Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
1999-01-15
2001-04-17
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S418000
Reexamination Certificate
active
06218717
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. H.10-6905 filed on Jan. 16, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor pressure sensor for detecting pressure and a manufacturing method thereof.
2. Description of Related Art
In a conventional semiconductor pressure sensor, a diaphragm portion having a thin thickness is formed in a silicon substrate. A plurality of gauge diffusion resistive layers (strain gauges) are formed on a surface of the diaphragm portion. As a result, displacement of the diaphragm portion is detected by strain gauges.
In this semiconductor pressure sensor, it is suggested that an electro-chemical etching is carried out with respect to the silicon substrate to accurately control the thickness of the diaphragm portion. In detail, a wafer is prepared by forming an n-type epitaxial layer on a p-type silicon substrate. When a diaphragm portion is formed, an anisotropic etching is carried out with respect to the p-type silicon substrate using an aqueous solution such as potassium hydroxide (KOH) or the like, in a state where a reverse voltage is applied to a region where the diaphragm portion is to be formed. At this time, because a pn junction in the wafer is reverse-biased, a depletion layer extending from the pn junction to a silicon substrate side is created. An front end of the depletion layer is exposed to the etchant, as the etching process advances. When the depletion layer is exposed to the etchant, the etching of the silicon substrate is ceased due to a difference in potential between the silicon substrate and the etchant. In this way, since the position at which the etching of the silicon substrate is ceased is specified by the thickness of the depletion layer, the diaphragm portion can be accurately formed.
In the semiconductor pressure sensor, a region (diaphragm formation region) where the diaphragm portion is formed in the epitaxial layer, is formed as an island region which is electrically insulated from the epitaxial layer (peripheral region) encompassing the diaphragm formation region. A plurality of (for example, four) gauge diffusion resistive layers are formed on a surface of the diaphragm formation region, and an integrated circuit is formed in the peripheral region. The plurality of gauge diffusion resistive layers are connected to form a bridge circuit. The integrated circuit supplies voltage to the bridge circuit. Therefore, the bridge circuit generates a voltage signal in correspondence with the displacement of the diaphragm portion. The potential of the diaphragm formation region is fixed by an aluminum wire running from the integrated circuit to the diaphragm formation region.
When the electro-chemical etching as described above is carried out, if current leaks from the integrated circuit formed in the peripheral region into the diaphragm formation region, the etching of the silicon substrate cannot be ceased at a desirable position. Therefore, for example, JP-A-6-45618 teaches that a diode is disposed in the aluminum wire for fixing the potential of the diaphragm formation region, which runs from the integrated circuit to the diaphragm formation region. The diode can prevent leak current from flowing from the integrated circuit into the diaphragm formation region.
FIG. 5
is a schematic plan view of the semiconductor pressure sensor as described above.
FIG. 5
shows one semiconductor pressure sensor chip
101
among a large number of semiconductor pressure sensors formed in a wafer. In a diaphragm formation region
102
, a plurality of gauge diffusion resistive layers (not shown) is formed and connected to make up a bridge circuit. In a peripheral region around the diaphragm formation region
102
, an integrated circuit portion
103
is formed. Power supply voltage is supplied to the integrated circuit
103
via a pad
104
.
A conductive pattern
105
for feeding voltage used for carrying out the electro-chemical etching is formed along scribing lines in a peripheral portion of the sensor chip
101
. The conductive pattern
105
is electrically connected to the diaphragm formation region
102
by way of an aluminum wire
106
. The aluminum wire
106
and the pad
104
are connected to each other by way of an aluminum wire
108
. Diodes
107
,
109
are disposed in the aluminum wires
106
,
108
, respectively.
Because the sensor chip
101
is structured as described above, when the electro-chemical etching is carried out, a positive voltage for creating a depletion layer is applied from the conductive pattern
105
to the diaphragm formation region
102
via the aluminum wire
106
. At this time, the diode
109
prevents current from flowing into the integrated circuit portion
103
via the aluminum wire
108
and the pad
104
. That is, leak current flowing into the integrated circuit portion
103
can be prevented by the diode
109
. It is to be noted that, when the wafer is cut up (diced) into plural sensor chips along the scribing lines, the conductive pattern
105
is separated from each sensor chip.
When the semiconductor pressure sensor is brought in an operating state, voltage is supplied to the diaphragm formation region
102
via the pad
104
, diode
109
and the aluminum wire
108
. The potential of the diaphragm formation region
102
is fixed by the voltage thus supplied. Because the diode
107
is provided in the aluminum wire
106
, it is possible to prevent leak current from flowing from the diaphragm formation region
102
to the conductive pattern remaining at the peripheral portion of the sensor chip
101
.
The integrated circuit portion
103
has a power supplying circuit for supplying electric power to the bridge circuit formed by the gauge diffusion resistive layers. As one example of the power supplying circuits, JP-B-62-55629 teaches a constant current circuit which supplies constant current to the bridge circuit by disposing a resistor in a power supply line connected to the bridge circuit and controlling current flowing through the resistor to a constant value. In this case, a maximum potential applied to the gauge diffusion resistive layers is lowered from the voltage of the power supply line (power supply voltage) by a voltage drop at the resistor. Therefore, when the potential of the diaphragm formation region
102
is fixed by the power supply voltage supplied via the pad
104
and the diode
109
, the fixed potential becomes higher than the maximum potential applied to the gauge diffusion resistive layers. As a result, it is possible to prevent current from leaking out of the gauge diffusion resistive layers.
The inventors of the present invention considered a power supplying circuit having a circuit structure shown in
FIG. 4
, as the power supplying circuit provided in the integrated circuit portion
103
. In the power supplying circuit shown in
FIG. 4
, a transistor
301
is provided on a ground side of a bridge circuit
200
formed by gauge diffusion resistive layers
201
-
204
, and a power supply side thereof is directly connected to a power supply line L. Resistors
302
,
303
, an operational amplifier
304
, a variable resistor
305
, and a transistor
306
constitute a constant current circuit. The constant current circuit causes constant current to flow between the collector and emitter of the transistor
306
. As a result, current proportional to that constant current flows between the collector and emitter of the transistor
301
, i.e., through the bridge circuit
200
. In this case, the value of the constant current flowing through the bridge circuit
200
is adjustable by adjusting a resistance value of the variable resistor
305
by means of trimming or the like.
According to the power supplying circuit as shown in
FIG. 4
, a value of voltage applied to the bridge circuit
200
can be increased comparing to the power supplying circuit in which the resistor is di
Endo Noboru
Tanaka Hiroaki
Toyoda Inao
Denso Corporation
Ngo Ngan V.
Pillsbury & Winthrop LLP
LandOfFree
Semiconductor pressure sensor and manufacturing method therefof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor pressure sensor and manufacturing method therefof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor pressure sensor and manufacturing method therefof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2526158