Impact of Al Melting on Diode Integrity.

The integrity of Al/barrier/CoSi sub 2 junctions subjected to Al melting has been studied. Melting was accomplished by irradiating Si wafers in a rapid thermal anneal system. Three types of barriers were studied; TiN, W:Ti and a bi-layer of W:Ti/TiN. Junction leakage measurements indicated that the W:Ti/TiN bi-layer was superior to the other two, and that it withstood temperatures at least 60C higher than the Al melting temperature. Rutherford backscattering, x-ray diffraction and etch back experiments were performed to determine the extent of interaction between the various layers after the melt. We found that W reacted readily with Al and Si, upon melting of Al, formed a ternary alloy of W(AlSi) sub 2 and possibly other phases including Co as a constituent. TiN on the other hand was an effective barrier against the reaction of Al or W on one side of it with the Si substrate on the other side.