Method for producing a semiconductor

Details Method for producing a semiconductor Method for producing a semiconductor

1999-11-09

2001-08-07

Gulakowski, Randy (Department: 1746)

Etching a substrate: processes

Etching of semiconductor material to produce an article...

C216S041000, C216S099000, C438S053000

Reexamination Certificate

active

06270685

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 7-341607 filed on Dec. 27, 1995, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an anisotropic etching mask used in a method for producing a semiconductor dynamic sensor for detecting an amount of acceleration, pressure or the like.
2. Related Arts
Semiconductor acceleration sensors, one of which is proposed in JP-A-6-104244, are conventionally used in an air bag system, an ABS system and the like of vehicles.
FIG. 30
shows a conventional semiconductor acceleration sensor as an example. The acceleration sensor is composed of a silicon substrate
60
, a weight
61
formed at the center of the silicon substrate
60
, a rectangular frame
62
formed at the periphery of the silicon substrate
60
, and thin beams
63
,
64
,
65
, and
66
connecting the weight
61
to the frame
62
. The beams
63
,
64
,
65
,
66
have strain gauges
67
,
68
,
69
and
70
formed thereon respectively. When acceleration is applied to the acceleration sensor in a direction indicated by an arrow Z in
FIG. 30
, the weight
61
is displaced, resulting in strain stress of the beams
63
,
64
,
65
, and
66
. The strain gauges
67
,
68
,
69
, and
70
, detect the strain stress and output as an electric signal respectively.
In manufacturing processes for producing the acceleration sensor, the silicon substrate
60
is etched to form grooves
71
and the thin beams
63
,
64
,
65
, and
66
by an anisotropic etching method using a potassium hydroxide (KOH) based etching solution or the like. When, the anisotropic etching method is performed on the silicon substrate
60
, predetermined areas of the silicon substrate
60
are covered by a silicon nitride film or the like functioning as an etching mask. Under the silicon nitride film, however, the silicon substrate
60
is undesirably etched, and the corners are rounded off with sloped side walls. Accordingly, various malfunctions of the acceleration sensor are caused. Thus formed rounded corners are hereinafter called as corner-undercut portions.
To solve the problem, an anisotropic etching technique is proposed in “Si micro-machining advanced studies”, PP. 117-118, published by Science forum Co. Ltd. in 1992. As shown in
FIG. 31
, this etching technique employs an etching mask having a rectangular pattern
72
with square form-compensation portions
73
as corner-undercut compensation patterns at the corners of the rectangular pattern
72
.
This etching mask is effective in the case that a space between the weight
61
and the frame
62
is sufficiently wide as shown in
FIG. 30
, that is, that a distance L
50
between the rectangular pattern
72
for the weight
61
and a frame pattern for the frame
62
is sufficiently wide as shown in FIG.
31
. However, as shown in
FIG. 32
, when the distance L
50
is narrow in a small size sensor, large corner-undercut portions
74
are formed under the etching mask as shown in
FIG. 33
even if the etching mask has the square form-compensation portions
73
.
When the corner-undercut portions are large, a width W between the beams
63
and
64
, and between the beams
65
and
66
, becomes narrow. Accordingly, the sensor catches the acceleration in a direction other than the direction of the arrow Z, giving rise to deterioration of directivity of the sensor. Further, the weight
61
becomes small, whereby sensitivity of the sensor decreases.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the above-mentioned problem and an object of the present invention is to provide a method for producing a semiconductor dynamic sensor with a miniaturized size, and more particularly to provide an anisotropic etching mask capable of minimizing the size of corner-undercut portions of the semiconductor dynamic sensor.
According to the present invention, in a method for producing a semiconductor dynamic sensor, an anisotropic etching mask is formed on a (
100
) crystal orientation silicon substrate with a main portion and form-compensation portions formed at the corners of the main portion. Each of the form-compensation portion has a rectangular shape with a long side and a short side. Further, one of the long and the short sides of the form-compensation portions stretches in the <011> direction of the silicon substrate, and the other side stretches in the <0{overscore (1)}1> direction of the silicon substrate.
When an anisotropic etching is performed on the silicon substrate with the anisotropic etching mask, the silicon substrate has a thick portion, the shape of which is approximately the same as the main portion of the etching mask, without having large corner-undercut portions.
Preferably, the thick portion of the silicon substrate has a rectangular shape with a long side and a short side, and the long side of the form-compensation portions is parallel to the long side of the thick portion.
Because each of the form-compensation portions has a rectangular shape, the corner-undercut portions are prevented from becoming large. Therefore, it is possible to make the sensor small.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawing figures.


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patent: 5-264572 (1993-10-01), None
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Buck et al., “A Comparison of Wet and Dry Chrome Etching with the CORE-2564”, 42-49.
“Si Micro Machining Advanced Studies”, Published by Science Forum on Mar. 31, 1992, pp. 117-118.
Cobb et al. “Fast, Low-Complexity Mask Design”, SPIE vol. 2440, 313-327 3/95.
Starvikov, “Use of a Single Size Square Serif for Variable Print Bias Compensation in Microlithography: Method, Design, and Practice.”, SPIE vol. 1088, 34-46.

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