High mechanical reliability of back-ground GaAs LSI chips with low thermal resistance

GaAs LSI-sized 6.35 mm square chips with mirror ground back surfaces (Rmax=0.1 μm) have been confirmed to be almost as reliable as chemically thinned ones through fracture stress experiments. Two fracture strength test methods, the four-point bending test and the biaxial tension test, were performed and the data were analyzed based on Weibull statistics. The 1 μm post-grinding chemical etching in the original wafer thinning technology was proven to be effective in eliminating the surface flaws due to grinding, which act as stress concentrators and reduce mechanical strength. The thermal resistance of back-ground 5 mm square GaAs chips was observed to be low by utilizing the surface temperature measurement technology based on the diode drop technique. The thermal resistance was judged to be independent of the back-surface treatment