Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
1998-06-11
2001-12-11
Bowers, Charles (Department: 2823)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S417000, C257S426000
Reexamination Certificate
active
06329696
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and more particularly, to a semiconductor devise with an electric converter element such as thermoelectric or electrothermal converter, which is applicable to various sensors, generators, and actuators using heat, such as an Infrared (IR)-ray sensor, flow sensor, gas sensor, pressure sensor, vacuum sensor, IR-ray generator, and manipulator.
2. Description of the Prior Art
A semiconductor sensor device or semiconductor micro-sensor using heat is typically comprised of a semiconductor substrate, a heat-sensing or heat-input microstructure formed over the substrate and thermally shielded or separated therefrom, and an electronic circuit for processing an electric output signal from the microstructure. The microstructure usually has a thermoelectric converter element to produce the electric output signal according to the heat or temperature of the microstructure.
An example of the conventional semiconductor sensor devices of this sort is shown in
FIGS. 1 and 2
, which serves as an IR-ray sensor This sensor device is disclosed in the Japanese Non-examined Patent Publication No. 8-105794 published in 1996.
As shown in
FIGS. 1 and 2
, this conventional semiconductor sensor device includes a lot of rectangular diaphragms
613
as the heat-input microstructures, which are arranged in a matrix array on a semiconductor substrate
601
.
As shown in
FIG. 2
, although roughly illustrated, a scanning circuit
602
is formed on a main surface of the semiconductor substrate
601
. The scanning circuit
602
includes Metal-Oxide-semiconductor Field-Effect Transistors (MOSFETs) (not shown). Polysilicon vertical selection lines
603
are formed over the scanning circuit
602
to scan or select the diaphragms
613
.
A silicon dioxide (SiO
2
) layer
635
is formed to cover the scanning circuit
602
and the vertical selection lines
603
. Cavities
604
with a same rectangular plan shape are formed in the SiO
2
film
605
.
Aluminum (Al) ground lines
606
and aluminum signal lines
607
are formed on the SiO
2
layer
605
. Titanium (Ti) bolometers
608
serving as thermoelectric converter elements are formed on the SiO
2
layer
605
to be overlapped with the corresponding cavities
604
. The signal lines
607
are electrically connected to the scanning circuit
602
through contact holes
612
penetrating the SiO
2
layer
605
.
Another SiO
2
layer
609
is formed to cover the bolometers
608
, the ground lines
606
, the signal lines
607
, and the exposed SiO
2
layer
605
.
An IR-ray absorption layer
610
is selectively formed on the SiO
2
layer
609
to be overlapped with the diaphragms
613
. The layer
610
is made of titanium nitride (TiN).
As shown in
FIGS. 1 and 2
, folded slits
611
a
and
611
b
are formed to penetrate the SiO
2
layers
609
and
605
and to surround the corresponding zigzag-shaped bolometers
608
. The slits
611
a
and
611
b
extend to the underlying cavities
604
in the SiO
2
layer
605
, thereby defining the rectangular diaphragms
613
which are matrix-arranged over the substrate
601
. The diaphragms
613
thus defined by the patterned SiO
2
layer
609
are thermally separated from the substrate
601
by the corresponding cavities
604
and from the adjoining parts of the SiO
2
layers
609
and
605
by the slits
611
a
and
611
b
. Thus, it is said that the diaphragms
613
are thermally shielded or isolated from the substrate
601
. The bolometers
608
are located on the corresponding diaphragms
613
.
As seen from
FIGS. 1 and 2
, each of the diaphragms
613
has two legs
613
a
and
613
b
that are mechanically connected to the substrate
601
through the remaining SiO
2
layer
605
. Each of the legs
613
a
and
613
b
is sandwiched by the adjoining slits
611
a
and
611
b.
Each of the bolometers
608
is comprised of a zigzag-shaped central part
608
c
and two end parts
608
a
and
608
b
located on the legs
613
a
and
613
b
of a corresponding one of the diaphragms
613
. The end parts
608
a
and
608
b
of the bolometer
608
are located on the legs
613
a
and
613
b
of the diaphragm
613
to extend along them, respectively. The end parts
608
a
and
608
b
of the bolometer
608
are electrically connected to the signal lines
607
which are electrically connected to the scanning circuit
602
.
The cavities
604
formed in the SiO
2
layer
605
are implemented by forming a sacrificial polysilicon layer, patterning the sacrificial polysilicon layer, and removing the patterned, sacrificial polysilicon layer. This removing process is performed by wet etching while an etching solution is contacted with the sacrificial polysilicon layer through the slits
611
a
and
611
b.
With the conventional semiconductor sensor device shown in
FIGS. 1 and 2
, all the rectangular diaphragms
613
arranged on the substrate
601
in a matrix array are electrically scanned by the scanning circuit
602
on operation.
When an incident IR-ray is irradiated to the diaphragms
613
, it is absorbed by the IR absorption layer
610
to thereby change the temperature of the diaphragms
613
. The temperature change thus caused is converted to an electric output signal by the bolometers
608
on the diaphragms
613
and then, the electric output signal is read out to the outside of the conventional semiconductor sensor device.
The above-described conventional semiconductor sensor device shown in
FIGS. 1 and 2
has the following problems.
A first problem is that the thermal shielding or blocking capability of the diaphragms
613
is unsatisfactory. This problem is applicable to any other semiconductor sensor devices.
Each of the diaphragms
613
is mechanically connected to the substrate
601
by the elongated legs
613
a
and
613
b
. The end parts
608
a
and
608
b
of the corresponding bolometer
608
a relocated on the legs
613
a
and
613
b
to thereby electrically connect the bolometer
608
to the signal lines
607
. The end parts
608
a
and
608
b
are typically made of popular metal such as titanium (Ti) to decrease their electric resistance. Since metals with a high electrical conductivity generally have a high thermal conductivity, the heat generated in each diaphragm
613
tends to be readily transmitted to the substrate
601
. This means that the thermal shielding or blocking capability of each diaphragm
613
will degrade.
The bolometer
608
may be made of oxide semiconductor while the end parts
608
a
and
608
b
thereof are made of metal. However, in this case, there is the same problem as above.
This first problem can be solved by decreasing the cross section of the legs
613
a
and
613
b
of the diaphragm
613
. However, in this case, there arises another problem that the mechanical strength of the legs
613
a
and
613
b
is lowered The decrease of the mechanical strength of the legs
613
a
and
613
b
increases the danger that the diaphragm
613
is mechanically contacted with the underlying SiO
2
layer
605
due to fluctuation or deviation of the process parameters in the fabrication process sequence of the conventional semiconductor sensor device, resulting in lowering of the fabrication yield.
A second problem is that the sensitivity of the bolometers
608
is unsatisfactorily low. This is because the bolometers
608
are made of Ti having a Temperature Coefficient of electric Resistance (TCR) as low as approximately 0.25% /K.
The bolometer
608
may be made of a vanadium oxide (VO
x
) or titanium oxide (TiO
x
). In this case, however, vanadium is not used in the popular fabrication processes of silicon ICs and as a result, it requires a dedicated process line. This means that the vanadium-based bolometer is difficult to be actually utilized.
If TiO
x
is used for the bolometer
608
, there arises another problem that the 1/f noise of the bolometer
608
becomes high due to the high electrical resistivity of TiO
x
.
Additionally. U.S. Pat. No. 5,2136,976 issued in 1994 discloses that the bolometer is made of vanadi
Bowers Charles
Kebede Brook
NEC Corporation
Young & Thompson
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