JPS62124778A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To form a diaphragm having extremely thin thickness and little dispersion by shaping the diaphragm by a substance having alkali-proof etching properties. CONSTITUTION:A diaphragm 11 is shaped by three layer films in which both the surface and back of a thin-film consisting of polycrystalline silicon are held by a nitride film (Si3N4), and the periphery of the diaphragm 11 is held by an silicon single crystal substrate 12 and an oxide film layer 13. Four piezo- resistors 14 are formed around the diaphragm 11, the piezo-resistors function as strain detectors, and the piezo-resistors 14 are connected to the outside by Al wirings 16 through contact holes bored to an insulating film 15. The Al wirings 16 except a bonding pad region not shown are coated with a protective film 17.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor pressure sensor that utilizes the piezo effect of a semiconductor.

[Prior art]

As a conventional semiconductor pressure sensor, for example, electronic material 1
Some of them are published in the February 1982 issue, p. 32-p. 34.

FIG. 5 is a sectional view of the semiconductor pressure sensor described above.

In the semiconductor pressure sensor shown in FIG. 5, a thin film portion 3 serving as a diaphragm is formed by etching a portion of a silicon single crystal substrate 1 from the back surface, and a diffused resistor 2 for failure detection is provided on the surface of the thin film portion 3. It has a built-in structure.

Further, the number of diffused resistors 2 is usually four.

These diffused resistors form a Wheatstone bridge circuit, and the circuit is configured to detect strain in the thin film portion 3 as an electrical signal when pressure is applied.

As for the manufacturing method of the diaphragm type semiconductor pressure sensor as described above, first, a diffused resistor 2 is formed on the surface of a silicon single crystal substrate 1, and then a mask that can withstand an alkaline etching solution is formed on the back surface of the silicon single crystal substrate 1. A method is used in which a thin film portion 3 having a thickness of about 20 to 30 grooves is formed by etching from the back side with an alkaline etching solution.

[Problem that the invention seeks to solve]

As mentioned above, in conventional diaphragm-type semiconductor pressure sensors, the thin film part that becomes the diaphragm is formed by removing a part of the silicon single crystal substrate by etching. It has been difficult to reduce the thickness of the diaphragm to about 20 mm or less because the thickness of the diaphragm varies due to variation in thickness and variation in etching speed.

Generally, in the diaphragm type semiconductor pressure sensor as described above, if the thickness of the diaphragm is constant, the sensitivity decreases as the area of the diaphragm decreases.

Therefore, if the thickness of the diaphragm is limited as described above, the area of the diaphragm cannot be reduced, making it difficult to realize a compact and highly sensitive pressure sensor.

The present invention has been made to solve the problems of the prior art as described above, and an object of the present invention is to provide a compact and highly sensitive semiconductor pressure sensor.

[Means to solve the problem]

In order to achieve the above object, in the present invention, the diaphragm is formed of a thin film that is resistant to alkali etching, so that the troublesomeness of the diaphragm can be avoided regardless of the variation in the thickness of the semiconductor single crystal substrate or the etching accuracy. It is configured so that it can be formed to any value with high precision.

By configuring as described above, it is possible to realize a diaphragm with an extremely thin thickness. Therefore, sufficient sensitivity can be obtained even if the area of the diaphragm is reduced, which allows the semiconductor pressure sensor to be further miniaturized. becomes possible.

[Embodiments of the invention]

FIG. 1 shows a first embodiment of the present invention, in which (A) is a sectional view and (B) is a bottom view.

In FIG. 1, the diaphragm 11 is formed from a three-layer film in which a thin film of polycrystalline silicon is sandwiched between two nitride films (S13N4) on both sides.

The periphery of this diaphragm 11 is a silicon single crystal substrate 1
2 and an oxide film layer 13.

Furthermore, four piezoresistors 14 are formed around the diaphragm 11, and these act as strain detectors.

Further, the piezoresistor 14 is connected to the outside through an Aα wiring 16 through a contact hole opened in the insulating film 15.

Note that the M wiring 16 is covered with a protection WX 17 except for a bonding pad area (not shown).

Next, the manufacturing process of the above semiconductor pressure sensor will be explained based on FIG. 2.

First, in FIG. 2(A), lXl015 pieces/cI1
After forming a 0 nitride film with a thickness of about 1000 on the surface of a (100) plane P-type silicon single crystal substrate 12 having about 13 p-type impurities by low pressure CVD, a piezoresistance formation region is formed using photoetching. A nitride film 20 and a resist film 21 are formed only in the portion 19.

Thereafter, using the nitride film 20 and the resist film 21 as a mask, the piezoresistance forming region 19 is formed by ion implantation.
High concentration of boron in other parts (5 x 1015 pieces/cI1
12). 8 Next, in CB), the resist film 2I is removed and phosphorus is implanted into the front surface by ion implantation. At this time, the accelerating voltage for ion implantation is set to a voltage that penetrates the nitride film 20.

Next, a heat treatment is performed to form the p+ layer 31 and the 0 layer 32.The surface concentration of the 60 layer 32 is about 1 to 3×10''/cm', and the depth is about (1.5 to 1. 5tRn.

Next, in (C), when anodization is performed in the HF region, since the 0 layer 32 is separated from the p-type silicon, it is not affected by the anodization, and only the p-type silicon changes to porous silicon.

At this time, if the width of the 0 layer 32 is sufficiently thin (5 to 6- or less), 6 to 10 mm in the depth direction. 0 while the porous area expands
The entire underside of layer 32 is also porous silicon.

Thereafter, the porous silicon is changed into an oxide film layer 13 by oxidation at about 1050° C. in a wet 0□ atmosphere.

Next, the nitride film 20 is removed and boron is implanted into the 0 layer 32 by ion implantation.

A p-type piezoresistor 14 having a large piezo effect is formed.

The concentration of the piezoresistor 14 is approximately 5×101” pieces/cIB3
It is.

Thereafter, the surface of the piezoresistor 14 is oxidized, and an insulating film 15 is formed by photoetching.

Next, apply a lower nitride film on the entire surface to a thickness of about 100 mm, then add a polysilicon film on top of it to a thickness of 1 to 10-1 as needed, and then apply an upper nitride film on top of that to a thickness of about 1000 mm, respectively. Formed by low pressure CVD method.

By photo-etching only the portion that will become the diaphragm, the three-layer film 33 that will become the diaphragm 11 is formed.
form.

Next, in (D), a contact hole is opened in the insulating film 15, and an M wiring 16 connected to the piezoresistor 14 is formed.

Next, a PSG film is formed on the surface to expose only the diaphragm portion to provide protection [17].

Next, for example, PS is applied to the back surface of the silicon single crystal substrate 12.
A diaphragm forming mask 22 is formed from a G film.

Next, etching is performed from the back side of the silicon single crystal substrate 12 using an alkaline etching solution to remove a portion of the silicon single crystal substrate corresponding to the diaphragm.

Subsequently, the PSG film on the surface is partially etched to expose the wiring at the bonding pad portion (not shown).

Finally, the oxide film layer 13 on the diaphragm portion is removed by etching to complete the semiconductor pressure sensor shown in FIG. 1.

In the semiconductor pressure sensor as described above, the thinner the diaphragm, the better the sensitivity. However, as mentioned above, in the semiconductor pressure sensor of the present invention, the diaphragm is extremely thin with a thickness of about 10 tM and has a high precision. This greatly improves the sensitivity of the half-door pressure sensor, and when keeping the sensitivity constant, the area of the diaphragm can be significantly reduced, making it possible to use an ultra-small semiconductor pressure sensor. It is possible to realize this.

Note that the polysilicon film is extremely thin, about 1 to 10
Moreover, a uniform film thickness can be easily formed, and
By covering both the front and back sides with a 1,000 nitride film, it is possible to provide alkali etching resistance, and when used as a diaphragm, it has the advantage of having little residual strain, so as mentioned above, polysilicon film By forming the diaphragm using a three-layer film in which both sides of the diaphragm are sandwiched between nitride films, it becomes possible to easily form an extremely thin and uniform diaphragm.

Next, FIG. 3 is a sectional view of a second embodiment of the present invention.

In the embodiment shown in FIG. 3, the diaphragm is
It is configured to be formed by a layer WA33 and a thin oxide film layer 23.

The thin oxide film layer 23 as described above is formed by controlling the etching of the oxide film layer 13 from the back surface so that a part of the oxide film layer 13 is left in the structure shown in FIG. 2(D). I can do it.

As mentioned above, when the thin oxide film layer 23 is provided on the back surface of the three-layer film 33, the strength of the diaphragm becomes stronger.
It can withstand high pressure and also has a thin oxide film layer 23.
By finely adjusting the thickness during etching, sensitivity can be adjusted.

Next, FIG. 4 is a sectional view of a third embodiment of the present invention.

In the embodiment shown in FIG. 4, the diaphragm is formed of only the oxide film layer 13.

The semiconductor pressure sensor as described above is shown in FIG. 2 (C).
In the step, after oxidizing the surface of the piezoresistor 14,
Immediately proceed to step (D) to form the oxide film 24 and the Aa wiring 1.
6. Protective film 17. A diaphragm forming mask 22 is formed.

Then, it can be formed by etching the diaphragm region of the silicon single crystal substrate 12 from the back surface, and then partially etching the PSGlil on the front surface to expose the M wiring at the bonding pad portion.

As described above, the semiconductor pressure sensor shown in FIG. 4 does not require the step of forming a three-layer film, so it is possible to manufacture a pressure sensor that does not require much precision with respect to sensitivity through a simple process.

〔Effect of the invention〕

As explained above, in the present invention, the diaphragm is formed of a material that is resistant to alkali etching, so that the thickness of the diaphragm hardly changes due to variations in the thickness of the semiconductor substrate or the state of etching. It is possible to form a diaphragm that is extremely thin and has little variation in thickness.

Therefore, even if the area of the diaphragm is reduced, by forming the diaphragm thinner, it is possible to obtain a sensitivity equal to or greater than that of the conventional pressure sensor, and the semiconductor pressure sensor can be further miniaturized. Therefore, since a large number of pressure sensors can be made from a semiconductor chip with the same area, costs can be reduced.

In addition, the embodiment shown in FIG. 3 can withstand high pressure and fine adjustment of sensitivity is possible by controlling the thickness of the thin oxide film layer 23, and the embodiment shown in FIG. .

Effects such as being able to manufacture a pressure sensor that does not require much precision with respect to sensitivity through a simple process and at low cost can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram of one embodiment of the present invention, FIG. 2 is a manufacturing process diagram of the device shown in FIG. 1, FIGS. 3 and 4 are sectional views of other embodiments of the present invention, and FIG. 5 is a sectional view of an example of a conventional device. Explanation of symbols> 11...Diaphragm 12...Silicon single crystal substrate 13...Oxide film layer 14...Piezoresistor 15...Insulating film 16...Insulating film 1
7...Protective film

Claims (1)

[Claims] 1. A diaphragm having alkali etching resistance;
a semiconductor single crystal substrate that holds the periphery of the diaphragm;
A semiconductor pressure sensor comprising: a strain detector that is made of a single crystal thin film having the same crystal plane as the semiconductor single crystal substrate and detects strain in the diaphragm. 2. The semiconductor single crystal substrate is a silicon single crystal substrate, and the diaphragm is formed of a multilayer film in which both the front and back surfaces of a polycrystalline silicon film are sandwiched between alkali etching-resistant thin films. Claim 1
Semiconductor pressure sensor described in Section 1. 3. The semiconductor single crystal substrate is a silicon single crystal substrate, and the diaphragm is formed of a multilayer film including a polycrystalline silicon film, and the lowest layer of the multilayer film in contact with the silicon single crystal substrate is a silicon oxide film. , the next layer is formed of an insulating film, and the strain detector is provided between the bottom layer and the next layer.
Semiconductor pressure sensor described in Section 1. 4. The semiconductor single crystal substrate is a silicon single crystal substrate, and the diaphragm is formed of a silicon oxide film,
The semiconductor pressure sensor according to claim 1, wherein the strain detector is embedded in the silicon oxide film.