Link explosion in laser programmable redundancy for one mega- bit DRAM repair.

Laser programmable redundancy has been used in one mega-bit DRAM devices to increase the yield through the replacement of defective elements with spare rows and/or columns. In this work, we first discuss the scaling effect on the laser repair rate due to chip size and density increase in VLSI. The effect on repair rate of different spare element encoder designs is also discussed. The laser target link material systems which were used to implement redundancy in recent generations of DRAM and the laser pulse characteristics are described. Various laser explosion patterns in Mb DRAM have been observed. The causes of their formation and their effects on repair rate are discussed. A theoretical model of link explosion has been used to understand some of our observations. Theoretical predictions about the link explosion of doped polysilicon link (64K DRAM) and poly-silicide sandwich link (256K and 1 Mb DRAM) are also analyzed by this model.