Appeal No. 1997-3979
Application No. 08/586,365
polysilicon layer 64 are implanted with two dopant species
having different diffusion rates in silicon, such as
phosphorous and arsenic (col. 5, line 43 to col. 6, line 4).
Next, all of polysilicon layers 64 and 68 are removed except
for the parts which are to function as gates 69g of the MOS
transistors and as emitter contact 69e of the bipolar
transistor (col. 6, lines 14-19). The implant conditions of
the aforementioned arsenic and phosphorous implants may be
adjusted independently from one another to optimize the
emitter depth and conductivity desired for the structure (col.
6, lines 10-13). After completing the steps depicted by
Figures 7-10, the structure is subjected to a high temperature
anneal, which inter alia diffuses dopant from emitter
electrode 69e into intrinsic base region 61 to form emitter
region 89 therein, as shown in Fig. 10 (col. 7, lines 17-26).
The specification explains that
the invention provides the advantage of a
shallow emitter junction with a high
impurity concentration in the emitter
electrode 69e. In this embodiment, since
emitter electrode 69e has both phosphorous
and arsenic dopant species therewithin, the
phosphorous implant dose may be selected to
define the desired emitter junction depth,
while the arsenic dose may be selected to
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