Israel A. Lesk

Silicon ribbon growth via the ribbon-to-ribbon (RTR) technique: Process update and material characterization

The current state of development of the RTR process for silicon ribbon growth is reviewed. Present growth capabilities, material characterization, and device performance are summarized. Specific process problems, such as poor laser coupling efficiencies, are discussed and approaches to their solution are described. Problems related to thermal stresses are discussed in some detail. Stress induced birefringence measurements are used to evaluate residual stresses. A linear temperature profile postheater is effective for reduction of residual stresses. A correlation may be obtained between minority carrier diffusion lengths, dislocation densities, and thermal stress levels.

Progression of damage caused by temperature cycling on a large die in a molded plastic package

Large silicon chips in molded plastic packages suffer physical damage to top-surface regions when subjected to repetitive thermal excursions. It is shown that a delamination between the molding compound and the die surface, progressing inward from a crack in the molding compound at a die corner, can enter an aluminum film through a crack in the passivation glass at an edge, travel through the metal, and exit at the opposite edge. This permits migration of glass and metal inward from corner regions. It is pointed out that reduced susceptibility to this effect may be obtained through the use of tougher metal, thicker passivation glass in lower metal edge corners, and tougher glass. A silicon integrated circuit chip approximately 250*290 mils in a 52-lead PLCC (plastic leaded chip carrier) was used as a test vehicle. Temperature and thermal shock cycling, from as low as -65 degrees C to +150 degrees C and for as many as 2000 cycles was performed.<<ETX>>