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Avoiding Leakage in "Abutted Emitter" Structures

IP.com Disclosure Number: IPCOM000087527D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Barson, F: AUTHOR

Abstract

For maximum circuit density in bipolar integrated circuits, it is desirable to abut diffused emitters as well as the base diffusion against the recessed oxide isolation (ROI). However, when this is done, an emitter-collector leakage path often occurs, apparently due to an N-type inversion layer next to the oxide sidewall, as shown in Fig. 1. A similar problem occurs with N channel metal-oxide semiconductor field-effect transistors (MOSFETS) which have source and drain regions abutting SiO(2) isolation. In this case also, the region beneath the SiO tends to invert to N type, resulting in an unwanted leakage path between the N+ diffusions.

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Avoiding Leakage in "Abutted Emitter" Structures

For maximum circuit density in bipolar integrated circuits, it is desirable to abut diffused emitters as well as the base diffusion against the recessed oxide isolation (ROI). However, when this is done, an emitter-collector leakage path often occurs, apparently due to an N-type inversion layer next to the oxide sidewall, as shown in Fig. 1. A similar problem occurs with N channel metal- oxide semiconductor field-effect transistors (MOSFETS) which have source and drain regions abutting SiO(2) isolation. In this case also, the region beneath the SiO tends to invert to N type, resulting in an unwanted leakage path between the N+ diffusions.

A boron diffusion through the ROI, just after the thick oxidation is done and with the Si(3)N(4) mask still in place to prevent diffusion into the active device areas bounded by the ROI, may be used to overcome this problem. Such a diffusion can be done with boron in a hydrogen-containing ambient, which is forming gas, pure H(2), or Ar-H(2) mixtures. The diffusivity of boron through SiO is increased by about three orders of magnitude when an ambient containing H(2) is used. In the bipolar structure shown, the amount of boron diffused must be sufficient to prevent an N-type path in the subsequent base region, but not so much as to convert that portion of the subcollector diffusion which intersects the bottom of the ROI since this must remain N-type for isolation to be intact. The p...