JPH01261872A - Manufacture of semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To obtain a diaphragm wherein the boundary between a strain generating part and a fixing part becomes a nearly regular octagon, by performing alkali anisotropic etching by using an etching mask whose aperture is in the form of a cross. CONSTITUTION:In the central part of a diaphragm mask 13, an aperture part 14 opened in the form of a cross is arranged, whose periphery is covered with an SiN film. Each side of the aperture part 14 is arranged and formed so as to coincide with the crystal axis (110) of a silicon substrate 12, and subjected to alkali anisotropic etching. In the course where etching of the crystal face (110) of a bottom 16 progresses, the silicon substrate 12 corresponding with corner parts A is etched, and inclined surfaces 16 appear. On the other hand, a crystal face (111) whose etching rate is low appears as inclined surfaces 17. When the etching is further progressed, the corner parts A vanish, and the boundary surfaces between the bottom surface 15 and the inclined surfaces 16, 17 turn to a regular octagon. Without using a mask with complicated form, an octagon diaphragm with large allowance is accurately formed.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for manufacturing a pressure sensor that converts pressure into an electrical signal by utilizing the piezoresistance effect of semiconductor crystals such as silicon, and in particular, The present invention relates to a method for manufacturing a semiconductor pressure sensor that is an improved method for manufacturing a diaphragm.

<Prior Art> FIG. 5 is a block diagram showing the structure of a conventional semiconductor pressure sensor.

FIG. 5(A) is a plan view of the semiconductor pressure sensor, and FIG. 5(B) is a cross-sectional view of the semiconductor pressure sensor. It has a strain-generating part 3 in which the thickness of the single crystal is reduced due to the formation of the recessed part 2, and a fixing part 4 around the strain-generating part 3.

The fixing part 4 is fixed to a substrate 6 having a communication hole 5 through a glass thin film 7 by anodic bonding or the like.The strain-generating part 3 has a single crystal whose crystal plane is the (100) plane. A pressure-sensitive element 8, such as a shear type gauge, is formed in a rectangular shape near the boundary between the strain-generating part 3 and the fixed part 4 in the <001> direction of the crystal axis passing through the center, with the conductivity type being P type due to the diffusion of impurities. ing.

This pressure sensitive element 8 has a power source end (not shown) formed in its longitudinal direction, to which a voltage or current is applied. When the applied pressure P is applied to the diaphragm 1, a resulting voltage corresponding to, for example, shear stress τ is obtained at an output end (not shown) formed approximately in the longitudinal center of the pressure sensitive element 8.

As a result, a voltage corresponding to the applied pressure P is obtained at the output end.

By the way, there are various methods for manufacturing such a diaphragm, but they can be roughly divided into (a) manufacturing using isotropic chemical etching, and (b) manufacturing using anisotropic chemical etching. Be taken.

In the case of the former circular diaphragm formed by isotropic etching, sagging occurs at the boundary between the strain-generating portion 3 and the fixed portion, and this sagging particularly causes variations in the linearity of the pressure versus output voltage of the pressure sensitive element 8 due to the applied pressure P. There are problems such as getting bigger.

Therefore, a manufacturing method is used in which a rectangular diaphragm with sharp edges is formed using the latter anisotropic etching in which the etching rate depends on the crystal direction.

However, in this case, a new problem arises in that stress is concentrated at the boundary between the strain-generating part and the fixed part due to the sharp edges, and the permissible range of the applied pressure P cannot be increased.

In order to alleviate this stress concentration, Japanese Patent Laid-Open No. 55-24408 discloses a method of forming an octagonal diaphragm by making holes by anisotropic etching. An overview of this will be explained below.

FIG. 6 shows the structure of the disclosed conventional diaphragm, (A) is a plan view, (B) is a partial sectional view showing the A-A section, and (C) is the B-- It is a partial sectional view showing a B-section.

Reference numeral 9 denotes a diaphragm made of single crystal silicon, and a thick fixing part 10 is formed around the periphery, and a thin strain-generating part 11 is formed in the center. This fixing portion 10 is joined to a well-known support member (not shown).

The strain-generating portion 11 is formed by forming an etching mask of a predetermined shape on a silicon substrate and excavating it by anisotropic etching.

In this case, the cross section A-/M that coincides with the crystal axis <110>
(Crystal plane <111 of the fixed part 10 shown in FIG. 5 (b))
) is a plane having an inclination of 54 degrees as shown in the figure, but the cross section B-B- which coincides with the crystal axis 100〉
Side surface Y corresponding to the crystal plane (110) of the fixed part 10 shown by
is a surface having an inclination of 45 degrees as shown in the figure. The etching rates of these crystal planes are different.

Therefore, in order to make the plane showing this boundary into a perfect octagonal shape, it is necessary to select and use an etchant whose etch rate ratio is different for each crystal plane.

<Problems to be Solved by the Invention> However, in such a conventional manufacturing method of a semiconductor pressure sensor, the shape of the etching mask must be made into a complicated shape other than an octagon in consideration of the etching speed ratio. There is the complication of having to use an etching solution that has a specific etch rate ratio for each crystal face.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides crystal planes (Zoo) of a silicon substrate with crystal axes <1, each side of which is perpendicular to each other.
An etching mask with a cross-shaped opening surrounded by 45 each for 100)
The diaphragm is formed by forming two types of side surfaces of the fixing part that make angles of 55° and 55°, and stopping the alkaline anisotropic etching when the boundary between the strain-generating part and the fixing part becomes a nearly regular octagon. It was designed to do so.

For Kukui> By forming an etching mask with cross-shaped openings surrounded by crystal axes <110> on a silicon substrate, and performing alkali anisotropic etching on this,
A 45 degree slope with respect to the (100) bottom surface appears, and a crystal plane (111) with a small etching rate, which was not present in the etching mask, appears, approaching an octagonal shape.

When this state progresses and the bottom surface of the strain-generating portion becomes approximately a regular octagon, the alkali anisotropic etching is stopped.

<Example> Fig. 1 is a plan view of a diaphragm showing the structure of one manufacturing process according to the present invention, Fig. 2 is a plan view showing the structure of a silicon substrate forming the diaphragm, and Fig. 3 is a plan view of the silicon substrate with a mask. FIG.

12 is a rectangular silicon substrate that will eventually become a diaphragm, each side of which is selected to coincide with the crystal axis 110〉 (Fig. 2); A pressure sensitive element is formed at a predetermined position on the bottom surface of the silicon substrate 12.

13 is a diaphragm mask for masking the silicon substrate 12. A cross-shaped opening 14 is formed in the center of the diaphragm mask 13, with the length of each opposite side being L and the length of each notch side being S, and the periphery thereof is covered with S and Nl. (Figure 3).

As shown in FIG. 1, each side of the opening 14 is arranged and formed to match the crystal axis <110> of the silicon substrate 12, and then etched with an alkaline etching solution of 20% to 50% (wt) KOH. Anisotropic etching is performed.

In the process of etching of the crystal plane (100) of the bottom part 15 by this alkali anisotropic etching, the silicon substrate 12 corresponding to the corner A of the diaphragm mask 13 is etched to form a crystal plane at approximately 45 degrees with respect to the bottom part 15. t
A slope 16 with t o ) appears.

On the other hand, the crystal plane (111) whose etching rate is extremely slow appears as a slope 17 at an angle of 55 degrees with respect to the bottom 15.

After this, when the silicon substrate 12 is further etched, the corner A disappears and the interface between the bottom surface 15 and the slopes 16 and 17 becomes a regular octagon, but at this point, this anisotropic etching is terminated.

As shown in FIG.
The boundary of 0 is in the shape of a regular octagon.

The operation of the diaphragm thus manufactured is almost the same as that of the diaphragm shown in FIG.

In FIG. 3, the etching depth of the octagonal strain-generating portion 20 changes by changing the dimension S while keeping the size of the diaphragm mask 13 constant, so the thickness of the strain-generating portion 20 changes depending on the pressure range. can be easily changed.

Further, after performing anisotropic etching to form an octagonal strain-generating portion, isotropic etching may be performed in order to remove the corners of the boundaries between the slopes 16 and 17 and the bottom surface 15.

<Effects of the Invention> As specifically explained above in conjunction with the examples, the manufacturing method according to the present invention has a large tolerance up to a high breakdown voltage suitable for mass production without using an etching mask with a complicated shape. An octagonal diaphragm can be formed accurately.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a diaphragm showing the configuration of one step in the manufacturing process of the present invention, FIG. 2 is a plan view showing the configuration of a silicon substrate forming the diaphragm, and FIG. 3 is a diaphragm mask for masking the silicon substrate. A plan view showing the configuration of
FIG. 4 is a plan view showing the shape of a diaphragm manufactured using the manufacturing process shown in FIG. It is an explanatory view explaining a manufacturing method of manufacturing a diaphragm. 1.9.18...Diaphragm, 3.11.20...
- Strain generating part, 4.10.19... Fixed part, 8... Pressure sensitive element, 12... Silicon substrate, 13... Diaphragm mask, 14... Opening, 15... Bottom surface , 16.
17...Slope. Figure 2 and A2

Claims (1)

[Claims] An etching mask is formed on the crystal plane (100) of the silicon substrate, each side of which is surrounded by crystal axes <110> that are perpendicular to each other, and has openings in a cross shape, and alkali anisotropic etching is performed on this etching mask. By doing so, the corners protruding inward of the opening are etched to form two types of side surfaces of the fixing part that form angles of 45° and 55° with respect to the crystal plane (100), respectively, and the strain-generating part and A method of manufacturing a semiconductor pressure sensor, characterized in that the diaphragm is formed by stopping the alkaline anisotropic etching when the boundary of the fixed part becomes a substantially regular octagon.