JPS62183190A - Manufacture of semiconductor pressure transducer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a method for manufacturing a semiconductor pressure transducer having a thin strain-generating portion in which a gauge resistor made of a layer of a different conductivity type is provided in a layer of a negative conductivity type.

[Prior art and its problems]

Conventionally, in order to obtain a strain sensitive part of a pressure transducer having small variations in pressure sensitivity, uniform characteristics, and uniform plate thickness, a single crystal silicon substrate 1 doped with impurities at a high concentration is used as shown in FIG. A low impurity concentration layer 2 is epitaxially grown on one side of the substrate, a strain gauge 3 of a different conductivity type is formed on this low impurity concentration layer 2, and an electrically insulating film is formed on the periphery of the substrate surface facing the strain gauge 3. , for example, oxide film 4
nickel (Ni) and chromium (C) are provided on this insulating film.
A metal film 5 of gold (Au) containing r) is deposited and used as an etching mask, and a high impurity concentration silicon substrate 1 and a platinum negative electrode 7 placed opposite thereto are coated in an etching solution 6. Electrochemical etching is performed by applying a DC voltage between the electrodes B8 and the impurity concentration boundary surface 11.
The etching was stopped at this point in order to obtain a pressure transducer strain-generating part with a uniform plate thickness. In such a method of forming a strain-generating part, as the etching progresses, current flows not only from the bottom surface 13 of the recess 12 but also from the side surface 14, and the formation of the recess progresses. At the same time, the resistance of the current supply path increases,
The rate of increase tends to be greater in the center than in the periphery. Due to this difference in resistance increase rate, the supplied current is larger at the periphery than at the center, and the etching speed tends to be larger at the periphery in proportion to the magnitude of the current, resulting in the progress of recess formation. This tendency will become even stronger. As a result, the peripheral part is etched faster than the vicinity of the central part of the bottom surface 13 of the recess, so that the peripheral part eventually reaches the concentration boundary surface 11 earlier as shown in FIG. The formation of the recess in the part stops at that point. At the same time, since the peripheral portion of the central portion of the bottom surface 13 of the concave portion has reached the concentration boundary surface 11, the current supply is cut off, and etching no longer progresses, resulting in an etched residue 15. This etching residue 15 has a diameter that is the final recess 11.
The diameter of the board is approximately 174-115 mm, and the remaining thickness is approximately 5 mm of the thickness of the substrate l.
The variation is about 10%, and the shape is also not uniform, which causes variation in pressure sensitivity and other variations in pressure transducer characteristics.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor pressure transducer in which the plate pressure of the strain-generating portion is uniform, the pressure sensitivity is uniform, and the characteristics are uniform.

[Key points of the invention]

In the present invention, a layer having an impurity concentration lower than that of the substrate is laminated on a substrate, a mask made of a metal film is deposited on the opposite side of the substrate surface from the low impurity concentration layer through an insulating film, and the layer is etched in an etching solution. When a DC voltage is applied between the substrate and an electrode placed opposite to the surface to which the mask is applied, electrochemical etching is performed to the impurity concentration interface to form a concave portion for the strain-generating portion. An insulating film that is thicker at the periphery than at the center and etched by an etching solution at a slower etching rate than the substrate is deposited on areas where the concave portion is not deposited, and as a result, the impurity concentration is lower at the periphery than at the center in the recess formation area. Since the time for etching to reach the boundary surface is delayed, the current supply is not cut off until the etching reaches the concentration boundary surface in the central region, making it possible to achieve the above objective. The insulating film provided in the area where the mask is not applied is
It is extremely effective for the present invention to be an extension of the insulating film that constitutes the mask together with the metal film.

[Embodiments of the invention]

The present invention will be described in detail below with reference to the drawings. The same parts in each figure as in FIG. 3 are given the same reference numerals. In FIG. 1, a high-concentration single-crystal silicon substrate 1 has a crystal orientation that provides an effective piezoresistance effect, and contains, for example, 10"/cc or more of arsenic or 10"/cc or more of antimony. A low impurity concentration layer 2 of 10"/cc or less is epitaxially grown by the thickness of the strain-generating part required for the purpose of the invention, and a strain gauge 3 made of layers of different conductivity types is formed on this low impurity concentration layer. On the other side of the substrate facing the gauge, an electrically insulating film, for example, an oxide film 4, is provided on the entire surface with a thickness of about IIrI, and on top of that is a metal film made of Au containing 14 to 30% Cr. 5. At the central part of this gold r%Wj!5 facing the strain gauge 3, a region with a diameter corresponding to the recess to be formed is removed, and then the lower oxide film is reduced to 1/40. Only a region corresponding to the above dimensions, for example, a diameter of 1/3 . A DC voltage of several volts is applied from a power source 9 between the platinum negative electrodes 7 installed in the liquid to perform electrochemical etching.At this time, the etching rate is approximately 2-7 minutes.The oxide film 4 is etched for about 0.02-7 minutes, and the oxide film 4 not covered by the metal film 5 is etched, and the silicon base @1 is etched.
It takes approximately 50 minutes for the 0 surface to be exposed. On the other hand, the portion of the surface of the silicon substrate 1 that is not covered by the oxide film 4 is etched to a depth of approximately 100 μm as shown in FIG. (The central part reaches the concentration boundary surface 11 earlier than the peripheral part. The peripheral part continues to be etched and finally reaches the concentration boundary surface 11 as shown in Fig. 5.
As indicated by C1, the peripheral portion also reaches the concentration boundary surface 11, and the formation of the recessed portion 12 is completed. Since the etching rate of the low impurity concentration layer 2 is sufficiently low, approximately 1/100 of that of the high concentration silicon substrate 1, the central portion, which reaches the concentration boundary surface 11 earlier than the peripheral portion, is not substantially deeper than that. , flat bottom 1
3 occurs. The concave portion 12 formed in this manner has no etching residue on the bottom surface, and a strain-generating portion having a uniform thickness can be obtained. Figure 6 ta+~(C1 shows the installation of the oxide film 4 in another embodiment of the present invention, and Figure 6 (al, (bl) shows the thickness of the oxide film 4 in the recess formation region from the periphery to the center. The oxide film 4 is also provided in the central part in FIG. In each of 0 or more examples in which a strain-generating portion similar to the strain-generating portion of the example is obtained, another insulating film can be used instead of the oxide film 4, but it can be etched with an etching solution at a lower etching rate than the substrate. In the actual manufacturing process, a large number of recesses 12 are simultaneously formed on one silicon wafer, the wafer is cut and divided, and a large number of semiconductor substrates for pressure transducers are simultaneously manufactured. [Effects of the Invention] According to the present invention, a semiconductor pressure transducer can be electrochemically fabricated by utilizing etching stoppage at the concentration interface between a high impurity concentration substrate and a low impurity concentration layer laminated thereon. When forming a recess for a strain-generating part, an insulating film that is thicker in the center than in the periphery is deposited on the recess forming area that is not covered by the mask, and the etching time of the insulating film is determined by the difference in etching time. By using etching to reach the impurity concentration boundary surface earlier in the center than in the periphery, it is possible to completely avoid etching residue in the center of the outer surface of the recess.As a result, a strain-generating part with a uniform plate thickness This makes it possible to manufacture semiconductor pressure transducers with small variations in pressure sensitivity and well-matched characteristics.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a substrate before creating a strain-generating portion in an embodiment of the present invention, FIG. 2 is a cross-sectional view of the substrate shown in FIG. 1 during etching to create a strain-generating portion, and FIG. 3 is a conventional etching process. FIG. 4 is a sectional view showing the progress of etching to create a strain-generating portion using a conventional method; FIG.
The figures are cross-sectional views sequentially showing the progress of etching shown in FIG. 2, and FIG. 6 is a cross-sectional view showing the state of oxide film installation in three different embodiments of the present invention. 1: Silicon substrate, 2: Low impurity concentration layer, 3: Strain gauge, 4 Dioxide film, 5: Metal film, 6: Etching solution, 7
: cathode, 11: impurity concentration interface.゛Core people 41; ヱ上、b ふ Busy X/ Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Awakening

Claims (1)

[Claims] 1) A metal film formed by laminating a layer having an impurity concentration lower than that of the substrate on a semiconductor substrate, and depositing an insulating film on the surface of the substrate opposite to the low impurity concentration layer. A mask is provided, and a DC voltage is applied in an etching solution between an electrode placed opposite to the surface to which the mask is applied and the substrate to electrochemically etch to the impurity concentration interface to form a concave portion for a strain-generating portion. A semiconductor pressure conversion method characterized by depositing an insulating film on a region of the semiconductor substrate surface where a mask is not deposited, which is thicker at the periphery than at the center and is etched by an etching solution at a lower etching rate than the semiconductor substrate. How to make the utensils. 2) A semiconductor pressure conversion method according to claim 1, characterized in that the insulating film applied to the area where the mask is not applied is an extension of the insulating film that constitutes the mask together with the metal film. How to make the utensils.