Integrated circuits complexity is controlled by defective sections which decrease IC yields and limit chip area to a few sq. cm. The post fabrication laser processing techniques of cutting lines and forming connections are effective in removing defects and enhancing fault tolerance in large VLSI circuits. Successful applications require designs which include redundant sections for substitution and the defect avoidance points built into the structure. Commercial devices have used cutting polysilicon lines to substitute rows and column blocks in memory chips (DRAM's), microprocessor's cache memory and Field Programmable Gate Arrays. More complex wafer scale systems of 25 sq cm have been built using combinations of additive connections and line cutting to route signals around defective areas thus creating defect free large working systems. These used laser diffused links consisting of two conductively doped lines in silicon separated by a gap. An argon ion laser pulse (100 microsec., 2 W, 1.2 micron FWHM) spreads dopant throughout the gap generating approximately 70 ohms connections. Metal links of two metal lines, separated by 1 micron), covered by intermetal insulator. A laser pulse expands the metal, fractures the SiO2 between the lines, and forces molten metal to make < 3 ohms connections. Both links show lower impedance alternative like active transistor switches (approximately 3 - 6 Kohm).
Glenn H. Chapman, Glenn H. Chapman,
"Laser applications to IC defect correction", Proc. SPIE 3274, Laser Applications in Microelectronic and Optoelectronic Manufacturing III, (3 June 1998); doi: 10.1117/12.309496; https://doi.org/10.1117/12.309496