Semiconductor device manufacturing: process – With measuring or testing – Electrical characteristic sensed
Reexamination Certificate
1999-02-11
2001-02-27
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
With measuring or testing
Electrical characteristic sensed
C438S053000, C438S701000, C438S977000, C438S753000
Reexamination Certificate
active
06194236
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an etching method for silicon substrates. More particularly, the present invention relates to an etching method for silicon substrates used for forming thinned portions of semiconductor sensors, e.g., a pressure sensor and an acceleration sensor.
2. Related Arts
In the conventional technique of manufacturing semiconductor pressure sensors, anisotropic etching using KOH is used for forming a thin diaphragm on a portion of a (110)-oriented silicon substrate, i.e., the (110)-oriented silicon substrate is etched by KOH through time control. However, due to the nature of the (110)-oriented silicon, this method results in the rough etching surface which causes unevenness to the characteristics of semiconductor pressure sensors. For this reason, there has been a need to smooth the etching surface.
As a solution to this problem, a SiO
2
(SP—SiO
2
) film formed by the spattering method is provided on the etching surface on which a diaphragm has been formed as disclosed in the Journal of NIPPONDENSO Technical Disclosure No. 88-002, published on Jan. 15, 1993.
However, this method of providing the SP—SiO
2
film requires another component material in addition to the silicon substrate and additional processes. Furthermore, even if electrochemical etching is used for etching the (110)-oriented silicon surface like etching a (100)-oriented silicon surface, the resultant etching surface is rough.
SUMMARY OF THE INVENTION
In view of the above, it is a primary object of the present invention to provide an etching method for silicon substrates which can easily smooth the etching surface of the (110)-oriented silicon.
The summary of an etching method for silicon substrates according to the present invention is that in electrochemically etching a (110)-oriented silicon substrate having PN junction by using anisotropic etchant, etching is started from one surface on which the PN junction is formed, and voltage application is terminated when the specified time lapses after the formation of an anodic oxide film is equilibrated with the etching of the anodic oxide film on the etching surface on the PN junction part.
Incidentally, the point of time when the above equilibrium state is obtained is determined by detecting flowing current and then a point of inflection of the detected flowing current to constant current after the peak of the flowing current.
Furthermore, the point of inflection may be regarded as a point of time when the specified time has lapsed since the detection of the peak current.
It should be noted here that AC wave would preferably be used for voltage application for the specified time after the point of time when the equilibrium state is obtained. In this case, the cycle of the AC wave might preferably be the time required for removing all the anodic oxide film from the etching surface by using anisotropic etchant.
According to the present invention, though the etching surface has concave parts and convex parts when the formation of the anodic oxide film is equilibrated with the etching of the anodic oxide film on the etching surface on the PN junction part, the etching surface is smoothed by the subsequent voltage application. This is presumably for the reason that the anodic oxide film on the concave parts can not easily be etched and the anodic oxide film on the convex parts is easily etched on the concave parts and convex--parts of the etching surface, and as a result, the silicon on the convex parts is removed.
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Abe Yoshitsugu
Fukada Tsuyoshi
Ikeda Kazuhisa
Ito Motoki
Mizuno Koki
Chaudhuri Olik
Denso Corporation
Eaton Kurt
Pillsbury Madison & Sutro LLP
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