JPS62252176A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To inexpensively obtain an absolute pressure sensor having high reliability by providing a pressure sensitive diaphragm chamber sealed in vacuum and a pressure sensitive diaphragm chamber to which pressure to be measured is introduced. CONSTITUTION:A semiconductor pressure sensor which utilizes a piezoresistance effect has an N-type epitaxial layer 3 and a silicon oxide film 3 on an N<+>type silicon substrate 1, a P-type diffused resistance region 4 in the silicon 2, a bonding pad 5 to be contacted with the region and always vacuum unit 7 directly under the diaphragm 6. The unit 7 is sealed with a silicon base 8, and a hole portion formed at the base 8 and a pedestal 9 become a pressure regulating region 10. Since the diaphragm contacted with the unit 7 is provided, an absolute pressure can be detected, and since the region 10 is contacted with the back surface of the diaphragm 6, no problem of corrosion with gas of the region 10 occurs, and a plastic package may be employed.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to semiconductor pressure sensors, and in particular to elements which also allow absolute pressure sensing and are also capable of reliable mounting in plastic packages.

BACKGROUND OF THE INVENTION In recent years, pressure sensors have been increasingly used in many fields such as automobiles and home appliances. Among these, semiconductor pressure sensors that utilize piezoresistance effects are being actively used due to significant advances in manufacturing technology and demands for smaller size and lower prices.

A typical conventional semiconductor pressure sensor utilizes a diffused resistance in an ultra-thin diaphragm of single crystal silicon. Typical examples thereof are shown in the cross-sectional views of FIGS. 2 and 3.

Figure 2 shows an N+ type silicon 1 and an N type epitaxial layer 2.
and silicon oxide film 3, and a P-type diffused resistance region 4 in the N-type silicon 2, and a permanent vacuum section 7 immediately below the bonding pad 5 and diaphragm section 6 in contact therewith. This is maintained by sealing the silicon base 8. The result is an absolute pressure sensor. The pressurization/depressurization region 1o is on the chip surface side where the diffused resistor 4 is located. FIG. 3 shows a type in which the front side of the chip is fixed by a pedestal 9, and a hole provided in the pedestal 9 serves as a pressurization area 10. When this chip is mounted on a plastic package, it becomes a gauge pressure sensor. However, the chip surface side is usually made with holes in the package at atmospheric pressure. If this chip were mounted in a metal package and vacuum sealed, it could become an absolute pressure sensor.

Problems to be Solved by the Invention Generally, it is desirable that the semiconductor pressure sensor described above can be used even at high altitudes even when atmospheric pressure changes due to weather. Therefore, first of all, it is desirable to have an absolute pressure sensor that is not affected by atmospheric pressure.

Moreover, secondly, it must be low cost, and thirdly, it must be highly reliable with respect to the gas in the pressurization and depressurization region 10.

The present invention is based on the above-mentioned first aspect. Second. The aim is to propose a semiconductor pressure sensor that simultaneously satisfies all the third requirements.

First, the structure shown in FIG. 2 satisfies the first condition of being an absolute pressure sensor. Since this chip can be mounted in a plastic package, it is less expensive than a metal package and can also satisfy the second condition. However, since the gas in the pressurization/depressurization region 10 comes into contact with the chip surface side, there is a risk that the gas may gradually deteriorate the chip surface during long-term use. Moreover, the surface of the diffused resistor 4 on the chip surface side, the aluminum of the bonding pad 5, etc. are corroded. As a result, the third condition is not satisfied. Therefore, the structure of FIG. 2 is not sufficient.

Next, in the structure of FIG. 3, if a metal package is used to make the sensor an absolute pressure sensor, the second condition of low cost will not be satisfied. On the other hand, after assembly into a low-cost plastic package, it is not possible to maintain a vacuum level better than about 1 mtorr. Therefore, it is not suitable for the absolute pressure sensor of the first condition.

Therefore, the structure of FIG. 3 is also insufficient.

Means for Solving the Problems The present invention provides a first chip having a piezoresistive diffusion section and a vacuum-sealed pressure-sensitive diaphragm chamber, and a piezoresistor diffusion section and a pressure-sensitive diaphragm into which a pressure to be measured can be introduced. This is a semiconductor pressure sensor incorporating a second chip having a chamber.

Function: With the structure of the present invention, absolute pressure can be detected since the diaphragm portion is in contact with the vacuum portion. Therefore, the above first condition is satisfied. Next, in another diaphragm that is in contact with the pressure adjustment area, the pressure adjustment area 10 is in contact with the back surface of the diaphragm. Therefore, the above-mentioned corrosion problem is eliminated for the gas in the pressurization/depressurization region 10, and therefore, the third condition is satisfied. Finally, it is also possible to use plastic packaging. Therefore, N/N ten type single crystal silicon was used as the second material. On the low resistance N + 10 type recon board l, resistivity 2Ω, thickness 2
It has an N-type epitaxial silicon layer 2 with a thickness of 0 μm. Next, a P-type diffused resistance layer 4 is formed on the surface side of the silicon wafer.
and a wide P-type diffusion region for low resistance wiring are simultaneously formed. Here, both chips having respective diaphragm portions corresponding to FIG. 1 are designed to be placed next to each other within the same silicon wafer. The diffused resistance layer 4 forms a bridge at each chip surface. Note that the bridges are formed in each diaphragm section that will be formed in a subsequent process immediately above the vacuum section 7 and the pressurization/depressurization region 10. Next, the back side of the wafer of the diffused resistance layer 4 is etched so that just the N-type epitaxial layer remains. As a result, a diaphragm portion 6 as shown in FIG. 1 is formed. On the other hand, a second single-crystal silicon wafer is prepared, and holes are formed in it to form silicon 8 in FIG.

Next, the first wafer having the diaphragm portion 6 and the second wafer having the hole are pasted with metallization. At that time, metallization is applied in a high vacuum. Then, aluminum wiring and bonding pads 5 are formed on the chip surface. As a result, as shown in FIG. 1, vacuum portions 7 are formed in the bonded wafer at every diaphragm portion. Also,
Holes for the pressurization and depressurization regions 10 of the bonded wafer are also formed at every seven diaphragm portions with the vacuum portion 7 in between. On the other hand, a separate stand IIE9 having a through hole is prepared. For the pedestal 9, we selected glass, which is a material with a coefficient of expansion similar to that of silicon.

Mount the pedestal 9 on the plastic package. After dicing the attached wafer, both chips are bonded onto a pedestal 9. As a result, the cross-sectional structure becomes as shown in FIG. The pressurization and depressurization region 10 must penetrate into the diaphragm section. Then wire bond the gold wire. Then, silicone gel is applied to the chip surface. Then, cap the plastic case with a plastic cap with a through hole.

Note that the present invention can also be applied to IC structures having other circuits. Moreover, the same thing as the present invention is also possible with compound semiconductors.

Effects of the Invention According to the embodiments described above, a semiconductor pressure sensor having the structure shown in FIG. 1 was manufactured as a prototype. This structure has the following advantages. It uses a low-cost plastic package. Nevertheless, high reliability is achieved. Furthermore, by using an IC or the like, it is useful as an absolute pressure sensor. Furthermore, by adopting this structure, a sensor for detecting atmospheric pressure, which was conventionally required separately, becomes unnecessary.

As described above, the structure of the present invention is extremely effective.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a semiconductor pressure sensor according to the present invention, and FIGS. 2 and 3 are schematic sectional views of conventional semiconductor pressure sensors on each side. 1... N+ type silicon, 2... N type silicon, 3... silicon oxide film, 4...
・P-type diffused resistor, 5...ponding pad,
6...Diaphragm part, 7...Vacuum part, 8...Silicon, 9...Pedestal, 10
・・・・・・Pressure and depressurization area.

Claims (1)

[Claims] A semiconductor incorporating a first chip equipped with a piezoresistive diffusion section and a vacuum-sealed pressure-sensitive diaphragm chamber, and a second chip equipped with a piezoresistance diffusion section and a pressure-sensitive diaphragm chamber into which a pressure to be measured can be introduced. pressure sensor.