Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Reexamination Certificate
2002-11-08
2004-05-04
Pham, Long (Department: 2814)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
C438S048000, C438S051000, C438S052000, C438S053000
Reexamination Certificate
active
06730535
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a silicon device manufacturing method, a silicon device, and an optical component.
2) Description of the Related Art
A silicon substrate is conventionally used to form micro electro mechanical systems (MEMS).
FIG. 12
is a plane view which shows an example of an optical switch that is disclosed in European Patent WO98/12589. The disclosed micro electro mechanical systems are fabricated using a silicon device.
FIGS. 13
to
15
are cross sectional diagrams of the silicon device that explain the manufacturing process of the silicon device.
FIG. 16
is a cross-section of a 2×2 optical switch having an optical fiber arranged on the silicon device shown in FIG.
12
.
With reference to
FIGS. 12
to
16
, a sandwich like silicon-on-insulator (SOI) wafer
139
consists of a supporting substrate
140
, an intermediate insulator layer
141
, and a silicon substrate
143
. The supporting substrate
140
is formed by monocrystalline silicon. The intermediate insulator layer
141
is provided on the supporting substrate
140
and is formed by non-crystalline silicon dioxide (SiO
2
) The silicon substrate
143
is provided on the intermediate layer
141
. A plurality of masks
144
are formed in positions corresponding to each narrow structure
145
and wide structure
147
on the surface of the silicon substrate
143
. The structures
145
and
147
correspond to the structure of the silicon device. An optical fiber
149
is inserted into insertion grooves
101
a
to
101
d
in the silicon device. The thickness of the silicon substrate
143
is decided based on the diameter of the optical fiber
149
. For example, if a single mode optical fiber is used the thickness of the silicon substrate
143
is 75 &mgr;m.
As shown in
FIG. 14
, the silicon in the regions of the silicon substrate
143
that are not masked (exposed areas) are etched by the deep anisotropic reactive ion etching method until the surface of the intermediate layer
141
is exposed. The reactive ion etching is carried out between the electrodes and the SOI wafer
139
. The reactive ion etching is carried out under conditions of pressure of 2.6 Pa, temperature of −95° C. and DC bias of −70 V, high frequency of 13.5 MH
z
, air flow SF of 200 cm
3
/min, oxygen supply of 16 cm
3
/min, air current CHF of 10 cm
3
/min, and an inductively coupled plasma that serves as the source of ion.
After the etching of the silicon substrate
143
, the intermediate layer
141
is etched. The portion of the intermediate layer
141
present between the narrow structures
145
and the supporting substrate
140
is completely removed by etching using 48% hydrofluoric acid. As shown in
FIG. 15
, the intermediate layer
141
present between the wide structures
147
and the supporting substrate
140
is partially etched. As a result, the wide structures
147
are supported by the supporting substrate
140
.
FIG. 12
is the linear representation of the narrow structures
145
that are formed by the etching process. The narrow structures
145
consists of a mirror
107
, a holder
119
, a plurality of elastic joint plates
113
a
to
113
d
, a plurality of support beams
121
a
to
121
d
, a plurality of spring members
127
a
to
127
d
, a plurality of narrow structures
131
,
133
and
135
, and a plurality of comb like structures
123
a
to
123
d
. Each of the spring members
127
a
to
127
d
consists of a plurality of plate springs. For example, spring member
127
a
has plate springs
130
a
,
130
b
,
132
a
,
132
b
,
134
a
,
134
b
,
136
a
, and
136
b
. The comb structures
123
a
to
123
d
and the intermediate layer
141
present under the comb structures are also etched during the etching process. The intermediate layer
141
present under the comb sections is held by a base
125
of the SOI wafer
139
.
The mirror
107
has a reflecting layer that reflects light. The optical fiber
149
is inserted into each insertion groove
101
a
to
101
d
(see FIG.
16
). A 2×2 optical switch is thus formed. In this 2×2 optical switch, the mirror
107
is used to change the direction of light. The mirror
107
is operated by a comb micro-actuator driven by electrostatic force.
Thus, conventionally, the deep anisotropic reactive ion etching method is used to remove the unmasked parts of the silicon substrate
143
and to obtain the structure shown in FIG.
14
. However, the duration for which the etching is performed (etching duration) should be very accurately controlled. For example, if the etching duration is too short, the silicon substrate
143
cannot be etched until the intermediate layer
141
and the narrow structures
145
, wide structures
147
, and the comb structures
123
a
to
123
d
are not formed as desired. On the other hand, if the etching duration is too long (over-etching), etching gas is expelled on both sides of the intermediate layer
141
so that even the lower sides of the narrow structures
145
are also etched and the narrow structures
145
are not formed again as desired. In addition, the parts of the intermediate layer
141
under the wide structures
147
are removed, making it difficult to hold the structures
147
.
FIG. 17
is a cross-section of the structures
145
when over-etching is performed. The sides of the structures
145
and
147
present on the intermediate layer
141
side are excessively etched causing the inaccurate formation of the structures
145
and
147
. Apart from etching duration management other factors such as pressure and temperature play an important role in the etching process.
The silicon device using a silicon substrate is cheaper than the silicon device using a SOI substrate. Hence there is a need for an inexpensive method to manufacture silicon device using silicon substrate.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a reliable method to manufacture a silicon device having high precision. It is also an object to provide an optical component that employs the silicon device.
According to one aspect of the present invention, there is provided a method for manufacturing silicon device by etching portions of a silicon substrate that has a first and a second surface. The method comprises masking the first surface with a resist in areas on the first surface of the silicon substrate where structures are not to be formed on the second surface. This is followed by etching the first surface of the silicon substrate until desired thickness of the structures to be formed on the second surface is obtained. Then the areas on the second surface of the silicon substrate corresponding to the structures are masked with a resist. Finally, the etching of the second surface of the silicon substrate by anisotropic reactive ion etching to form the structures is performed.
According to another aspect of the present invention, a silicon device manufacturing method in which the portions of a silicon-on-insulator substrate are etched. A supporting silicon substrate, an intermediate substrate, and a silicon substrate are deposited successively on the silicon-on-insulator substrate. The areas on the supporting silicon substrate where structures are not to be formed on the silicon substrate are masked with a resist. This is followed by etching the silicon of the supporting silicon substrate until the intermediate layer is exposed. Then the intermediate layer which is exposed is etched followed by masking areas on the silicon substrate with a resist to form the structures. Finally the etching of the silicon substrate by anisotropic reactive ion etching to form the structures is performed.
According to still another aspect of the present invention, the structures of the silicon device are combs and beams of a comb drive.
According to still another aspect of the present invention, the optical component comprises of the silicon device, two optical waveguides, and an optical element.
These and other objects, features and advantages of the present invention are spe
Morimoto Koji
Morimoto Masahito
Sato Kouki
Toriumi Kazuhiro
Tsuchiya Taichi
Knobbe Martens Olson & Bear LLP
Pham Long
The Furukawa Electric Co. Ltd.
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