ULTRAVIOLET EXCITED CL-RADICAL ETCHING OF SI THROUGH NATIVE OXIDES

Si etching at over 200 degrees C by ultraviolet (UV) irradiation-generated Cl radicals was found to occur by diffusion through native oxides present on Si surfaces. The Si etch rate and surface morphologies formed by the Cl radicals depended on the various native oxides formed by different wet chemical treatments before etching. The ''etching through the native oxide film'' phenomenon was confirmed by scanning electron microscopy observation of caves on the etched Si surfaces when poly-Si deposition formed lids on the existing native oxide layer. The native oxide layer was supported by the thermally grown thick-oxide (SiO2) etching mask and did not collapse during Cl-radical etching.