Shallow trench isolation top corner rounding using Si soft etching following diluted hydrofluorine solution

Shallow Trench Isolation (STI) technology is important for realizing high-speed and high-packing-density complementary metal oxide semiconductor very large scale integrated (CMOS-VLSI) technologies. To obtain top corner rounding in STI, a new process was evaluated. This technique utilizes Si soft etching by O-2+CF4 plasma following pad oxide shift in dilute hydrofluorine (HF) solution after STI formation, which effectively suppresses subthreshold slope (hump) for n- and p-channel devices even when 4 V of substrate bias is applied. This technique also does not cause top corner rounding (TCR) imbalance between narrow and wide spaces caused by the conventional sidewall generation technique in pad nitride etching. This new STI formation method markedly improves STI top corner rounding. As a result, it has been found that this technique is very effective for sub-0.18 mum STI formation.