Active solid-state devices (e.g. – transistors – solid-state diode – With means to increase breakdown voltage threshold – Field relief electrode
Reexamination Certificate
1998-05-19
2001-04-10
Saadat, Mahshid (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
With means to increase breakdown voltage threshold
Field relief electrode
C257S490000, C257S583000, C257S585000, C257S587000, C257S630000, C257S652000
Reexamination Certificate
active
06215167
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a power semiconductor device and a manufacturing method thereof, and more particularly to a power semiconductor device employing a field plate and a manufacturing method thereof.
As the scale and capacitance of appliances become large, the power semiconductor device must have a high breakdown voltage at high current. Also, to pass high current with low power consumption, the power semiconductor device requires a low saturation voltage. A high breakdown voltage characteristic is further required to withstand a high voltage of a reverse direction applied to the power device in an OFF state, and at the moment that a switch is turned off.
The breakdown voltage of the semiconductor device is determined by the size of a depletion layer of an associated pn junction. This is because most of the voltage applied to the pn junction drops across the depletion layer. It is known that a curvature in the shape of the depletion layer also affects the breakdown voltage. That is due to an electric field crowding effect, whereby an electric field is more concentrated on a portion having a curvature than on a plane portion. The effect is exacerbated at edges of the depletion layer having a high curvature. Accordingly, avalanche breakdown is more easily generated at such edges, which reduces the breakdown voltage of the entire depletion layer.
A method for dealing with this problem in the prior art is disclosed in Power Semiconductor Devices, pp. 100-102, written by B. J. Baliga, 1996. The method is by forming an insulator and a field plate on the edge portion of the depletion layer. A voltage applied to the field plate controls the surface electric potential, which in turn controls the size and shape of the depletion layer. Thus the applied voltage can improve the size and curvature of the depletion layer, and thereby increase the breakdown voltage.
The breakdown voltage of a power semiconductor device is a value obtained by integrating the electric field E in the depletion layer with respect to a horizontal length ‘X’ of the depletion layer. Accordingly, when the field plate voltage is applied such that it increases the length of the integrated area, the breakdown voltage increases. This happens because the electric field concentration in each curved portion of the depletion layer is reduced, which thereby prevents avalanche breakdown at each such portion.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power semiconductor device in which an electric field distribution area is enlarged to increase a breakdown voltage.
It is another object of the present invention to provide a manufacturing method of a power semiconductor device appropriate for the above object.
A power semiconductor device according to the present invention includes a breakdown voltage improving structure. The device includes a collector region of a first conductivity type and a base region of a second conductivity type formed in the collector region. The two regions create between them a pn junction. The device also includes at least one accelerating region of the first conductivity type. The accelerating region is formed at a first predetermined distance from the base region, and at a dose higher than that of the collector region. The device further includes a field plate formed on an insulating layer. The field plate overlaps the pn junction and the accelerating region. The field plate has an edge portion that extends past the accelerating region by a second predetermined distance.
Preferably the accelerating region is formed at a dose 5-100 times as high as that of the collector region, and is in the shape of a circle surrounding the pn junction.
A method is also provided for manufacturing the device of the invention.
According to the method, a collector region of a first conductivity type is formed on a substrate. Then a first mask pattern is used for implanting a first impurity of the first conductivity type at a dose 5-100 times as high as that of the collector region. Then a second mask pattern is used for implanting a second impurity of a second conductivity type, opposite to the first conductivity type. The impurities are then diffused at high temperature to form respectively an accelerating region and a base region. The base region and the collector region create a pn junction. The accelerating region is spaced from the base by a first predetermined distance, and preferably forms a circle around the pn junction. Then an insulating layer is formed over the junction and the accelerating region. Then a field plate is formed on the insulating layer. The field plate overlaps the junction and the accelerating region, and extends past the accelerating region by a second predetermined distance.
When a voltage of a reverse direction is applied to the power semiconductor device of the invention, an electric field is concentrated on the accelerating region as well as on the pn junction and on the field plate edge. This increases an electric field distribution area and thus also increases the breakdown voltage of the device.
REFERENCES:
patent: 4667393 (1987-05-01), Ferla et al.
patent: 4757363 (1988-07-01), Bohm et al.
patent: 5283202 (1994-02-01), Pike, Jr. et al.
patent: 5541439 (1996-07-01), Mojaradi et al.
patent: 5898199 (1999-04-01), Mori et al.
Baliga, B. Jayant, Modern Power Devices, General Electric Company, Schenectady, New York 1948, pp. 92-100.
Baliga, B. Jayant, Power Semiconductor Devices, North Carolina State University, 1995, pp. 100-102.
Fenty Jesse A.
Marger & Johnson & McCollom, P.C.
Saadat Mahshid
Samsung Electronics Co,. Ltd.
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