Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2001-12-13
2004-04-13
Williams, Hezron (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514320, C438S052000
Reexamination Certificate
active
06718824
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon Japanese Patent Application No. 2000-387622 filed on Dec. 20, 2000, 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 sensor, for example, an acceleration sensor or an angular velocity sensor that employs a structure movable in accordance with physical quantity applied thereto, and manufacturing method of the same.
2. Related Art
Recently, a semiconductor sensor that detects dynamic quantity such as acceleration or pressure can be provided by micro-machining process in which a laminated substrate such as a SOI (Silicon On Insulator) substrate is employed.
FIG. 6
shows a schematic cross sectional view of a semiconductor dynamic quantity sensor
100
. The semiconductor dynamic quantity sensor
100
has a laminated substrate
110
that is composed of a first semiconductor substrate
111
and a second semiconductor substrate
112
to support the first semiconductor substrate
111
with an oxide film
113
interposed therebetween. A structural portion is formed in the first semiconductor substrate
111
.
The oxide film
113
and the second semiconductor substrate are partially removed at a region corresponding to the structure
101
. As a result, the structure
101
forms a diaphragm shape. Incidentally, the structure
101
may form a one-end supporting beam structure (hereinafter, cantilevered beam structure) in accordance with a sensor structure.
The semiconductor dynamic quantity sensor
100
is formed with the following steps. First, the laminated substrate
110
is prepared. Then, a circuit or the like is formed on the first semiconductor substrate
111
. After that, the second semiconductor substrate is partially removed by etching to form an opening
102
. Moreover, the oxide film is removed at a portion corresponding to the opening
102
so as to form the structure
101
in the first substrate
111
on the opening
102
.
It is easy to make the structure
101
having very fine and narrow gap by employing the oxide film
103
as a sacrificial layer in the laminated substrate
110
, which is removed by etching in the process to form the minute structure
101
, and to control thickness of the structure
101
when employing the laminated substrate.
When dynamic quantity is applied to the semiconductor dynamic quantity sensor
100
, the structure having the diaphragm structure or the cantilevered beam structure is slightly deformed or displaced, so that the dynamic quantity can be detected. Recently, high accuracy in detection is required in the semiconductor dynamic quantity sensor
100
.
It is, however, difficult to obtain the high accuracy in the semiconductor dynamic quantity sensor
100
.
FIG. 7
shows a schematic cross sectional view of a semiconductor dynamic quantity sensor
100
having a cantilevered beam structure. The structure
101
cambers to a direction opposite to the opening
102
.
In the acceleration sensor, acceleration applied to the sensor is detected by detecting change in capacitance based on change in distance between a movable electrode and a fixed electrode as the cantilevered beam structure. Therefore, when the structure
101
cambers, it is difficult to face the movable electrode to the fixed electrode appropriately. As a result, it is difficult to detect the acceleration precisely.
SUMMARY OF THE INVENTION
This invention has been conceived in view of the background as described above and an object of the invention is to provide a semiconductor sensor capable of detecting dynamic quantity precisely.
The inventors in the present invention found a fact that the structure
101
formed in the first semiconductor substrate
111
cambers by a stress layer
114
formed on a surface (back surface) of substrate
111
that faces the opening
102
.
It is supposed that the stress layer
114
is formed at a surface portion of the first substrate
111
adhering to the oxide film
113
by diffusion of oxygen when adhering the first substrate
111
to the second substrate
112
through the oxide film. The oxygen diffused in the first substrate is supposed to cause lattice stress.
This stress layer causes deterioration in detection in the pressure sensor as well as the acceleration sensor.
The inventors measured amount of camber in the structure
101
having the cantilevered beam as a sample of the semiconductor dynamic quantity sensor after removing the back surface of the structure
101
. The sensor structure is shown in FIG.
7
. Beam length L is 5.2 mm, thickness S of the first substrate
111
is 15 &mgr;m. In this situation, the amount of camber &dgr; is measured when etching amount in the back surface of the structure
101
is changed. The amount of camber &dgr; is defined with distance between a surface of the first substrate
111
and a top of the cambered structure
101
.
FIG. 5
shows a result of measurement of the camber. The amount of camber is reduced when the back surf ace of the structure
101
is etched by 0.2 &mgr;m. Moreover, the amount of camber is reduced as the etching amount is increased. When the etching amount is 0.4 &mgr;m or more, the amount of camber is reduced prominently as shown in FIG.
5
.
After the first substrate
111
is adhered to the oxide film
113
, the oxide film is removed and oxygen concentration is measured while the first substrate
111
is etched gradually from the back surface that adhered to the oxide film
113
to convince that the stress layer
114
is formed by the oxygen in the oxide film
113
.
As a result, the oxygen concentration is highest at the back surface that adhered to the oxide film. Moreover, the oxygen concentration is reduced as the first substrate
111
is etched. Besides, dependency in the oxygen concentration with respect to the etching amount is similar to dependency in camber with respect to the etching amount shown in FIG.
5
. Therefore, the stress layer
114
including oxygen in the first substrate
111
should be removed so that the camber is reduced sufficiently.
According to a first aspect of the invention, a semiconductor sensor has a structure formed in a first substrate that is formed on a second substrate with an oxide film interposed therebetween. The oxide film under the structure is removed. Besides, a part of the structure is removed at a portion that adheres to the oxide film before the oxide film is removed. The removed portion of the structure includes oxygen at high concentration in comparison with the bulk of the first substrate.
Preferably, a thickness of removed portion of the structure is 0.2 &mgr;m or more to improve sensitivity of the sensor.
More preferably, the thickness of removed portion of the structure is 0.4 &mgr;m or more.
Other features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings.
REFERENCES:
patent: 6117701 (2000-09-01), Buchan et al.
patent: 6287885 (2001-09-01), Muto et al.
patent: A-5-343705 (1993-12-01), None
patent: A-9-257564 (1997-10-01), None
Takeuchi et al., “Control of deformation of a structure composed of poly-silicon by ion implantation,”T. IEE Japan, vol. 116-E, No. 7, 1996, pp. 303-304.
Asami Kazushi
Fukada Tsuyoshi
Higuchi Hirofumi
Ito Takeshi
Nippon Soken Inc.
Posz & Bethards, PLC
Saint-Surin Jacques
Williams Hezron
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