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Process for Fabricating Polysilicon Base Bipolar Transistors

IP.com Disclosure Number: IPCOM000051023D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Chu, SF: AUTHOR [+3]

Abstract

The control of etch end point of the extrinsic base polysilicon in the fabrication of polysilicon base transistors has long been a problem. Base polysilicon over-etch or under-etch is frequently encountered because there is little or no etch rate difference between polysilicon and the single crystal silicon substrate in most reactive ion etching (RIE) systems. To alleviate this problem, a metal pad composed of, for example, a refractory metal, such as W, Mo, Ti, etc., is used as the base polysilicon etch stopper or end-point indicator. Compared to Si, refractory metals have a much smaller etch rate and a much larger optical surface reflectivity. Therefore, polysilicon etch end point can be easily detected in a polysilicon/metal layered structure.

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Process for Fabricating Polysilicon Base Bipolar Transistors

The control of etch end point of the extrinsic base polysilicon in the fabrication of polysilicon base transistors has long been a problem. Base polysilicon over-etch or under-etch is frequently encountered because there is little or no etch rate difference between polysilicon and the single crystal silicon substrate in most reactive ion etching (RIE) systems. To alleviate this problem, a metal pad composed of, for example, a refractory metal, such as W, Mo, Ti, etc., is used as the base polysilicon etch stopper or end-point indicator. Compared to Si, refractory metals have a much smaller etch rate and a much larger optical surface reflectivity. Therefore, polysilicon etch end point can be easily detected in a polysilicon/metal layered structure. After the emitter window is opened through the extrinsic base polysilicon layer, the remaining refractory metal padding in the emitter region can then be selectively etched away by suitable chemical etchant; for example, for Mo, HCl + H(2)O82) can be used. The metal padding that is left underneath the base polysilicon is then converted to silicide by a high temperature annealing step. This high temperature annealing also drives the base dopant from the extrinsic base polysilicon into the silicon substrate to form the extrinsic base region of the device.

The following illustrates one fabrication process:

1) After the fabrication of the recessed oxide isolation (...