Browse Prior Art Database

An Ion Implantation Process for Making Bipolar Devices

IP.com Disclosure Number: IPCOM000086679D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Ko, W: AUTHOR [+2]

Abstract

Where recessed silicon dioxide is used for dielectric isolation bipolar integrated circuitry, the "bird's beak" is well-known among present problems. The prior art has disclosed the "bird's beak" problems associated with silicon dioxide-silicon nitride composite masks. [1, 2]

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An Ion Implantation Process for Making Bipolar Devices

Where recessed silicon dioxide is used for dielectric isolation bipolar integrated circuitry, the "bird's beak" is well-known among present problems. The prior art has disclosed the "bird's beak" problems associated with silicon dioxide-silicon nitride composite masks. [1, 2]

The "bird's beak" problems are particularly significant when silicon dioxide- silicon nitride composite masks are used in the formation of recessed silicon dioxide to be used for dielectric isolation. In such recessed oxide formation techniques, the silicon dioxide-silicon nitride composite masks are first used as an etch barrier while recesses are etched through the mask openings in the silicon substrate. These recesses are subsequently subjected to thermal oxidation to form recessed silicon dioxide regions, providing dielectric isolation extending into the silicon substrate from the surface. Such recessed silicon dioxide regions should be coplanar with the remainder of the silicon surface.

However, because of the "bird's beak", an undesirable bump in the order of from 4,000 angstroms to 5,000 angstroms in height is present at the surface. Even more significantly, as a result of the "bird's beak", a lateral junction or edge of the recessed silicon dioxide isolation region is very vaguely defined. With any recessed oxide isolation, it is highly desirable that the lateral edges of the recessed silicon dioxide be substantially vertical, i.e., perpendicular to the semiconductor substrate surface. Instead, as a result of the "bird's beak", the edges of the recessed silicon dioxide are gradually sloped with respect to the silicon surface, being at an angle which varies from 15 degrees to 30 degrees with respect to the surface, instead of the desirable 90 degree angle.

Because of this gradual lateral junction in the recessed silicon dioxide, the recessed region does not clearly define abutting regions introduced by diffusion. Fig. 1 illustrates the problem. The P-type base region 10 and and N+emitter region 11 are formed by conventional diffusion techniques so as to abut recess silicon dioxide region 12. During the conventional etching of opening 13 through which the emitter would be formed, a thin portion of the "bird's beak" was inadvertently removed, resulting...