JPH02184080A - Manufacture of semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To facilitate the growth of a single crystal in a polysilicon layer and reduce variations of the thickness and characteristics of a silicon diaphragm by a method wherein a silicon seed section to be formed in a thermal oxide film is formed into a 4mum square or smaller, or a stripe form of 4mum wide or less, anisotropic etching is performed from the other side of a substrate regarding the formation of the silicon diaphragm, and the thermal oxide film is made to function as an etching stopper. CONSTITUTION:A thermal oxide film 5 is formed on the main side of a semiconductor substrate 1 composed of silicon single crystals. A stripe silicon seed section 11, a 4mum square or smaller, or 4mum wide or less, is formed on the surface of the thermal oxide film 5. A polysilicon layer 6 is formed on the main side of the semiconductor substrate 1 so as to cover the thermal oxide film 5. Next, the polysilicon layer 6 is irradiated with laser beams to recrystallize the polysilicon 6 on the thermal oxide film 5. A gauge resistance is formed on the recrystallized polysilicon layer. Anisotropic etching is performed from the other side of the substrate. The thermal oxide film 5 is made to function as an etching stopper. Thus, the other side of the thermal oxide film is exposed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] Which invention relates to a method of manufacturing a semiconductor pressure sensor.

[Conventional technology]

Figure 2 shows the conventional SOI (5iltcon On In
FIG. 5 is a diagram illustrating the manufacturing process of a semiconductor pressure sensor using the 5ulation) technology in order of process. First, as shown in (A), an N-type or P-type silicon single crystal wafer substrate (1) with a crystal plane of (100) or (110) and a resistivity of several ohms to several tens of ohms is prepared. The main surface of this substrate (1) is mirror polished.

Next, the above substrate is oxidized at a high temperature of 900 to 1000°C in an oxygenated atmosphere to form a thermal oxide film (2) with a thickness of several hundreds on the surface of the substrate (1), as shown in (B). do.

Further, a nitride film (3) is formed on the upper surface of the thermal oxide film (2) to a thickness of several hundred layers by reacting the S tH2R2*NHs mixed gas at a high temperature of about 800°C.

Next, as shown in (C) using photolithography, predetermined portions of the thermal oxide film (2) and nitride film (3) are removed, and the same area (4) of the substrate (1) is removed by plasma etching. Etch and remove to a depth of thousands of people.

Next, by oxidizing the substrate (1) at a high temperature of around 1000°C in an oxidizing atmosphere containing water vapor, a thermal oxide film (5 ) is formed to a thickness of approximately 1 μm.This is so-called selective oxidation using the nitride film (3) as a mask.

Thereafter, the nitride film (3) serving as a mask portion is removed, and the oxide film (2) on the entire substrate is etched until the silicon surface of the substrate is exposed. The result is as shown in (E). When the silicon surface of the substrate is exposed, Si is applied to the entire surface.
H4 and N-type impurity gases are reacted at a relatively low temperature of around 600° C., and as shown in (F), a polysilicon layer (6) is deposited on the main surface of the substrate and covered with a thermal oxide film (5). Next, a nitride film is formed on the polysilicon layer (6) to a thickness of several hundred by the same method as in step (B), and as shown in (G), it is formed at regular intervals of several tens to 100 μm. The other nitride films are removed, leaving a striped nitride film (7) with a width of several tens of μm.

Next, the polysilicon layer (6) is irradiated with a laser beam (8) with a long wavelength of around 10 μm, and a single crystal is grown on the thermal oxide film (5) by recrystallizing the portion deposited on the silicon surface. let

In this case, the striped nitride film (7) acts as an anti-reflection film during laser beam irradiation, and the purpose is to ensure that the laser beam is efficiently absorbed by the polysilicon layer (6). After irradiation with rays.

The polysilicon layer (6) is removed once it has become a single crystal.

Thereafter, as shown in (H), a gauge resistor (9) is formed on the single crystal part on the thermal oxide film (5) using a known IC manufacturing technique, and an aluminum wiring (not shown) is attached to this. Rub.

Furthermore, APW-? from the other surface of the substrate (1), that is, the bottom surface in FIG. As shown in (H), the silicon substrate (1) is deeply etched (200-500 μm) using an anisotropic etching solution such as 1IKOH to form a thermal oxide film (500 μm).
) is formed into an exposed silicon diaphragm frame. As is well known, this silicon diaphragm αQ acts as the main body of the pressure sensor.

[Problem to be solved by the invention]

Conventional semiconductor pressure sensors are constructed as described above, and a thermal oxide film is formed over the entire area of the silicon diaphragm, so it is not easy to grow a single crystal on the polysilicon layer (6) provided on top of the thermal oxide film. Especially for chips used as pressure sensors,
It was difficult to obtain the area of the mouth using SOI technology. Note that this point can be improved by arranging silicon sheet parts in which the single crystal silicon of the substrate (1) is exposed on the thermal oxide film at intervals of several tens of micrometers in a part of the thermal oxide film. It is known as a preparatory lecture for the Diffraction Functional Element Technology Symposium (held in Osaka from November 5th to 6th, 1988), but the form of the silicon sheet part that facilitates the growth of single crystals in the polysilicon layer is well known. It was not fully clarified. Furthermore, since deep etching is required from the other side of the substrate when forming the silicon diaphragm, there is a problem in that the thickness and characteristics of the silicon diaphragm vary widely, resulting in poor yield.

This invention was made to solve the above-mentioned problems, and provides a method for manufacturing a semiconductor pressure sensor that facilitates the growth of a single crystal in a polysilicon layer and reduces variations in the thickness and characteristics of a silicon diaphragm. This is what we are trying to provide.

[Means to solve the problem]

A method of manufacturing a semiconductor pressure sensor according to the present invention is as follows.

By forming the silicon sheet portion formed on the thermal oxide film in the form of stripes with a width of 4 μm or less or a width of 4 μm or less, it is possible to facilitate the growth of single crystals in the polysilicon layer.
To form the silicon diaphragm, anisotropic etching is performed from the other side of the substrate, and a thermal oxide film is used as an etching stopper.

[Function] According to the present invention, since the thermal oxide film and the square hole-like or stripe-like silicon sheet portion are provided thereon, deep etching with an anisotropic etching solution is performed from the other side of the substrate. When the etching reaches the thermal oxide film, the etching rate decreases and acts as a stopper. Furthermore, silicon etching progresses beyond the thermal oxide film on the silicon sheet portion, but since the silicon sheet portion is formed into stripes with openings of 4 μm or less or widths of 4 μm or less, the etching progresses by approximately 3 μm.111) Etching stops when a pyramid-shaped hole surrounded by a surface is formed. This is because the etching rate is extremely low on the (111) plane and virtually stops. As a result, pyramid-shaped holes with a depth of about 3 μm are formed on the surface of the silicon diaphragm at intervals of several tens of μm, but compared to the 20 to 30 μm thickness of the diaphragm, the depth of the holes is ignored. Therefore, there is no problem even if the thickness is regarded as almost uniform, and there is no particular influence on the characteristics of the pressure sensor.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

Although FIG. 1 sequentially shows the manufacturing steps of the embodiment, the steps up to step (D) in FIG. 2 are the same as the conventional manufacturing method, so illustrations are omitted and only the subsequent steps are shown.

That is, in FIG. 1(A), the thermal oxide film (5
), a large number of thermal oxide films are formed at intervals of several tens of micrometers, and then the same method is used to form the film shown in FIG. 2 (E). A large number of silicon sheet portions Ql) are arranged at intervals of several tens of μm.

In this case, the silicon sheet part 0]) is the silicon single crystal of the substrate exposed on the surface of the thermal oxide film (5), as described above, and the polysilicon layer provided on the silicon sheet part is reused as described later. It facilitates crystallization,
It is formed in a stripe shape with an opening of 4 μm or less or a width of 4 μm or less.

Next, as shown in FIG. 1(B), a polysilicon layer (6) is formed.
is deposited on the thermal oxide film (5) and other surfaces of the substrate (1).

Thereafter, as shown in FIG. 1(C), a polysilicon layer (
A striped nitride film (7) is placed on the top surface of 6) in Figure 2 (G
), and then a wavelength of 10 μm.
The polysilicon layer (6) is irradiated with front and back laser beams (8) to first remelt and recrystallize the polysilicon layer located on the silicon sheet portion (11). Then the laser beam (
8) is scanned slowly to recrystallize the polysilicon layer on the thermal oxide film (5) except for the silicon sheet portion. Since the silicon sheet portions aυ are arranged at intervals of several tens of μm, recrystallization of polysilicon progresses easily. In addition,
The thickness of the single crystal layer recrystallized in this way is several μm.
Therefore, in order to obtain a sufficient thickness, we used well-known silicon epitaxial growth technology to increase the film thickness to 20~20cm.
Raise it to about 30 μm.

The SOI substrate (1) obtained in this way can be used in exactly the same way as a conventional silicon single crystal wafer or an epitaxially grown wafer.
As shown in FIG. 1(D), a gauge resistor (9) is formed on the diaphragm by ion implantation of manufacturing technology, and an aluminum wiring 4! J(6) is provided to form the pressure sensitive part of the pressure sensor.

Next, using an anisotropic etching solution and using the nitride film as a mask, the other surface of the substrate (1), that is, the lower surface in the figure is shown in FIG.
) Perform anisotropic etching similar to

This etching is (100
) The etching process is performed so as to form a hole tapered at an angle of about 55° with respect to the etching surface, but when it reaches the thermal oxide film (5), the etching rate decreases rapidly and acts as a stopper. Generally, the main surface and the other surface of the substrate (1) are not perfectly square, so there is a variation of around 10 μm, and the etch rate of the etching solution is often unstable.
The time it takes to reach the thermal oxide film (5) varies in each part of the substrate (1). Therefore, if the silicon etch is completed after the etching time of the portion that reaches the thermal oxide film (5) the latest, the remaining thickness corresponding to the diaphragm thickness will be extremely uniform.

Note that the silicon sheet portions Ql) provided in the form of stripes of 4 μm or less or 4 μm or less in width at intervals of several tens of μm on the surface of the thermal oxide film (5) are exposed to heat during anisotropic etching.
Silicon will be etched beyond the t-film (5), but as shown in Figure 1(E), a characteristic of anisotropic etching is that a pyramidal hole (to) surrounded by (111) planes is formed. There is a phenomenon in which etching does not proceed any further once a 4 .mu.m opening or 4 .mu.m medium or less striped silicon sheet portion 01) is formed, so that etching does not proceed beyond a depth of approximately 3 .mu.m. Stop in this state.

The silicon diaphragm completed by this etching has a depth of approximately 3
Although it appears as if countless micrometer-sized pyramidal bits are formed, it does not affect the function of the diaphragm itself, so it does not affect the characteristics of the semiconductor pressure sensor. In addition, as mentioned above, the depth of the pit is negligible compared to the thickness of the diaphragm, and the thickness of the thermal oxide film (5) can be formed with high precision, so the thickness of the diaphragm is small. Therefore, a high-yield semiconductor pressure sensor with little variation in characteristics can be obtained.

〔Effect of the invention〕

This invention is configured as described above.

Facilitates the growth of single crystals in polysilicon layers, as well as
It is possible to manufacture a semiconductor pressure sensor with less variation in silicon diaphragm thickness and characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention in order of manufacturing steps, and FIG. 2 is a schematic diagram showing a conventional method for manufacturing a semiconductor pressure sensor in order of steps. In the figure, (1) is a silicon single crystal substrate, (2) (5
) is a thermal oxide film, (3) (7) is a nitride film, (6) is a polysilicon layer, (8) is a laser beam, (9) is a gauge resistor, aQ is a silicon diaphragm, aυ is a silicon sheet part, ( 2) is a pyramid-shaped hole. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A step of forming a thermal oxide film on the main surface of a semiconductor substrate made of single crystal silicon, a step of forming a striped silicon sheet portion with a width of 4 μm or less or a width of 4 μm or less on the surface of the thermal oxide film, and the above thermal oxidation. a step of forming a polysilicon layer on the main surface of the semiconductor substrate so as to cover the film; a step of irradiating the polysilicon layer with a laser beam to recrystallize the polysilicon on the thermal oxide film; A method for manufacturing a semiconductor pressure sensor, comprising the steps of: forming a gauge resistor on the polysilicon layer which has been oxidized; and performing anisotropic etching from the other surface of the semiconductor substrate to expose the other surface of the thermal oxide film. (2) forming a thermal oxide film on the main surface of a semiconductor substrate made of single crystal silicon; forming a silicon sheet portion on the surface of the thermal oxide film; forming a polysilicon layer on the main surface;
A step of irradiating the polysilicon layer with a laser beam to recrystallize the polysilicon on the thermal oxide film, a step of forming a gauge resistor on the recrystallized polysilicon layer, and a step of forming a gauge resistor on the other side of the semiconductor substrate. A method for manufacturing a semiconductor pressure sensor, comprising the step of exposing the other surface of the thermal oxide film by performing directional etching and causing the thermal oxide film to act as an etching stopper.