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Deliberate Design for Assuring Adequate Thermal Oxide Sidewall at the Corners of Trenches

IP.com Disclosure Number: IPCOM000121067D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Mis, JD: AUTHOR [+2]

Abstract

Most of the present technologies incorporate right angle trenches in their designs. Isolation leakage failures have been observed near these corners. This leakage has been linked to a thinning of the trench liner at the outside corner of the device cell. Although thinning of the oxide occurs at all corners, it is more pronounced at the outside corner. Oxide thinning is not observed along the straight portions of the trench liner. The thinning of the oxide has been shown [*] to be more pronounced as the radius of curvature decreases which is the same effect seen in our trench technology.

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Deliberate Design for Assuring Adequate Thermal Oxide Sidewall at
the Corners of Trenches

      Most of the present technologies incorporate right angle
trenches in their designs.  Isolation leakage failures have been
observed near these corners.  This leakage has been linked to a
thinning of the trench liner at the outside corner of the device
cell.  Although thinning of the oxide occurs at all corners, it is
more pronounced at the outside corner.  Oxide thinning is not
observed along the straight portions of the trench liner.  The
thinning of the oxide has been shown [*] to be more pronounced as the
radius of curvature decreases which is the same effect seen in our
trench technology.

      One solution to the problem of isolation fails as a result of
oxide thinning would be to thicken up the trench liner.  The negative
effect of this type of change would be the increased process time,
higher trench stresses, and it would require a reevaluation of the
trench isolation process.  A more direct solution is to redesign the
isolation mask at the trench corners.  Instead of using a right angle
corner, break the corner up into two or more larger angles, thereby
increasing the overall curvature of the corner (in the figure).  This
would increase the amount of oxide coverage at the corner without
requiring any process changes or a reevaluation of the trench
process.

      Reference
(*)  D. B. Kao et al., "Two-Dimensional Silicon Oxidation Experiments
and The...