Browse Prior Art Database

TUNNELING BASE CONTACT FOR PEDESTAL TRANSISTORS

IP.com Disclosure Number: IPCOM000005633D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-22
Document File: 2 page(s) / 98K

Publishing Venue

Motorola

Related People

Gary J. Seiter: AUTHOR [+2]

Abstract

Advanced bipolar devices built with sidewall contacts and utilizing a selective epitaxial growth (SEG) process can be improved by adding a process step which forms a thin tunneling nitride film on the sidewall base contact. This nitride may be fabricated by a thermal nitridation of the exposed polysilicon prior to the SEG and will prevent the formation of polysilicon protrusions during SEG.

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MOTOROLA Technical Developments Volume 7 October 1987

TUNNELING BASE CONTACT FOR PEDESTAL TRANSISTORS

by Gary J. Seiter and Raymond M. Roop

ABSTRACT

   Advanced bipolar devices built with sidewall contacts and utilizing a selective epitaxial growth (SEG) process can be improved by adding a process step which forms a thin tunneling nitride film on the sidewall base contact. This nitride may be fabricated by a thermal nitridation of the exposed polysilicon prior to the SEG and will prevent the formation of polysilicon protrusions during SEG.

INTRODUCTION

   One method of achieving high performance bipolar devices is to fabricate the devices within silicon pedestals using SEG and employing sidewall base contacts. A typical cross-section is shown in Figure 1. The structure improves device performance through a reduction in parasitic capacitances. This reduction in parasitic capacitance arises when an oxide layer 10 is used to separate the base contact 11 from the substrate 12 thus eliminating the parasitic base-collector junction while forming asidewall base contact 13. In order to build this type of device, a three layered structure consisting of Si02 lo/doped polysilicon lllSiO2 14 is used to mask the SEG 15. During SEG, silicon is allowed to nucleate only on the substrate at the bottom of the well 16. The silicon pedestal is grown to a height approximately equal to the thickness of the SiO2/poly/SiO2 mask. The doped polysilicon layer is used to make contact to base region 17 of the device. After the SEG step, the base 17 and emitter 18 regions are implanted into the SEG area. Standard contacts, metallization and passivation finish the process.

DISCUSSION

   It has been found that under certain conditions during SEG, silicon will nucleate on the exposed polysilicon sidewall base contact (1). This silicon will nucleate in polycrystalline form 19 in Figure 2 and can grow to such an extent that it can project above the surface of the SEG. As a...