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 structural damage induced in Si(100) substrate under ultrathin SiO₂ layers by gate etching was examined by low-energy ion-scattering spectroscopy (LEIS) and high-resolution X-ray photoelectron spectroscopy. The crystal structure of the topmost surface of the Si substrate was modified when the residual SiO₂ layer 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 irradiation 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 bias voltage when the RF power was 70 W).