0007]

The Si single crystal substrate used in the present invention may be a commercially available one for manufacturing a semiconductor device, and a known semiconductor manufacturing technique can be applied as it is to manufacture a diaphragm and a resistor strain gauge. Since the piezoresistive semiconductor pressure sensor has the above structure, the diaphragm and the resistor strain gauge can be formed by processing only one side of the substrate.
Positioning of the diaphragm part and the strain gauge parts such as the piezoresistor and the electrodes on the front and back sides of the Si substrate, which has been a problem in the photolithography process, becomes unnecessary, and the device can be manufactured much more easily. Further, the photolithography apparatus to be used can also be a standard product because the alignment on one side is sufficient. Further, since the strain gauge is manufactured on the same surface after the diaphragm is formed, there is no fear of contamination or damage to the strain gauge portion which has been caused by the strain gauge becoming the bottom surface when the diaphragm is formed.

[0008]

FIG. 1 is a sectional view conceptually showing an example of the structure of a piezoresistive semiconductor pressure sensor of the present invention. The Si single crystal substrate 21 is provided with a recess having a flat bottom portion on the upper surface side to form a diaphragm 22 with a rim and a thickness of 1 mm.
An oxide film 23 is formed on the diaphragm 22 having a thickness of 0 to 100 μm, and an impurity-doped polycrystalline Si layer 24 serving as a piezoresistor is formed on the oxide film 23. An internal electrode 25 is provided on the polycrystalline Si layer 24, and the internal electrode 25 and the external electrode 26 arranged on the rim are connected by a wiring 27. The polycrystalline Si layer 24, the internal electrode 25, the external electrode 26, and the wiring 27 are separated by an insulating film 28 between them, and the uppermost portion is covered with a passivation film 29. The strain gauge is an impurity-doped polycrystalline Si layer. 24,
Wiring 2 connecting the internal electrode 25, the external electrode 26 and the electrodes
The structure is composed of 7.

In FIG. 1, two strain gauges on the left and right are shown, but if these are made piezoresistors having sensitivity in the horizontal direction and two strain gauges having sensitivity in the vertical direction are arranged, the strain gauges can be arranged in each direction. The resistivity of the piezoresistor increases / decreases as the pressure increases / decreases in accordance with the respective directions, and the pressure can be detected by forming a bridge circuit with these two sets of strain gauges.

The procedure for manufacturing such a piezoresistive semiconductor pressure sensor is as follows. First, the Si single crystal substrate 21 is thermally oxidized to form an oxide film, and a recess is formed in the oxide film on the upper surface of the substrate 21 by photolithography and etching. Open the window for. Next, etching is performed from the above-mentioned windowed portion with an etchant capable of anisotropically etching silicon to form a recess having a flat bottom portion in the Si substrate 21, and at the same time, a diaphragm 22 with a rim is formed. Then, the surface of the diaphragm 22 is further thermally oxidized for cleaning, and the formed oxide film is completely removed by etching. Through the above steps, the diaphragm 22 having a clean surface and made of Si is formed.

Next, an oxide film is formed on the diaphragm 22 by thermal oxidation, and the impurity-doped polycrystalline S is formed on the oxide film.
By depositing the i layer and performing patterning, the oxide film 23 is left only on the diaphragm 21, and an independent piezoresistor 24 is formed on the oxide film 23. After the resistor pattern is formed, an oxide film 28 for element isolation is formed on the entire surface, and a hole 50 for forming an electrode is formed in the oxide film 28 on the resistor 24 by photolithography and etching. Then, a conductive material is deposited, and the inner electrode 25, the outer electrode 26, and the wiring 27 are formed by photolithography and etching. Then, a passivation film 29 is deposited on the entire upper surface, and finally a lead wire for extracting a detection signal to the outside is connected to the external electrode 26 to complete the sensor.

According to the piezoresistive semiconductor pressure sensor of the present invention, the sensitivity which is almost the same as the characteristic of the sensor by the conventional device structure can be obtained, and the yield is greatly improved as compared with the device having the conventional structure. .

[0013]

According to the present invention, a piezoresistive semiconductor pressure sensor can be manufactured inexpensively and with high precision,
It can be expected that the applications will be further expanded.

[Brief description of drawings]

FIG. 1 is a sectional view conceptually showing an example of the structure of a piezoresistive semiconductor pressure sensor of the present invention.

FIG. 2 is a sectional view conceptually showing the structure of a conventional piezoresistive semiconductor pressure sensor.

[Explanation of symbols]

 21 Si Single Crystal Substrate 22 Diaphragm 23 Oxide Film 24 Polycrystalline Si Layer 25 Internal Electrode 26 External Electrode 27 Wiring 28 Insulating Film 29 Passivation Film

Claims (1)

[Claims] 1. A Si single crystal substrate is provided with a recess having a flat bottom on one main surface side to form a diaphragm with a rim, and at least one piezoresistive strain gauge is provided on the diaphragm at the bottom of the recess. Piezoresistive semiconductor pressure sensor formed.