JPH01170054A - Manufacture of semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To contrive the improvement of the dimensional accuracy in the radial direction of the strain-generating part of a diaphragm by a method wherein an n<+> buried layer is removed by isotropic electrolytic etching applying the action of a self-electrode, which is used as one pole of a p-type Si substrate. CONSTITUTION:A high-concentration n<+> buried layer 11 is formed in a p-type Si substrate 10, an n-type epitaxial layer 12 is further grown on this layer 11 to form a gauge 13 here and after this, a recessed part (interconnected hole) 17, which is connected to the layer 11, is formed in the substrate 10 by anisotropic etching. Moreover, the layer 12 is held in a positive potential to an etching liquid in a state that a reverse bias voltage is applied between the substrate 10 and the layer 12 and the layer 11 is subjected to electrolytic etching and is removed to form a strain-generating part 20.

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.

2. Prior Art> FIG. 2 is a block diagram showing the structure of a conventional semiconductor pressure sensor.

Figure 2 (A) is a plan view of the semiconductor pressure sensor, and Figure 1 (B) is a cross-sectional view of the semiconductor pressure sensor. Furthermore, 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 thin glass film 7 by anodic bonding or the like.

The strain-generating portion 3 is a (100) plane of a single crystal, and a sensor such as a shear type gauge is placed on the surface near the boundary between the strain-generating portion 3 and the fixed portion 4 in the <001> direction of the crystal axis passing through its center. Pressure element 8
is formed into a rectangular shape with the conductivity type being P type due to the diffusion of impurities.

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 an applied pressure P is applied to the diaphragm 1, a voltage corresponding to, for example, shear stress τ generated thereby 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 generally there are two methods: (a) manufacturing by isotropic chemical etching, and (b) manufacturing by anisotropic chemical etching. However, in addition to this (
c) There is also a manufacturing method in which an n-type epitaxial layer is stacked on an n'' silicon substrate, and a hole is formed in the n1 silicon substrate by electrolytic etching using the n-type epitaxial layer as an etching stop layer.

<Problems to be Solved by the Invention> However, such a conventional method for manufacturing a semiconductor pressure sensor has the following problems.

(b) When processing the concave portion of the diaphragm using the first manufacturing method (a), it is not easy to achieve dimensional accuracy. Even if a method for controlling the thickness is adopted, the dimensional accuracy in the radial direction is poor. The shape of the strained part is limited to quadrangles, octagons, etc., and corners are formed where surfaces intersect, stress concentration acts on these parts, making it difficult to use under high stress. When processing the concave portion of the diaphragm using the manufacturing method (C) of No. 3, there are problems such as it is difficult to obtain a high concentration n+ silicon substrate, and the dimensional accuracy of the concave portion of the diaphragm in the radial direction is not sufficient.

Means for Solving the Problems> In order to solve the above problems, the present invention has a buried layer of high concentration n-type silicon patterned in the shape of a strain-generating portion that is displaced by measurement pressure. An n-type epitaxial layer is formed by epitaxial growth on the buried layer of the p-type silicon substrate held on the surface, and a P-type gauge is further formed on this layer, and then p-type is etched to the depth of the buried layer by anisotropic etching. A recess is formed in a portion of the silicon substrate corresponding to the buried layer, and the n-type epitaxial layer is brought to a positive potential with respect to the etching solution while applying a reverse bias voltage between the p-type silicon substrate and the n-type epitaxial layer. The buried layer is retained and removed by electrolytic etching to form a strain-generating portion.

Function> A highly concentrated n-type buried layer is formed on a p-type silicon substrate, an n-type epitaxial layer is grown on top of this to form a gauge, and then an anisotropic layer is formed on the p-type silicon substrate. A recess leading to this buried layer is formed by etching,
Furthermore, with a reverse bias voltage applied between the P-type silicon substrate and the n-type epitaxial layer, the n-type epitaxial layer is held at a positive potential with respect to the etching solution, and the buried layer is electrolytically etched and removed. form.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1(a) shows a p-type wafer-shaped silicon substrate 10 doped with n-type impurities at a high concentration (
A diffusion process for forming a buried N11 by diffusing N+) is shown.

On the buried layer formed by this diffusion process, as shown in FIG.
An n-type epitaxial layer 12 is formed by performing n-type epitaxial growth as shown in FIG.

In the gauge forming process of Fig. 1 (c), this Fig. 1 (b)
A p-type gauge 13 is formed by diffusion or the like on the epitaxial layer 12 formed by the process, and is covered with an insulating film 14 such as a nitride film to protect the gauge 13, and the bottom surface of the silicon substrate 10 is also nitrided. It is covered with an insulating WA film 15 and used as a mask for the next anisotropic etching process.

In this step, an n+ electrode 16 is formed on the n-type epitaxial layer 12 in preparation for a subsequent step.

FIG. 1(D) shows the anisotropic etching process. In this process, the insulating film 15 is patterned into a rectangular shape and opened in a portion of the silicon substrate 10 corresponding to the buried layer 11 where a communication hole 17 is to be made. Anisotropic etching is performed using an etching solution of potassium hydroxide (KOH) using the n♦ dipping layer 11 as an etch stop surface to form a communicating hole 17 having a rectangular cross section in the silicon substrate 10.

FIG. 1(e) shows the electrolytic etching process.

In this step, reverse bias DC voltages E1 and E2 are applied between the n-type epitaxial layer 12 and the p-type silicon substrate 10 via the electrode 16, and hydrogen fluoride (HF) or ammonium fluoride, etc. A platinum electrode 18 is provided in the etching solution, and this electrode [! Isotropic electrolytic etching is performed by applying a DC voltage E with 18 as the (-) pole and the n-type epitaxial layer 12 as the (+) pole.

By this electrolytic etching, the n+ type buried layer 11 is etched to form a circular recess 19, and the portion of the n type epitaxial layer 12 facing this recess 19 becomes a circular strain-generating portion 20 (FIG. 1). A diaphragm 21 shown in is formed.

The semiconductor pressure sensor manufactured by the above manufacturing method is
Pressure P is introduced through the communication hole 17 and the recess 19, thereby distorting the strain generating portion 20, and this distortion is detected by the gauge 13 as an electric signal.

In addition, instead of the electrolytic etching shown in FIG. 1(e), machining such as ultrasonic grinding may be used as needed.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, the circular n+ buried layer for forming the recess is
Due to the self-electrode action of the shaped silicon substrate as the (-) pole, the N4 buried layer deep inside the recess is reliably removed by isotropic electrolytic etching, resulting in good dimensional accuracy in the radial direction of the strain-generating part of the diaphragm. In addition, there is no need to use n+ silicon substrates, which are difficult to obtain, and the diaphragm can be processed in units of eight, making mass production possible.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing a manufacturing method according to an embodiment of the present invention, and FIG. 2 is a configuration diagram showing the configuration of a semiconductor pressure sensor manufactured by a conventional manufacturing method. 1.21...diaphragm, 2.19...recess, 3
．． 20... Strain part, 5.17... Communication hole, 8...
Pressure sensitive element, 10... Silicon substrate, 11... Buried layer, 12... N-type epitaxial layer, 13... Gauge, 14.15... Insulating film. Figure 2: Rod! (a) Omu beak (b) A charvet surface (c) Lean type 1 collection (d) 1! λ'Y1 Etch〉F1 (E) Electrolytic Enochire 7゛(H) Ear 7 Ram

Claims (1)

[Claims] An n-type epitaxial layer is formed by epitaxial growth on the buried layer of a p-type silicon substrate, which has a buried layer of highly concentrated n-type silicon on one side, which is patterned in the shape of a strain-generating portion that is displaced by the measurement pressure. Then, after forming a p-type gauge on this, a recess is formed in a portion of the p-type silicon substrate corresponding to the buried layer to the depth of the buried layer by anisotropic etching, and the p-type silicon substrate and the n-type epitaxial layer while applying a reverse bias voltage between the n-type epitaxial layer and the etching solution, the n-type epitaxial layer is held at a positive potential with respect to the etching solution, and the buried layer is electrolytically etched and removed to form the strain-generating portion. A method of manufacturing a semiconductor pressure sensor, characterized in that: