JPH02177369A - Manufacture of silicon diaphragm - Google Patents

Abstract

PURPOSE:To enhance the dimensional precision of a diaphragm by a method wherein isotropical electrolytic etching process is performed even in a buried layer in a deep recess by self electrode operation using a circular buried layer to form a recess as a cathode of a silicon substrate. CONSTITUTION:An n type buried layer 11 is formed in a p type silicon substrate 10 and then an n type epitaxial layer 12 is formed on the whole surface. Next, an electrode 16 comprising an n type diffused layer in high concentration passing through the layer 12 and connecting to the layer 11 while taking a ring shape along the edge part is formed. Furthermore, a connecting hole 17 to the layer 11 is formed in the substrate 10 by anisotropical etching process and then an inverse bias voltage is impressed on the space between the layer 12 and the substrate 10 through the intermediary of the electrode 16. In such a state, the layer 11 is etched away supplying the layer 12 with the positive potential as to an etchant to form a stain imposing part 20. Through these procedures, uneven etching processes can be eliminated thereby enhancing the dimensional precision in the radial direction of the strain imposing part 20 of a diaphragm.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a silicon diaphragm that is mass-producible, inexpensive, and accurate.

<Prior Art> FIG. 4 is an explanatory diagram of the configuration of a conventional example that has been commonly used in the past, and shows an example used in a semiconductor pressure sensor.

FIG. 4(A) shows a plan view of the semiconductor pressure sensor, and FIG. 4(B) shows a cross-sectional view of the semiconductor pressure sensor.

In the figure, reference numeral 1 denotes a diaphragm made of n-type silicon single crystal, which has a concave part 2, and a strain-generating part 3 in which the thickness of the single crystal has become thinner due to the formation of the concave part 2, and a fixed part around it. 4.

The fixing part 4 is fixed to a substrate 6 having a communication hole 5 via a glass thin 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 voltage is applied. When an applied pressure P is applied to the diaphragm 1, a voltage corresponding to, for example, shear stress τ generated by this is generated at an output @i (not shown) approximately in the longitudinal center of the pressure sensitive element 8.
can be obtained.

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, the two methods are (a) manufacturing by isotropic chemical etching or (b) manufacturing by fl-tropic chemical etching. However, there is also a manufacturing method (c) in which an n-type epitaxial layer is stacked on an n+ silicon substrate and a hole is formed in the n'' 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 problems as described below.

(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 thickness control method is adopted, dimensional accuracy in the radial direction is poor.

(b) When machining the concave portion of the diaphragm using the second manufacturing method (b), a dimension of 117 degrees is good, but the shape of the strain-generating portion of the diaphragm is limited to a quadrangle, an octagon, etc. A corner is formed where the two intersect, and stress concentration acts on this part, making it difficult to use under high stress.

(C) When processing the concave portion of the diaphragm using the third manufacturing method (C), 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.

There is a head between such things.

The present invention solves this problem.

An object of the present invention is to provide a method for manufacturing a silicon diaphragm with good reliability, low cost, and high precision.

Means for Solving the Problems In order to achieve this object, the present invention provides a buried layer of highly concentrated n-type silicon patterned in the shape of a strain-generating portion that is displaced by a measuring pressure on a p-type silicon substrate. forming an n-type epitaxial layer on one surface of the buried layer, epitaxially growing it on the buried layer, and forming a ring along the peripheral edge of the buried layer by penetrating the n-type epitaxial layer and connecting to the buried layer. forming a highly concentrated n-type silicon diffusion layer, forming a recessed portion of the p-type silicon substrate corresponding to the buried layer by anisotropic etching to the depth of the buried layer; The n-type epitaxial layer is held in a positive position with respect to the etching solution while a reverse bias voltage is applied between the buried layer and the n-type epitaxial layer, and the buried layer is electrolytically etched to remove the strain-generating portion. A method for manufacturing a silicon diaphragm is adopted.

Effect〉 A highly concentrated n-type buried layer is formed on a p-type silicon substrate,
An n-type epitaxial layer is further grown on this layer, and a ring-shaped high-concentration n-type layer is formed on this n-type epitaxial layer to reach the buried layer along the periphery of the high-concentration n-type buried layer.
After that, a concave portion communicating with this buried layer is formed in the p-type silicon substrate by anisotropic 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 to remove the strain-generating portion. form.

<Embodiment> FIG. 1 is an explanatory diagram of the main part configuration of an embodiment of the present invention, and an example in which it can be used as a semiconductor pressure sensor will be described.

FIG. 1(a) shows a p-type wafer-shaped silicon substrate 10 doped with circular impurities at a high concentration (
A diffusion process of forming the buried layer 11 by diffusing with n+) is shown.

On the buried layer formed in this diffusion step, circular epitaxial growth is performed to form a circular epitaxial layer 12, as shown in FIG. 1(b).

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 film 15 such as a film, and serves as a mask for the next anisotropic etching process.

An isolation layer 131 is formed by high concentration P type isolation diffusion for element isolation.

Further, the buried layer 1 penetrates through the circular epitaxial layer 12.
An electrode 16 made of a circular high-concentration silicon diffusion layer is formed in a ring shape along the peripheral edge of the buried layer 11.

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) to the depth of the n+ buried layer 11 to form a communicating hole 7 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 E and E2 are applied between the circular epitaxial layer 12 and the p-type silicon substrate 10 via tix6, and hydrogen fluoride (HF) is applied.
Alternatively, a platinum electrode 18 is provided in an etching solution such as ammonium fluoride, and a DC voltage E is applied with the electrode 18 set to (-)i and the circular epitaxial layer 12 set to (+)4It to perform isotropic electrolysis. Perform etching.

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

In the semiconductor pressure sensor manufactured by VJ using the above manufacturing method, pressure P is introduced through the communication hole 17 and the recess 19, thereby the strain-generating portion 20 is distorted, and this distortion is detected by the gauge 13 as an electrical signal. .

As a result, the circular n4 buried layer 11 for forming one recess is isotropically extended to the n+ buried layer deep inside the recess due to the self-like action of the P-type silicon substrate 10 as a (-) balance. Since it is electrolytically etched and there is no side etching of the film in the recessed part, the dimensional accuracy of the strain-generating part 20 of the diaphragm in the radial direction is good, there is no need to use N4 silicon substrates that are difficult to obtain, and the diaphragm can be processed on a wafer basis. ] 2, it has various effects such as mass production processing becomes possible.

Furthermore, it penetrates the circular epitaxial layer 12 and the buried layer 1]
Since a highly concentrated circular silicon diffusion layer is formed in a ring shape along the periphery of the buried layer 11, the electrode can be formed in a ring shape, the etching current is uniform, the etching is uniform, and the N+ buried layer is formed. Since the layer weight 1 can be reliably removed by isotropic electrolytic etching, it is possible to obtain a strain-generating portion 20 of the diaphragm with improved radial dimensional accuracy.

FIG. 3 is an explanatory diagram of the main part configuration of another embodiment of the present invention.

In this embodiment, a cross section 111 is provided in the buried layer 11 to prevent portion 94]6 of n4 from being etched when electrolytic etching is performed near the outer periphery of the buried layer 11. It is.

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

<Effects of the Invention> As explained above, the present invention forms a buried layer of highly concentrated n-type silicon on one surface of a p-type silicon substrate, which is patterned in the shape of a strain-generating portion that is displaced by measurement pressure. , forming an n-type epitaxial layer by epitaxial growth on the implanted layer, penetrating the n-type epitaxial layer and connecting to the buried layer, and forming a high concentration layer in a ring shape along the periphery of the implanted layer; forming a diffusion layer of n-type silicon; forming a recessed portion to the depth of the buried layer in a portion of the p-type silicon substrate corresponding to the buried layer by y4-directional etching; The strain-generating portion is formed by electrolytically etching and removing the n-type epitaxial layer by holding the n-type epitaxial layer at a positive potential with respect to the etching solution while applying a reverse bias voltage between the n-type epitaxial layer and the etching solution. A manufacturing method for silicon diaphragms was adopted.

As a result, the circular n+ buried layer for forming the recess is isotropically etched to the n+ buried layer deep inside the recess by the self-electrode action of the p-type silicon substrate as the (-) pole. There is no side etching on the side wall of the
The strain-generating part of the diaphragm has good radial dimensional accuracy, and there is no need to use N+ silicon substrates, which are difficult to obtain.Furthermore, diaphragm processing can be performed on a wafer basis, making it possible to process on-demand production. There is an effect.

Furthermore, a high concentration n-type silicon diffusion layer was formed in a ring shape along the periphery of the buried layer, penetrating the n-type epitaxial layer and connected to the buried layer, so that the electrode could be formed in a ring shape and the etching current could be reduced. Since the n+ buried layer can be reliably removed by isotropic electrolytic etching without any uneven etching, it is possible to obtain a diaphragm with improved radial dimensional accuracy of the strain-generating portion.

Therefore, according to the present invention, the silicon diaphragm has 'IIl'ft' which is easy to mass-produce, is reliable, and has good precision.
The method can be implemented.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing the manufacturing method of one embodiment of the present invention, FIG. 2 is a completed plan view of FIG. 1, and FIG. (A) is a plan view, (B) is a front view, and FIG. 4 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, ] 11... Cross portion, 12... N-type epitaxial layer, 13... Gauge, 131... Isolation layer, 14 .15... Insulating film, 16... Electrode, Engineering 8
···electrode. Number 1

Claims (1)

[Claims] A buried layer of highly concentrated n-type silicon patterned in the shape of a strain-generating portion that is displaced by measurement pressure is formed on one surface of a p-type silicon substrate, and epitaxial growth is performed on the buried layer. forming an n-type epitaxial layer, penetrating the n-type epitaxial layer and connecting to the buried layer, and forming a ring-shaped highly doped n-type silicon diffusion layer along the periphery of the buried layer; A recess was formed in a portion of the p-type silicon substrate corresponding to the buried layer by anisotropic etching to the depth of the buried layer, and a reverse bias voltage was applied between the p-type silicon substrate and the n-type epitaxial layer. 1. A method of manufacturing a silicon diaphragm, characterized in that the buried layer is removed by electrolytic etching while the n-type epitaxial layer is held at a positive potential with respect to an etching solution to form the strain-generating portion.