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Implanted Transistor With Lateral Injection Compensation

IP.com Disclosure Number: IPCOM000089103D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Lebesnerais, G: AUTHOR [+2]

Abstract

Lateral injection and two dimensional effects usually make the gain beta of a bipolar transistor a function of the emitter size. Usually beta decreases when emitter size decreases.

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Implanted Transistor With Lateral Injection Compensation

Lateral injection and two dimensional effects usually make the gain beta of a bipolar transistor a function of the emitter size. Usually beta decreases when emitter size decreases.

This new process takes advantage of ion implantation properties to compensate for this phenomenon.

A thin oxide layer (1500 angstroms) is grown in the region of the future base of the transistor. Then, the emitter window is etched in this oxide. Next, ion implantation of the emitter region is performed (preferably with arsenic, energy: 40 KeV, and dose: 5 x 10/15/ at/cm2), followed by the first heat treatment at 1000 degrees C during 30 minutes to drive the ions into the epitaxial layer. At this stage the base is formed by two implants of boron with photoresist as masking material: a shallow base to get a low R(bb), (60 KeV and 1 x 10/14/ at/cm2) and a deep base (200 KeV and 0.5 x 10/13/ at/cm2).

Finally, a final heat treatment is performed. The deep base will reproduce in the silicon the shape of the oxide step (1500 angstroms) at the edge of the emitter. So, in the transition region the active base doping will decrease and the beta will increase. This phenomenon of higher beta at the periphery of the emitter will compensate for the loss of the base current due to the wall effect of the emitter region.

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