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SIMOX AND INDUCED LATERAL OVERGROWTH FOR PEDESTAL BIPOLAR AND 3D DEVICES

IP.com Disclosure Number: IPCOM000005731D
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2001-Oct-31
Document File: 2 page(s) / 98K

Publishing Venue

Motorola

Related People

H. Ming Liaw: AUTHOR

Abstract

Speed performance in a bipolar device can be improved by optimization of extrinsic device parameters. These include the reduction of the collector to substrate capacitance (Ccs), the collector to base capacitance (Ccb), the extrinsic base resistance (Rb), and collector resistance (Rc). Various device structures have been reported aiming for reduction of parasitic capacitances. They include local isolation of silicon (LOCOS), sidewall contacted oxidized silicon (SICOS), and pedestal typed bipolar devices by selective epitaxial growth. More recently, Schubert et al* have proposed a selective epitaxy and double epitaxial overgrowth process to eliminate the need of n+ buried layer as a subcollector. This results in a further reduction of Ccs, Ccb and Rc.

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MOTOROLA Technical Developments Volume 8 October 1988

SIMOX AND INDUCED LATERAL OVERGROWTH FOR PEDESTAL BIPOLAR AND 3D DEVICES

by H. Ming Liaw

   Speed performance in a bipolar device can be improved by optimization of extrinsic device parameters. These include the reduction of the collector to substrate capacitance (Ccs), the collector to base capacitance (Ccb), the extrinsic base resistance (Rb), and collector resistance (Rc). Various device structures have been reported aiming for reduction of parasitic capacitances. They include local isolation of silicon (LOCOS), sidewall contacted oxidized silicon (SICOS), and pedestal typed bipolar devices by selective epitaxial growth. More recently, Schubert et al* have proposed a selective epitaxy and double epitaxial overgrowth process to eliminate the need of n+ buried layer as a subcollector. This results in a further reduction of Ccs, Ccb and Rc.

Epitaxial lateral overgrowth is severely limited by its low ratio of lateral growth rate to vertical growth rate
(11). In other words, when a distance of several micrometers is needed for silicon to grow laterally over the oxide, the thickness of silicon deposited on the oxide becomes too thick for fabrication of high performance devices. The excess thickness of silicon is removed by mechanical polishing. It is very difficult to obtain precise thickness of thin silicon by polishing.

   We can eliminate one lateral overgrowth step if the starting wafer already has a silicon layer over buried oxide such as SIMOX (separation of silicon by implantation of oxygen). The top silicon layer in SIMOX is doped to form n+ for contact to the collector. A layer of CVD or thermal oxide is deposited on n+ silicon. A photolithographic patterning and a reactive ion etching are applied to open the active region of devices. Pedestal- type bipolar devices with the collector and base fully isolated can be made by selective epitaxial growth and lateral overgrowth. We can solve the problem of a slow l...