1. Field of the Invention
The present invention generally relates to a semiconductor sensor having a piezoresistance element such as a semiconductor acceleration sensor and a semiconductor angular velocity sensor and a method of manufacturing the same. More specifically, the present invention relates to a semiconductor sensor and a method of manufacturing the same in which the position of a weight shifts, which weight is supported by a flexible part where a piezoresistor is formed so as to detect a change in resistance of the piezoresistor, and thereby the sensor measures acceleration.
The semiconductor sensor is used for measuring the acceleration of a moving car in a forward direction or in a crosswise direction. The semiconductor sensor is also used for measuring the degree of jiggling of a hand upon using a camcorder.
In the present specification, a semiconductor substrate includes not only a substrate in which only a semiconductor is used but also an SOI (Silicon-on-Insulator) substrate in which an insulating film is formed therein.
2. Description of the Related Art
As for the semiconductor sensor, an acceleration sensor which is mounted on a car is publicly known. For example, as shown in FIGS. 10A through 10D, a cantilever acceleration detection unit in which a piezoresistor is used is disclosed in Japanese Patent Application Publication No. H8-7228.
FIGS. 10A through 10D are views illustrating a conventional semiconductor sensor. FIG. 10A is a perspective view. FIG. 10B is a plan view. FIG. 10C is a cross-sectional view taken along a line A-A′ shown in FIG. 10B. FIG. 10D is a cross-sectional view taken along a line B-B′ shown in FIG. 10B.
A semiconductor sensor 71 is formed by processing an SOI substrate 3 in which an insulating layer 7 is sandwiched between a second semiconductor layer 5 and a semiconductor layer 9.
On a surface side 3a of the SOI substrate 3, plural flexible parts 73 comprising the semiconductor layer 9 are formed adjacent to a supporting part 11 comprising the SOI substrate 3, which supporting part 11 is shaped as a frame. The flexible parts 73 are connected to the supporting part 11. In the semiconductor layer 9 of each of the flexible parts 73, a piezoresistor 19 is formed.
In the vicinity of the center of the semiconductor sensor 71, a weight 75 is formed apart from the supporting part 11, which weight 75 comprises the semiconductor layer 9, the insulating layer 7, and the second semiconductor layer 5. The semiconductor layer 9 of the weight 75 is linked to the semiconductor layer 9 of the flexible parts 73, and thereby, the weight 75 is supported by the flexible parts 73.
On the surface 3a of the SOI substrate 3, an insulating film 21 is formed. In FIGS. 10A and 10B, the piezoresistors 19 are shown for the sake of convenience. On the insulating film 21, plural metal wiring patterns 23 and plural pad electrodes 25 are formed. The metal wiring patterns 23 are electrically connected to the corresponding piezoresistors 19 via through holes formed in the insulating film 21.
On the insulating film 21 including a region where the metal wiring patterns 23 are to be formed, a protection film 27 is formed. In the protection film 27 on the pad electrodes 25, an opening is formed. In FIGS. 10A and 10B, the protection film 27 is not shown.
A glass substrate 29 is bonded onto the supporting part 11 on the other side 3b of the SOI substrate 3 by an anodic bonding. An edge surface of the weight 75 is apart from the glass substrate 29.
FIGS. 11A through 11F are cross-sectional views illustrating the semiconductor sensor taken along the line A-A′ shown in FIG. 10B. A brief description is given of a manufacturing method of a conventional semiconductor sensor with reference to FIGS. 10A through 11F.
(1) Referring to FIG. 11A, a thermal oxide film 69 is formed on the other side 3b of the SOI substrate 3 comprising the second semiconductor layer 5, the insulating layer 7 and the semiconductor layer 9. Then, the piezoresistor 19 is formed in the vicinity of the surface of the semiconductor layer 9 of the surface 3a of the semiconductor sensor 3. The insulating film 21 is formed on the surface 3a of the semiconductor layer 9. In a certain region of the insulating film 21, a through hole is formed. Next, on the insulating film 21 including the region where the through hole is formed, the metal wiring patterns 23 and the pad electrodes 25 are formed (shown in FIGS. 10A through 10C). Thereafter, the protection film 27 is formed on the surface of the insulating film 21. In the protection film 27 on the pad electrodes 25, an opening (not shown) is formed.
(2) According to a photoengraving method or an etching method, a region of the thermal oxide film 69 where the flexible parts 73 and the weight 75 are to be formed is selectively removed except for at least a region where the supporting part 11 is to be formed (shown in FIG. 11B).
(3) According to the photoengraving method, on the other side 3b of the SOI substrate 3, a resist pattern 77 is formed having an opening in a region where the flexible parts 73 are to be formed. The resist pattern 77 covers the region where the supporting part 11 and the weight 75 are to be formed. According to the etching method, the resist pattern 77 is masked so as to selectively remove a region of the second semiconductor layer 5 where the flexible parts 73 are to be formed (shown in FIG. 11C).
(4) After the resist pattern 77 is removed, the region of the second semiconductor layer 5 where the weight 75 is to be formed is etched from the other side 3b of the SOI substrate 3. Thus, the thickness is reduced of the region of the second semiconductor layer 5 where the weight 75 is to be formed so as to form the weight 75. A resist pattern (not shown) is formed on the other side 3b of the SOI substrate 3 for delimiting a region where the flexible parts 73 and the weight 75 are to be formed. The insulating layer 7, the semiconductor layer 9, the insulating film 21, and the protection film 27 are removed according to the etching method except for the region where the flexible parts 73 and the weight 75 are to be formed, which region is surrounded by the region where the supporting part 11 is to be formed. Thus, the flexible parts 73 and the weight 75 are formed (shown in FIGS. 10A through 10D and 11D).
(5) The thermal oxide film 69 is removed. At this time, the region of the insulating layer 7 where the flexible parts 73 are to be formed is removed simultaneously so as to form flexible parts 13 comprising the semiconductor layer 9 (shown in FIG. 11E).
(6) By the anodic bonding, a regulating board 29 is bonded onto a surface of the second semiconductor layer 5 of the other side 3b of the SOI substrate 3 including the region where the supporting part 11 is to be formed (shown in FIG. 11F).
(7) Thereafter, the semiconductor sensor 1 is cut out of the SOI substrate 3. Accordingly, the manufacturing steps of the semiconductor sensor 1 are completed (shown in FIGS. 10A through 10D).
Here, the semiconductor sensor 71 is formed by utilizing the SOI substrate 3 as the semiconductor substrate, but the semiconductor sensor may be formed by utilizing a semiconductor substrate comprising only a normal semiconductor.
In a conventional method of manufacturing the semiconductor sensor, a weight and flexible parts are formed from a semiconductor substrate. Hence, there is a problem in that the flexible part is fractured by inertia of the weight according to mechanical oscillation after the weight and the flexible parts are formed or water pressure caused by a washing operation.