Impact of Al melting on diode integrity

The integrity of Al/barrier/CoSi/sub 2/ junctions subjected to Al melting was studied. Melting was accomplished by irradiating Si wafers in a rapid thermal anneal system. Three types of barrier were studied: TiN, W:Ti, and a bilayer of W:Ti/TiN. Junction leakage measurements indicated that the W:Ti/TiN bilayer was superior to the other two and that it withstood temperatures at least 60 degrees C higher than the Al melting temperature for one second or less. Rutherford backscattering, X-ray diffraction, and etchback experiments were performed to determine the extent of interaction between the various layers after the melt. The authors found that for the W:Ti barrier, upon melting of Al, W reacted readily with Al and Si, forming the ternary alloy, W(Al,Si)/sub 2/, and possibly other phases including Co as a constituent. TiN on the other hand effectively prevented the reaction of Al and W with Co and Si.<
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