JPS629247A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To shield a semiconductor pressure sensor completely from a disturbance noise and a heat noise by covering a pressure sensing part and a signal processing part with a conductive film which has a coefficient of thermal expansion nearly equal to that of a sensor body substrate and connecting the conductive film to the sensor body substrate electrically. CONSTITUTION:The pressure sensing part 14 provided at the upper part of the sensor body 13 and the signal processing part formed at its peripheral part 13a are covered with the conductive film 17 which functions as a shield. The film 17 is constituted as a conductive shield polysilicon film by laminating a field oxide film 17a, an insulating undoped oxide film 17b, and a conductive film body 17c formed of polysilicon in order, providing a glass film 17d of phosphorus silicate glass, etc., on the film body 17c, and then diffusing them thermally. The corresponding part of the film 17b is projected to contact the pressure sensing part 14 and the film body 17c is also projected to contact the sensor body substrate; and they are connected electrically so as to have the same potential, obtaining shield effect.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a semiconductor pressure sensor that utilizes the piezoresistive effect of a semiconductor, and particularly relates to a semiconductor pressure sensor that takes measures to eliminate the influence of external noise. .

[Technical background of the invention and its problems]

Semiconductor pressure sensors are constantly exposed to the outside world and are used under harsh conditions. In particular, semiconductor pressure sensors are often surrounded by a dielectric liquid such as silicone oil as a pressure medium, and are therefore susceptible to external electromagnetic disturbances, resulting in distortion of the pressure sensing part. The resistance value of the gauge resistance layer may change, and if the sensor itself has a signal processing section or the like, incorrect signal processing may occur, making the sensor extremely unstable.

Therefore, semiconductor pressure sensors having the following configuration have been developed as semiconductor pressure sensors having electromagnetic shielding means. That is, this semiconductor pressure sensor has a pressure sensitive part as a strain gauge resistance layer on a diaphragm part on a substrate inside a concave-shaped envelope (hereinafter referred to as a stem), and a pressure sensitive part as a strain gauge resistance layer on the outside of the diaphragm part. A semiconductor pressure sensor main body, which is equipped with a signal processing section, etc., is housed and supported in the periphery of the stem, and a cap with a pressure medium inlet is placed over the stem. By attaching a shield plate and electrically connecting the shield plate and the semiconductor pressure sensor main body board so that they have the same potential, the influence of electromagnetic disturbance from the outside is prevented. That is, in this semiconductor pressure sensor, the pressure medium is wrapped between the diaphragm part that is a part of the semiconductor pressure sensor body and the shield plate, thereby preventing polarization of the pressure medium and preventing the influence of external noise. There is.

However, with the above configuration, thermal fluctuations occur in the pressure medium that exists between the diaphragm part and the shield plate, and this causes noise in the pressure sensing part, signal processing part, etc., so it is still not possible to achieve a perfect shielding effect. I couldn't say it was what I had. In addition, the structure of the cap that covers the stem has a complicated structure, which increases the cost.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and is designed to protect either or both of the pressure sensing section and the signal processing section from disturbance noise and thermal noise without providing a special shield plate on the outside of the semiconductor pressure sensor body. The object of the present invention is to provide a semiconductor pressure sensor that can be completely shielded.

[Summary of the invention]

The present invention provides a diaphragm part constituting a part of a semiconductor pressure sensor main body, and a pressure sensitive part and a signal processing part provided in a peripheral part located outside the diaphragm part. It is covered with a conductive film having a coefficient of thermal expansion approximately equal to that of the sensor main body substrate, and the conductive film of the bracket and the sensor main body substrate are electrically connected to provide a shielding effect.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of a semiconductor pressure sensor according to the present invention. In the figure, reference numeral 10 denotes a stem having a concave cross-section. A shaft 11 passes through the substantially central portion of the stem 10, and a silicon pedestal 12 is fixed to this. Roughly speaking, a semiconductor pressure sensor main body 13 is placed on the top of the silicon pedestal 12. This semiconductor pressure sensor main body 13 is constructed as a circular or rectangular substrate using an N-type single crystal silicon wafer having 100 planes, and a P-type impurity is added at a predetermined position on the upper side, that is, at a position corresponding to a diaphragm portion to be described later. A pressure sensitive part 14 as a strain gauge is formed by partially diffusing boron. Further, a signal processing section including a monolithically formed detection section for detecting static pressure, temperature, etc. is provided in the peripheral section 13a of the semiconductor pressure sensor main body 13, and the back side thereof is etched or mechanically etched into a circular shape. Alternatively, the thin diaphragm portion 13b is formed by hollowing out a rectangular shape. The semiconductor pressure sensor main body 13 is bonded to the silicon pedestal 12 using low melting point solder.

15 indicates a low melting point solder layer. The pressure sensitive section 14 is led out to the outside by a lead pin 16 that is penetrated through the peripheral edge of the stem 10, and is connected to an external measurement circuit (not shown) or the like. Furthermore, the pressure sensitive part 14 provided on the upper part of the semiconductor pressure sensor main body 13 and the signal processing part formed in the peripheral part 13a thereof are provided with a conductive material 1 that functions as a shield.
117.

As shown in FIG. 2, this conductive layer 1117 includes a filled oxidation layer 11117a, an insulating UDO (and-butoxide) lI1 which functions as a barrier to external diffusion of boron impurities for forming a gauge resistor and as a diffusion mask for Linnean purity.
17b, conductive film body 1 formed of polysilicon
7c, a glass film 17d containing phosphorus as an N-type impurity, such as phosphorus silicate glass, is provided roughly above the conductive film body 17c, and is thermally diffused to form a conductive shield polysilicon film. It consists of A corresponding portion of the LIDO full 17b is protruded and provided so as to be in contact with the pressure sensitive part 14, and similarly, the conductive film body 17G is also protruded so as to be in contact with the semiconductor pressure sensor main body substrate so that they are electrically at the same potential. and is configured to provide a shielding effect. In addition, the conductivity I
T! The reason why the glass 1117d is provided above the glass 1117c is that if an insulating film is formed above the glass 1117d, it is possible to further provide a conductive circuit. Therefore, if no new conductive circuit is required, it is not necessary to provide the glass 1117d.

Therefore, according to the above configuration, the conductive film 17 having a shielding function and the pressure sensitive part 14. Since no pressure medium exists between the signal processing section and ', there is no cause for thermal fluctuations caused by, for example, convection of the pressure medium, and thermal noise can be completely eliminated. Furthermore, with such a configuration, not only the stem 10 is not required, but also a conductive shield plate is not required, and the configuration can be simplified accordingly. Further, since the conductive material 1117 covering the upper part of the semiconductor pressure sensor 12 can be manufactured by a semiconductor manufacturing process, it is possible to manufacture a small-sized sensor at low cost, and a highly reliable sensor. In addition, the conductive film 1
7 and the substrate single crystal silicon constituting the semiconductor pressure sensor body 13 are made of the same material, the thermal distortion of the conductive material 1117 can be reduced, and thermal and mechanical hysteresis can be eliminated. In general, the conductive material 11117 not only has a shielding effect that can completely eliminate external noise, but also can eliminate electrical noise and thermal noise caused by the pressure medium as described above.

Note that in the above embodiment, both the pressure sensitive section and the signal processing section are covered using conductive material [117], but for example, a structure may be adopted in which only the pressure sensitive section or only the signal processing section is covered. . In particular, a structure that covers only the pressure sensitive part can have a function of ensuring long-term stability of leakage current between gauge resistors, etc. Further, as a means for manufacturing the conductive film 17, for example, after forming a piezoresistive layer on the semiconductor pressure sensor body 13, removing the filled oxidized Nl 117a and depositing the conductive film body 17C of N-type polysilicon, the conductive film body 17
A window with a predetermined shape is installed in c, making it LJDOIIi! 117b
It is also possible to cover the entire area and provide a window again to form the electrode part of the pressure sensitive part 14. Even in this case, UDOII117t:+ can be easily formed as a filled oxide film by thermal diffusion or the like. With this configuration, only the pressure sensitive section 14 is shielded, and the influence of disturbance on the resistance value of the pressure sensitive section can be prevented. Further, the present invention is not particularly limited to the other components shown in FIG. 1 as long as the conductive material 1117 having a shielding effect is covered on the upper part of the semiconductor pressure sensor main body 13. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

〔Effect of the invention〕

As described in detail above, according to the present invention, the pressure sensing part and the signal processing part in the upper part of the semiconductor pressure sensor body have conductivity of 1!117.
Since the structure has a shielding effect, it is possible to eliminate not only noise from the outside but also noise caused by thermal fluctuations of the pressure medium, achieving a complete shielding effect. Since the semiconductor pressure sensor can be manufactured using the same method, it is possible to provide a semiconductor pressure sensor that is smaller in size and lower in cost, and that can improve reliability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a semiconductor pressure sensor according to the present invention, and FIG. 2 is a diagram showing the relationship between a conductive film and a sensor body. DESCRIPTION OF SYMBOLS 10... Stem, 11... Shaft, 12... Silicon pedestal, 13... Semiconductor pressure sensor body, 14...
...Pressure sensitive part, 15...Solder layer, 16...Lead bin, 17...Conductive film, 17a...Filled oxide film,
17b... LJDOI film, 17C... Conductive film body, 17d... Glass film. 1 representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Procedural amendment 1, A Chapter 1.6 - 3, 1 Commissioner of the Patent Office Michibe Uga 1, Display of the case % Application No. 60-146819 2, Name of the invention Semiconductor pressure sensor 3, Relationship with the person making the amendment Patent applicant (307) Toshiba Corporation 4, Agent 5, Voluntary amendment 6, Subject of amendment 7, Amendment Contents (1) In the specification, page 3, line 17 to line 18 of the same page, the phrase ``In addition, what is to be covered with the stem...'' has been replaced with ``In addition, a sealing plate must be placed inside the stem cap.''"Things," he corrected. 12) The phrase ``Not only does the stem 10 become unnecessary'' on page 7, line 13 to line 14 of the same page of the specification is corrected to ``not only does the scale 10 have a simple structure.''

Claims (2)

[Claims] (1) A semiconductor pressure sensor main body in which a pressure sensitive part and a signal processing part are formed in a diaphragm part on the upper part of the substrate and a peripheral part located outside the diaphragm part, and the pressure sensitive part formed in this semiconductor pressure sensor main body. and a conductive film applied to cover either or both of the signal processing section, and the conductive film is used as an electromagnetic shield. (2) The conductive film has the same potential or approximately the same potential as the substrate of the semiconductor pressure sensor main body, and electromagnetically shields either or both of the pressure sensing section and the signal processing section. A semiconductor pressure sensor according to scope 1.