Browse Prior Art Database

Bipolar Polysilicon Base Process

IP.com Disclosure Number: IPCOM000052178D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Nagarajan, A: AUTHOR [+2]

Abstract

It has been determined that ion beam milling can be used to provide considerably tighter control of etched images and a more reproducible control of gain in bipolar transistors, particularly in those utilizing a polysilicon base process.

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Bipolar Polysilicon Base Process

It has been determined that ion beam milling can be used to provide considerably tighter control of etched images and a more reproducible control of gain in bipolar transistors, particularly in those utilizing a polysilicon base process.

Polysilicon base processes have been used to improve performance of bipolar transistors. Doped polysilicon can also be used for local wiring, which provides an additional density advantage. The polysilicon base process requires both extrinsic and intrinsic base dopings. The intrinsic base doping always has a higher value since the intrinsic base controls the integrated base doping and the gain of the transistor. The extrinsic base doping is lower to insure good contact resistance. Etching of the base dopings in polysilicon is complex since none of the available dry etching processes guarantee reproducibility or reliability. Reliability depends on the control of the slope of the etched image.

Use of ion beam milling to supplant dry etching processes provides a more reproducible control of the etching process. The structure to be etched consists of a two-micron epitaxial layer and a 15 ohm/cm substrate, which is a composite of polysilicon (500-1000 nm), silicon oxide (50-100 nm) and silicon nitride (500- 2000 nm). Ion beam milling is effected at 500 to 1000 eV at an argon pressure of 5 to 7 x 10/-s/ torr at an incidence angle of 90 degrees. The time required for etching is adjusted by changing the d...