JPH06323941A - Capacitance-type sensor - Google Patents

Abstract

PURPOSE:To provide a high-reliability and small-sized pressure sensor. CONSTITUTION:A frame 3 which supports a diaphragm 4 elastically is made of a single-crystal silicon wafer, and a movable electrode 5 is formed on the diaphragm 4. A cover 2 is made of another single-crystal silicon wafer, and a fixed electrode 7 is formed so as to face the movable electrode 5. An oxide film 6 of SiO2 is formed on the whole rear surface of the cover 2 by a CVD method, and a detection circuit 9 which is used to detect a change in the capacitance C of a capacitor which is constituted of the movable electrode 5 and the fixed electrode 7 is formed by a semiconductor manufacturing process. The frame 3 and the cover 2 which have been made in this manner are bonded by using a low-temperature bonding technique, and a pressure sensor 1 is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type sensor. More specifically, the present invention relates to a capacitance type sensor used to detect a change in capacitance that occurs in proportion to the displacement of a detection unit and measure the acceleration of a vehicle or the gauge pressure of air or the like.

[0002]

2. Description of the Related Art In a conventional semiconductor capacitance type pressure sensor, a movable electrode is formed on a diaphragm portion of a silicon substrate and fixed on a glass substrate as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-9727. 2. Description of the Related Art There is known a pressure sensor having a structure in which an electrode is formed and a silicon substrate and a glass substrate are anodically bonded to form a capacitor. Further, in the pressure sensor disclosed in the above publication,
A detection circuit for detecting a change in the electrostatic capacitance of the capacitor is separately formed on the IC chip and mounted on the glass substrate.

[0003]

However, in the pressure sensor having such a structure, when the detection circuit is formed integrally with the pressure sensor, the detection circuit must be provided on the silicon substrate having the diaphragm portion. . On the other hand, in order to form the diaphragm portion on the silicon substrate, anisotropic etching is usually performed using an etching solution containing alkali metal ions such as KOH solution. Therefore, a passivation layer such as a SiN film that does not allow the passage of alkali metal ions must be provided on the detection circuit of the silicon substrate, which causes a problem of increasing the manufacturing process of the pressure sensor.

Further, when the detection circuit is provided on the silicon substrate having the diaphragm portion, the alkali metal ions remaining on the silicon substrate adversely affect the detection circuit,
There was also the problem of lacking long-term stability.

Further, the detection circuit must be formed in a region other than the diaphragm portion of the silicon substrate, and it is necessary to make the silicon substrate large in order to secure a space for providing the detection circuit. There was a problem that the sensor became large (Journal of the Institute of Electronics, Information and Communication Engineers, August 1992, Vol. J75-C-II).
No. 8 P. 451-461).

The present invention has been made in view of the drawbacks of the above-mentioned conventional examples, and an object thereof is to bond silicon substrates to each other to form a detection circuit on a silicon substrate having a fixed electrode formed thereon. The problem is to be solved by forming the detection circuit through the insulating film below the fixed electrode.

[0007]

According to the capacitance type sensor of the present invention, a detecting portion having elasticity is provided on a semiconductor supporting substrate, and a semiconductor fixed substrate is bonded to either surface of the supporting substrate to detect the detection. In a capacitance type sensor in which a fixed electrode is provided on the inner surface of the fixed substrate so as to face a movable electrode provided in the section, and a capacitor is configured by the movable electrode and the fixed electrode, a change in the capacitance of the capacitor is detected. The detection circuit is provided on the fixed substrate.

In addition, an insulating film may be provided on the detection circuit provided on the fixed substrate, and the fixed electrode may be provided on the fixed substrate by overlapping at least a part of the detection circuit with the insulating film interposed. Good.

[0009]

In the capacitance type sensor of the present invention, the fixed substrate is provided with the detection circuit for detecting the change in the capacitance of the capacitor formed in the sensor. Since it is not necessary to perform etching treatment on the fixed substrate to form the detection portion, a passivation layer for protecting the detection portion such as the diaphragm portion from the alkaline etching solution used when forming the detection portion on the supporting substrate is unnecessary. Become. Therefore, the manufacturing process of the sensor can be reduced and the process cost can be reduced.

Further, since the fixed substrate can be eliminated from etching, the alkali metal ions of the alkali etching solution do not remain, the detection circuit is not adversely affected by the alkali metal ions, etc., and the reliability of the capacitance type sensor is improved. And improved long-term stability.

Further, if an insulating film is provided on the detection circuit provided on the fixed substrate and at least a part of the detection circuit is overlapped with the insulating film, the fixed electrode is provided on the fixed substrate.
The space for forming the detection circuit outside the area where the fixed electrode is provided can be reduced. Therefore, it is not necessary to enlarge the fixed substrate itself in order to provide the detection circuit on the fixed substrate, and the capacitance type sensor can be downsized.

[0012]

1 is a sectional view of a pressure sensor 1 according to an embodiment of the present invention, FIG. 2 is a bottom view of a cover 2 which constitutes the pressure sensor 1, and FIG. 3 shows a frame 3 which constitutes the pressure sensor 1. It is a top view. Embodiments will be described in detail below with reference to FIGS. 1, 2, and 3.

In the pressure sensor 1, a cover 2 is superposed on an upper surface of a frame 3 in which a thin film diaphragm 4 is elastically supported on the entire surface of a rectangular frame, and a peripheral portion of the cover 2 is the cover 2 or the frame. A glass material is applied in a thin film form on one of the joint surfaces of 3 and adhered to each other, and then low temperature treatment (about 100
It is joined to the frame 3 by a low temperature joining technique in which the joining is performed at about 200 ° C.

The frame 3 and the diaphragm 4 are integrally formed from a single crystal silicon wafer by anisotropic etching with a potassium hydroxide solution, and the diaphragm 4 is formed by elastic deformation so that it can be freely minutely displaced in its thickness direction. For example, the diaphragm 4 has a thickness of about 10 μm, and the gap amount between the cover 2 and the fixed electrode 7 is about 2 μm.
It is formed so that. A movable electrode 5 is formed on the inner surface of the diaphragm 4.

The cover 2 is made of a single crystal silicon wafer, and a CVD (Chemical
An insulating oxide film 6 of SiO ₂ composition is formed by the vapor deposition method. A fixed electrode 7 is formed on the surface of the oxide film 6 with a small gap from the movable electrode 5 of the diaphragm 4, and the movable electrode 5 and the fixed electrode 7 form a capacitor. A detection circuit 9 is formed inside the oxide film 6 of the cover 2 by a semiconductor manufacturing process, and the detection circuit 9 converts the capacitance C of the capacitor into a frequency by a capacitance-frequency conversion circuit (C- f conversion circuit) and the like, and can detect changes in the capacitance C of the capacitor.

The fixed electrode 7 is connected to the input terminal of the detection circuit 9 through a contact hole 10 formed in the oxide film 6. On the other hand, the movable electrode 5 provided on the diaphragm 4 is connected to the connection wiring 11 provided on the upper surface of the frame 3, and the connection wiring 11 comes into contact with the connection wiring 12 provided on the cover 2 by pressure bonding during joining. , Is electrically connected to the input terminal of the detection circuit 9 through another contact hole 10. The output terminal of the detection circuit 9 is
Further contact hole 1 provided in oxide film 6
0 and 10 are connected to drawer pads 13 and 13 provided on the joint surface of the cover 2 to cover the cover 2 and the frame 3.
By the crimping at the time of joining, the external lead wires 14, 14 on the frame 3 are contacted and electrically connected.

However, when air pressure is applied to the diaphragm 4, the diaphragm 4 is displaced in proportion to the air pressure, the gap amount between the movable electrode 5 and the fixed electrode 7 changes, and the static capacitance of the capacitor concerned is changed. The capacitance C changes. This change in the electrostatic capacitance C is detected by the detection circuit 9 and can be taken out from the external lead-out wirings 14, 14 on the frame 3. In this way, the pressure of the air applied to the pressure sensor 1 can be known.

A method of manufacturing the pressure sensor 1 will be described below with reference to FIGS. First, the detection circuit 9 is formed in the silicon substrate 21 which will be the cover 2, for example, the silicon substrate 21 which is a (100) single crystal silicon wafer, by a normal semiconductor manufacturing process. Next, the detection circuit 9
Low temperature CVD over the entire surface of the silicon substrate 21 so as to cover
By the method, an oxide film 6 made of PSG (Phosphosilicate glass) is deposited as an interlayer insulating film to a thickness of 1 μm (FIG. 4A). Four contact holes 10 are formed in this oxide film 6 by etching. A metal film 23 made of aluminum is formed on the surface of the oxide film 6 by sputtering, and the metal film 23 is connected to the input terminal and the output terminal of the detection circuit 9 through the contact holes 10 (FIG. 4B). Then, the metal film 23 is etched to form the fixed electrodes 7, the connection wirings 12, and the extraction pads 13 and 13 to produce the silicon substrate 21 to be the cover 2 (FIG. 4C).

Next, as shown in FIG. 5, a silicon substrate 22 to be the frame 3 supporting the diaphragm 4 is prepared. For example, SiN is used as a mask thin film on both surfaces of a silicon substrate 22 made of a (100) single crystal silicon wafer.
The film 24 is formed by the CVD method [FIG. 5 (a)]. Next, patterning for forming a gap is performed and the SiN film 24 is etched [FIG. 5 (b)]. The silicon substrate 22 having the SiN film 24 opened by etching is oxidized by a local oxidation (LOCOS) method, and the formed oxide film is removed by buffer hydrofluoric acid to form a recess 25 for forming a gap. [FIG. 5 (c)]. The remaining SiN film 24 on the surface of the silicon substrate 22 on which the concave portion 25 is formed is removed by dry etching, aluminum is deposited by sputtering to form the movable electrode 5, an aluminum film is formed, and then the aluminum film is etched. Movable electrode 5 and connection wiring 1 after processing
1 and the external lead-out wiring 14 are formed [FIG.
(D)]. Subsequently, in order to form the diaphragm 4, the SiN film 24 on the surface opposite to the surface on which the movable electrode 5 is formed is patterned. At the time of this patterning, since alignment of the mask with the movable electrode 5 is important, the SiN film 24 is partially removed by dry etching after using the double-sided mask aligner [FIG. 5 (e)]. The patterned surface of the silicon substrate 22 formed in this way is 45w
Anisotropic etching is performed using a t% KOH solution,
The etching is terminated when the thickness of the etched portion of the silicon substrate 22 becomes 10 μm, and the silicon substrate 22 that will become the frame 3 supporting the diaphragm 4 is manufactured.

The two silicon substrates 21 and 22 manufactured as described above are aligned with each other so that the movable electrode 5 and the fixed electrode 7 face each other, and are bonded by using a low temperature bonding technique. Finally, the pressure sensor 1 is manufactured by cutting it into a predetermined size by dicing.

In this way, the pressure sensor 1 can be easily manufactured. Further, in the pressure sensor 1, the detection circuit 9 for detecting the pressure of the air applied to the pressure sensor 1 is provided in the cover 2 so as to overlap the fixed electrode 7 with the oxide film 6 interposed therebetween. Since the pressure sensor 1 can be made small and the alkali metal ions of the etching liquid do not remain on the detection circuit 9, the reliability of the pressure sensor 1 can be improved.

In the above embodiment, the case of the pressure sensor has been described, but it goes without saying that the present invention can be applied to a capacitance type acceleration sensor.

[0023]

According to the capacitance type sensor of the present invention, the detection circuit for detecting the change in the capacitance of the capacitor formed in the sensor is provided on the fixed substrate, so that the detection circuit is formed by the alkaline etching solution. A passivation layer for protection from the need is eliminated, the number of sensor manufacturing steps can be reduced, and the process cost can be reduced.

Further, the alkali metal ions in the alkali etching solution do not remain and do not adversely affect the detection circuit, and the reliability and long-term stability of the sensor can be improved.

Further, since the detection circuit is provided on the fixed substrate, the distortion due to the deformation of the detection section is not transmitted to the detection circuit, and the reliability of the detection circuit is improved.

If an insulating film is provided on the detection circuit provided on the fixed substrate, and at least a part of the detection circuit is overlapped with the insulating film, the fixed electrode is provided on the fixed substrate.
The space for forming the detection circuit outside the region where the fixed electrode is provided can be reduced, and the capacitance type sensor can be downsized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a pressure sensor that is an embodiment of the present invention.

FIG. 2 is a bottom view of a cover constituting the pressure sensor of the above.

FIG. 3 is a plan view of a frame forming the pressure sensor of the above.

4 (a), (b), and (c) are cross-sectional views showing a method for manufacturing a cover that constitutes the above pressure sensor.

5 (a), (b), (c), (d), (e), and (f) are cross-sectional views showing a method for manufacturing a frame constituting the pressure sensor of the above.

[Explanation of symbols]

 2 cover 5 movable electrode 6 oxide film 7 fixed electrode 9 detection circuit 11 connection wiring 12 connection wiring 14 external extraction wiring 24 SiN film

Claims (2)

[Claims] 1. An elastic detection part is provided on a semiconductor support substrate, and a semiconductor fixed substrate is bonded to one surface of the support substrate, and the semiconductor fixed substrate is opposed to a movable electrode provided on the detection part. In a capacitance type sensor in which a fixed electrode is provided on an inner surface and a capacitor is configured by the movable electrode and the fixed electrode, a detection circuit for detecting a change in capacitance of the capacitor is provided on the fixed substrate. Capacitive type sensor. 2. An insulating film is provided on the detection circuit provided on the fixed substrate, and the fixed electrode is provided on the fixed substrate so as to at least partially overlap with the detection circuit via the insulating film. The capacitance type sensor according to claim 1, which is characterized in that.