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Eliminating Cooperative Diffusion in Silicon Devices

IP.com Disclosure Number: IPCOM000093328D
Original Publication Date: 1967-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Joshi, ML: AUTHOR [+2]

Abstract

Either cooperative diffusion or base push-out is a commonly occurring phenomenon in transistor fabrication. The phenomenon occurs when the surface concentration in the emitter region exceeds about 8 x 1019 atoms/ cc. Drawing A shows an NPN transistor having the cooperative diffusion parameter X = Xbe - Xb. The manufacture of this transistor is by the conventional procedure of first diffusing base region B and then emitter region E. The cooperative diffusion phenomenon introduces difficulties, particularly as the trend is to more narrow base and shallow emitter regions.

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Eliminating Cooperative Diffusion in Silicon Devices

Either cooperative diffusion or base push-out is a commonly occurring phenomenon in transistor fabrication. The phenomenon occurs when the surface concentration in the emitter region exceeds about 8 x 1019 atoms/ cc. Drawing A shows an NPN transistor having the cooperative diffusion parameter X = Xbe - Xb. The manufacture of this transistor is by the conventional procedure of first diffusing base region B and then emitter region E. The cooperative diffusion phenomenon introduces difficulties, particularly as the trend is to more narrow base and shallow emitter regions.

The cooperative diffusion can be eliminated by use of a pre-emitter diffusion step prior to the base diffusion. This dissusion process involves a proper combination of the base push-out and the base junction retardation to give a substantially zero cooperative diffusion. The base-junction retardation parameter is Y = Ybe - Yb in drawing B. The retardation is after diffusion of acceptors through a highly N+ region.

A process for eliminating the cooperative diffusion phenomenon is shown in drawings C, D, and E. Epitaxial N layer is grown on a P silicon wafer. The wafer is then thermally oxidized and holes opened for the pre-emitter diffusion using conventional techniques to produce the structure of drawing C. The pre-emitter diffusion is then made in order to build a very thin N+ region. The N-type impurities in this deposition are preferably antim...