JPS6356962A - Manufacture of semiconductor pressure transducer - Google Patents

Abstract

PURPOSE:To enable an etching operation to be stopped exactly at a predetermined plane for providing a strain creating section with a diaphragm having a uniform thickness and for providing semiconductor pressure transducers having little variance in pressure sensitivity and uniform characteristics, by providing a pair of layers having different dopant concentrations and applying a positive voltage to the outer layer and a negative voltage to a cathode in an etching solution while an equal potential is provided between the inner layer and the cathode. CONSTITUTION:A silicon plate 10 is dipped in an etching solution 5 in which fluoric acid and pure water are mixed at a mixing ratio of 1 : 9. A platinum cathode 7 is opposed to the substrate surface on which a mask is to be adhered and a DC voltage of several volts is applied between the substrate 1 and the cathode 7 by a power supply 6 so that the substrate is etched electrochemically and a recess 9 is formed. A P-type layer 2 is connected to the cathode 7 to provide an equal potential therebetween. The substrate 1 is etched electrolytically in such arrangement so that the etching is stopped when the recess 9 reaches the boundary plane 8. It does not constitute an essential condition for stopping the etching at the boundary plane between different dopant concentrations that the (P-type) layer 2 having a lower dopant concentration has a conductivity type from that of the (N-type) substrate 1, but it is advantageous to form the boundary plane in P-N junction because an electrically insulating effect can be thereby obtained and it is possible to prevent noises from entering into the output of a strain gage 4. /1.

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 diaphragm having a thickness thinner in the central part of a semiconductor plate than in the peripheral part, and having a construction part provided with a strain gauge in that part.

[Prior art and its problems]

In order to obtain a strain generating part with uniform characteristics and small variations in pressure sensitivity of a semiconductor pressure transducer, it is necessary to form a diaphragm having a uniform plate thickness. One method for forming such a diaphragm is to epitaxially grow a P-type low impurity concentration layer 2 on one side of a N2 polycrystalline silicon substrate 1 doped with high impurities, as shown in FIG. On top of that, an N-type low impurity concentration layer 3
is grown, and P is added to this layer 3 by impurity diffusion from the surface.
After forming the shaped strain gauge 4, this semiconductor plate 10 is
The peripheral part of the surface on the side of the substrate 1 is masked and immersed in the etching solution 5, and a voltage of several square meters is applied, with the substrate 1 being positive with a DC current a6 and the negative electrode 7 being negative, and electrolytic etching is performed. N′ substrate 1 and P1! Etching was stopped at the interface 8 with I2, and a recess 9 was formed in the unmasked central portion. However, according to this method, N substrate 1 of the semiconductor board
If there is a defect in the P-N junction between and two layers 2,
Since the voltage applied to the substrate 1 was also applied to the PrB6 through the defective portion, the formation of the recess at the PN junction surface 8 could not be stopped.

[Purpose of the invention]

According to the present invention, when a diaphragm is formed by etching from one side of a semiconductor board, the etching is reliably stopped at a predetermined surface to form a diaphragm with a uniform thickness of the strain-generating part, and the variation in pressure sensitivity is small. It is an object of the present invention to provide a method for manufacturing a semiconductor pressure transducer with well-matched characteristics.

[Key points of the invention]

In the present invention, a first layer with a high impurity concentration is provided on the multi-sided side of a semiconductor plate on which strain gauges are formed on the negative side, and a second layer with a low impurity concentration and a high density is provided inside the layer, and this semiconductor (back side) is etched. Electrolytic etching is performed by applying a negative voltage to the electrode electrically connected to the second layer and positive to the first layer. By forming a concave portion with a depth equal to the thickness, etching is reliably stopped at the impurity concentration interface between the second layer and the first layer, which are equipotential with the cathode, and the above-mentioned object is achieved. Embodiment] An embodiment of the present invention will be described below with reference to FIG. 1, in which parts common to those in FIG. 2 are given the same reference numerals. N containing <lTo> crystal direction, for example, containing 10"/cc or more of arsenic or 10"/cc or more of antimony.
° On one side of the high concentration single crystal silicon substrate 1, 10”/cc
The following boron-doped P-type impurity concentration N2 is grown by epitaxial method, and then 1
An N-type image impurity concentration N3 doped with phosphorus of 0"/cc or more is evixically grown, and a strain gauge 4 made of a P-type layer is formed in this layer. A peripheral portion of the surface of the substrate 1 on the opposite side from this strain gauge is formed. Although not shown, for example, one-color perforation such as an oxide film (Nifkel, chromium 14~ on the film)
The mask is coated with a corrosion-resistant gold alloy such as gold containing 30% gold. As shown in the figure, such a temporary silicone 10 is placed in an etching solution 5 with a mixing ratio of hydrofluoric acid and pure water of 1:9, and a platinum negative electrode 7 is placed opposite the surface to which the mask is applied.
A DC voltage of several square meters, with the substrate being positive, is applied between the substrate 1 and the negative electrode 7 by the power supply 6 to perform electrochemical etching to form the recess 9. At this time, PJ! ! 2 and the negative electrode 7 are connected as shown in the figure to make them equipotential. By electrolytically etching with such a configuration, even if there is a defect in the interface 80P-N junction between the substrate 1 and the second layer 2, the potential of the PIFJ 2 becomes the potential of the negative electrode 7. When the recess 9 reaches the boundary surface 8, etching does not proceed any further and the etching stops. The PFJ 2 with a low impurity concentration does not necessarily have a different conductivity type from the N-type substrate 1, but it is possible to stop etching at the impurity concentration interface between them, but this interface can be made into a P-N junction. This produces an electrical insulation effect and can prevent noise from entering the output of the strain gauge 4. [Effects of the Invention] According to the present invention, positive and
A negative voltage is applied to the cathode 11 in the etching solution, and 2
By making the inner layer of the layer equipotential with the cathode, electrolytic etching can be reliably stopped at the interface between the two layers. can be formed, and there is little variation in pressure sensitivity.
A semiconductor pressure transducer with well-defined characteristics can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of an etching apparatus according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional etching apparatus. 1: N0 silicon substrate, 2: P epitaxial layer, 3:
N epitaxial layer, 4: strain gauge, 5: etching solution, 7: negative electrode, 9: recess, 10; Fig. 1 Fig. 2

Claims (1)

[Claims] 1) A concave portion is formed in the center of the semiconductor board leaving a diaphragm having a thinner thickness than the peripheral portion, and a strain-generating portion is provided on one surface of the diaphragm with a strain gauge. When manufacturing a semiconductor board, a first layer with a high impurity concentration is provided on the side opposite to the side where the strain gauge is formed, and a second layer with a low impurity concentration is provided inside that layer, and the semiconductor board is immersed in an etching solution. Then, electrolytic etching is performed by applying a negative voltage to the electrode electrically connected to the second layer and positive to the first layer, and making the thickness of the first layer the same as the depth. A method of manufacturing a semiconductor pressure transducer, comprising forming a recess. 2) A method for manufacturing a semiconductor pressure transducer according to claim 1, characterized in that the first layer is of N type and the second layer is of P type.