Hewlett-packard Company

Jean-Pierre Colinge

Theodore I Kamins

John L Moll

Paul J Marcoux

Lynn M Roylance

An improved method for fabricating a bipolar transistor reduces base current resistance which heretofore has limited the switching frequency and current handling ability of bipolar transistors. The transistor base and emitter are formed as a diffusion through an emitter contact pedestal formed on an epitaxial layer over a substrate. Access to the n-type emitter is through the emitter contact pedestal while access to the lightly doped p-type base is through a nearby heavily doped p-type base insert. Electrical isolation between the pedestal and the base insert is ensured by forming oxide sidewall spacers on the emitter contact pedestal during the implant used to form the base insert. Defining the isolation with sidewall spacers permits reliable isolation of emitter and base insert while minimizing their physical separation. The minimized physical separation provides a base current path with considerably less total resistance than is found in the background art in which the isolation is defined photo-lithographically.

Bipolar transistor process using sidewall spacer for aligning base insert

A method for producing buried oxide layers in selected portions of a semiconductor substrate including the steps of applying a patterned mask made from a high-density material over a semiconductor substrate and selectively forming buried oxide layers by oxygen ion implantation. The high-density material of the mask is preferably tungsten, but can also be made from other suitable materials such as silicon nitride. A MOS transistor is made by the process of the present invention by applying the high-density mask material over the gate of the transistor, and forming buried oxide layers by ion implantation beneath only the source region and drain region of the transistor. The completed MOS transistor has the characteristics of reduced drain and source capacitance, reduced leakage, and faster response, but does not suffer from the floating-body effect of MOS transistors made by SOI processes.

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Palo Alto, CA, United States of America

Jean-Pierre Colinge