Gate oxide thickness in 1µm CMOS is 20 nm. On S/D areas, it is thinned during gate polyplasma etching, but re-grown during poly oxidation. Calculate the oxide thickness under the following assumptions:
• poly etch rate is 250 nm/min;
• poly thickness is 250 nm;
• Si:SiO2 etch selectivity is 20:1;
• overetch time is 20 s;
• re-oxidation is 900 ?C, 10 min (dry).