Dept. of Applied Physics
Oregon Graduate Institute of Science & Technology
Memory devices redundancy repair by link laser processing and laser trimming of components have been two widely used applications of lasers in the electronics industry. Constantly shrinking memory feature sizes and industry's technology tendency to use metals as link materials rather than polysilicon impose new challenges for link laser processing. Maximizing the volume of the molten link material before the rupture of the overlying passivation has been considered in the past to be a key factor in enhancing the process. Unfortunately, this criterion doesn't work well for processing metal links, due to their small optical absorption depth. New physical models and analyses of optical interference effects, pre-rupture temperature distribution, mechanical stress within the passivation and post-rupture processes have been developed and are presented in this thesis. The effects of link width and overlying passivation thickness on mechanical stress and link process have been revealed. A new approach of emphasizing laser absorption contrast between the link material and silicon substrate at longer wavelengths is proposed and analyzed. Higher absorption contrast allows the use of higher laser energy to cleanly cut links without damaging the silicon substrates. While light absorption of most metals remains almost unchanged within wavelength range of 1 to 2 Î¼m, it drops dramatically for silicon at longer than 1.2 Î¼m. Simulation of laser processing windows at both laser wavelengths of 1 and 1.32 Î¼m are in good agreement with experiment results which have proved the expected advantages of using 1.32 Î¼m lasers over 1 Î¼m lasers for link processing. Severe parameter drift of semiconductor based devices during exposure to laser pulses has been a major problem for functional trimming. Although the excitation of excessive electron-hole carriers within the semiconductor material by the laser beam has been identified as the cause, no real solution had been found. By using laser wavelengths beyond the range within which excessive electron-hole carriers can be excited, such as 1.32 Î¼m, laser induced device parameter drift is virtually eliminated. Higher trimming through-put thus becomes achievable.
Sun, Yunlong, "Laser Processing Optimization for Semiconductor Based Devices" (1997). Scholar Archive. 3.