Measuring and testing – Fluid pressure gauge – Electrical
Reexamination Certificate
1999-01-29
2001-06-26
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Electrical
Reexamination Certificate
active
06250165
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority of the prior Japanese Patent Applications No. 10-21343, filed on Feb. 2, 1998, and No. 10-21344, filed on Feb. 2, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor sensor for detecting a physical quantity such as acceleration, pressure, vibration, or angular speed, and to a method of manufacturing the semiconductor sensor.
2. Description of the Related Art
JP-A-9-211022 disclosed this kind of semiconductor physical quantity sensor formed through steps of forming an SOI substrate from two silicon substrates by bonding, forming trenches in the SOI substrate at an upper silicon substrate side, and carrying out sacrifice layer etching to form a beam structure with a movable electrode. In this method using the SOI substrate, however, it is necessary to additionally perform steps of forming a wiring pattern on a lower side silicon substrate before bonding, flattening a surface of one of the substrates for the bonding, polishing the upper side silicon substrate after the bonding, and the like, resulting in complicated processes.
On the other hand, JP-A-6-123631 discloses a method of manufacturing an angular speed sensor having a movable portion. Specifically, a wafer composed of a silicon substrate on which an N-type epitaxial layer is formed and in which a P-type buried layer is formed is prepared. Then, trenches are formed in the N-type epitaxial layer with a specific pattern, and the P-type buried layer is removed by electrochemical etching through the trenches so that the movable portion is formed. In this method, because the sensor dispenses with an SOI substrate, the manufacturing process is simplified. However, the wafer composed of the silicon substrate on which the N-type epitaxial layer is formed and in which the P-type buried layer is formed must be utilized.
When this kind of semiconductor physical quantity sensor is formed by electrochemical etching, a wafer composed of a P-type silicon substrate on which the N-type epitaxial layer is formed can be used. For example, when a semiconductor pressure sensor is manufactured from the wafer, a diaphragm for the pressure sensor can be formed by electrochemically etching the wafer from a wafer back surface.
It is also possible to manufacture the acceleration sensor having the same structure as that disclosed in JP-A-9-211022 from the wafer including the P-type silicon substrate on which the N-type epitaxial layer is formed. Specifically, after trenches are formed in the wafer on a front surface side, electrochemical etching is carried out on the wafer from the front surface side so that the movable portion of the sensor is formed. At that time, however, the N-type epitaxial layer is not etched and the P-type silicon substrate is etched. Therefore, it is difficult to precisely control etching conditions such as etching time for accurately forming the movable portion.
In addition, when the electrochemical etching step is carried out on the wafer, the wafer is immersed into an anisotropic etching solution, and a positive voltage is applied to the N-type epitaxial layer so that only the P-type silicon substrate is etched. Therefore, it is necessary to form wiring segments within respective chips for applying the positive voltage to the N-type epitaxial layer during the electrochemical etching step. This makes an area of each chip large.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems. A first object of the present invention is to provide a semiconductor physical quantity sensor including a movable portion (displaceable portion) which is accurately formed by electrochemically etching a substrate. A second object is to reduce an area of a wiring segment used for electrochemically etching a substrate when a displaceable portion is formed.
To achieve the first object described above, in a semiconductor physical quantity sensor according to the present invention, an N-type semiconductor layer is formed on a main surface of the P-type semiconductor substrate, and a displaceable portion is formed by electrochemically etching the P-type semiconductor substrate from a side of the main surface. At that time, a buried insulation film formed to penetrate the N-type semiconductor layer and to extend into the P-type semiconductor substrate is used as a stopper for the etching. Accordingly, an etched region can be controlled by the buried insulation film, so that the displaceable portion can be precisely formed.
The displaceable portion can be formed to be electrically isolated from the P-type silicon substrate. Accordingly, current leak from the displaceable portion does not occur, resulting in high sensing accuracy.
To achieve the second object described above, when a wafer composed of a P-type semiconductor substrate and an N-type semiconductor layer formed on the P-type semiconductor substrate is used to manufacture the semiconductor physical quantity sensor, a pad for outputting an output signal of the sensor is formed to be electrically connected to the N-type semiconductor layer and an etching wiring segment is formed along a scribe line to be electrically connected to the pad. Then, the P-type semiconductor substrate is electrochemically etched while applying an etching voltage to the N-type semiconductor layer through the etching wiring segment and the pad. After that, the wafer is cut along the scribe line. Thus, because the pad necessary for the physical quantity sensor is used for applying the etching voltage to the N-type semiconductor layer, resulting in decreased chip area. In this case, a buried insulation film may be formed to penetrate the N-type semiconductor layer and to extend into the P-type semiconductor substrate. Accordingly, the P-type semiconductor substrate can be electrochemically etched using the buried insulation film as a stopper.
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Murata Minoru
Sakai Minekazu
Toyoda Inao
Denso Corporation
Oen William
Pillsbury & Winthrop LLP
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