JPH03238875A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To form a boundary stress-strain layer on the boundary between a semiconductor substrate and a film being different in a thermal expansion coefficient from the semiconductor substrate and thereby to prevent substantially the breakdown of a recessed part even when a pressure is applied to this part, by providing this film on the surface of the recessed part of the semiconductor substrate. CONSTITUTION:A metal impurity is diffused in a silicon wafer 1 by heat treatment and then a nitride film 8 having a thickness of about 1mum is formed by CVD on the rear side of the silicon wafer 1 including the surface of a recessed part for forming a diaphragm part 7. When the wafer 1 is coold to a normal temperature after the formation of the nitride film 8, an interface stress-strain layer 100 having no dislocation is formed on the boundary between the silicon wafer 1 and the nitride film 8 due to the difference in a thermal expansion coefficient between the silicon wafer 1 and the nitride film 8. When a semiconductor pressure sensor is employed in a high temperature, the metal impurity 100 to cause a crystal defect is subjected to segregation by the gettering action of the boundary stress-strain layer 100, according to this constitution, and thereby the breakdown of the diaphragm part 7 being thin the thickness is prevented when a pressure is applied to the recessed part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor pressure sensor, and more particularly to a semiconductor pressure sensor that performs a gettering action during use.

[Conventional technology]

FIG. 3 is a sectional view of a conventional semiconductor pressure sensor. In the figure, 1 is a silicon wafer, 2 is an oxide film formed on the silicon wafer 1 and has a window at a predetermined position, 3 is a boron diffusion region formed in the silicon wafer 1 through the window, and 4a is a boron diffusion region. 4b is an oxide film formed on the back surface of silicon wafer 1; 5a is a nitride film formed on oxide film 2.4a; 5b is the back surface of silicon wafer 1. oxide film 4
a nitride film formed on b; 6 is an A1 wiring that makes contact with the boron diffusion region 3 through the contact hole;
7 is a diaphragm portion.

Next, an outline of the manufacturing process will be explained. An oxide film 2 and a boron diffusion layer 3 are formed on the surface of the silicon wafer 1 by a well-known method.
．． Nitride films 5a, Aj) and interconnections 6 are sequentially formed. At this time, during the boron drive, the oxide films 4a, 4b and the nitride film 5
A nitride film 5b is formed during the a-form heating (FIG. 4). Then, a silicon wafer 1 on which a boron diffusion region 3 is formed.
The surface portion becomes the element region. Next, the oxide film 4b and the nitride film 5b are subjected to photolithography to remove the oxide film 4b and the nitride film 5b in the region corresponding to the element region. Thereafter, by etching the silicon wafer 1 using KOH, a semiconductor pressure sensor having a diaphragm portion 7 as shown in FIG. 3 is obtained. The thickness of this diaphragm portion 7 is approximately 30μ
Thin as m. The wafer thus obtained is diced, assembled, and manufactured into a product.

[Problem to be solved by the invention]

A conventional semiconductor pressure sensor is manufactured through the steps described above, and unnecessary metal impurities are diffused into the silicon wafer 1 from the surfaces of the oxide films 5a and 5b by the heat treatment performed during this manufacturing process. When this metal impurity mixes inside the silicon wafer 1, it becomes a crystal defect, and when pressure is applied to the thin diaphragm part 7, there is a problem that the diaphragm part 7 is easily damaged due to the presence of the crystal defect.

The present invention was made to solve the above-mentioned problems, and therefore, an object of the present invention is to obtain a semiconductor pressure sensor that is less likely to be damaged.

[Means to solve the problem]

A semiconductor pressure sensor according to the present invention includes: a semiconductor substrate having a recess; an element region provided on one main surface of the semiconductor substrate to face the recess of the semiconductor substrate; and an element region formed on the surface of the recess of the semiconductor substrate. and a film having a different coefficient of thermal expansion from the material of the semiconductor substrate.

[Effect]

In this invention, since a film having a thermal expansion coefficient different from that of the semiconductor substrate is provided on the surface of the concave portion of the semiconductor substrate, a boundary stress strain layer is formed at the boundary between the semiconductor substrate and the film, so that it is difficult to use the semiconductor pressure sensor at high temperatures. In this case, metal impurities that cause crystal defects segregate due to the gettering effect of the boundary stress strain layer.

〔Example〕

FIG. 1 is a sectional view showing an embodiment of a semiconductor pressure sensor according to the present invention. In the figure, the difference from the conventional semiconductor pressure sensor shown in FIG. 3 is that a nitride film 8 is newly provided on the surface of the recess for forming the diaphragm part 7. Other configurations are the same as before.

Next, the manufacturing method will be explained. The method up to forming the diaphragm portion 7 is the same as the conventional method.

Due to the heat treatment performed during the manufacturing process, metal impurities (Na, Fe, etc.) are present in the silicon wafer 1 as in the conventional case.

Cu, etc.) diffuses.

Next, the back surface of the silicon wafer 1, including the surface of the recess for forming the diaphragm portion 7, is coated with a thickness of 1 μm by CVD.
A nitride film 8 of about 100 mL is formed. After forming the nitride film 8, the temperature is returned to room temperature. Then, due to the difference in thermal expansion coefficient between the silicon wafer 1 and the nitride film 8, an interfacial stress strain layer 100 without dislocations is formed at the boundary between the silicon wafer 1 and the nitride film 8. Thereafter, the silicon wafer 1 is diced and assembled into a finished product.

Semiconductor pressure sensors manufactured in this manner are generally used under conditions of 100° C. or higher. As is well known, the strained layer generally exhibits a gettering effect under such high temperatures. Therefore, the interfacial stress strain layer 100 also exhibits a gettering effect under high temperature conditions, and the metal impurities 200 diffused into the silicon wafer 1 segregate into the interfacial stress strain layer 100 as shown in FIG. As a result, silicon wafer 1
Crystal defects will not occur within the diaphragm portion 7, and the thin diaphragm portion 7 will not be damaged even if pressure is applied.

In addition, although the combination of the silicon wafer 1 and the nitride film 8 was shown in the above embodiment, the material is not limited to these materials, and any materials having mutually different coefficients of thermal expansion may be used. Further, in the above embodiment, a case has been described in which the nitride film 8 is provided on the entire back surface of the silicon wafer 1, but the same effect as in the above embodiment can be obtained even if the nitride film 8 is provided only on the surface of the recessed portion.

Further, as described above, since a strained layer generally exhibits a gettering effect at high temperatures, it is also conceivable to provide a processing strain instead of the interfacial stress strained layer 100. However, processing strain has dislocations, and these dislocations cause significant deterioration of device characteristics, so this is not appropriate. On the other hand, since the interfacial stress strain layer 100 does not have dislocations, there is no significant deterioration in device characteristics.

〔Effect of the invention〕

As described above, according to the present invention, by providing a film having a coefficient of thermal expansion different from that of the semiconductor substrate on the surface of the concave portion of the semiconductor substrate, a boundary stress strain layer is formed at the boundary between the semiconductor substrate and the film.
When a semiconductor pressure sensor is used at high temperatures, metal impurities in the semiconductor substrate that cause crystal defects are segregated due to the gettering effect of the boundary stress strain layer. As a result, there is an effect that the concave portion is less likely to be damaged even if pressure is applied to the concave portion.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the semiconductor pressure sensor according to the present invention, FIG. 2 is a diagram for explaining the operation of the semiconductor pressure sensor shown in FIG. 1, and FIG. A sectional view of the sensor, FIG. 4 is a sectional view for explaining the manufacturing process of the semiconductor pressure sensor shown in FIG. 3. In the figure, 1 is a silicon wafer, 2 and 4a are oxide films, 3 is a boron diffusion region, 5a and 8 are nitride films, and 6 is an aluminum film.
1 wiring, 7 is a diaphragm part. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A semiconductor substrate having a recess, an element region provided on one main surface of the semiconductor substrate to face the recess of the semiconductor substrate, and a semiconductor substrate formed on the surface of the recess of the semiconductor substrate, A semiconductor pressure sensor comprising a membrane made of materials having different coefficients of expansion.