Appeal No. 2000-0733
Application No. 08/310,041
known to form the body region in a two-step process wherein the body region was
diffused with a P-type dopant to form the body and then the periphery of the body area
was counter-doped to reduce the density of the P-type dopant around the lateral
portions of the source area. Because this method produced difficulties in diffusing
adjacent to the trench in trench devices and resulted in a PN junction that was complex
in shape with unpredictable characteristics, the instant invention seeks to solve these
problems by forming the body area using dopants with either (a) relatively low
segregation coefficients, such as indium or aluminum, or (b) relatively high diffusion into
a gate oxide, such as gallium, either alone or in combination with a dopant with a
relatively high segregation coefficient, such as boron.
Representative independent claim 32 is reproduced as follows:
32. A method of suppressing activation of a parasitic NPN transistor in
FETs, IGBTs and MCTs with a P-type body region having a channel
region adjacent a gate oxide layer, the method comprising the steps of:
doping said P-type body region with boron to a first impurity
concentration appropriate for said channel region;
doping said P-type body region with one of the dopants selected
from the group of other P-type dopants consisting of indium, aluminum
and gallium to a second impurity concentration, the combination of said
first impurity concentration and said second impurity concentration being a
third impurity concentration that is appropriate for said P-type body region,
wherein said third impurity concentration decreases about to said
first impurity concentration in said channel region by depletion of
said other P-type dopants into said gate oxide layer.
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