JPH04192370A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To eliminate the mounting step for manufacturing a highly reliable sensor with high precision by a method wherein a cantilever and the spaces encircling the catilever are formed using the thin film technology on the surface of a silicon substrate so that the cantilever and the spaces may be integrated to form the title acceleration sensor. CONSTITUTION:The title semiconductor acceleration sensor is a capacitance type sensor composed of two capacitors comprising a p<+> silicon region 11 and a polycrystalline silicon layer 12 formed above and beneath a cantilever 10 used as a common electrode respectively through the intermediary of the first silicon film 13 and the second silicon nitride film 14. This p<+> silicon region 11 is formed on the surface of an n-type silicon substrate 16. When this sensor is accelerated, the cantilever 10 approaches to the p<+> silicon region 11 so that the capacitance between the cantilever 10 and the P<+> silicon layer 11 may be increased while the capacitance between the cantilever 10 and the polycrystalline silicon layer 12 may be decreased. In such a constitution, the acceleration can be measured by measuring the fluctuation in the capacitance.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a semiconductor acceleration sensor.

(Prior art) In recent years, ultra-small semiconductor distortion devices have been developed to detect -acceleration, etc. by detecting resistance changes due to piezoresistance effects and minute capacitance changes due to displacement of semiconductor regions formed on semiconductor substrates. The Chero device is attracting attention.

Since such semiconductor acceleration sensors are formed using integrated circuit technology, the length of the vibrating portion is, for example, 100 μm.
m, thickness is about 1 μm, whole chip size is about 1 m
It is possible to form an extremely small element with discoloration of about m square.

Furthermore, it has the excellent feature that it can be formed on the same substrate as other elements by using an integrated circuit.

For example, as an example of such a conductor acceleration sensor,
Usually, as shown in FIGS. 10 and 11, a silicon substrate 1 is sandwiched between two glass substrates 2.3, and a vibrating section 7 having the thickness of the silicon substrate 1 is provided at the tip, and a piezoresistor is provided on the surface. A cantilever beam consisting of a thin region 4 formed by disposing a cantilever beam 5 is etched from the front and back surfaces, leaving a support ring 9, which is sealed with glass substrates 2 and 3 to form a vibrating section 7. and the cantilever beam 4 are configured to be freely displaceable within the closed space 8 (IEEE
Electronic Communication Devices Vol. 26, (1979), “Batch Formed Silicon Accelerometers”).

A piezoresistor 6 identical to the piezoresistor 5 is also formed on this support ring portion 9, forming a bridge circuit.

The vibrating section 7 functions as a weight to increase the sensitivity of the device.

This acceleration sensor detects the displacement of the cantilever 4 due to acceleration as a change in the resistance value of the piezoresistor 5.

Such a sensor can be manufactured by etching the silicon substrate 1 using an IC manufacturing process and by batch processing.

(Problem to be solved by the invention) However, in such an acceleration sensor, the semiconductor substrate is etched from the front and back surfaces of the wafer to form structures such as a weight portion and a cantilever beam.
In addition to being prone to misalignment during backside etching, there was also the problem that the cantilever beams were damaged during the process, reducing yield.

In addition, since mounting must be performed on two glass plates, the mounting cost becomes excessive, and it is extremely difficult to control the gap.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide an acceleration sensor that eliminates misalignment of etching and is easy to mount.

[Structure of the invention]

(Means for Solving the Problems) Therefore, in the present invention, a small acceleration sensor is formed using so-called micromachining, and is made of a polycrystalline silicon film that extends into a space formed on the surface of a silicon substrate. A beam is formed and this space is closed with a polycrystalline silicon film to constitute an integrated acceleration sensor.

That is, this acceleration sensor includes a fixed part made of a semiconductor substrate, a cantilever made of polycrystalline silicon laminated on the fixed part via a spacer layer and having a mass part at the tip, and a spacer on the upper layer. A camp portion made of a polycrystalline silicon film formed through layers is provided, and a space formed around the cantilever is closed with the polycrystalline silicon film by a cap portion.

(Function) According to the above structure, the cantilever and the space surrounding it are formed using thin film technology on the surface of the silicon substrate,
Since the acceleration sensor is integrally formed, there is no need for a mounting process, making it possible to obtain a highly accurate and reliable sensor extremely easily.

For example, a region in which a space is to be formed is defined in advance, a film with different etching characteristics (such as a PSG film) is embedded in this region, and after lamination, a selective etching technique is used to etch this film to form a space. It is possible to easily create a highly accurate space.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

As shown in a cross-sectional view in FIG. 1 and a plan view in FIG. The p+ silicon region 11 and the polycrystalline silicon layer 12 formed through the second silicon nitride film 14 constitute two capacitors, and are a capacitive type sensor. This p+ silicon region 11 is formed on the surface of an n-type silicon substrate 16.

The second cantilever consists of a narrow support section 23 and a wide section 15; the support section 23 is minimized to maximize sensitivity, while the wide section 15 increases the moment around the fixed end. and is used to magnify the capacitance to be measured.

When acceleration is applied, the support beam 10 approaches the p+ silicon region 11 as shown in FIG. The capacitance between silicon layer 12 is reduced.

By measuring changes in these capacitances, acceleration can be measured.

Next, the shape processing process of this semiconductor acceleration sensor will be explained with reference to FIGS. 4(a) to 4(C).

First, a silicon nitride film pattern 13 is formed on the surface of an n-type silicon substrate 16, and impurities are diffused using this pattern as a mask to form a p+ silicon layer 11.

A PSGS upper film is deposited on this upper layer by the CVD method to planarize the surface, and then a p-type doped polycrystalline silicon layer 10 is deposited and the surface is oxidized to form a silicon oxide film 32.

Thereafter, the cantilever beam 10 is patterned by a normal photolithography process (FIG. 4(a)).

Further, as shown in FIG. 4(b), a silicon nitride film pattern 14 is formed on this upper layer, a PSG film 21 is deposited by CVD method to flatten the surface, and a polycrystalline silicon layer 12 is further formed on this upper layer. is deposited and impurities are injected into it.

After forming contacts (not shown) in the usual manner, a silicon oxide film 3 is formed as shown in FIG. 4(C).
2 as a mask, the PSGS upper film and the PSG film 21 are selectively etched away to form a free space, and the silicon oxide film 32 exposed on the cantilever tile 10 is etched away. The acceleration sensor shown in the figure is completed.

In this method, PS is applied to the area where the space is to be formed in advance.
Since the G film 9 and the PSG film 21 are buried and then etched away by selective etching to form a free space, a highly accurate space can be formed.

In addition, the acceleration sensor formed in this way does not require a mounting process, and is formed by processing a single silicon substrate using only thin film technology, making it possible to process extremely fine and highly accurate shapes. be.

In the embodiment described above, a capacitive acceleration sensor has been described, but as a second embodiment of the present invention, a piezoresistive acceleration sensor will be described.

As shown in FIGS. 5 and 6, this acceleration sensor includes a polycrystalline silicon layer 25 provided on the surfaces of two beams 17 and 18 that support the mass part 31, and a piezoresistor that detects the deviation of the beams. It is composed of The mass portion 31 and the two beams 1.7.18 have a double structure in which a silicon oxide film or a silicon nitride film 24 is sandwiched between the first and second polycrystalline silicon layers 22.25. There is.

Next, the shape processing process of this semiconductor acceleration sensor will be explained with reference to FIGS. 7(a) to 7(d).

First, as shown in FIG. 7(a), an n-type silicon substrate 1
A silicon nitride film pattern 13 is formed on the surface of the silicon nitride film pattern 13, and a PSGS upper film is deposited on this upper layer by the CVD method to flatten the surface, and then a p-type doped first polycrystalline silicon layer 22 is deposited. After lightly oxidizing the surface to form a silicon oxide film and further forming a silicon nitride film 24, a second polycrystalline silicon layer 25 is deposited and impurities are implanted into this.

When using the silicon nitride film 24 as a layer sandwiched between the first and second polycrystalline silicon layers, it is desirable to make it thin in order to reduce strain. Also, when using a silicon oxide film, the P-8G film 19 and the PSG film 21
It is desirable to have a thin layer to minimize etching during the etching process. Furthermore, the impurity concentration of polycrystalline silicon is selected so as to provide good film characteristics. Furthermore, the reason why the beam has a double structure with a silicon oxide film or a silicon nitride film 24 sandwiched between the beams is to insulate the surfaces of the cantilever beams 17 and 18 with the film 24 so that the strain level is maximized. This is to ensure that the polycrystalline silicon layer 25 as a detection layer is located on the same surface.

This eliminates the need to form a piezoresistor on the surface of the cantilever in a separate process.

Thereafter, the cantilever beams 17 and 18 having the mass portion 31 are patterned by a normal photolithography process (Fig. 7(b)
)).

Further, as shown in FIG. 7(C), a silicon nitride film pattern 14 is formed on this upper layer, a PSG film 21 is deposited by CVD method to flatten the surface, and a polycrystalline silicon layer 26 is further formed on this upper layer. is deposited and impurities are injected into it.

After forming contacts (not shown) and the like in a usual manner, as shown in FIG. 7(d), the PSG film 19 and the PSG film 21 are selectively etched away to form a free space. An acceleration sensor as shown in FIGS. 5 and 6 is completed.

Like the acceleration sensor of Example 1, the acceleration sensor formed in this manner does not require a mounting process, and is formed by processing two silicon substrates using only semiconductor technology, and is extremely fine and highly accurate. shape processing is possible.

In the first embodiment, a capacitive acceleration sensor has been described, but as a third embodiment of the present invention, an acceleration sensor with a self-check function will be described.

In this acceleration sensor, the first embodiment (see Fig. 2)
Polycrystalline silicon layer 12 as a capping layer in
Instead, as shown in FIG. 8, the polycrystalline silicon layer 27 is electrically divided into two parts, one 28 being used for excitation and the other 29 used for capacitance detection.

That is, an isolation region 30 containing no impurities exists in the quotient of these polycrystalline silicon layers 28 and 29, thereby achieving electrical isolation.

When checking, a voltage is applied to one part 28 of the beam, and when detecting the capacitance, the other part 29, which is the measuring part, is applied.
It is measured by

Further, as a modification of the acceleration sensor with a self-check function, the acceleration sensor used in the first embodiment is replaced with a ninth embodiment.
As shown in the figure, an excitation voltage may be applied to the entire polycrystalline silicon layer 12 as a capping layer, and the capacitance between the cantilever beam 10 and the silicon substrate 16 may be detected.

〔Effect of the invention〕

As explained above, according to the present invention, two polycrystalline silicon layers formed on the surface of a silicon substrate are integrally formed by micromachining, eliminating the need for a mounting process and providing high precision and reliability. This makes it possible to obtain a semiconductor acceleration sensor with high performance.

[Brief explanation of the drawing]

1 to 3 are diagrams showing a semiconductor acceleration sensor according to a first embodiment of the present invention, and FIGS. 4(a) to 4(e) are diagrams showing the manufacturing process of the semiconductor acceleration sensor. 5 and 6 are diagrams showing a semiconductor acceleration sensor according to a second embodiment of the present invention, FIGS. 7(a) to 7(d) are diagrams showing the manufacturing process of the semiconductor acceleration sensor, and FIG. The figure shows a semiconductor acceleration sensor according to a third embodiment of the present invention, FIG. 9 shows a modification of the semiconductor acceleration sensor according to a third embodiment of the present invention, and FIGS. 10 and 11 show a conventional example. FIG. 3 is a diagram illustrating an example semiconductor acceleration sensor. 1... Silicon substrate, 2.3... Glass substrate 4... Thin region, 5... Piezoresistor 6.
...Piezoresistance 7...Vibration part 8...Space 9...Support ring 10...Cantilever beam 11...P+ silicon region 12...Polycrystalline silicon layer 13...First Silicon nitride film 14... Second silicon nitride film 15... Wide portion, 19, 21 PSG film 23...
Support portion 24.25...Silicon nitride film 26.27.
28... Polycrystalline silicon layer 30... Separation region
32・Silicon oxide film. Applicant's agent Hidekazu Miyoshi Figure 1 Figure 5 Figure 8

Claims (1)

[Claims] A fixed part made of a semiconductor substrate, a cantilever made of polycrystalline silicon laminated on the fixed part with a spacer layer interposed therebetween and having a mass part at the tip, and a cantilever made of polycrystalline silicon laminated on the fixed part with a spacer layer interposed therebetween. 1. A semiconductor acceleration sensor comprising: a cap portion made of a polycrystalline silicon film; the cap portion closes a space formed around the cantilever with the polycrystalline silicon film.