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This method, which permits the direct contacting of the active intrinsic base area, is described by means of a transistor produced in accordance with the collector diffused isolation principle.
English (United States)
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Method of Producing Transistors with Optimum Base Contact
This method, which permits the direct contacting of the active intrinsic base
area, is described by means of a transistor produced in accordance with the
collector diffused isolation principle.
As shown in Fig. 1, P- epitaxial layer 1' on P- substrate 3 with N+ subcollector
2 serves as the intrinsic transistor base 1. The transistor is isolated by a deep N+
isolation zone 4 extending down to subcollector 2 and by means of which the
collector is connected later on. Emitter 5 consists of an N+ zone embedded in P-
base 1. Then, the outer edge of the transistor layer sequence N+P-N+, thus
prepared, is bared in the area adjacent to N+ isolation zone 4 by etching trench 6.
During the subsequent oxidation step (Fig. 2) carried out under appropriate
process conditions, a relatively thick oxide layer 7 (800 nm) is obtained on the
very highly doped N+ regions 2, 4, 5, while a thin oxide layer 8 (for example, 100
nm) is grown on the more lightly doped intrinsic base 1.
In the next step (Fig. 3), oxide layers 7, 8 are approximately uniformly etched
by a thickness value equalling at least, or slightly in excess of, the thickness of
oxide layer 8, baring intrinsic base 1. Then, trench 6 is filled with a suitable
conductive material 9 (Fig. 4), preferably P-type polysilicon, which directly
contacts intrinsic base 1, but is separated from emitter 5 and collector 2 by oxide
layer 7. Finally, contacts B (base), E (emitter)...