Analysis of surface damage induced in silicon substrates by reactive ion etching of silicon dioxide

We have investigated methods of removing dry-etching damage after RIE of SiO₂. Chemical dry etching by CF4/O₂ gas can remove the surface damage that remains after the reactive ion etching of SiO₂ and restore the crystalline structure of the topmost layers to the reference structure level. However, very rough surfaces (roughness exceeding 10 nm p-v) can result from the chemical dry etching. We found that this roughness occurs because the etch-rate of the Si substrate is higher than that of the surface damage layer. Science the thickness of the surface damage is uneven, isotropic etching of the Si occurs where the damage is thin and quickly removed; i. e., the residual damage acts as a micromask. We also found that the rough surface after chemical dry etching also formed at the bottom of contact holes with a diameter of 0.5 μm.