JPH0862078A - Pressure sensor and its manufacturing method - Google Patents

Abstract

PURPOSE: To increase output, to stabilize breakdown voltage characteristics and output characteristics, and at the same time to continuously measure small to large pressure in a semiconductor pressure sensor. CONSTITUTION: The title sensor is provided with a first cavity part 3 provided on a substrate 2, a second cavity part 5 formed inside the substrate 2, and a diaphragm 4 for sensing the pressure formed at one portion of a thin part 44 laminated on the substrate 2. The second cavity part 5 is formed by eliminating the diffusion layer of an impurity and the second cavity part 5 is formed in an arbitrary shape such as an elliptical shape, thus forming the diaphragm 4 in an arbitrary shape such as the elliptical shape viewed from an upper portion. The first cavity part 3 is formed by anisotropic etching. Also, the substrate 2 and a second substrate 16 are joined by anode joint.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor for measuring atmospheric pressure, water pressure and the like and a method for manufacturing the same, and more particularly to a semiconductor pressure sensor having a plurality of cavities having different shapes.

[0002]

2. Description of the Related Art As a prior art relating to the present invention, there is, for example, Japanese Patent Application Laid-Open No. 4-148834. Japanese Patent Laid-Open No. 4-1
The structure of Japanese Patent No. 48834 is shown in FIG. 1 of the same publication, and as described in claim (1), it has an opening for introducing pressure into the single crystal semiconductor substrate and has the opening inside. It had a circular thin film diaphragm with a larger cavity. Further, as described in detail in the invention from the second clause on page 7 to the first clause on page 8, the invention uses a silicon substrate to form a thin film epitaxial layer on the substrate, A part of the epitaxial layer is etched from an opening formed on the surface of the silicon substrate to be joined to the borosilicate glass to form a cavity larger than the opening, and the diaphragm is formed by the cavity.

Further, as described in the third sentence on page 8 of the same publication, the displacement amount of the diaphragm is made small by thinning the sacrificial layer, and the high withstand voltage when an excessive pressure is applied is strengthened. It was

[0004]

However, in the conventional semiconductor pressure sensor having the above-mentioned structure, the cavity for forming the diaphragm is formed by isotropic etching, so that the shape of the cavity is only circular. There is a problem in that the design of the diaphragm (thin-wall portion that senses pressure) is restricted because it is limited. For example, when a bridge circuit is configured with four gauge electrodes and the voltage difference between the gauge electrode pairs in the XY2 directions is output, the diaphragm shape is rectangular or elliptical and the XY dimension ratio is the same. However, the pressure sensor having the above-described structure cannot produce a shape other than such a circular shape.

Further, there is a problem in that the size of the diaphragm varies due to the change in the etching stop time when forming the cavity, and the output voltage characteristic fluctuates. That is, there is a problem that the shape and size of the diaphragm cannot be accurately controlled.

When the sacrificial layer is thin, the pressure resistance of the thin film diaphragm is improved because the thin film diaphragm is in contact with the bottom surface of the cavity when an excessive pressure is applied. It had a problem that it could not be perceived.

Therefore, the present invention solves such a problem, and an object of the present invention is to provide a pressure sensor capable of increasing the output voltage of the sensor with respect to the applied pressure and having stable pressure resistance and output characteristics. It is to provide a manufacturing method.

Another object of the present invention is to provide a pressure sensor capable of continuously measuring a wide range of pressures from a minute pressure to a large pressure.

[0009]

A pressure sensor of the present invention detects pressure by displacement of a thin portion laminated on a substrate, and two characteristic hollow portions are formed inside the substrate. It is a thing.

The first hollow portion has an opening on the opposite surface side of the thin wall portion, and the second hollow portion communicates with the first hollow portion and is in contact with the thin wall portion, and at the same time as the thin wall portion. It has a shape such that the area of the contacting area is larger than the opening area of the communicating portion with the first cavity.

Further, the pressure sensor of the present invention is characterized in that three characteristic hollow portions are formed inside the substrate, and two different types of sensors are provided in one pressure sensor.

First, the third hollow portion has an opening on the opposite surface side of the thin wall portion, and the first hollow portion has an opening at a portion of the third hollow portion on the thin wall portion side to form a third hollow portion. The second cavity has a volume smaller than that of the third cavity communicating with the cavity.
Has a shape such that the area of the region that is in communication with the hollow portion and is in contact with the thin portion and that is in contact with the thin portion is larger than the opening area of the communicating portion with the first hollow portion. Then, a first diaphragm formed of a thin wall portion facing the second hollow portion and a first diaphragm formed on the thin wall portion facing the second hollow portion.
A set of strain gauges, a second diaphragm formed of a portion of the substrate configured to be displaceable with a contour shape determined by the first, second and third cavities, and a third And a second set of strain gauges formed on the thin portion facing the cavity, and these constitute two sensors.

Further, the pressure sensor of the present invention is characterized by including the following manufacturing steps.

A step of forming an impurity-diffused portion on one surface of the single crystal substrate, a step of forming a thin portion in contact with the impurity-diffused portion, the substrate is etched from the surface opposite to the impurity-diffused portion of the substrate. A step of forming the first hollow portion, and etching a portion in which impurities are diffused from the first hollow portion side so as to communicate with the first hollow portion and contact the thin wall portion and a region contacting the thin wall portion. Is a step of forming a second hollow portion having a shape in which the area of is larger than the opening area of the communicating portion with the first hollow portion.

[0015]

The operation of the pressure sensor and the manufacturing method thereof according to the present invention is as follows.

First, since the diffusion layer is formed in the substrate and the diffusion layer is selectively etched to form the second cavity portion, the shape of the cavity portion can be made arbitrary. Since this hollow portion serves as an element constituting the diaphragm, the shape of the diaphragm can be made arbitrary as a result. Then, by utilizing this, if the shape of the diaphragm is not an isotropic shape (for example, a square or a circle) (for example, a rectangle or an ellipse), the dimension ratios in the XY directions can be made different. The present invention utilizes this difference in size to increase the output of the pressure sensor.

Since the cavity is formed by etching the diffusion layer, it can be formed with high precision.
Therefore, the shape (size) of the diaphragm corresponding to this cavity is also highly accurate. Therefore, even when a large number of diaphragms are formed, the shapes thereof do not vary so much, and as a result, the characteristics (breakdown voltage, output voltage, etc.) of the pressure sensor using these diaphragms also do not vary.

Further, by comprising the inner peripheral pressure sensor based on the displacement of the first diaphragm and the outer peripheral pressure sensor based on the displacement of the second diaphragm, continuous pressure measurement over a wide range from a minute pressure to a large pressure becomes possible. It is intended to do. That is, the first diaphragm has a limited displacement amount and is mainly used for detecting a small pressure. When the displacement amount is equal to or larger than a predetermined displacement amount, the displacement of the second diaphragm, which is larger than that of the first diaphragm, is substituted for the first diaphragm. Is mainly used for detecting large pressure. In this case, the first diaphragm used for detecting a small pressure is not destroyed even if a large pressure is applied because its displacement amount is limited.

[0019]

Embodiments will be described in detail below according to embodiments. In addition, Example 1 is an example in which two cavities are provided inside the substrate to form one diaphragm to form a pressure sensor, Example 2
Is an example in which three cavities are provided inside the substrate to form two diaphragms to form a pressure sensor.

(Embodiment 1) FIG. 1 is a sectional view of a pressure sensor 1 according to a first embodiment of the present invention. 2 is a top view of the pressure sensor 1 according to the first embodiment. However, in FIG. 2, the extraction electrode 15 is omitted.

As shown in FIG. 1, the pressure sensor 1 according to the present embodiment has a pyramid-shaped first hollow portion 3 provided on the substrate 2, and a first hollow portion 3 formed inside the substrate 2 as well.
A second cavity portion 5 communicating with the thin wall portion 44 and in contact with the thin wall portion 44, a diaphragm 4 for sensing pressure (a portion of the thin wall portion 44 in contact with the second hollow portion 5), and a second substrate on which the substrate 2 is placed. 16
And so on. The substrate 2 in this example is (100) plane single crystal silicon.

In this embodiment, the second cavity 5 has an elliptical shape when viewed from above, as shown in FIG. That is, the diaphragm 4 has an elliptical shape. on the other hand,
Similarly, as shown in FIG. 2, the opening 6 of the first cavity portion 3 and the opening of the communication portion of the first cavity portion 3 with the second cavity portion, which are provided on the opposite side of the diaphragm 4 of the substrate 2. The shape is rectangular. The area of this elliptical shape is set to be larger than the area of the opening shape of the communicating portion of the first hollow portion 3 with the second hollow portion. Furthermore, a total of four gauge electrodes 7 (strain gauge group) of two pairs are formed on the diaphragm 4 so that the pairs are orthogonal to each other (in the XY directions).

* Manufacturing Method of Pressure Sensor Here, a manufacturing method of the pressure sensor shown in FIGS. 3A to 3C are cross-sectional views for explaining the manufacturing process of the pressure sensor 1 of this embodiment in the order of processes. The manufacturing process of the pressure sensor 1 according to the present embodiment will be described below with reference to FIG. 3, and the reason why the shape of the second cavity 5 viewed from above can be elliptical (that is, arbitrary shape) will be described.

First, as shown in FIG. 3A, the insulating films 8a and 8b are formed on both surfaces of the substrate 2. In this embodiment, the substrate 2 is (100) plane single crystal silicon, and the insulating films 8a and 8b are silicon oxide, which are formed by thermal oxidation.

Next, as shown in FIG. 3B, an opening 9 is formed in a part of the insulating film 8a, and the impurity diffusion layer (hereinafter simply referred to as a diffusion layer) 10 is formed by using the insulating film 8a as a mask.
To form. In this embodiment, the diffusion layer 10 is a high concentration boron doped layer and is formed by ion implantation. The boron concentration is 10 ²⁰ pieces / cm ³ . The diffusion layer 10 shown in FIG. 3B matches the shape of the opening 9. Therefore, the diffusion layer 10 can be formed into an elliptical shape (arbitrary shape) when viewed from above by forming the opening 9 into an elliptical shape (arbitrary shape).

Next, as shown in FIG. 3C, the insulating film 8a is removed, and a second film is formed on the surface of the substrate 2 opposite to the insulating film 8b.
The insulating film 11 and the gauge electrode film 12 are formed. In this embodiment, the second insulating film 11 is a silicon oxide film, an n-type silicon film, and a silicon oxide film, and the gauge electrode film 12 is a high-concentration boron-doped polysilicon film. The boron concentration is 10 ¹⁹ pieces / cm ³ and is formed by ion implantation.

Next, as shown in FIG. 3D, the gauge electrode film 12 is patterned to form the gauge electrode 7, and the third insulating film 13 is further formed on the gauge electrode 7. In this embodiment, the third insulating film 13 is a silicon nitride film.

Next, as shown in FIG. 3E, an opening 6 is formed in a part of the insulating film 8b, and the substrate 2 is etched through the opening 6 using the insulating film 8b as a mask to etch the first cavity 3. To form. In this embodiment, the etching is anisotropic etching and the etching solution is an aqueous potassium hydroxide solution. Further, the etching stops at the diffusion layer 10.
This is because the diffusion layer 10 is a high-concentration boron layer and is not dissolved in a potassium hydroxide solution which is an etching solution.

Next, as shown in FIG. 3 (f), the diffusion layer 10 is removed by etching to form the second cavity portion 5. For etching the diffusion layer 10, hydrofluoric acid + nitric acid + acetic acid (composition ratio 1: 3: 8) is used. This etching solution selectively etches only the diffusion layer 10.

Next, as shown in FIG. 3G, an opening window (not shown) is formed in a part of the third insulating film 13, and the gauge electrode 7 is formed.
An extraction electrode 15 is formed in order to make contact with. In this embodiment, the extraction electrode 15 is a laminated film of Pt and Ti.

Next, as shown in FIG. 3H, the insulating film 8
b is removed and the second substrate 16 is bonded to the substrate 2. In this embodiment, the second substrate 16 is borosilicate glass, and anodic bonding is used to bond the substrate 2 and the second substrate 16.

According to this embodiment, the shape and arrangement of the diaphragm 4 can be built by the photolithography process from the surface. That is, the diffusion layer 10 becomes the second cavity 5, and therefore the shape of the diaphragm 4 viewed from above matches the shape of the opening 9. Therefore, the shape of the diaphragm 4 can be set arbitrarily. In the case of this embodiment, since the opening 9 is elliptical as described above, the shape of the diaphragm 4 is elliptical when viewed from above. The ratio of the long side to the short side of the elliptical shape in this embodiment is 2: 1.

The output of the pressure sensor 1 according to this embodiment is
It was about 1.5 times the output of the conventional pressure sensor consisting of a circular diaphragm. This is the X of diaphragm 4
This is because the dimensional ratio in the -Y2 direction is different and the output of the bridge circuit including the two gauge electrode pairs becomes larger.

Similarly, since the shape and the arrangement of the diaphragm 4 are built by the photolithography process from the front surface, the position of the gauge electrode 7 and the position of the diaphragm 4 should be more accurately matched than the case where they are manufactured by the photolithography process from the back surface. You can

Further, since the second cavity 5 is determined by etching only the diffusion layer 10 and the periphery of the diffusion layer 10 is not etched, the diaphragm 4 can be accurately formed.

In the present embodiment, the second insulating film 11 is a laminated film of a silicon oxide film, an n-type silicon film and a silicon oxide film, but other insulating films such as aluminum oxide and calcium fluoride and an n-type film. A laminated film with a silicon film is also possible. It is also possible to use a structure having only an insulating film, a semiconductor film, or the like. In addition to the n-type silicon film, a silicon film in which other impurities are diffused may be used.

Although the diaphragm 4 has an elliptical shape in this embodiment, it may have a rectangular shape or any other shape.

Although the substrate 2 is (100) plane single crystal silicon, it may be single crystal silicon of another orientation, or may be a single crystal substrate of quartz, gallium arsenide, magnesium oxide, lithium tantalate, or the like. .

Modified Example of Embodiment 1 FIG. 4 is a top view showing a modified example of the pressure sensor according to the present invention, in which two pressure sensors 30 and 31 are arranged adjacent to each other. Further, FIG. 5 is a sectional view of a portion A-AA in FIG.

In this embodiment, two second hollow portions A35 and B36 are formed in the upper portion of the first hollow portion 33. A total of eight gauge electrode sets 37 are provided above the second cavity portion A35 and the second cavity portion B36 via the thin portion 34.
Therefore, the pressure sensors 30 and 31 can be independently formed corresponding to the second cavity portion A36 or B36 and the gauge electrode sets 37, respectively.

Further, the two second cavities 35 and 36 form one cavity via the connecting portion 39. This is because, when the second cavities 35 and 36 are formed by etching, the etching liquid easily flows into the adjacent cavities to improve the circulation fluidity, which is advantageous in manufacturing in terms of etching rate and etching performance. Is. However, the connecting portion 39 does not have to be particularly formed because it has no remarkable advantage in its characteristics when viewed as a pressure sensor.

In the case of the present embodiment, when measuring the pressure due to the difference in the measurement position, two independent pressure sensors can be formed close to each other, so that the interval between the respective pressure sensors can be shortened. . As a result,
The measurement resolution is improved, and highly accurate measurement can be performed. Further, since the pressure sensors can be arranged at high density, a smaller pressure sensor array can be realized.

Pressure sensors 30, 31 according to this embodiment
Can be manufactured by the same method as the manufacturing method of the pressure sensor 1 of the first embodiment. That is, by forming the layer for diffusing the impurities into the shapes of the second cavities A35, B36 and the connecting portion 39, the layer can be formed after the first cavities 33 are obtained.

In the present embodiment, the number of pressure sensors is two, but more pressure sensors can be continuously manufactured. Also,
Not only a linear arrangement but also a planar arrangement is possible, in which case a two-dimensional pressure sensor array can be obtained. Then, the position resolution in the plane in the pressure measurement can be significantly improved.

(Embodiment 2) FIG. 6 shows a sectional view of a pressure sensor 20 according to a second embodiment of the present invention. The pressure sensor 20 shown in FIG. 6 includes an inner circumference pressure sensor 221 for measuring a minute pressure and an outer circumference pressure sensor 22 for measuring a large pressure.
2 pressure sensors.

The inner peripheral pressure sensor 221 includes the substrate 21, the thin portion 44 formed on the substrate 21, and the second cavity portion 2 formed in a portion in contact with the thin portion 44 of the substrate 21.
3, the first formed on the second cavity 23 of the thin portion 44
Of the diaphragm 22, the first gauge electrode set 26 (first strain gauge set) formed on the first diaphragm 22, and the surface of the substrate 21 opposite to the surface on which the thin portion 44 is formed. The third cavity 2 formed by
4. The first cavity portion 25 is formed by etching a part of the surface of the third cavity portion 24 and has a smaller volume than the third cavity portion 24.

Further, the outer peripheral pressure sensor 222 includes the second diaphragm 28 and the second gauge electrode set 27 (the second gauge electrode set 27) formed on the thin wall portion 44 of the second diaphragm 28 facing the third cavity portion 24. Of strain gauges).

The first, second and third cavities are communicated with each other, and the pressure sensor 20 is constructed by bonding the substrate 21 to the second substrate 16.

According to the configuration of this embodiment, when a minute pressure is applied to the pressure sensor 20, only the first diaphragm 22 is deformed and an output appears on the first gauge electrode set 26. On the other hand, when the applied pressure increases, the first diaphragm 22 contacts the bottom surface 29 of the second cavity portion 23,
Since it is not deformed more than the depth of the second hollow portion 23, the first diaphragm 22 can be prevented from being broken.

If a larger pressure is applied after the deformation of the first diaphragm 22 comes into contact with the bottom surface 29 of the second cavity portion 23, the first diaphragm 22 is pressed.
Deforms the bottom surface 29 of the second cavity 23, the second
The diaphragm 28 of is deformed. An output appears in the second gauge electrode set 27 due to the deformation of the second diaphragm 28.

As described above, according to the pressure sensor 20 of this embodiment, it is possible to continuously measure from a small pressure to a large pressure. For example, when pressure measurement is performed by the pressure sensor 20 of the present embodiment, the linearity is good over a wide range from 0.02 megapascals (about 1/5 of atmospheric pressure) to 5 megapascals (about 50 atmospheres). Output was obtained.

The manufacturing method described above can also be applied to the manufacture of the pressure sensor of this embodiment.
That is, instead of forming the first hollow portion 3 by the etching shown in FIG. 3E, the third hollow portion 24 of the present embodiment is formed.
The formation of the first cavity 25 may be divided into two stages of etching.

In this embodiment, the substrate 21 is (100) plane single crystal silicon, and the first diaphragm 22 is a laminated film of a silicon oxide film, an n-type silicon film and a silicon oxide film, but aluminum oxide and calcium fluoride are used. It is also possible to use a laminated film of another insulating film such as the above and an n-type silicon film. It is also possible to use a structure having only an insulating film, a semiconductor film, or the like. Also, n
Other than the type silicon film, a silicon film in which other impurities are diffused may be used.

Although the substrate 21 is (100) plane single crystal silicon, it may be single crystal silicon of another orientation.
Alternatively, a single crystal substrate of quartz, gallium arsenide, magnesium oxide, lithium tantalate, or the like can be used.

[0055]

As described above, the present invention has the following effects.

Since the diffusion layer having an arbitrary shape is formed in the substrate and the diffusion layer is selectively etched, the shape of the diaphragm can be set arbitrarily. Therefore, the output of the pressure sensor can be increased.

Further, since the second cavity can be accurately formed by etching the diffusion layer, the size of the diaphragm is stable, and thus the breakdown voltage characteristic and the output characteristic are stable.

Further, since the shape and arrangement of the diaphragm are built by the photolithography process from the surface, when aligning the position of the gauge electrode, it is more difficult than the conventional photolithography process in which the position of the diaphragm cannot be determined by the thin portion. , Can be adjusted accurately.

Further, since it is composed of two pressure sensors, the inner pressure sensor and the outer pressure sensor, after the first diaphragm of the inner pressure sensor is in contact with the bottom surface, the second diaphragm of the outer pressure sensor is changed to the first diaphragm. Since the diaphragm is flexed by being pressed, it is possible to continuously measure from a small pressure to a large pressure.

[Brief description of drawings]

FIG. 1 is a sectional view of a pressure sensor according to a first embodiment of the present invention.

FIG. 2 is a top view of the pressure sensor according to the first embodiment of the present invention.

FIG. 3 is a sectional view of each step of manufacturing the pressure sensor according to the first embodiment of the present invention.

FIG. 4 is a top view showing an example in which a plurality of pressure sensors of the present invention are provided adjacent to each other.

5 is a cross-sectional view taken along the line AA of FIG.

FIG. 6 is a sectional view of a pressure sensor according to a second embodiment of the present invention.

[Explanation of symbols]

 1, 20, 30, 31 Pressure sensor 2, 21, 32 Substrate 3, 25, 33 First cavity 4 Diaphragm 5, 23 Second cavity 6 Opening 7 Gauge electrodes 8a, 8b Insulating film 9 Opening 10 Impurity diffusion layer 11 Second insulating film 12 Gauge electrode film 13 Third insulating film 15 Extraction electrode 16,38 Second substrate 22 First diaphragm 24 Third cavity 26 First gauge electrode set 27th 2 gauge electrode set 28 2nd diaphragm 29 Bottom face 34,44 Thin part 35 2nd hollow part A 36 2nd hollow part B 37 Gauge electrode set 39 Connection part 221 Inner circumference pressure sensor 222 Outer circumference pressure sensor

Claims (3)

[Claims] 1. A pressure sensor for detecting a pressure by displacing a thin portion laminated on a substrate, comprising: a first cavity portion having an opening on a surface opposite to a surface of the substrate on which the thin portion is laminated. A shape that is in communication with the first hollow portion and is in contact with the thin portion and has an area of a region in contact with the thin portion that is larger than an opening area of a communication portion with the first hollow portion. 2. A pressure sensor, characterized in that two cavities are formed inside the substrate. 2. A pressure sensor for detecting a pressure by displacing a thin portion laminated on a substrate, comprising: a third cavity having an opening on a surface of the substrate opposite to the surface on which the thin portion is laminated. A first cavity portion having an opening in a portion of the third cavity portion on the thin wall portion side and communicating with the third cavity portion, and having a volume smaller than that of the third cavity portion; A second shape having a shape that is in communication with the first hollow portion and is in contact with the thin wall portion, and an area of a region in contact with the thin wall portion is larger than an opening area of a communication portion with the first hollow portion. A cavity is formed inside the substrate, and is formed on the first diaphragm formed by the thin portion facing the second cavity and on the thin portion facing the second cavity. The first set of strain gauges and the first, second, and third cavities. A second diaphragm formed of a part of the substrate whose shape is determined and configured to be displaceable; and a second strain gauge formed on the thin portion facing the third cavity. A pressure sensor having a pair. 3. A step of forming an impurity diffused portion on one surface of a single crystal substrate, a step of forming a thin portion in contact with the impurity diffused portion, and a surface of the substrate opposite to the impurity diffused portion. A step of etching the substrate to form a first cavity portion, etching a portion where the impurities are diffused from the first cavity portion side to communicate with the first cavity portion, and the thin portion And a second cavity portion having a shape in which an area of a region which is in contact with the thin wall portion and which is in contact with the thin wall portion is larger than an opening area of a communication portion with the first cavity portion. Method of manufacturing pressure sensor.