New isolation technique for a low frequency low noise monolithic L.I.C.

The realization of an ultra low noise Monolithic Linear Integrated Circuits (M.L.I.C) with a 3 dB noise figure at 10 Hz has been made possible by a new isolation technique under low temperature. The major cause of inferior noise performance of a transistor in the M.L.I.C. was found to be due to contaminants or diffusion - induced dislocations associated with high temperature (1250°C) impurity diffusion for an isolation. Elimination of the high temperature isolation process from the wafer processing has been attempted. Thus a new low temperature process, involving forming a porous silicon instead of diffused isolation, has been successfully achieved.