JPH05196525A - Pressure sensor, composite sensor using the same, and its manufacture - Google Patents

Abstract

PURPOSE:To improve the pressure resistance of a composite sensor and, at the same time, to reduce the size of the composite sensor by efficiently arranging pressure sensors by using a single-crystal silicon plate and providing a compensation pattern in a mask pattern for etching, and making the shape of the central rigid section octagon or dodecagon. CONSTITUTION:An octagon central rigid section 2 mostly surrounded by (311) planes are formed by performing deep anisotropic etching on a (001)-plane single-crystal silicon substrate 1 by using a strong basic etching solution, such as KOH, etc. When a difference DELTAP is produced between the pressures applied to the upper and lower surfaces of such diaphragm, the diaphragm is bent and displaced in the vertical direction. At the same time, a stress peak is generated in the peripheral area of the outside thin wall section of the section 2. When four pieces of strain/resistance elements, such as piezo-resistance elements 14, etc., the electric resistance of which changes when stresses are impressed upon the elements in the (110) direction in which their sensitivity becomes the highest, are arranged in the peripheral area and a bridge circuit is formed by connecting the elements 14 to each other, a resistance change and bridge output which are nearly proportional to the differential pressure DELTAP can be obtained and the bridge circuit functions as a differential pressure sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor processed by etching silicon, an etching mask, and a manufacturing method thereof.

[0002]

2. Description of the Related Art A conventional silicon etching diaphragm with a central rigid body for a pressure sensor has a groove-shaped groove formed by alkali etching a (100) plane single crystal substrate as described in JP-A-56-133877. The parts were processed to form a quadrangular central rigid body part and a quadrangular outer shape. Thus, when the (100) plane silicon is alkali-etched, the etching rate of the (111) plane is significantly smaller than that of the other planes.
11) Only the slope of the surface remains. Therefore, the outer shape of the central rigid body portion was a quadrangle surrounded by the (111) plane.

[0003]

In the above-mentioned prior art, since the central rigid body portion has a quadrangular shape, stress is likely to concentrate on the quadrangular corner portion when an overpressure is applied to the diaphragm, causing breakage, resulting in a high withstand pressure. There was a problem of lowering. Further, since the outer shape is also quadrangular, there is a problem in that when another sensor, for example, a static pressure sensor is combined on the same substrate, the chip size becomes large, which hinders mass production.

An object of the present invention is to provide a structure having a high breakdown voltage by devising a pattern of an etching mask in a pressure sensor formed by using anisotropic etching of silicon, and further to provide a manufacturing method thereof. The purpose is to do. Another object of the present invention is to efficiently arrange the differential pressure sensor and the static pressure sensor in the same substrate, and to provide a composite sensor having a small chip size.

[0005]

In order to achieve the above object, a single crystal substrate of (100) plane silicon is used for etching for forming a diaphragm with a central rigid body portion in consideration of etching rates in respective crystal directions. A compensation pattern is provided on the mask pattern, and the shape of the central rigid body portion is set to an octagon or a dodecagon where the angle of the corner is gentler so that the shape becomes closer to a circle. Further, in order to achieve another object, the outer shape of the diaphragm is octagonal, and the static pressure sensor is efficiently arranged without reducing the effective area of the diaphragm.

[0006]

When the diaphragm with the central rigid body portion is processed by anisotropic etching, the central rigid body portion becomes a polygon.
When excessive pressure is applied to the diaphragm, stress concentrates on this corner. The steeper the angle of the corner, the higher the stress generated, and the more easily it breaks. Therefore, in order to improve the breakdown withstand voltage, it is necessary to process into a shape closer to a circle with a gentle corner. Therefore, if the central rigid body portion is octagonal, dodecagonal or more polygonal, the pressure resistance can be improved more than that of the rectangular central rigid body portion shown in the conventional example.

[0007]

FIG. 1 shows an embodiment of the present invention. This is (1
(00) plane single crystal silicon substrate 1 with KOH, NaOH,
This is an example of a differential pressure sensor in which an octagonal central rigid body portion 2 surrounded by approximately (311) planes is formed by performing deep anisotropic etching to a depth of 300 μm or more with a strong alkaline etching solution such as NH ₄ OH. When a pressure difference ΔP is generated between the upper surface and the lower surface of the diaphragm, the diaphragm is distorted and vertically displaced. At this time, a stress peak occurs in the area around the thin portion outside the central rigid body portion. Four strain-resistive elements such as piezoresistive elements 14 whose electric resistance changes in the direction of highest sensitivity (<110> direction) are arranged in this portion, and these are connected to each other to form a bridge circuit. When formed, a resistance change and a bridge output which are approximately proportional to the differential pressure ΔP are obtained, and the differential pressure sensor functions. In particular, as shown in FIG. 1 (FIG. 1), the structure having the rigid body portion 2 at the center of the diaphragm is known to have better output linearity as compared with the structure having no rigid body portion 2. However, like the conventional example, 4
Since the angle θ of the corner portion of the rectangular central rigid body portion is as small as 90 degrees, high stress is concentrated here, and there is a problem that the pressure at which the diaphragm breaks, that is, the breakdown voltage is small.

According to the present embodiment, the planar shape of the central rigid body portion 2 is an octagon with more gentle corners (θ = 135 degrees>
Since it is 90 degrees), the stress generated at the corners can be reduced, so that the breakdown voltage can be improved and the reliability of the sensor can be improved. Further, in this embodiment, since the outer shapes of the central rigid body portion and the diaphragm are octagonal, that is, the shape in which the corners of the conventional quadrangle are removed, the comparison with the conventional example is performed.
While the effective area of the diaphragm remains unchanged, the bonding area with the pressure introduction base, which is usually bonded to the lower surface of the silicon chip, can be increased, and the bonding strength can be improved.

In FIG. 2, the central rigid body portion is shown as (311) plane and (1
11) A dodecagon surrounded by faces (θ = 150 degrees> 90 degrees)
Here is an example. In this embodiment, the central rigid body portion is closer to a circular shape than that shown in FIG. 1 and the angles of the corner portions are gentler, so that a withstand voltage higher than that of the octagonal shape can be obtained.

FIG. 3 shows an embodiment of a photomask pattern when anisotropically etching silicon to realize an octagonal or dodecagonal central rigid body portion. According to experiments, the (311) plane, which has a high etching speed of about 1.7 times the (100) plane, erodes from the corner of the mask pattern 3 for forming the central rigid body portion. Therefore, the shape of the central rigid body portion is controlled by providing the compensation pattern 4 and adjusting its size (c in the figure). The length of one side of the quadrangle excluding the compensation pattern portion 4 of the mask pattern 3 is L
And the etching depth is d, the conditions for forming an octagon are

[0011]

[Equation 3]

Is calculated as Furthermore, the conditions for forming a dodecagon are as follows.

[0013]

[Equation 4]

As for the mask pattern 5 for forming the outer shape of the diaphragm, the mask pattern 5 (31
1) Since the surface is eroded, the compensation pattern 6 is required to form an octagon. The etching rate of each crystal orientation is measured, and the size h of this compensation pattern 6 is

[0015]

[Equation 5]

[0016] It has been found that the following.

As described above, the octagonal or dodecagonal central rigid body portion can be formed by defining the size c of the compensation pattern 4 with respect to the arbitrary etching depth d as shown in the equation 3 or the equation 4. it can. Further, similarly to the outer shape of the diaphragm, an octagonal outer shape can be realized for an arbitrary etching depth by similarly defining the size h of the compensation pattern 6 as shown in Formula 5.

As a result of conducting experiments on the central rigid body part,
When the etching depth is 0.31 mm and the size of the central rigid body part pattern is 1.76 mm, the compensation pattern size c is

[0019]

[Equation 6]

When, it becomes an octagon,

[0021]

[Equation 7]

At the time of, it was verified that it becomes a dodecagon.
Also, regarding the outer shape

[0023]

[Equation 8]

It was verified that an octagon was obtained by setting

In FIG. 4, a photomask having the above-described shape is used to pattern a protective film for protecting a silicon substrate during etching, and a window having a necessary shape is formed only in a portion to be etched. It shows the progress of etching using an alkaline etching solution. The outer shape of the diaphragm portion etched to half the predetermined etching depth is 51, and the shape of the central rigid body portion is 31.
In both cases, the compensation pattern portion is largely eroded.
When the etching is further advanced to reach a predetermined etching depth, the outer shape of the diaphragm portion becomes 52 and the shape of the central rigid body portion becomes 32.
It is possible to form a rectangular central rigid body. Also,
If the size c of the compensation pattern 4 is set to a value of 1.1d or more, deviating from the above-described conditions of the equations 3 and 4, the central rigid body portion has a protrusion, and the withstand voltage is lowered. Therefore, (10
The shape of the high withstand voltage central rigid body portion obtained by anisotropically etching the (0) plane silicon is either an octagon or a dodecagon.

In FIG. 5, in a composite sensor in which a differential pressure sensor 12, two absolute pressure type static pressure sensors 7 and a temperature sensor 8 are integrated in one chip, the outer shape of the differential pressure diaphragm is octagonal. An example is shown. By making the differential pressure diaphragm octagonal, a space can be created at the corner of the chip without reducing the effective pressure receiving area as compared with the conventional quadrilateral. By providing the absolute pressure type static pressure sensor in this portion, there is an advantage that these two types of diaphragms can be efficiently arranged and the size can be reduced. Further, the diaphragm having the central rigid body portion described in the above embodiment can be used as the diaphragm for the differential pressure sensor to improve the pressure resistance against the differential pressure.

The embodiment shown in FIG. 6 is a composite sensor having a structure in which the surface of the diaphragm is also etched. Since the recessed region 9 is provided by etching from the upper surface, the nonlinear error of the sensor output is small even if the diaphragm plate thickness is thin, and it is effective when used for a sensor for low differential pressure.

The embodiment of FIG. 7 is a composite sensor having a structure in which a differential pressure diaphragm 12 having a polygonal central rigid body portion, four static pressure detecting diaphragms 7 and a temperature sensor 8 are integrated in one chip. According to this embodiment, the sensitivity of the static pressure sensor can be increased by forming the four piezoresistive elements forming the Wheatstone bridge on each static pressure diaphragm. Further, as shown in this embodiment, the static pressure diaphragm is set to <100> with respect to the differential pressure diaphragm.
By arranging in the direction, it is possible to eliminate the influence of the differential pressure input. This will be described below with reference to FIG.

By arranging the static pressure diaphragm in the <001> direction as viewed from the differential pressure diaphragm, the piezoresistive element 14 for the static pressure sensor receives the stress σ due to the differential pressure input at an angle of 45 degrees. Therefore, the component force in the parallel direction and the component force in the vertical direction of the piezoresistive element become equal (σ ′).
On the other hand, the resistance change ΔR / R of the piezoresistive element formed on the (001) plane silicon is expressed by the following equation.

[0030]

[Equation 9]

Here, σl is a parallel stress, σt is a vertical stress, and π44 is a piezoresistance coefficient. Therefore, by taking the configuration as in this embodiment, σl = σ
Since t = σ ′, the resistance change due to the differential pressure input can be made almost zero.

FIG. 12 shows an example of a transmitter using the above-described composite sensor (this is referred to as a composite transmitter). In this figure, 16 is a composite sensor composed of a differential pressure sensor, a static pressure sensor, and a temperature sensor, 104 is a transmitter main body, and 107 is a center diaphragm that separates the high-pressure side and low-pressure side liquid chambers.
The external pressure introduced through the pressure introducing ports 105a and 105b is received by the seal diaphragms 103a and 103b and transmitted to the composite sensor 16. Here, the composite sensor is configured to send signals to the signal processing unit 106 that are substantially proportional to the differential pressure, the static pressure, and the temperature.

Next, the flow of signal processing in the signal processing unit 106 will be described with reference to FIG. Compound sensor 1
The bridge voltage of the differential pressure sensor, the static pressure sensor, and the temperature sensor included in 6 is output, selectively taken in by the multiplexer 40, and amplified by the programmable gain amplifier 41. Next, it is converted into a digital signal by the A / D converter 42 and transmitted to the microcomputer 44. Each of the characteristics of the differential pressure, static pressure, and temperature sensor is stored in the memory 43 in advance.
In step 4, the crosstalk between the characteristics of the sensors is corrected and calculated, and the differential pressure and static pressure are calculated with high accuracy. The calculated differential pressure value and static pressure value are converted again into analog signals by the D / A converter 45 and output from the transmitter via the voltage-current converter 46.

FIG. 9 is a cross-sectional view showing a process of manufacturing a high pressure resistant pressure sensor having a central rigid body portion. First, an etching protection film 10 such as silicon dioxide or silicon nitride is formed on a single crystal silicon substrate, and this etching protection film is patterned using the mask shown in FIG. 3 (A
Figure). Next, anisotropic etching with high processing accuracy is performed using an alkaline solution such as KOH, NaOH, NH ₄ OH,
Form most of the diaphragm (Figure B). Further, isotropic etching is performed with a mixed solution of hydrofluoric acid and nitric acid, CF ₄ + O ₂ or SF ₆ gas to round the corners 11 to obtain a desired diaphragm plate thickness (Fig. C). In this way, the central rigid body is processed into an octagon or a dodecagon close to a circular shape by using anisotropic etching, and the corners of the cross section where stress is likely to concentrate are sufficient compared with the case of only anisotropic etching. By further rounding it to have a large radius of curvature,
The breakdown voltage can be further improved while maintaining high processing accuracy.

FIG. 10 shows a method of manufacturing a polygonal diaphragm using electrochemical anisotropic etching. First,
A silicon substrate having a P-type phase 101 and an N-type phase 102, for example, an epitaxial silicon wafer in which an N-type epitaxial layer is laminated on a P-type substrate is prepared, and an etching protection film 10 such as silicon dioxide or silicon nitride is provided on this. Form (FIG. A). A desired etching mask is patterned on this (FIG. B). Next, KOH, Na
Anisotropic etching is performed using an alkaline solution such as OH or NH ₄ OH, and an etching stop potential is applied to the N layer by the external power source 13 to stop the etching just at the interface between the P layer and the N layer (Fig. C). .. By further proceeding the etching while applying a potential, it is possible to reduce only the central rigid body portion while keeping the diaphragm plate thickness as it is (FIG. D). FIG. 11 is a view seen from the etching surface. According to such a method, the shape of the central rigid body part is set to 1
It is also possible to convert the digon (2) to the octagon (21). As described above, when used together with the electrochemical etching method, there is an advantage that the size of the central rigid body portion can be adjusted without changing the diaphragm plate thickness and the shape can be changed.
Furthermore, by applying isotropic etching with acid or etching gas, the corners can be rounded and the breakdown voltage can be increased (Fig. E).

[0036]

According to the present invention, since a substantially circular central rigid body portion is formed on the diaphragm for a pressure sensor processed by anisotropic etching, concentration of stress can be prevented and the breakdown voltage can be improved. .. Further, since the outer shape of the diaphragm can be octagonal, the effective pressure receiving area remains unchanged, and the bonding area with the base can be made wider than the conventional quadrangular diaphragm, and the bonding strength can be increased. Due to the improvement in pressure resistance and the increase in adhesive strength as described above, there is an effect that the reliability of the sensor and the system using the sensor can be greatly improved. Further, a composite sensor in which a static pressure sensor having a small diameter diaphragm is integrated in one chip has an effect of reducing the chip size.

[Brief description of drawings]

FIG. 1 is a plan view and a cross-sectional view of a differential pressure sensor having an octagonal outer shape of a diaphragm and an octagonal central rigid body portion, which is an embodiment of the present invention.

2A and 2B are a plan view and a sectional view of a differential pressure sensor having an octagonal outer shape of a diaphragm and a dodecagonal central rigid body portion, which is an embodiment of the present invention.

[Fig. 3] The outer shape of the diaphragm is octagonal, and the central rigid body is 8
It is a mask pattern for forming a prismatic or dodecagonal differential pressure sensor.

FIG. 4 is a view showing a process in which a (100) plane single crystal substrate of silicon patterned by the mask of FIG. 3 is anisotropically etched.

[Fig. 5] The outer shape of the diaphragm is octagonal, and the central rigid body is 1
FIG. 3 is a plan view and a cross-sectional view of a composite sensor in which a rectangular differential pressure sensor, two static pressure sensors and a temperature sensor are integrated.

FIG. 6 is a plan view and a cross-sectional view of a composite sensor using a differential pressure sensor having a diaphragm etched from the surface.

FIG. 7 is a plan view and a cross-sectional view of a composite sensor provided with four static pressure sensors.

FIG. 8 is a diagram for explaining the influence of stress due to a differential pressure input applied to a static pressure sensor.

FIG. 9 is a cross-sectional view showing a process of manufacturing a high pressure resistant pressure sensor having a central rigid body portion.

FIG. 10 is a cross-sectional view showing a method of manufacturing a pressure sensor having a polygonal diaphragm using electrochemical anisotropic etching.

FIG. 11 is a diagram showing an etching shape of a pressure sensor created by using electrochemical anisotropic etching.

FIG. 12 is an example of a transmitter (composite transmitter) to which the composite sensor of the present invention is applied.

FIG. 13 is a block diagram showing a signal processing flow of the composite transmitter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Single-crystal silicon substrate, 2 ... Central rigid body part, 3 ... Central rigid body part mask pattern, 4 ... Central rigid body part mask compensation pattern, 5 ... Outline mask pattern, 31, 51 ... Etching intermediate shape, 32, 52 ... Shape after etching, 6 ... External mask compensation pattern, 7 ... Static pressure sensor, 8 ... Temperature sensor, 9 ... Etching region from upper surface,
DESCRIPTION OF SYMBOLS 10 ... Etching protective film, 11 ... Corner part by anisotropic etching, 12 ... Differential pressure diaphragm, 13 ... External power supply, 1
4 ... Piezoresistive element, 16 ... Composite sensor, 21 ... Reduced central rigid body part, 40 ... Multiplexer, 41 ... Programmable gain amplifier, 42 ... A / D converter, 43 ... Memory, 44 ... Microcomputer, 45 ... D / A converter, 46 ... V / I converter, 101 ... P-type layer, 102 ... N
Mold layers, 103a, 103b ... Seal diaphragm, 10
4 ... Composite transmitter main body, 105a, 105b ... Pressure inlet, 106 ... Signal processing unit, 107 ... Center diaphragm.

Claims (18)

[Claims] 1. A diaphragm having a central rigid body portion and a support portion for supporting the diaphragm from the surroundings, a strain-resistance element is arranged in a thin portion of the diaphragm, and the diaphragm changes from the resistance change of the strain-resistance element. In the pressure sensor for detecting the difference in pressure applied to both surfaces of the pressure sensor, the shape of the central rigid body portion is a polygon of pentagon or more. 2. A diaphragm having a central rigid body portion and a support portion for supporting the diaphragm from the surroundings, a strain-resistance element is arranged in a thin portion of the diaphragm, and the diaphragm changes from the resistance change of the strain-resistance element. In the pressure sensor for detecting a difference in pressure applied to both surfaces of the central rigid body portion, the shape of the central rigid body portion is substantially polygonal, and the angle size of the corner portions is larger than 90 degrees at all corner portions. And pressure sensor. 3. The pressure sensor according to claim 1 or 2, wherein the central rigid body portion has an octagonal shape or a dodecagonal shape. 4. A pressure sensor according to claim 1, wherein the diaphragm with the central rigid body portion is made of a silicon semiconductor. 5. The pressure sensor according to claim 1 or 2, wherein the diaphragm with the central rigid body portion is formed of a (100) plane single crystal silicon substrate. 6. The diaphragm according to claim 1 or 2, wherein a thin region of the diaphragm is formed by providing a recessed region on a surface opposite to a surface on which the central rigid body portion of the diaphragm is formed. Pressure sensor. 7. The corner of the diaphragm according to claim 1 or 2, wherein a radius of curvature is sufficiently larger than a radius of curvature of a corner formed by anisotropic etching of silicon. A pressure sensor characterized in that 8. A diaphragm having a central rigid body portion for detecting a differential pressure and a diaphragm for detecting a static pressure are provided on the same substrate, and a strain-resistance element is arranged in a thin portion of each of the diaphragms. A composite sensor for detecting a differential pressure and a static pressure from a resistance change, wherein the shape of the central rigid body portion is a pentagon or more polygon. 9. The composite sensor according to claim 8, wherein the shape of the central rigid body portion is an octagon or a 12 polygon. 10. A diaphragm for detecting a differential pressure and a diaphragm for detecting a static pressure are provided on the same substrate, and a strain-resistive element is arranged in a thin portion of each diaphragm, and a differential pressure is determined based on a resistance change of the strain-resistive element. And a static pressure detecting composite sensor, wherein the differential pressure detecting diaphragm and the static pressure detecting diaphragm have a polygonal shape of a quadrangle or more. 11. The composite sensor according to claim 9, wherein the differential pressure detecting diaphragm has an octagonal outer shape. 12. A sensing means comprising a differential pressure sensor, a static pressure sensor and a temperature sensor, a pressure receiving means for protecting the sensing means and indirectly transmitting an external pressure to the sensing means, and a differential pressure from the sensing means. In a composite transmitter that inputs a static pressure signal and a temperature signal, corrects and calculates the crosstalk between the characteristics of the three sensors, and outputs a differential pressure signal and a static pressure signal, the differential pressure sensor has a pentagonal shape or more. A composite transmitter comprising a diaphragm having a polygonal central rigid body portion and a support portion for supporting the same from the surroundings, and a strain-resistance element being arranged in a thin portion of the diaphragm. 13. The composite transmitter according to claim 12, wherein the differential pressure sensor has a diaphragm with an octagonal or dodecagonal central rigid body portion. 14. The composite transmitter according to claim 12, wherein the differential pressure sensor, the static pressure sensor and the temperature sensor are integrally formed. 15. A mask for processing a diaphragm for a pressure sensor by anisotropically etching a (100) plane silicon single crystal substrate by a depth d, wherein a side length L having an apex in the <100> direction. In the mask pattern for forming the central rigid body portion, which is formed by adding the quadrangle-shaped compensation pattern to the vertices of the quadrangular body pattern, the compensation pattern is projected by the following formula c. A mask pattern for forming an octagonal central rigid body, characterized by: 16. A mask for processing a diaphragm for a pressure sensor by anisotropically etching a (100) plane silicon single crystal substrate to a depth d, wherein a side length L having an apex in the <100> direction is L. The protrusion amount c of the compensation pattern in the mask pattern for forming the central rigid body part, which is obtained by adding the quadrangle compensation pattern to the vertices of the quadrangular body pattern, by A mask pattern for forming a dodecagonal central rigid body portion, wherein 17. A silicon dioxide film or a silicon nitride film is formed as an anisotropic etching protection film on a (100) plane silicon single crystal substrate, and a part of the anisotropic etching protection film is removed to form a predetermined shape. After opening a window, anisotropically etch with an alkaline etching solution, and then perform isotropic etching with an acidic etching solution or etching gas to form rounded corners. Method. 18. The method of manufacturing a silicon sensor according to claim 17, wherein the silicon sensor is a pressure sensor.