Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
2001-10-19
2003-03-04
Ngo, Hung V. (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C073S862473, C029S592100, C029S825000
Reexamination Certificate
active
06528724
ABSTRACT:
TECHNICAL FIELD
The invention relates to a micro device used in inertial force sensor, optical switch or the like, and particularly to a micro device comprising an insulating substrate and a beam-like structure made of silicon formed on the insulating substrate, and a method of manufacturing the same.
BACKGROUND ART
Recently it has been made possible to etch silicon as deep as 100 &mgr;m by means of reactive ion etching (RIE) technology using inductively coupled plasma (ICP) as the activation energy source (hereinafter referred to as ICP-RIE process). This technique is viewed as a promising new technique for making silicon structures of high aspect ratios with a sufficiently high etching rate, in the field of device development by a micromachining. In the past, the wet process using an alkali solution was predominant as the process of deep etching of silicon substrates. But it is difficult to make a desired structure by the wet process, because the direction of etching depends on the crystal orientation of silicon in the wet process. In contrast, the ICP-RIE process is not subject to anisotropy of etching because it is a dry process. Thus the ICP-RIE process has such an advantage over the wet process that far higher degree of freedom in designing the configuration of structure can be achieved than in the case of the wet process.
When machining by dry etching a silicon substrate whereon a mask film has been formed in a desired pattern by photolithography or the like, however, there occurs such a problem that a wider area (exposed through a wider aperture) is etched at a higher rate than a narrower area. This is caused by micro loading effect, which is a well-known phenomenon in the field of semiconductor manufacturing processes. This phenomenon has such an adverse effect as described below on the micro devices which fall in the scope of the present invention, namely micro devices comprising an insulating substrate and a beam-like structure made of silicon formed on the insulating substrate.
FIG.
15
and
FIG. 16
show the structure of an inertial force sensor as an example of basic structure of a micro device
100
of the prior art.
FIG. 15
is a schematic plan view and
FIG. 16
is a sectional view taken along lines XVI-XVI′ of FIG.
15
. The inertial force sensor
100
comprises an insulating substrate
101
having a recess formed in the surface thereof, and a beam-like structure
104
made of silicon so as to interpose the recess on the surface of the insulating substrate
101
. The beam-like structure
104
further comprises two electrodes
105
,
105
. The electrode
105
comprises a supporting section
106
and a plurality of cantilevers
107
. The cantilevers
107
are arranged to oppose each other via a minute clearance.
FIGS. 17A-17G
are sectional views schematically showing the manufacturing process of the inertial force sensor shown in
FIG. 15
of the prior art. A similar manufacturing process has been proposed, for example, by Z. Xiao et al. in Proc. of Transducers ′99, pp. 1518-1521, and S. Kobayashi et al. in Proc. of Transducers ′99, pp. 910-913.
A silicon substrate
103
is provided in the step of
FIG. 17A
, and a glass substrate
101
is provided in the step of
FIG. 17B. A
mask film
108
is formed on the surface of the glass substrate
101
by photolithography in the step of
FIG. 17C
, and a recess
102
is formed by etching the surface of the glass substrate
101
to a depth in a range from several micrometers to several tens of micrometers with a dilute solution of hydrofluoric acid in the step of FIG.
17
D. In the step of
FIG. 17E
, the silicon substrate
103
is bonded onto the surface of the glass substrate
101
by anodic bonding. In the step of
FIG. 17F
, a mask film
109
having a pattern that corresponds to the planar configuration of the beam-like structure
104
shown in
FIG. 15
is formed by photolithography. In the step of
FIG. 17G
, the silicon substrate
103
is etched through by the ICP-RIE process, to form a cantilever
107
. Then the resist remaining on the surface of the silicon substrate is removed.
The step of
FIG. 17G
involves a problem. The mask film
109
in the step of
FIG. 17F
generally has both of wide apertures and narrow apertures. Consequently, when a dry etching process such as the ICP-RIE process is applied to the silicon substrate
103
that has the mask film
109
, the silicon substrate is etched at a higher rate in a portion exposed through the wider aperture than in a portion exposed through the narrower aperture due to the micro loading effect. As a result, the wider portion is etched through earlier than the narrower portion in the silicon substrate
103
. At this time, etching gas enters into the clearance between the recess
102
of the glass substrate
101
and the back surface of the silicon substrate
103
through the hole which has been etched out in the silicon substrate
103
earlier. The etching gas which has entered erodes the back surface of the silicon substrate
103
till the narrowest portion is completely etched out. Thus the side wall of the supporting section
106
and the bottom surface or the side wall of the cantilever
107
are eroded. As a result, dimensions of the beam-like structure
104
deviate significantly from the designed values, making it impossible to obtain the target characteristics of the device.
Erosion of the supporting section and the cantilever due to the micro loading effect can be restricted by making the sizes of all apertures comparable when designing. However, this approach imposes severe limitation to the freedom of designing the device structure. Even when the dimensions of apertures are set to be the same in design, it is difficult to completely prevent the erosion of the supporting section and the cantilever in the actual process. This is because it is a common practice to apply over-etching to some extent in order to etch through reliably.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a micro device which has a beam-like structure that provides a sufficient degree of freedom in the design of the device structure by restricting the erosion of the supporting section and the cantilever due to the micro loading effect, and a method of manufacturing the same.
The present inventors have completed the present invention by finding that the problem described above can be solved by a micro device having an electrically conductive film which is formed on a recessed surface at least in a portion right under a cantilever of an insulating substrate and is electrically connected with a supporting section.
Specifically, the micro device of the present invention comprises an insulating substrate having a recess formed on the surface thereof, and a beam-like structure made of silicon formed on the front surface of the insulating substrate to surround the recess, wherein the beam-like structure comprises at least one functional section and the functional section has a supporting section bonded onto the insulating substrate and at least one cantilever formed integrally with the supporting section while extending across the recess. The micro device also has an electrically conductive film formed on the surface of the recess at least in a portion right under a cantilever.
The micro device of the present invention has the following features.
Erosion of the supporting section made of silicon and the cantilever is caused, as described above, by the etching gas which enters into the clearance between the recess of the insulating substrate and the back surface of the silicon substrate which has been etched through earlier during the dry etching process. The silicon substrate is etched in such a mechanism of dry etching as activated ions having positive charge are accelerated by a negative bias formed right above the silicon substrate thereby to collide with the silicon substrate with a sufficient energy. In the case of the ICP-RIE process, the activated etching gas is usually sulfur fluoride ion (SFx
+
). The ion turns into
Chabloz Martial
Jiao Jiwei
Matsuura Tsukasa
Tsutsumi Kazuhiko
Yoshida Yukihisa
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Ngo Hung V.
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