A Radiation-Hard Insulator for MOS LSI Device Isolation

A total-dose radiation-hard insulator that is suitable for trench isolation material in MOS LSI, is presented. The insulator consists of a relatively thick PSG (phosphosilicate glass) layer deposited on a thin thermally grown SiO2 film. Experimental results on radiation-induced flat-band voltage shift and surface-state generation in MIS capacitor and on trench isolation characteristics showed that the stacked insulator is radiation tolerant even up to 106 rads(Si). Measurement on radiation-induced charge density profile in the insulator suggested that the hardness is attributable to a high recombination rate in the PSG and to enhanced hole trapping at the PSG/SiO2 interface. The insulator is a quite promising material for trench isolation in high-density fine-patterned MOS LSI's.