Design and fabrication of rugged FRED, power MOSFET or IGBT
View Patent ↗An improved Fast Recovery Diode comprises a main PN junction defining a central conduction region for conducting high current in a forward direction and a peripheral field spreading region surrounding the central conduction region for blocking high voltage in the reverse direction. The main PN junction has an avalanche voltage equal to or lower than an avalanche voltage of the peripheral field spreading region so substantially the entire said main PN junction participates in avalanche conduction. This rugged FRED structure can also be formed in MOSFETS, IGBTS and the like.
1. A MOS gate-controlled power device having enhanced avalanche ruggedness, the device comprising:
a semiconductive substrate including a first layer ( 112 , 213 ) having a doping type of a first polarity in a first concentration (N+);
a second layer ( 114 , 214 ) having a doping type of the first polarity in a second concentration (N) less than the first concentration;
a body region ( 122 , 322 ) formed in the second layer having a doping type of a second polarity opposite the first polarity in a third concentration (P);
a first enhanced region ( 222 , 422 ) formed in the body region having a doping type of the second polarity in a fourth concentration (P+) greater than the third concentration;
a source region formed in a portion of the body region adjoining the enhanced region ( 222 , 422 ) and body region ( 122 , 322 ) having a doping type of the first polarity in a fifth concentration (N+) greater than the second concentration;
an insulated gate structure formed on a surface of the second layer in position to overlie a channel portion of the body region extending along the surface between the source region and a drift region of the second layer; and
a second enhanced region ( 120 , 220 ) of the doping type of the first polarity in a sixth concentration (N+) greater than the second concentration (N);
the body region extending to a first depth and the first enhanced region extending to a second depth within the second layer to form a PN junction therewith; and
the second enhanced region extending to a third depth within the second layer, the third depth exceeding both the first depth and the second depth so that avalanche breakdown occurs in the first enhanced region.
2. A MOS gate-controlled power device according to claim 1 in which the device is a vertical device having a first contact to the first enhanced region and the source region on the surface of the device and a second contact on a backside of the device such that current flows between the surface of the device and the backside of the device vertically through the substrate, the second layer and the second enhanced region.
3. A MOS gate-controlled power device according to claim 2 arranged and operable as a power MOSFET in which the second contact lies in contact with a backside surface of the first layer.
4. A MOS gate-controlled power device according to claim 2 arranged and operable as a insulated gate bipolar transistor in which the substrate includes a backside layer having a doping type of a second polarity opposite the first polarity of the first layer and the second contact lies in contact with the backside surface of the backside layer.
5. A MOS gate-controlled power device according to claim 1 in which the first depth of the body region extends to a greater depth within the second layer than the second depth of the first enhanced region extends within the second layer.
6. A MOS gate-controlled power device according to claim 1 in which the first depth of the body region extends to a lesser depth within the second layer than the second depth of the first enhanced region extends within the second layer.
7. A MOS gate-controlled power device according to claim 1 in which the sixth concentration of the second enhanced region is diffused from a dose of between 5E11/cm 2 to 5E14/cm 2 .
8. A MOS gate-controlled power device according to claim 1 in which the surface of the second layer includes a trench alongside the gate structure, the source region extending laterally from a side of the trench and the first enhanced region extending depthwise from a bottom of the trench below the source region.