Excellent electrical characteristics of ultra-fine trench isolation

An ultra-fine trench isolation, by which a narrow-channel metal-oxide-semiconductor field-effect-transistor (MOSFET) can be isolated with excellent electrical properties, was formed by use of new fabrication processes. A void-free shape was realized by two-step filling and the trench edge shapes were drastically improved by oxide spacer formation. Down to the ultra-narrow field space of 0.13 mu m, the isolation breakdown voltage and the parasitic MOSFET's threshold voltage were maintained as high as 7.7 V and more than 6 V, respectively. The reduction in the effective channel width for the MOSFET, furthermore, was estimated to be as small as 0.05 mu m, while it was shown that kink-free MOSFET subthreshold characteristics were kept even without a sidewall implantation to suppress the concentration of the electric field at the channel edges.