Silicon-gate

Development of the silicon-gate technology at Fairchild

The SGT was the first process technology used to fabricate commercial MOS integrated circuits that was later widely adopted by the entire industry in the 1960s. In late 1967, Tom Klein, working at the Fairchild Semiconductor R&D Labs, and reporting to Les Vadasz, realized that the work function difference between heavily P-type doped silicon and N-type silicon was 1.1 volt lower than the work function difference between aluminum and the same N-type silicon. This meant that the threshold voltage of MOS transistors with silicon gate could be 1.1 volt lower than the threshold voltage of MOS transistors with aluminum gate fabricated on the same starting material. Therefore, one could use starting material with [111] silicon orientation and simultaneously achieve both an adequate parasitic threshold voltage and low threshold voltage transistors without the use of a channel-stopper mask or ion implantation under the field oxide. With P-type doped silicon gate it would therefore be possible not only to create self-aligned gate transistors but also a low threshold voltage process by using the same silicon orientation of the high threshold voltage process.