JPS58103633A - Semiconductor pressure transducer - Google Patents

Abstract

PURPOSE:To simplify an insulating and supporting structure, by forming semiconductor epitaxial layers on both surfaces of a sapphire substrate and forming an insulating layer acting as a solid electrolyte at high temp. on the side of the surface to be joined to a support. CONSTITUTION:Piezoresistance elements 2 consisting of silicon expitaxial layers are formed on the surface of a sapphire substrate 1, and a surface protective insulating film 3 consisting of SiO2 is provided thereon; at the same time, electrodes 4 of the elements 2 are formed. A silicon epitaxial layer 5 is provided on the rear surface of the substrate 1 and is thermally oxidized to form an SiO2 layer 6. Electrodes 8 contacting with the epitaxial layer by penetrating the layer 6 are provided. Voltage is applied to a metallic support 7 as anode and the electrodes 8 as cathode, to join the support 7 electrostatically to the layer 6, whereby a diaphragm part 1a is formed. Thus the insulating and supporting structure part is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a semiconductor pressure transducer 11KIll equipped with a diaphragm made of a sapphire substrate.

Generally, when a cup diaphragm type pressure transducer using a silicon substrate is packaged as a pressure sensor, it is necessary to provide some kind of electrical imaging means in relation to the metal housing. This is because while the withstand voltage required for a pressure detector is 5oov (Do) [1 degree, the breakdown voltage of the semiconductor PN junction itself is usually 10~-to
'ov@JJi! By being.

In this case, the above-mentioned insulating means is, of course, subject to material and structural constraints in order to prevent this portion from having any adverse effects on the pressure transducer, such as hysteresis and temperature l1ll characteristics. Even when using a diaphragm formed by epitaxially growing silicon, conventionally the sapphire strip itself has not been used as an insulation means from the metal housing, but a glass support has been used.

The present invention has been made in view of the above circumstances, and its purpose is to provide a semiconductor piezoelectric transducer with a simplified insulating support structure between an i-earphragm made of a sapphire substrate and a metal housing. In order to achieve such an object, the present invention forms semiconductor epitaxial layers on both sides of a sapphire substrate, and
A piezoresistive element is formed using the epitaxial layer, and an insulating layer that acts as a solid electrolyte at high temperature is formed on the second epitaxial layer, and electrostatically bonded to the metal support.

That is, in general, semiconductor pressure transducers made by growing a semiconductor epitaxial layer on a sapphire substrate do not have to worry about leakage current (, PNN Kanakura Vm - Iz This has the advantage that the impurity concentration can be selected by focusing only on the piezoresistance effect without being restricted by the characteristics, but on the other hand, due to the constraints mentioned above, it is difficult to directly fit this sapphire substrate to the metal housing. It is not possible to do so, requiring the intervention of a glass pedestal, etc.
h9. Therefore, in the present invention, an insulating layer made of an insulating material that acts as a solid electrolyte at high temperature is formed on the joint surface of the sapphire substrate with the metal support via the second semiconductor epitaxial layer. It is used as an electrical insulating means between the substrate and the metal support, and thereby allows electrostatic bonding to be used for bonding the substrate and the metal support.

Here, electrostatic bonding refers to gold I1. A method of bonding a semiconductor to an insulating material such as glass or ceramics that acts as a solid electrolyte at high temperatures. A stable mechanical bond can be obtained by heating the two to below their melting point by applying an electric field. Yes, 41km! This is because there is almost no movement between the two objects being combined.

If this is used for bonding to a metal support, it is possible to create an extremely sharp diaphragm.In this case, the metal support must be bonded to something that acts as a solid electrolyte at the bonding temperature. From this point of view, it is impossible to directly bond the sapphire substrates, but this problem was solved by interposing the epitaxial layer and insulating layer of II2. The voltage is applied by using the insulating layer side as a cathode and the metal support side as an anode. below,
The figure is a cross-sectional view showing one embodiment of the present invention. A piezoresistance element made of the first silicone/epitaxial layer formed, 3 a surface protection insulating film 810 formed on the surface of the piezoresistance element 20, 4 an electrode of the piezoresistance table 2, and 5 a sapphire substrate 1. The #I2 silicon/epitaxial layer 6 formed on the other surface is formed on this epitaxial layer 5 by thermal oxidation.
Otya's 7 is the epitaxial layer 5 and the reflection 8. It is bonded to the sapphire substrate 1 via the Kos layer and is a nine-metal support. Although not shown in the figure, the metal support T is made of a material having a coefficient of thermal expansion similar to that of sapphire, such as invar in copal, and is integrally formed with other parts of the housing as a part of the metal housing. A central portion of the sapphire substrate 1 that is not constrained by the ζO support T constitutes a diaphragm portion 1m that is strained by pressure, and the piezoresistive element 2 is attached to this diaphragm portion 1m. It is a provision. The piezoresistive element 2 constitutes a bridge circuit, and the pressure is detected and heated by its output voltage. Also, 8c thermal oxidation 8i0@
This is one pole for electrostatic bonding that is provided through the layer 6 and in contact with the epitaxial layer 5KIm. )9
are arranged symmetrically with respect to the center point AK. During electrostatic bonding, a voltage is applied using the electrode 8 side as a cathode and the metal support T side as an anode.

By electrostatically bonding the thermally oxidized layer 6 and the metal support 1 in this manner, the thermally mirrored 8108 layer 6 and the metal support 1 are bonded together. -N and the second epitaxial layer 5, the sapphire substrate 1 is stably bonded to the metal support T, and the above! The fire substrate 1 and the metal support 1 are thermally oxidized 1
Complete insulation is maintained by the 01 layer 6.

In this case, the above 810. The layer 6 is made more stable by thermally oxidizing the surface of the second epitaxial layer 50 as described above.
Since the IK is formed and the metal support T is integrally formed as a part of the metal housing, the insulating support structure is extremely simplified.

(9) In this case, since the electrodes for electrostatic bonding are arranged symmetrically with respect to the bonding TM9, the potential distribution during energization on the bonding surface 9 is made uniform, and a more uniform bonding can be obtained. In this case, the electrodes 8 for electrostatic bonding are basically desirably distributed almost evenly on the bonding surface 9, for example, in a continuous shape so as to surround the entire diaphragm portion 1a. Of course, it will be stormy even if it is set up. Also,
In this case, especially when the second epitaxial layer 5 is made of n-type silicon and a Schottky barrier is formed between it and the electrode 8, a highly conductive bulk contact is provided at the portion in contact with the electrode 8. It is necessary to establish a section. In such a case, the pulverizer/tact portion may be considered as an electrode, and the pulverizer/tact portion may be continuously and uniformly connected to the joint surface 9, for example, so as to surround the diaphragm portion 11. If provided, it goes without saying that even if the electrode 8 itself is placed in one place, the same effect as if it were provided all around the circumference can be obtained.
It is.

Figure fs3 is a sectional view showing another embodiment of the present invention,
The same parts as in FIG. 1 are designated by the same symbols, and detailed explanation thereof will be omitted. That is, in this example, an insulating layer 10 is further interposed between the thermally oxidized 8101 layer 6 and the metal support #1. This insulating layer 10 is made of the thermally oxidized StO layer 6.
810. by OVD method, reactive sputtering method, etc. It can be formed by depositing and K. That is, the thickness of the thermally oxidized Sin layer 6 is limited. Therefore, the required withstand voltage and bonding yield should be determined according to the conditions of the 8i0 silicon treatment, etc. It is very advantageous to provide a supplementary layer 10, in which case a close bonding takes place between this insulating layer 10 and the metal support T. Therefore:
The insulating layer 10 must be one that interacts with the solid electrolyte at high temperatures during bonding, and if it is such a layer, it may be formed, for example, by a sputtering method and a nine-gafs layer or the like may be used.

FIG. 1114 is a sectional view showing still another embodiment of the present invention, and the same or equivalent parts as in FIG. 1 are designated by the same symbols.
ing. That is, as is clear from the figure, in this example,
The epitaxial layer 5 of s2 is removed from the lower surface of the diaphragm portion 1m, and there are no factors that could harm the characteristics of the pressure transducer, that is, hysteresis. The aim is to improve the characteristics by eliminating as much as possible factors that may cause hysteresis.

As explained above, according to the present invention, semiconductor epitaxial layers are grown on both sides of a sapphire substrate, and an insulating layer made of an insulating material that acts as a solid electrolyte at high temperature is formed on the side that is bonded to the support. By electrostatically bonding the sapphire substrate to the metal support, it is possible to mechanically stably connect the diaphragm made of the sapphire substrate to the metal support, and to maintain reliable insulation between the metal support and the diaphragm. became.

Therefore, there is no need to interpose and join a separate member such as a glass pedestal between the metal housing and the metal housing for insulation, which simplifies the insulation support structure and improves the characteristics of the piezoelectric transducer. It has nine effects.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention. FIG. 2 is a top view, FIG. 2 is a bottom view, and FIGS. 3 and 4 are sectional views showing other embodiments of the present invention. 1.φ...Sapphire substrate, la...Diaphragm part, 2...Piezoresistance element, 5...Is2 silicon epitaxial layer, 61I...Thermal oxidation 8i
0. Layer, T...Metal support, 8...Electric body, 9...
...Jointing surface, 10...Insulating layer.

Claims (3)

[Claims] (1) In a semiconductor pressure transducer comprising a diaphragm formed in the center by bonding the peripheral portion of a sapphire substrate having a semiconductor epitaxial layer on the main surface to a metal support, the epitaxial layer is formed on the sapphire substrate. a first epitaxial layer constituting a cup piezoresistive element formed on the main surface opposite to the bonding surface with the support; and an lI2 epitaxial layer formed on the main surface of the sapphire substrate on the bonding surface side. In addition, the epitaxial layer of Shoganki 2 has nine insulating layers formed on the surface of an insulating material that acts as a solid electrolyte at high temperatures, and the insulating layer and the metal support are electrically bonded. Semiconductor pressure transducer. (2) The semiconductor pressure transducer according to claim 1, wherein the insulating layer is a thermally oxidized layer of the second epitaxial layer. (3) A patent claim characterized in that the insulating layer is a layer consisting of a thermally oxidized layer of the second epitaxial layer and another insulating material that acts as a solid electrolyte at high temperatures and is deposited on the thermally oxidized layer of the second epitaxial layer. 42. The semiconductor pressure transducer according to item 41.