DocumentCode :
897689
Title :
Self-Aligned Transistors with Polysilicon Emitters for Bipolar VLSI
Author :
Cuthbertson, A. ; Ashburn, P.
Volume :
20
Issue :
1
fYear :
1985
fDate :
2/1/1985 12:00:00 AM
Firstpage :
162
Lastpage :
167
Abstract :
A new bipolar process technology for fabricating self-aligned transistors with polysilicon contacted emitters is described. The extrinsic base regions of the transistor are self-aligned to the emitter contact by exploiting the effects of concentration-dependent oxidation to selectively oxidize the polysilicon. The shallow emitter is fabricated with a thin oxide layer at the polysilicon-silicon interface, thereby enhancing the emitter efficiency and thus the current gain of the device. It is demonstrated that this gain enhancement can be traded for a considerable increase in active base doping, with a resulting decrease in base resistance and potential improvement in switching performance. Under certain circumstances, non-ideal electrical characteristics can be obtained from the self-aligned transistor which are caused by lateral spread of the extrinsic base region beneath the sidewall oxide of the polysilicon emitter contact. Tlris leads to the formation of p+ -n+ junction at the periphery of the emitter and hence to tunneling of carriers across this region. It is shown that the same tunneling mechanism also limits the extent to which the active base doping can be increased. In order to avoid the formation of the peripheral p+-n+ junction, a polysilicon base contact is employed which allows a self-aligned extrinsic base region to be fabricated with negligible lateral movement.
Keywords :
Bipolar integrated circuits; Integrated circuit technology; VLSI; Bipolar transistors; Circuits; Delay; Doping; Electric resistance; Etching; Oxidation; Performance gain; Silicon; Very large scale integration;
fLanguage :
English
Journal_Title :
Solid-State Circuits, IEEE Journal of
Publisher :
ieee
ISSN :
0018-9200
Type :
jour
DOI :
10.1109/JSSC.1985.1052290
Filename :
1052290
Link To Document :
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