JPH0439969A - Manufacture of semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To provide a semiconductor pressure sensor having a diaphragm with uniform thickness by forming interchip isolation layers on a wafer, and subjecting the wafer to self-ending etching. CONSTITUTION:N-type epitaxial layers 2 and interchip isolation layers 3 are formed on a p-type substrate 1. A diffused n<+> electrode 6 is formed in the periphery of the wafer 9, and a diffused + electrode 5 is formed on each chip 10. After a passivation film 7 is provided, a conductive film 8 for connecting the electrodes 5 with the electrode 6 is formed and it is connected to the positive electrode of an external power source. The reverse side of the substrate is subjected to self-ending etching to remove the other areas than masked by an oxide film 11, so that thin-film diaphragms 4 are formed. Then, the surface of the wafer 9 is etched to remove the conductive film 8. The wafer is cut into chips, and each is packaged to assemble a semiconductor pressure sensor. The sensors thus provided have less variation in sensitivity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor pressure sensor, and more particularly to a method for manufacturing a semiconductor pressure sensor in which a wafer on which an inter-chip isolation layer is formed is subjected to automatic stop etching. .

[Conventional technology]

Conventionally, such semiconductor pressure sensors have been manufactured by forming a pressure testing element on the front surface of a P-type semiconductor substrate and etching the back surface to form a thin film diaphragm portion.

FIG. 5 is a cutaway perspective view of a semiconductor pressure sensor for explaining a conventional example.

As shown in FIG. 5, the conventional sensor has an N-type epitaxial layer (hereinafter abbreviated as N-type epitaxial layer) 2 grown on a P-type substrate 1, and an inter-chip separation layer 3 for isolating the chips. , N+ electrode 5, pressure detection element 18, and pressure detection element 1
8 are formed, and a passivation film 7 is provided as the uppermost layer to protect them. Further, a thin film diaphragm portion 4 is formed by etching at the center of the back side of the P-type substrate 1.

In manufacturing such a semiconductor pressure sensor, since there is an interchip separation layer 3, the back surface of the P-type substrate 1 is etched using an etching method with time-release control to form a thin film diaphragm portion 4.

FIG. 6 is a sectional view of an etching tank for explaining another conventional example.

As shown in FIG. 6, in manufacturing a conventional semiconductor pressure sensor in which a wafer 9 is not provided with an inter-chip separation layer, the surface of an N-type epitaxial layer 2 formed on a P-type substrate 1 of a wafer 9 to be etched is first etched. Boron is diffused around the area,
An N+ electrode 6 is formed. This N+ electrode 6 and external power supply 15
Connect the wiring to the + power supply side. In other words, P of wafer 9
A reverse bias is applied between the mold substrates 1. Thereafter, the wafer 9 is placed in an etching tank 14 having an etching liquid 13 and a counter electrode 16 connected to one side of an external power source 15. As a result, the P-type substrate 1 of the wafer 9 is etched, and the N-type epitaxial layer 2 is exposed to the etching solution 13. Here, when the N-type epitaxial layer 2 is exposed to the etching solution, there is no electrical barrier between the N-type epitaxial layer 2 and the etching solution 13, and a current flows through the etching solution 13. The energy of this current forms an anodic oxide film 21 on the surface of the N-type epitaxial layer 2 on the P-type substrate 1 side, and etching is stopped. The phenomenon of forming this oxide film 21 is generally called anodic oxidation.

In this manner, when there is no inter-chip separation layer 3, an anodic oxide film is formed and etching of the wafer 9 is automatically stopped.

[Invention or problem to be solved]

The above-mentioned conventional semiconductor pressure sensor having an inter-chip separation layer is manufactured by controlling the etching time to manufacture the diaphragm part of a predetermined thickness, and cannot be manufactured using an etching solution that automatically stops the wafer. .

In other words, even if a voltage is applied to the N° electrode at the periphery of the wafer, the N-type epi layer inside the chip is separated from the N-type epi layer at the wafer periphery because of the inter-chip separation layer. There is no bias condition between the P-type substrates. Therefore, etching progresses and N inside the chip is removed.
Even if the mold epitaxial layer is exposed to the etching solution, no current flows, so anodic oxidation does not occur. In other words, etching does not stop automatically.

In this way, the only way to form a diaphragm part with a predetermined thickness having a separation layer is to control the etching time. The drawback is that it varies.

Further, in the case of a wafer without a separation layer, although the wafer is automatically oxidized, problems such as variations in the thickness of the diaphragm portion and irregular variations remain.

An object of the present invention is to provide a semiconductor pressure sensor that can realize automatic oxidation of a wafer having such an inter-chip separation layer and eliminate variations in the thickness of a tire flam portion.

``[Means for Solving the Problems] A method for manufacturing a semiconductor pressure sensor of the present invention includes forming a semiconductor pressure sensor on a wafer having an epitaxial layer on a substrate having first and second electrodes and a separation layer for separating chips. a step of forming a conductive film for electrically connecting the chips; etching the wafer by anodic oxidation from the surface opposite to the surface on which the conductive film is formed; and automatically etching near the epitaxial layer. The process includes the steps of stopping the wafer and forming a thin film diaphragm portion, and removing the conductive layer on the wafer and separating it into chips.

〔Example〕

Next, embodiments of the present invention will be described using the drawings.

FIG. 1 is a sectional view of a semiconductor wafer for explaining a first embodiment of the present invention.

As shown in FIG. 1, in this embodiment, an N-type epitaxial layer 2 is formed on a P-type substrate 1. An interchip isolation layer 4 is formed on this N-type epitaxial layer 2 so that each chip 10 is electrically isolated. That is, the separation layer 4 is formed to surround the periphery of each chip 10.

Next, in order to perform electrochemical etching on the wafer 9, an N+ electrode 6 is formed by diffusion on the periphery of the wafer 9, and an N+ electrode 5 of each chip 10 is also formed by diffusion. Furthermore, after covering the passivation film 7, a conductive film 8 is formed to connect the N+ electrode 6 on the periphery of the wafer 9 and the N'' electrode 5 of each chip 10.This conductive film 8 is connected to an external power source (not shown). Thereafter, the portion of the back surface of the P-type substrate 1 where the oxide film 11 is not present as an etching mask is etched, and the thin film diaphragm portion 4 is formed.

FIG. 2 is a sectional view of an etching tank for explaining the first embodiment of the present invention.

As shown in FIG. 2, the wafer 9 described in FIG. Connected to the conductive film 8.

Next, the mechanism for automatically stopping etching will be explained.

First, during etching, the N-type epi layer 2 is connected to the power source 15 via the N+ electrode 6, so that a reverse bias is applied between the N-type epi layer 2 and the P-type substrate 1. Next, when the etching progresses and the diaphragm portion 4 of the P-type substrate 1 is removed,
Similar to a conventional semiconductor pressure sensor, a current flows from the N1 voltage &5 of each chip 10 through each N type epitaxial layer 2 to the etching liquid 13 and the counter electrode 16. As a result, the surface of the N-type epitaxial layer 2 is oxidized by anodic oxidation, and etching is automatically stopped.

FIGS. 3(a) and 3(b) are chip cross-sectional views for explaining the conductive film removal step and chip separation step, respectively, after forming the tire flam portion by etching according to the present invention.

As shown in Figure 3(a), when etching is completed,
The conductive film 8 on the surface of the wafer 9 is removed by etching. -For example, if the conductive film 8 is made of polysilicon,
As the etching liquid 13, a hydrofluoric acid type liquid is used.

Next, as shown in FIG. 3(b), the chips 10 are separated by a method such as dicing. This separated chip 10 is mounted in various packages and assembled as a semiconductor pressure sensor.

FIG. 4 is a sectional view of a semiconductor wafer for explaining a second embodiment of the present invention.

As shown in FIG. 4, this embodiment includes forming an inter-chip isolation layer 3 for electrically isolating each chip 10 on an N-type epitaxial layer 2 formed on a P-type substrate 1, and etching. For this purpose, the N+ electrode 6 is formed on the periphery of the wafer 9, and the N+ electrode 5 is also formed inside each chip 10, as in the first embodiment described above. The difference is that this embodiment includes a step of forming an aluminum layer 17 on this N+ electrode from which the passivation film 7 has been removed, and the N+ electrode pass conditions for this aluminum layer 17 can be controlled. This can be used to prevent leakage current from the gauge resistor.

Furthermore, the N+ electrode 6 on the periphery of the wafer 9 and each chip 10
The N+ electrode 5 is connected to the conductive film 8 formed on the passivation film 7. This conductive film 8 is made of, for example, polycrystalline silicon (polysilicon). Next, the anode of the external electrode 15 (see FIG. 2) is connected to this conductive film 8, and etching is performed. Note that the etching method and subsequent assembly process are the same as in the first embodiment described above.

〔Effect of the invention〕

As explained above, the method for manufacturing a semiconductor pressure sensor of the present invention includes a step of forming a conductive layer for electrically connecting chips on a wafer formed by forming an inter-chip separation layer and an electrode on an epitaxial layer on a substrate. etching by anodic oxidation from the surface opposite to the surface on which the conductive layer is formed on the wafer, and automatically stopping the etching near the epitaxial layer to form a thin film diaphragm portion; By including the step of removing the conductive layer of the wafer and separating it into chips, variations in the thickness of the diaphragm part within the wafer can be reduced, so semiconductor pressure sensors with less variation in sensitivity can be stably manufactured. There is an effect.

[Brief explanation of the drawing]

1 and 2 are a cross-sectional view of a semiconductor wafer and a cross-sectional view of an etching layer, respectively, for explaining the first embodiment of the present invention, and FIGS. FIG. 4 is a cross-sectional view of a semiconductor wafer for explaining the conductive film removal process and chip separation process after forming the diaphragm portion, and FIG. 5 is a cross-sectional view of a semiconductor wafer for explaining the second embodiment of the present invention. 6 is a cutaway perspective view of a conventional semiconductor pressure sensor, and FIG. 6 is a sectional view of an etching tank for explaining an example of the conventional semiconductor pressure sensor. 1...P type substrate, 2...N type epitaxial layer (N
type epitaxial layer), 3... Inter-chip isolation layer, 4... Thin film diaphragm portion, 5, 6... N+ electrode, 7... Passivation film, 8... Conductive film, 9... Wafer 10
... Chip, 11 ... Oxide film (etching mask), 12 ... Etching tank, 13 ... Etching liquid, 14 ... Heater, 15 ... External electrode, 16 ...
Counter electrode, 17...aluminum layer.

Claims (2)

[Claims] 1. forming a conductive film for electrically connecting the chips on a wafer having first and second electrodes on an epitaxial layer on a substrate and a separation layer for separating the chips; etching by anodic oxidation from the surface opposite to the surface on which the conductive film is formed, and automatically stopping the etching near the epitaxial layer to form a thin film diaphragm portion; and removing the conductive layer on the wafer. A method for manufacturing a semiconductor pressure sensor, comprising the step of separating the semiconductor pressure sensor into chips. 2. A step of forming first and second electrodes on the periphery of the wafer and within each chip, respectively, by forming an inter-chip isolation layer on an epitaxial layer on the substrate, and forming an aluminum layer on the second electrode. a step of electrically connecting the first electrode and the second electrode on the wafer on which the aluminum layer is formed; and an anodizing method from the side of the wafer opposite to the side on which the conductive film is formed. a step of forming a thin film diaphragm by etching the wafer and automatically stopping the etching near the epitaxial layer; and a step of removing a conductive layer on the wafer and separating it into chips. How to manufacture the sensor.