JPS6376484A - Manufacture of semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To realize a semiconductor pressure sensor equipped with a piezoresistance element excellent in performance by a method wherein an impurity region is formed on the surface of an SOI substrate, crystallization is accomplished by selective annealing, and the rear side is subjected to anisotropic etching for the formation of a polycrystalline silicon thin film. CONSTITUTION:An SOI substrate 4 is constituted of a silicon substrate 1 on whose surface a nitride or oxide film is formed to be an insulating layer 2 and a polycrystalline silicon thin film 3 to cover the insulating layer 2. An impurity region 6 is formed in the polycrystalline silicon thin film 3 by selective implantation and, in the impurity region 6, crystallization is accomplished by local annealing for the formation of a pressure-sensing resistance layer 7. A process follows wherein a prescribed region in the SOI substrate 4 is subjected to anisotropic etching which is selectively accomplished from the side of the silicon substrate 1 for the formation of a silicon thin film 10. This process results in a semiconductor pressure sensor with a piezoresistance element built in its silicon thin film 10. Said anisotropic etching is accomplished by using a potassium hydroxide solution or the like as etchant.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor pressure sensor, and particularly to a method for manufacturing a semiconductor pressure sensor in which a piezoresistive element is formed on a silicon thin film portion having a desired shape. Regarding.

[Prior art and its problems]

With advances in semiconductor technology, semiconductor pressure sensors that utilize the piezoresistive effect of semiconductors such as silicon and germanium have been attracting attention in recent years.

Various structures have been proposed for semiconductor pressure sensors, but the most widely used one is one made of single-crystal silicon with a diffusion layer 101a as a pressure-sensitive resistance layer, as shown in FIG. The diaphragm 101 is attached to the pedestal 102
This is a diaphragm-type pressure sensor that is adhesively fixed to the Here, 103 indicates an adhesive layer.

This pressure sensor detects a change in resistance value that occurs when a diaphragm is subjected to pressure and is distorted. Therefore, it is necessary to form a diaphragm that generates the correct strain depending on the pressure. For this reason, the thickness t of the diaphragm needs to be uniform and needs to be as designed.

During manufacturing, the following method is usually used. First, a diffusion layer 101a as a pressure sensitive resistance layer is formed in a silicon substrate.
Alternatively, after forming electrodes (not shown) and the like, the surface of the silicon substrate is covered and protected with a resist, and a pattern of resist R is formed on the back surface by photolithography. (
FIG. 4(a)) Then, after this, potassium hydroxide (KO
Using H) as an etching liquid, the silicon substrate is etched from the back side to form a thin part as a diaphragm. (FIG. 4(b)) Since the thickness of this diaphragm greatly affects the performance of the pressure sensor, various efforts have been made to improve the etching accuracy.

For example, a method is used in which the required etching time is calculated based on the etching rate of the etching solution used, and the etching amount (depth) is controlled accordingly.

In this method, it is difficult to accurately form the thickness of the thin portion that will become the diaphragm due to the thickness and unevenness of the silicon substrate as a starting material and the deterioration of the etching solution.

Further, as shown in FIG. 5(a), an n-type silicon substrate 20
After forming a p-type medium silicon layer 201 on the surface of 0, an (i-type) silicon thin film layer 2 is formed by epitaxial growth.
There is a method in which a p-type silicon layer formed by epitaxial growth of 02 is used as a starting material and the p-type silicon layer is used as an etching stop layer. In this method, first, a diffusion layer 202a and an electrode (
(not shown) etc. After the surface is coated with resist R and the pattern of resist R in the same manner as described above, the p medium silicon layer 201 as an etching stop layer is exposed from the back side as shown in FIG. 5(b). A method is used in which etching is continued until the end.

However, even with this method, the etching selectivity between the p-type silicon layer and the n-type silicon substrate is at most 10 to 2.
Since it is about 0, the tolerance for the deviation in etching time is small. Additionally, when forming the p-type silicon layer, autodoping causes impurities to diffuse into the silicon substrate surface, and the interface between the p-type silicon layer and the n-type silicon layer moves, which also affects the thickness of the diaphragm due to etching. This causes unevenness.

Furthermore, although a method of measuring and controlling the etching rate by electrical means has been proposed, the apparatus is complicated and therefore cannot be mass-produced. Further, with this method, it is impossible to form a pattern with a complicated shape.

Therefore, the present inventors formed a nitride film or an oxide film on the surface of a silicon substrate, then formed a silicon thin film of a desired thickness as a starting material, and used the nitride film or oxide film as an etching stop layer for anisotropic etching. We have proposed a method for selectively removing the silicon substrate from the back side by chemical etching to form a thin silicon portion in a desired shape. (Patent application 61-160
No. 151) According to this method, a silicon thin film layer can be formed extremely easily and with good controllability.

On the other hand, single crystal silicon is usually used as the pressure sensitive resistance layer. This single-crystal silicon has significant restrictions on growth conditions. Therefore, a method has been proposed in which polycrystalline silicon, which is easy to form, is first formed and then crystallized by annealing. (JP 61-121478) However, in this method of annealing the entire surface,
It is difficult to crystallize uniformly and with good controllability, and there is a problem that sufficient sensor characteristics cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor pressure sensor using a piezoresistive element that is easy to manufacture and has good sensor characteristics.

[Means for solving problems]

Therefore, in the method of the present invention, a nitride film or an oxide film is formed on the surface of a silicon substrate, and then a polycrystalline silicon thin film layer of a desired thickness is formed on a Sol substrate (silicon on silicon substrate).
A process of forming a mask pattern of a desired shape made of silicon oxide etc. on the surface of the SOI substrate using 1nsulaton) as a starting material, and using this mask pattern as a mask, impurities are implanted into the polycrystalline silicon thin film layer to form impurity regions. selectively annealing and crystallizing the impurity region; and selectively removing the silicon substrate from the back side by anisotropic etching using the nitride film or oxide film as an etching stop layer. The method includes a step of forming a thin portion of polycrystalline silicon having a desired shape.

[Effect]

According to the method of the present invention, the silicon layer of the SOI substrate is polycrystalline rather than single crystal, and only the portion that will become the pressure-sensitive resistance layer is selectively annealed and crystallized, making workability extremely easy. A pressure-sensitive resistor layer pattern can be formed with good precision.

In addition, as an etching stopper for buttering thin portions of polycrystalline silicon, a silicon oxide or silicon nitride film is used that has a selectivity of more than 30 times with respect to the anisotropic etchant of silicon, which reduces the etching time. It has a large margin, and it is possible to extremely easily control the film thickness with high precision just by immersing it in an etchant. Furthermore, the thickness of the etching stop layer can be reduced, and the overall thickness can also be reduced.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 1(a) to 1(g) explain the manufacturing process of a semiconductor pressure sensor according to an embodiment of the present invention.

First, as shown in FIG. 1(a), a first silicon nitride film as an insulating layer with a film thickness of 0.5 IU is deposited on an n-type silicon substrate 1 having a thickness of 300 and having orientation in the (100) direction. 2
and a polycrystalline silicon film 3 with a thickness of 10 nm are sequentially deposited.
A substrate 4 is prepared.

Next, as shown in FIG. 1(b), a first silicon oxide film 5 with a thickness of 0.5 fl is formed on the surface of the SO1 substrate 4 by a thermal oxidation method, and this is patterned by photolithography. A window W for diffusion is formed.

Subsequently, as shown in FIG. 1(c), after boron (B) is diffused through the window W, boron (B) is diffused only into the diffusion region formed within the window using the first silicon oxide film as a mask. ,
By irradiating with laser light and performing annealing, the diffusion region is crystallized to form a pressure sensitive resistance layer 6 made of a p-type silicon diffusion layer. At this time, the surface of the pressure sensitive resistance layer 6 has a second
A silicon oxide film 7 is formed.

Subsequently, as shown in FIG. 1(d), So
A second silicon nitride film 8a is formed on the front and back surfaces of the first substrate↓.
, 8b are deposited, and then a contact hole H is formed in the second silicon nitride film 8a (and the second silicon oxide film 7) on the front surface side by photolithography.

Further, an aluminum thin film is formed by electron beam evaporation, and patterned by photolithography to form a wiring pattern 9.

(Fig. 1(e)) After forming the pressure-sensitive resistance layer 6 and the wiring pattern 9 on the surface so as to constitute a piezoresistive element, the second The silicon nitride film 8b is patterned. (Figure 1 (f
)) Finally, using the pattern of the second silicon nitride film as a mask, anisotropic etching is performed using a potassium hydroxide (KOH) aqueous solution to expose the first silicon nitride film 2, as shown in FIG. As shown in (g), thickness 10
A thin wall portion 10 as a continuous diaphragm is formed to complete a semiconductor pressure sensor.

Here, since the etching selectivity of the n-type silicon substrate 1 by potassium hydroxide to the silicon nitride film is 300 times or more, the first silicon nitride film functions as a good etching stop layer.

Therefore, without requiring strict control of etching time,
It is possible to easily obtain a semiconductor pressure sensor having a diaphragm (thin wall portion) whose thickness is controlled with high accuracy (±11) with good reproducibility.

In addition, the silicon nitride film used as the etching stop layer has an extremely sharp interface with the n-type silicon substrate 1 and the (polycrystalline) silicon thin film 3, and has high etching selectivity, so it is sufficient even if it is thin. It is possible to enhance the characteristics.

In addition, when forming the pressure-sensitive resistance layer, an SOI substrate in which the silicon film is made of polycrystalline silicon is used as a starting material, and only the portion that will become the pressure-sensitive resistance layer is selectively annealed and crystallized. It becomes possible to form a semiconductor pressure sensor with good reproducibility extremely easily.

In the embodiment, a silicon nitride film is used as the insulating layer of the SO1 substrate, but a nitride film such as a boron oxide film, or an oxide film such as a silicon oxide film may also be used. Incidentally, the etching rate of a silicon oxide film is 1/200 times or less of the etchant used for anisotropic etching of silicon.

Furthermore, the etchant is not limited to potassium hydroxide (it goes without saying that other etchants may be used).

In addition, in the example, the sensor on the diaphragm (thin wall part)
Although the semiconductor pressure sensor having the above-mentioned structure has been described, it is not limited thereto, and as shown in FIGS. Needless to say, it is also applicable.

〔effect〕

As explained above, according to the present invention, when forming a semiconductor pressure sensor, an So1 substrate in which a polycrystalline silicon film is formed on a silicon substrate via a nitride film or an oxide film as an insulating layer is used as a starting material. , impurities are selectively implanted into a region that will become a pressure-sensitive resistance layer, and then the region is selectively annealed and crystallized, and the pressure-sensitive resistance layer is formed in this way. Since the substrate is selectively etched from the substrate side by anisotropic etching using the nitride film or oxide film as an etching stop layer, it is possible to easily form a semiconductor pressure sensor with good reproducibility (and sensor characteristics). can do.

[Brief explanation of the drawing]

FIGS. 1(a) to (g) are process diagrams for manufacturing a semiconductor pressure sensor according to an embodiment of the present invention, and FIGS. 2(a) and (b) are diagrams showing other application examples of the method of the present invention. FIG. 3 is a diagram showing an example of the structure of a conventional semiconductor pressure sensor, and FIGS.
It is a figure which shows the formation process of (thin part). DESCRIPTION OF SYMBOLS 101...Diaphragm, 101a...Diffusion (resistance) layer, R...Resist, 200...N type silicon substrate, 201...P medium size silicon layer, 202...Silicon thin film layer, 202a. ... Diffusion layer, 1... N-type silicon substrate, 2... First silicon nitride film, 3... Polycrystalline silicon thin film layer, Soil... So1 substrate, 5... First oxidation Silicon film, 6... p-type diffusion layer (pressure sensitive resistance layer), 7... second silicon oxide film, 8a, 8b...
Second silicon nitride film, 9... Wiring pattern, 10.
・Thin part. Figure 1 (Q) Figure 1 (e) Figure 1 (b) Figure 1 (f) Figure 1 (d) Figure 2 (Q) Figure 4 (Q) Figure 4 (b) Figure 5 Figure (b)

Claims (1)

[Claims] A method for manufacturing a semiconductor pressure sensor comprising a sensor part and a silicon thin film part, and a piezoresistive element formed in the silicon thin film part, comprising: as a starting material a nitride film as an insulating layer on the surface of a silicon substrate; Alternatively, SOI (Silicon On Insula) is formed by forming an oxide film and a polycrystalline silicon thin film.
tor) preparing a substrate, selectively implanting impurities into the polycrystalline silicon thin film to form an impurity region, and selectively annealing and crystallizing the impurity region to form a pressure-sensitive resistance layer. and an etching step of forming the silicon thin film portion by selectively etching a predetermined region of the SOI substrate from the silicon substrate side by anisotropic etching using the insulating layer as an etching stop layer. A method for manufacturing a semiconductor pressure sensor, characterized in that: (2) The method for manufacturing a semiconductor pressure sensor according to claim (1), wherein the nitride film is made of silicon nitride (Si_3N). (3) The method for manufacturing a semiconductor pressure sensor according to claim (1), wherein the nitride film is made of boron nitride (BN). (4) The method for manufacturing a semiconductor pressure sensor according to claim (1), wherein the oxide film is made of silicon oxide (SiO_2). (5) The anisotropic etching step includes potassium hydroxide (
The method for manufacturing a semiconductor pressure sensor according to any one of claims (1) to (4), characterized in that the step uses KOH (KOH) as an etchant.