Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-11-12
2001-08-21
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514320
Reexamination Certificate
active
06276207
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon Japanese Patent Application Nos. Hei. 10-323748 filed on Nov. 13, 1998 and Hei. 11-262319 filed on Sep. 16, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor physical quantity sensor, and particularly to a semiconductor physical quantity sensor in which a movable electrode and a fixed electrode confronting to the movable electrode are formed by forming a trench in a semiconductor layer of a semiconductor substrate, and a method of manufacturing the same.
2. Related Art
This kind of a semiconductor physical quantity sensor has proposed in WO 93/22690 (or EP 591554A1), or JP-A-9-211022, for example. These documents disclose a capacitor detection type semiconductor acceleration sensor, which has a support portion formed by a elastic beam supported by an anchor portion fixed to a semiconductor substrate, a weight portion connected to the support portion, a movable portion consists of a comb-shape movable electrode integrally formed with the weight portion, and a comb-shape fixed electrode fixed to the semiconductor substrate so as to confront to the movable electrode.
In this kind of semiconductor acceleration sensor, a structure in which the movable portion and the fixed electrode are released is formed by using photolithography technique and by etching a semiconductor layer of the semiconductor substrate in general.
According to this semiconductor acceleration sensor, since one of two intervals between detection surface of the movable electrodes and detection surface of the fixed electrodes is increased and another interval is decreased, the sensor can detect an acceleration to be applied thereto by differentially detecting a change of capacitance due to the interval changes.
However, this kind of semiconductor sensor having such a structure, the movable portion may adhere to the semiconductor substrate or the fixed portion such as the fixed electrode. This adhesion may be caused by van der Waals bonding or hydrogen bonding generated at a contacted portion because this structure is made of a semiconductor. It is found that this adhesion is caused by the following factors.
The first factor is an electrostatic force generated during a handling the semiconductor sensor. In the case such the semiconductor sensor having the structure made by the photolithography is handed with a jig, the jig needs to contact with somewhere of the semiconductor sensor. When the jig contacts with the semiconductor sensor, a potential difference occurs between the movable portion and the fixed portion by being partly charged. As a result, the movable portion confronted the fixed portion is attracted to and contacted to the fixed portion by the electrostatic force, and is stuck there.
The second factor is a surface tension of an etchant or detergent used in manufacturing the semiconductor sensor. In general, after an etching (release etching) for releasing the movable portion from the fixed portion is performed, the semiconductor sensor is soaked in liquid such as pure water so as to substitute the etchant with the pure water, and then the semiconductor sensor is dried (evaporated) at a room temperature. In this step, the movable portion and the fixed portion are attracted each other by the surface tension of the liquid stagnated therebetween.
The adhesion due to the surface tension is likely to occur between a detection surface of the movable electrode and a detection to surface of the fixed electrode confronted with a small interval (detection interval), or between a weight portion and the fixed portion confronted to the weight portion in moving direction. The reason will be explained hereinafter.
Because it is effective to enlarge a detection capacitance to improve a sensibility of the capacitance type sensor, it is preferable to enlarge a confront area between the movable electrode and the fixed electrode or to reduce an interval therebetween. Furthermore, it is effective to lower a spring constant in a detection direction or a direction in which the interval between the movable electrode and the fixed electrode changes to enlarge a displacement due to the acceleration (physical quantity). That is, the spring constant in the detection direction of the movable electrode or weight portion is lowered.
It is known that an attraction force due to the surface tension of the liquid stagnated between the confronted surfaces depends on an area to be contacted with the liquid and the interval therebetween. On the contrary, the liquid is likely to finally stagnate at a narrow portion due to capillary phenomenon, as the evaporation of the liquid proceeds. Therefore, since the interval between the movable electrode and the fixed electrode is small, these electrode may be stuck each other, because the liquid is likely to stagnate therebetween, the area contacting with the liquid is large enough to cause a large surface tension, and the spring constant is small. Furthermore, since the weight portion also has a small spring constant, the weight portion is likely to adhere a confronted portion by the surface tension. In other words, the movable portion and the fixed portion are likely to adhere each other as the sensibility to be required is increased.
The third factor is an excessive shock (acceleration) externally applied to the semiconductor sensor when the sensor is dropped down during being handled, for instance. When the excessive shock is applied to the semiconductor sensor in a direction that movable portion moves, the movable electrode adheres to the fixed electrode at a portion where the detection interval is small. Here, the bonding described the above is generated at the stuck portion. Although the movable portion may be released from the fixed portion by applying a restore (spring) force, which is larger than the bonding force for restoring the structure, it is not preferable to do so because it may decrease the displacement due to the physical quantity and decrease the sensibility.
SUMMARY OF THE INVENTION
This invention has been conceived in view of the background thus far described and its first object is to prevent an adhesion of a movable portion to a fixed portion due to an electrostatic force generated during being handled.
Its second object is to prevent an adhesion of a movable portion to a fixed portion due to a surface tension of liquid during manufacture.
Its third object is to prevent an adhesion of a movable portion to a fixed portion due to an excessive force being externally applied thereto.
According to the present invention, a handling portion is formed on the semiconductor substrate by being insulated from the sensor portion by an insulation portion. By contacting a jig with only the handling portion, it can prevent the sensor portion from being charged so that an adhesion due to an electrostatic force generated during the handling can be prevented.
According to another aspect of the present invention, at least one of the movable electrode and the fixed electrode is formed so that an interval between the non-detection surface and a surface confronted to this non-detection surface is smaller than the detection interval. In the case liquid is used in a manufacturing step of this structure, the liquid is likely to finally stagnate at the interval between the non-detection surface and a surface confronted to this non-detection surface smaller than the detection interval, but not detection interval. When the liquid does not stagnate at detection interval having a large area, a tensile stress due to a surface tension generated by the evaporation also reduces. Therefore, it can precisely prevent the adhesion, because the total area where the tensile stress due to the surface tension is to be applied can be largely reduced so that an adhesion due to the surface tension at the detection interval can the prevented.
According to the other aspect of the present invention, the support portion is movable to a predetermi
Ishio Seiichiro
Kawasaki Eishi
Murata Minoru
Muto Hiroshi
Sakai Minekazu
Denso Corporation
Moller Richard A.
Pillsbury & Winthrop LLP
LandOfFree
Semiconductor physical quantity sensor having movable... 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 physical quantity sensor having movable..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor physical quantity sensor having movable... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2534046