Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Responsive to non-optical – non-electrical signal
Reexamination Certificate
1998-06-10
2002-05-14
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Responsive to non-optical, non-electrical signal
C257S253000, C257S254000, C257S415000, C257S417000, C438S050000, C438S053000
Reexamination Certificate
active
06388279
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority of Japanese Patent Applications No. H.9-153746 filed on Jun. 11, 1997, No. H.9-321022 filed on Nov. 21, 1997 and No. H.10-119089 filed on Apr. 28, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for manufacturing a semiconductor substrate having a pressure reference chamber therein, used for a pressure sensor or the like and relates to a semiconductor pressure sensor and a manufacturing method thereof.
2. Related Art
Semiconductor pressure sensors for detecting the pressure acting on a diaphragm include those constructed with a pressure reference chamber provided thereinside. In this case, in order to maximize the detecting accuracy of the sensor, the amount of gas remaining inside the pressure reference chamber is made as small as possible to reduce fluctuations of the reference pressure inside the pressure reference chamber resulting from temperature variations.
As semiconductor substrates used in the manufacture of this kind of semiconductor pressure sensor, substrates wherein a part corresponding to a pressure reference chamber is formed in advance have been used. This kind of semiconductor substrate is made for example by laminating together two silicon substrates so as to form a pressure reference chamber thereinside, as shown in
FIGS. 23A through 23C
.
That is, first, as shown in
FIG. 23A
, a concavity
2
used as a pressure reference chamber is formed in a first silicon substrate
1
by a method such as etching. Also, an oxide film
4
is formed on the surface of a second silicon substrate
3
. Then, the first silicon substrate
1
and the second silicon substrate
3
are laminated together so that the concavity
2
in the first silicon substrate
1
is covered by the face of the second silicon substrate
3
on which the oxide film
4
is formed. This lamination is carried out in a vacuum. As a result, in the laminated state, the concavity
2
is covered by the second silicon substrate
3
and forms a pressure reference chamber
5
containing a vacuum (see FIG.
23
B).
Then, by polishing the exposed face of the first silicon substrate
1
, the thickness of the bottom part of the pressure reference chamber
5
is brought to a predetermined thickness to form a part to become a diaphragm
6
. After that, a plurality of resistors having a piezoresistance effect are formed in the diaphragm
6
and these are connected in the form of a bridge circuit to complete a semiconductor pressure sensor.
When the pressure of an environment in which the semiconductor pressure sensor has been placed acts on the diaphragm
6
, the diaphragm
6
is displaced by a force corresponding to the difference between this pressure and the pressure inside the pressure reference chamber
5
. In correspondence with this displacement of the diaphragm
6
, the resistances of the resistors are changed by a piezoresistance effect. At this time, a voltage corresponding to the pressure of the environment is outputted to output terminals of the bridge circuit, and by detecting this output voltage it is possible to detect the pressure.
However, this kind of semiconductor pressure sensor detects the pressure acting on the diaphragm
6
as a change in the resistances of resistors changing in correspondence with the displacement of the diaphragm
6
. Consequently, the thickness dimension of the diaphragm
6
is a factor determining the precision of the pressure detection. That is, if the diaphragm
6
is made thin, the detection precision can be increased correspondingly. And, to reduce the area of the diaphragm
6
without decreasing the detection precision it is necessary to make the thickness of the diaphragm
6
thin.
However, with the kind of semiconductor substrate manufacturing method described above, after the pressure reference chamber
5
is formed with its interior nearly at a vacuum state it is necessary for a polishing step to be carried out to form the diaphragm
6
. But when polishing progresses so as to make the diaphragm
6
thin (for example about 1 to 10 &mgr;m), during polishing the diaphragm
6
undergoes stress due to the pressure difference between the inside of the pressure reference chamber
5
and the outside and deforms as shown in FIG.
23
C.
When deformations of the diaphragm
6
during polishing becomes large as much as not to be negligible, the thickness of the diaphragm
6
formed is uneven and the accuracy of the displacement of the diaphragm
6
corresponding to the pressure being detected falls. And, in some cases, the central part of the diaphragm
6
may come into contact with the opposite wall of the pressure reference chamber
5
so that further displacement of the diaphragm
6
is obstructed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for manufacturing a semiconductor substrate which, when a diaphragm constituting the rear wall of a pressure reference chamber is processed to a low thickness, does not adversely affect the diaphragm due to stress causing the diaphragm to deform, which is generated based on the pressure difference between the inside and the outside of a pressure reference chamber and to provide a semiconductor pressure sensor and the manufacturing method thereof.
According to a first aspect of the invention, in a concavity forming step a concavity is formed in a first substrate, and in a laminating step the first substrate is laminated with a second substrate in an atmosphere at atmospheric pressure and the concavity is thereby formed as a pressure reference chamber, after which the pressure reference chamber is evacuated in an evacuating step. The laminating step does not have to be carried out in an evacuated atmosphere, and therefore the laminating step can be carried out simply and easily. Furthermore, problems such as the substrate being deformed by a pressure difference between the inside and the outside of the pressure reference chamber do not arise when the thickness of a part of the substrate where the pressure reference chamber is formed is processed by polishing or the like or a step of forming devices there is carried out prior to executing the evacuating step, and consequently this processing can be carried out with good precision.
Preferably, in a connecting hole forming step, a connecting hole is formed in at least one of the first and second substrates so that when the first and second substrates have been laminated together the concavity to be used as a pressure reference chamber is connected to the outside. When this is done, after the laminating step is carried out, in carrying out the evacuating step, if the gas inside the pressure reference chamber is removed through this connecting hole and a sealing step is carried out to close the connecting hole after the evacuation, the pressure reference chamber can be evacuated surely.
The evacuating step is preferably carried out after a device forming step of forming devices constructing a pressure sensor is carried out. By this means, when a part of the substrate in which the pressure reference chamber is formed is used as a diaphragm, the diaphragm can be prevented from deforming due to a pressure difference across it while the substrate is being processed or the devices are being formed. Therefore, restrictions on the processing for diaphragm formation or device formation can be reduced and the accuracy of this processing can be increased.
In the laminating step, the concavity used as a pressure reference chamber may be sealed so that the inside thereof is isolated from the outside, and then in the evacuating step, by heat treatment being carried out, the gas inside the concavity may be made to combine with the substrate material and thereby consumed. By this means, it is possible to evacuate the inside of the pressure reference chamber simply and surely. In this evacuating step, oxygen remaining inside the concavity is combined w
Kawasaki Eishi
Sakai Minekazu
Suzuki Yasutoshi
Terada Masakazu
Toyoda Inao
Denso Corporation
Harness Dickey & Pierce PLC
Lee Eddie
Ortiz Edgardo
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