JPH0533018Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a semiconductor pressure sensor that detects measured pressure as a change in electrical resistance corresponding to the measured pressure with a gauge formed on a silicon diaphragm. The present invention relates to a semiconductor pressure sensor with an improved diaphragm configuration.

<Prior Art> FIG. 3 is a longitudinal sectional view showing the configuration of a conventional semiconductor pressure sensor.

Reference numeral 10 denotes a diaphragm made of n-type silicon single crystal and has a recess 11, and the diaphragm 10 includes a strain-generating part 12 in which the thickness of the single crystal is reduced due to the formation of the recess 11, and a fixed part 13 around it. It has

A gauge 14 is formed near the boundary between the strain-generating part 12 and the fixed part 13 with a P-type conductivity due to the diffusion of impurities. The upper surface of the diaphragm 10 is covered with an oxide film (SiO ₂ ) 15 to protect the gauge 14.

The fixed part 13 has a through hole 16 through which the measurement pressure P is introduced.
The substrate 17 is fixed to a silicon substrate 17 with a glass thin film or the like by anodic bonding, for example, and the substrate 17 is further bonded to a metal casing 18.

When the measurement pressure P is applied to the diaphragm 10, this causes strain in the strain-generating portion 12, this strain is transmitted to the gauge 14, and the resistance of the gauge 14 changes in response to the measurement pressure P. Therefore, the measured pressure can be determined from the change in resistance of the gauge 14.

FIG. 4 is a process diagram showing an outline of the process for manufacturing such a semiconductor pressure sensor.

FIG. 4A shows a step in which a gauge 14 for sensing measurement pressure is formed by diffusing, for example, a P-type impurity in a predetermined position of an n-type silicon substrate 19, and the gauge 14 is covered with an oxide film 15. .

After this, as shown in FIG. 4B, the silicon substrate 1
A recess 11 is formed on the side opposite to the gage formation side of 9 by means such as grinding or etching, thereby forming a strain-generating portion 12.

The diaphragm 10 manufactured as described above is bonded to the substrate 17 by a bonding method such as anodic bonding, as shown in FIG. 4C.

Next, the diaphragm 10 insulated by the substrate 17 is fixed to a metal housing 18 (FIG. 4D).

The semiconductor pressure sensor shown in FIG. 3 is manufactured through the steps outlined above.

<Problems to be solved by the invention> However, such conventional semiconductor pressure sensors have the following problems.

(a) When forming the recess 11 by grinding, especially when the pressure range is low, it is necessary to grind the silicon substrate 19, which has a thickness of 300 to 500 μm, to about 50 μm. Difficult to control. In addition, in the case of grinding, the fifth
As shown in the figure, the protrusions 20 tend to remain at the bottom of the strain-generating portion, making it difficult to process them flat.

Furthermore, since it is not possible to form a large number of diaphragms 10 by forming a plurality of holes on the silicon substrate 19 on a flat surface, it is difficult to reduce costs through mass production. Furthermore, it is necessary to secure the forming surface of the gauge 14 against vibrations during processing.

(b) When forming the recess 11 by etching, it is not possible to form a circular hole when using anisotropic etching, and it is not possible to form a deep hole when using isotropic etching.

In order to ensure insulation between the housing 18 and the diaphragm 10, it is necessary to sandwich the insulating substrate 17 therebetween. In this case, anodic bonding or the like is used particularly for bonding between the diaphragm 10 and the substrate 17, but it is difficult to do this simultaneously in multiple cases, and it is difficult to reduce costs through mass production.

There are problems such as:

<Means for solving the problem> In order to solve the above problem, this invention uses a silicon substrate with a through hole for introducing measurement pressure, and a polycrystalline silicon substrate on one side and the other side. A diaphragm on which an oxide film is formed, a piezoresistive element that is formed at a predetermined position on the oxide film on one side of this diaphragm and whose resistance value changes when a measuring pressure is applied, and the other side of this diaphragm and a silicon substrate. A semiconductor pressure sensor is constructed by joining them together.

<Operation> When measurement pressure is applied to the diaphragm through the through hole, this thin diaphragm deforms and stress is generated, and a gauge formed on the surface of the diaphragm detects the measurement pressure as a change in resistance value.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.

21 is a silicon substrate, its thickness is 0.3mm
~1 mm, and its external shape is approximately 3 mm to 5 mm square. A through hole 22 having a diameter of 1 to 2 mm is made in this silicon substrate 21 by sand blasting or a grinding machine.

23 is a polycrystalline silicon substrate, the thickness of which is
It is 50 μm to 300 μm. Oxide films (SiO ₂ ) 25 and 26 are formed on the upper and lower surfaces, and a gauge 24 is formed on the oxide film (SiO ₂ ) 25 on the upper surface.

These polycrystalline silicon substrates 23, gauges 2
4. A diaphragm 27 is composed of oxide films 25, 26, etc.

The silicon substrate 21 is bonded to the diaphragm 27 via the oxide film 26 of the diaphragm 27, and the silicon substrate 21 is further fixed to a casing 29 having an introduction hole 28 through which the measurement pressure P is introduced.

Next, the process of making such a semiconductor pressure sensor will be explained with reference to FIG.

First, a thick support substrate 3 made of silicon.
An oxide film 31 is grown on 0 (FIG. 2A), and a polycrystalline silicon layer 32, which will become the base of the polycrystalline silicon substrate 23, is grown to a thickness t (FIG. 2B).

Next, an oxide film 2 is formed on the lower surface of the polycrystalline silicon layer 32.
6, a silicon substrate 21 with a through hole 22 formed in advance through this oxide film 26 is grown.
(Figure 2 C).

Thereafter, as shown in FIG. 2D, the silicon support substrate 30 is etched and removed. During this removal, oxide film (SiO ₂ ) and silicon (Si)
Use an etching solution with a significantly different etching rate. For example, in the case of a potassium hydroxide (KOH) aqueous solution, since the etching rate of an oxide film is significantly lower than that of silicon, the supporting substrate 30 is removed using the oxide film 31 as a stopper.

Next, a gauge 24 is formed on the oxide film 31 through processes such as masking, etching, and diffusion (FIG. 2E).

After this, divide it into chips as shown in (second
(F) It is mounted on a housing 29 and fixed (FIG. 2 (G)) to form the semiconductor pressure sensor shown in FIG. 1.

<Effects of the Invention> As described above in detail with the embodiments, the configuration of the present invention provides the following various effects.

(a) In this invention, a silicon substrate having a through hole is bonded to a polycrystalline silicon substrate.
There is no need to form the recess by grinding or the like, and therefore the flatness of the bottom surface of the recess can be easily ensured.

(b) Since polycrystalline silicon substrates can be made by growing them thinly, semiconductor pressure sensors in the low pressure range can be easily made. As a result of this increased sensitivity, the diameter of the diaphragm can be reduced in the normal pressure range, and the size of the chip can therefore be reduced.

(c) Since the silicon substrate on which the polycrystalline silicon substrate is placed can be made thicker, the temperature zero point error due to the difference in thermal expansion coefficients can be reduced even when bonded to this polycrystalline silicon substrate.

(d) The configuration of the present invention is a configuration that can reduce costs, and is suitable for mass production because all processes can be performed on a wafer basis. Therefore, it is easy to achieve scale merits by increasing the diameter of the wafer, and the cost is low. It becomes possible to

(e) Since the gauge can be formed by etching a polycrystalline silicon substrate, the offset voltage can be determined from its geometric shape.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing one embodiment of the present invention;
The figure is a process diagram showing the process of making the semiconductor pressure sensor shown in Fig. 1, Fig. 3 is a vertical cross-sectional view showing the configuration of a conventional semiconductor pressure sensor, and Fig. 4 is the process of making the semiconductor pressure sensor shown in Fig. 3. FIG. 5 is an explanatory diagram illustrating problems with the semiconductor pressure sensor shown in FIG. 3. 10, 27...diaphragm, 11...recess,
12... Strain generating part, 14, 24... Gauge, 17...
... Base, 18, 29 ... Housing, 21 ... Silicon substrate, 22 ... Through hole, 23 ... Polycrystalline silicon substrate, 25, 26, 31 ... Oxide film, 32 ... Polycrystalline silicon layer.

Claims (1)

[Scope of utility model registration request] A silicon substrate with a through hole for introducing measurement pressure, a diaphragm with an oxide film formed on one side and the other side of the polycrystalline silicon substrate, and a diaphragm formed at a predetermined position on one of the oxide films of this diaphragm. A semiconductor pressure sensor characterized in that a piezoresistive element whose resistance value changes upon application of the measurement pressure, and the other surface of the diaphragm and the silicon substrate are bonded.