Etching a substrate: processes – Forming or treating optical article
Reexamination Certificate
2001-07-20
2003-12-16
Mills, Gregory (Department: 1763)
Etching a substrate: processes
Forming or treating optical article
C438S051000, C438S052000
Reexamination Certificate
active
06663789
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to bonded substrate structures and to a method for fabricating bonded substrate structures. For example, the invention relates to bonded substrate structures with a plurality of substrates being bonded together, including those with a glass substrate bonded to a semiconductor substrate and those with a plurality of different semiconductor substrates bonded together, and relates to a method for fabricating such bonded substrate structures. In particular, the technique of the invention is suitable to bonded substrate structures with a glass substrate bonded to a semiconductor substrate, and to a bonding method for fabricating such bonded substrate structures. The bonded substrate structures and the bonding method for them of the invention are especially useful in the field of MEMS (micro-electro-mechanical systems).
2. Description of the Related Art
In the field of semiconductors, much used are bonded substrate structures with a plurality of substrates being bonded together, including, for example, those with a glass substrate bonded to a semiconductor substrate and those with a plurality of different semiconductor substrates bonded together. For example, known is a bonded substrate structure with a glass substrate bonded to a semiconductor substrate, in which various devices are housed in device-housing recesses formed in the glass substrate and the recesses are covered and sealed with the semiconductor substrate. Another bonded substrate structure is also known, in which movable devices such as mirrors, lenses and the like are fitted to the upper layer substrate and devices for driving the movable devices are fitted to the lower layer substrate.
A micro-mirror device is one example of a bonded substrate structure with a semiconductor substrate bonded to a glass substrate.
FIGS. 1A
,
1
B and
1
C show an ordinary micro-mirror device structure. in such a micro-mirror device, the mirror angle is variable, and a voltage is applied to the driving electrode housed in the device-housing recess formed in the glass substrate thereby to drive the mirror movably fitted to the semiconductor substrate.
FIGS. 1A and 1B
are referred to, which show the structure of such a micro-mirror device. Precisely,
FIG. 1A
is an outline view of a micro-mirror device; and
FIG. 1B
is an exploded view thereof in which the upper semiconductor substrate is separated from the lower glass substrate. As in
FIGS. 1A and 1B
, the micro-mirror device comprises a semiconductor substrate
101
and a glass substrate
102
. As therein, a mirror
104
is fitted to the semiconductor substrate
101
. The mirror
104
is supported by beams
105
at the facing two corners, and its angle is variable around the pivotal axis of each beam
105
. The electrode for driving the mirror
104
is formed in the device-housing recess of the glass substrate
102
. Various devices are housed in the device-housing recess
103
shown in FIG.
1
C. After the devices to be in the device-housing recess
103
have been formed, the glass substrate
102
is bonded to the semiconductor substrate
101
.
FIGS. 2A
to
2
E show a process of fabricating such micro-mirror devices. In the process illustrated, a plurality of micro-mirror devices are formed on one laminate substrate composed of a semiconductor substrate and a glass substrate and having a size of 20 mm×20 mm, and these are finally cut into individual devices.
As in
FIG. 2A
, a glass substrate
202
with a mirror-driving electrode and other devices having been formed in each device-housing recess
203
is bonded to a semiconductor substrate
201
of silicon. For bonding them, for example, the two substrates are subjected to anodic bonding at 300 to 400° C. and at a voltage falling between 0.5 and 1.0 kV.
After the two substrates are thus bonded together, an Al film
204
for mirrors is formed on the Si substrate
201
through vapor deposition, as in FIG.
2
B. Next, a resist pattern
206
for mirrors is formed, as in FIG.
2
C. This is put into a solution of, for example, phosphoric acid, by which the Al film
204
except the area below the resist pattern is removed to give resist-coated mirrors, as in FIG.
2
D. Next, the resist film is removed to form mirrors, as in FIG.
2
E. The process does not interfere with the devices in the glass substrate
202
.
In order that the mirror in each device thus formed is supported by two beams, as in
FIGS. 1A and 1B
, the area around the mirror must be etched away, for example, through dry etching. Dry etching shall be effected in a vacuum of from a few mTorr to tens mTorr.
The glass substrate
202
is bonded to the Si substrate
201
, for example, through anodic bonding as in the above. In case where they are bonded in that manner at an atmospheric pressure, a vapor of around 0.4 atmospheres will be sealed in the device-housing recesses
203
in the glass substrate
202
. Accordingly, when the area around the mirrors is etched in dry in a vacuum falling between a few mTorr and tens mTorr, the gas remaining in the sealed device-housing recesses
203
will jet out at a high speed immediately after the Si substrate around the mirrors has been removed to give through-grooves reaching the device-housing recesses
203
. As a result, the fine structures formed in the device-housing recesses
203
and even the mirror-supporting beams will be broken or damaged.
To prevent the gas from jetting out of the sealed device-housing space in the dry-etching process as above, employable is a method of forming openings running outside through any one of the glass substrate and the semiconductor substrate in the direction of their depth before the two substrates are bonded together. In the bonded substrate structure formed in the method, gas is not sealed in the device-housing space but could pass through the openings formed. Another method employable for that purpose comprises bonding the two substrates in vacuum. In this, the sealed device-housing recesses
203
in the glass substrate
202
are kept in vacuum before the substrate
202
is bonded to the other semiconductor substrate.
FIGS. 3A
to
3
C show a process for fabricating a micro-mirror device, in which openings are formed through the semiconductor substrate so as to prevent gas ejection from the sealed device-housing recesses. These is to typically illustrate the process of fabricating one micro-mirror device.
In the process of
FIGS. 3A
to
3
C, a glass substrate
302
with a device-housing recess
303
formed therein is bonded to a semiconductor substrate
301
. For example, they are bonded together through anodic bonding at 300 to 400° C. under atmospheric pressure, like in the manner mentioned above. As in
FIG. 3A
, openings
309
are first formed in the region
308
to be etched (this is surrounded by the dotted line), around the mirror-forming region
307
.
Next, the glass substrate
302
is bonded to the semiconductor substrate
302
through anodic bonding, as in FIG.
3
B.
Finally, the region
308
to be etched (surrounded by the dotted line in
FIG. 3A
) is etched in dry to finish the structure of
FIG. 3C
in which the mirror
304
is supported by beams
305
. The dry etching is effected in a vacuum falling between a few mTorr and tens mTorr. In this process, since the device-housing space
303
is open to the outside through the openings
309
, the pressure inside it could be kept the same as that outside it with no rapid pressure change during the etching step.
However, the method for preventing rapid pressure change in the device-housing space by forming openings running outside through any one of the glass substrate and the semiconductor substrate in the direction of their depth before the two substrates are bonded together, as in
FIGS. 3A
to
3
C, requires the additional step of forming the openings. For example, it additionally requires resist patterning and dry-etching for forming the openings. As being so complicated, the method is therefore unfavorable. In addition, the strength of the
Culbert Roberts P
Mills Gregory
Sonnenschein Nath & Rosenthal LLP
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