Low-energy ion-scattering spectroscopic analysis of structural damage in Si substrate under ultrathin SiO2 after gate etching

The relationship between wafer-bias power during over-etching and structura l damage induced in Si(100) substrate under ultrathin SiO2 layers by gate e tching was examined by low-energy ion-scattering spectroscopy (LEIS) and hi gh-resolution X-ray photoelectron spectroscopy. The crystal structure of th e topmost surface of the Si substrate was modified when the residual SiO2 l ayer was 2.5 nm thick at a wafer-bias RF power of 70 W during over-etching. This structural damage was shown to be due to ions coming from plasma irra diation because the residual SiO2 thickness was close to the projected ion range at an ion energy of 310 eV (which was estimated from the Vpp of the b ias voltage when the RF power was 70 W).