1 µm 256K RAM process technology using molybdenum-polysilicon gate

The process technology of 1µm 256K RAM is discussed with emphasis on improvement in device characteristics degradations caused by use of reactive ion etching, electron-beam direct writing, thinner gate oxide and molybdenum films. Heavy metal contamination, caused by reactive ion etching was prevented by two step etching of Si
3
N
4
/SiO
2
for selective oxidation mask formation. Si
3
N
4
mask, which is frequently cracked at its sharp pattern corners during the field oxidation, was removed in hot phosphoric acid after the oxidation. The gate oxide pinhole density was reduced by perfoming a sacrifice oxidation prior to the gate oxidation. Yield of molybdenum interconnection was improved by using parallel plate plasma etching in CCl
4
+O
2
.