Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2002-12-27
2004-09-14
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504120
Reexamination Certificate
active
06789423
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micro inertia sensor and a method thereof, the micro inertia sensor such as a micro gyro comprising a device wafer used as a lower structure, a cap wafer used as an upper structure, and a bonding and wiring structure-thereof. The present invention provides a micro sensor being in a new structure as miniaturized in comparison to the existing structure and enabling to sense the up-and-down movement.
2. Description of the Related Art
In general, in the related art of manufacturing a micro sensor such as a micro gyro, the way of accomplishing a wafer-level packaging is used by anodically bonding a silicon micro structure formed on the silicon or glass wafer to the glass wafer.
However, in such a related method, there is one problem that a bending occurs on the bonded surface due to a different coefficient of thermal expansion between the silicon. There is also the other problem such as degassing phenomenon that oxygen generates from the glass when anodic bonding is applied.
Therefore, in order to solve the above-mentioned problems, eutectic bonding between silicon (Si) and gold (Au) is used instead of anodic bonding between glass and silicon. In case of applying the eutectic bonding, there is no stress between the bonded surfaces, thereby improving yield; and there occurs no degassing, thereby enabling to maintain a high vacuum. As a consequence, it has the merit of improving the features of the inertia sensor such as gyro.
In the related art of carrying out the eutectic bonding, a device wafer is manufactured by forming an insulation layer on a first silicon; forming a second silicon on the insulation layer; and patterning, etching and forming a structure body to sense the movement at a border, fixed points and sides.
To prevent any pollution in the process on the device wafer and to keep a sealed state, a cap wafer is manufacture by forming a first insulation layer on a third silicon; forming an electric conduction wiring on the first insulation layer; forming a second insulation layer on the electric conduction wiring; and evaporating Cr/Au layer. A micro inertia sensor is manufactured by bonding the device wafer to the cap wafer by means of the eutectic bonding.
An embodiment according to the related art will be described in detail, on the basis of the attached drawings.
FIGS. 1
a
-
1
f
are outlined schematic diagrams to illustrate a hermetic packaging process of a micro sensor by forming a device wafer and a cap wafer according to the related art.
FIG. 2
is a front cross-sectional structure view illustrating a bonding state of the device wafer to the cap wafer in the hermetic package, wherein a groove portion is formed in the sealing bonded portion of the micro sensor according to the related art.
FIG. 1
a
illustrates a sensor's surroundings of a silicon device wafer
140
including a silicon
110
being about 500 &mgr;m in thickness, an insulator
120
of an oxidation film being interposed on the upper portion of the silicon
110
, a micro sensor
130
being provided on the upper portion, and an internal fixed point
150
and an external fixed point
160
being formed at regular intervals. Here, a sealing bonding portion
170
having a low melting point, which is sealed by the micro sensor when bonding to a cap wafer
210
, is formed between the internal fixed point
150
and the external fixed points
160
. A groove
300
forms by etching and removing the lower side of the sealing bonding portion
170
.
The device wafer
140
is manufactured and accomplished by removing the insulator
120
excluding the internal fixed point
150
, the external fixed point
160
and the sealing bonding portion
170
of a low melting point by means of the etching process as illustrated in
FIG. 1
b.
A cap wafer
210
of silicon being in regular thickness, which is to bond to the device wafer
140
is provide and insulator
220
and an electric conduction film
230
. The insulator
220
is evaporated on the upper portion of the cap wafer
210
. The electric conduction film pattern
230
to be bonded to the internal fixed point
150
and the external fixed point
160
of the device wafer
140
is formed on the upper portion of the insulator
220
.
FIG. 1
c
shows the conductive film pattern.
A second insulator
220
′ is evaporated on the upper portion of the electric conduction film pattern
230
to protect the conductive film; and Cr/Au is evaporated on the upper portion of the electric conduction film pattern
230
for patterning (as shown in
FIG. 1
d
).
In
FIG. 1
f
, a wire bonding is provided by etching the outside of the portion of the cap wafer
210
to be connected with the external fixed point
160
of the device wafer
140
, wherein the etching is performed by photo-resist not to effect on Cr/Au.
After the device wafer
140
and the cap wafer
210
are manufactured as above, as shown in
FIG. 2
, heat of 400° C. and pressure are applied to the device wafer
140
and the cap wafer
210
. Then, due to the low melting point bonding, Au melts and seals the micro sensor
130
of the device wafer
140
. Having conductivity, Au performs two roles of bonding and electric conduction at a time.
Au—Si alloy as melted by heat and pressure by the low melting point bonding is gathered on the corner of the groove
300
formed on the sealing bonding portion
170
when the device wafer
140
is bonded to the cap wafer
210
, thereby improving the sealing of the micro inertia sensor
130
positioned on the device wafer
140
.
However, the related art as described above has the problems that it is difficult to miniaturize the micro sensor and it is complicate to manufacture and fix it. That is, when power is supplied to the external fixed point
160
as the silicon (Si) layer, the power is connected to the internal fixed point
150
through the wiring between the insulation layers
220
and
220
′. Hereby, the change of the side movement is sensed according to the variation of the capacitance. In this regard, the external fixed point
160
must necessarily exist for the power supply from the outside, and the space for the external fixed point
160
must be necessary secured.
There is the trial to form electrodes by removing the external fixed point and forming a via hole on the cap wafer. However, such a trial has a risk to touch the wiring which passes between the insulation layers since the via hole should be most deeply formed to prevent the effects of occurrence such as undercut. In this connection, as the via hole cannot be properly made on the place as desired, there still exits the problem that it is difficult to reduce the size.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a micro inertia sensor forming a device wafer on the lower portion and a cap wafer (SOG: silicon on glass) on the upper portion as the MEMS structure body; and a via hole in the direction from the upper surface of the cap wafer to the device wafer, thereby providing a micro inertia sensor miniaturized and manufactured in a simplified manner.
To achieve the above object, there is provided a micro inertia sensor includes a lower glass substrate; a lower silicon including a first border, a first fixed point and a side movement sensing structure; an upper silicon including a second border, a second fixed point being connected to a via hole, in which a metal wiring is formed, on an upper side, and an sensing electrode, which correspond to the first border, the first fixed point and the side movement sensing structure; a bonded layer by a eutectic bonding between the upper silicon and the lower silicon; and a upper glass substrate, being positioned on an upper portion of the upper silicon, for providing the via hole on which an electric conduction wiring is formed.
The side movement sensing structure comprises a structure being movable in a horizontal direction and a sensing electrode senses a variation of a capacity as the structure horizontally moves, while the sensing electr
An Seung Do
Cho Ji Man
Kim Kyoung Soo
Darby & Darby
Kwok Helen
Samsung Electro-Mechanics Co. Ltd.
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