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Improved Silicide Fuses for VLSI Circuits

IP.com Disclosure Number: IPCOM000120878D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Barmak, K: AUTHOR

Abstract

This article presents improvements to the use of silicides as fuses for VLSI (very large-scale integrated) circuits. The improvements make use of the characteristics of titanium silicide formation in order to retain a larger fraction of the high resistivity C49 phase. This phase that forms during the reaction of Ti and Si has a faster agglomeration rate than the lower resistivity C54 phase and is, therefore, preferable as the fuse material. (The lower resistivity C54 TiSi2 phase is preferable as the contact or local interconnect material.) In addition, substrate materials or ambients that enhance the agglomeration process should be used.

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Improved Silicide Fuses for VLSI Circuits

      This article presents improvements to the use of
silicides as fuses for VLSI (very large-scale integrated) circuits.
The improvements make use of the characteristics of titanium silicide
formation in order to retain a larger fraction of the high
resistivity C49 phase.  This phase that forms during the reaction of
Ti and Si has a faster agglomeration rate than the lower resistivity
C54 phase and is, therefore, preferable as the fuse material.  (The
lower resistivity C54 TiSi2 phase is preferable as the contact or
local interconnect material.)  In addition, substrate materials or
ambients that enhance the agglomeration process should be used.

      In order to retain a larger fraction of the C49 phase, the
following techniques are used:
 1.  Narrower, thinner lines.  The C49 to C54 phase is a phase
transformation from one crystal structure to another and is,
therefore, a low driving force nucleation-controlled transformation.
Use of narrower, thinner lines leads to smaller probability of
nucleation of the second phase, C54; hence, the retention of a higher
fraction of the C49 phase.
 2.  Use of dopants, e.g., As, in the reacting Si to increase the
fraction of the C49 phase by retardation of the rate of formation of
TiSi2 and rate of transformation of C49 to C54. (1,2)  It has been
found that titanium silicide formed on n+ Si substrates is more prone
to agglomeration than that on p+ substrates.
 3.  Formation or deposition of the silicide on an oxide pad or use
of oxide capping layers which have been shown to slow the C49/C54
transformation and enhance the agglomeration rate of the silicide.

      4.  Use of a single anneal at a temperature which leads to the
formation of the C49 phase only.  This temperature is usually lower
than that necessary for the formation of the C54 phase.
 5.  Avoidance of the use of any techniq...