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IN-SITU OXIDE REMOVAL IN A LPCVD FURNACE SYSTEM

IP.com Disclosure Number: IPCOM000006349D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2001-Dec-27
Document File: 2 page(s) / 110K

Publishing Venue

Motorola

Related People

Ron Pennell: AUTHOR [+2]

Abstract

Several problems arise when working with polysili- con films in the fabrication of high density BiCMOS circuits, demonstrated in the attached figure. The first involves the contact made between the deposited polysili- con layer and the emitter opening in the NPN transistor. A native oxide exists on the single crystal surface and gets covered by the polysilicon deposit. This interfacial oxide film has several negative effects on the bipolar device performance. One is emitter contact resistance which will adversely effect the speed of the device. Another is the control of the electrical parameter, beta or current gain. By having the native oxide between the poly and single crystal surface, breakup of the oxide during subsequent heat treatments controls the uniformity of this parameter instead ofthe base and emitter dopant profiles.

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MOTOROLA INC. Technical Developments Volume 14 December 1991

IN-SITU OXIDE REMOVAL IN A LPCVD FURNACE SYSTEM

by Ron Pennell and Mitch Barton

PROBLEM

  Several problems arise when working with polysili- con films in the fabrication of high density BiCMOS circuits, demonstrated in the attached figure. The first involves the contact made between the deposited polysili- con layer and the emitter opening in the NPN transistor. A native oxide exists on the single crystal surface and gets covered by the polysilicon deposit. This interfacial oxide film has several negative effects on the bipolar device performance. One is emitter contact resistance which will adversely effect the speed of the device. Another is the control of the electrical parameter, beta or current gain. By having the native oxide between the poly and single crystal surface, breakup of the oxide during subsequent heat treatments controls the uniformity of this parameter instead ofthe base and emitter dopant profiles.

  The second problem is contact resistance between polysilicon layers deposited on top of each other. This interfacial oxide results in a reduction in the speed per- formance of the circuit and may also cause it to use more power then desired. Another significant problem is when dry etching poly layers in a reactive ion etcher. In the reactors, controlling the etch of these films is done by using end-point detection. When the etching proce- dure clears through the polysilicon layer, the change in etch chemistry inside the chamber alerts the system to stop. However if the interfacial oxide exists between two layers, the machine senses this change in chemistry wh...