Computer-simulated explosion of poly-silicide links in laser-programmable redundancy for VLSI memory repair

A computer model has been used to describe the temperature evolution of link targets as they are typically processed in laser programmable redundancy. Three such infrared laser simulations are described: (1) short-pulse polysilicon targets, (2) short-pulse TaSi/sub 2/-polysilicon targets, and (3) long-pulse TaSi/sub 2/-polysilicon targets. Reliability issues involved with each of these three laser target systems are discussed. Good correlation has been noted between the model results and two experiments involving ambient wafer temperature and long-pulse laser processing. The poly-silicide target is shown to present short-pulse infrared laser processing difficulties not encountered in a solid polysilicon link. These are caused by the strong optical absorption of the TaSi/sub 2/, the subsequent screening of deeper target material, and the high melting and vaporization temperatures of this silicide. The transparent top dielectric and the optical properties of solid and liquid silicon play important roles in the suggested reliability of the solid polysilicon link. Although the use of a long-pulse laser on poly-silicide targets appears to overcome some of the above-mentioned difficulties, subsequent reliability and performance degradation casts doubt on this technique for high-volume manufacturing.>