Silicon device

Details Silicon device Silicon device

2003-02-06

2004-07-06

Ngo, Hung V. (Department: 2831)

Electricity: conductors and insulators

Boxes and housings

Hermetic sealed envelope type

C073S514320

Reexamination Certificate

active

06759591

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a silicon device used in inertial force sensor or the like, and particularly to a silicon device comprising an insulating substrate and a beam-like structure made of silicon formed on the insulating substrate.
DESCRIPTION OF THE RELATED ART
Recently it has been made possible to etch silicon as deep as 100 &mgr;m by reactive ion etching technology using an 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 micromachining. In the past, wet processing using an alkaline solution was predominant as the process for deep etching of silicon substrates. But it is difficult to make a desired structure by wet processing, because the direction of etching depends on the crystalline orientation of silicon in the wet process. In contrast, the ICP-RIE process is not subject to the anisotropy of etching because it is a dry process. Thus the ICP-RIE process has such an advantage over the wet processing that far higher degree of freedom in the design of the configuration of structure can be achieved than in the case of wet processing.
However, such problems as described below have been encountered when the ICP-RIE process is applied to the manufacture of an inertial force sensor such as acceleration sensor or angular velocity sensor having such a structure as a beam-like structure made of silicon in the form of cantilever, simple beam or the like is supported on an insulating substrate made of glass or the like.
FIG. 12
shows the structure of an inertial force sensor
100
as an example of the fundamental structure of a silicon device of the prior art. FIG.
13
A through
FIG. 13F
schematically show the manufacturing process of the inertial force sensor
100
. 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.
FIG. 12
is a schematic plan view and
FIG. 13F
is a sectional view taken along lines XIII-XIII′ of FIG.
12
. The inertial force sensor
100
includes an insulating substrate
101
that has a recess
102
formed in the surface thereof, a beam-like structure
104
made of silicon bonded onto the surface of the insulating substrate
101
so as to interpose the recess therebetween and a frame
108
that surrounds the beam-like structure
104
made of silicon with a space kept therefrom and is bonded onto the insulating substrate
101
. The beam-like structure
104
further includes two electrodes
105
,
105
′. The electrodes
105
,
105
′ include a supporting section
106
and a plurality of cantilevers
107
, a supporting section
106
′ and a plurality of cantilevers
107
′, respectively. The cantilevers
107
and
107
′ are arranged to oppose each other via a minute clearance.
A silicon substrate
103
is provided in the step of
FIG. 13A
, and the glass substrate
101
is provided in the step of
FIG. 13B. A
mask film is formed on the surface of the glass substrate
101
by the photolithography process, and a recess
102
is then formed by etching the surface of the glass substrate
101
to a depth in a range from several micrometers to several tens of micrometers by means of a diluted solution of hydrofluoric acid in the step of FIG.
13
C. In the step of
FIG. 13D
, the silicon substrate
103
is bonded onto the surface of the glass substrate
101
by anodic bonding method. In the step of
FIG. 13E
, a mask film
109
having a pattern that corresponds to the planar configuration of the beam-like structure
104
shown in
FIG. 12
is formed on the surface of the silicon substrate
103
by the photolithography. In the step of
FIG. 13F
, the silicon substrate
103
is etched through by the ICP-RIE process, thereby to form of the beam-like silicon structure
104
and the frame
108
. Then the resist remaining on the surface of the silicon substrate is removed.
The step of
FIG. 13F
involves such a problem as described below. The mask film
109
shown in
FIG. 13E
generally has both 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 portion of the silicon substrate
103
exposed through wider aperture is etched through earlier than the portion exposed through narrower aperture. 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 that has entered erodes the back surface of the silicon substrate
103
till the portion exposed through the narrowest aperture 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 design values, making it impossible to obtain the target characteristics of the device and resulting in lower reliability.
The present applicant found that the problem described above is caused by positive charging of the recess of the insulating substrate by the etching gas that has positive charge. Accordingly, the present applicant proposed a method for suppressing the erosion of the beam-like silicon structure by providing the recessed portion with an electrically conductive film that has electrical continuity with the supporting section (M. Chabloz, J. Jiao, Y. Yoshida, T. Matsuura, K. Tsutsumi, A Method to Evade Microloading Effect in Deep Reactive Ion Etching for Anodically Bonded Glass-Silicon Structures, Proc. MEMS2000, pp.283-287, Miyazaki, Japan, 2000). However, there is still a demand to further suppress the erosion of the beam-like silicon structure in order to improve the reliability.
There is also such a problem that an attempt to make the aperture sizes equal for the purpose of eliminating the microloading effect leads to a significant decrease in the degree of freedom in the design of the device structure.
Even when the aperture sizes 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. In the case of an acceleration sensor, for example, a cantilever of a movable electrode and a cantilever of a fixed electrode are arranged to oppose each other via a minute clearance, with the minute clearance being formed in such a pattern as the width increases and decreases repetitively. The sensor has higher sensitivity as the ratio the clearance of the larger width to the clearance of the smaller width becomes higher. When the ratio becomes too high, however, the etching rate varies significantly from point to point over the surface due to the microloading effect, thus resulting in a lower etching rate in the narrow clearance region. This makes it necessary to apply over etching to the narrow clearance region, that causes more damages on the back surface of the silicon substrate during the etching process.
An object of the present invention is therefore to provide a silicon device that has higher reliability and offers a sufficient degree of freedom in the design of the device structure, by suppressing the erosion of the beam-like silicon structure due to the micro loading effect.
SUMMARY OF THE INVENTION
A silicon device of the present invention includes an insulating substrate having a

Affiliated with

Also associated with

Rating

Silicon device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Silicon device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Silicon device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3199210