Roughening during XeF2 etching of Si(100) through interface layers: H:Si(100) and a-Si∕Si(100)

Abstract

Real-time spectroscopic ellipsometry has been applied in situ in an Ar + / XeF 2 beam-etching experiment to study the roughening of Si͑100͒ etched by XeF 2 at room temperature. The role of initial surface conditions has been examined. For the etching of hydrogen-terminated ͑H:͒Si͑100͒, the roughness evolution as a function of XeF 2 dose can be characterized by an initially fast roughening phase followed by a slower, final roughening phase. Similar behavior is observed when etching through an amorphous silicon ͑a-Si͒ layer on top of crystalline Si͑100͒ bulk as obtained by sputter cleaning of Si͑100͒ substrates. These observations can be explained as follows. Both H termination and a-Si lead to patch formation on the surface where etching is impeded and hence, high aspect-ratio etch pits develop. The quantitative differences in roughening can then be attributed to the duration and timing of the influence of the H-terminated and a-Si patches on the etch process until H-bonded Si surface atoms or a-Si are totally removed from the surface. Surface area increase due to the roughening can therefore be held responsible for observed trends and differences in etch rates, reaction layer thickness, and composition as a function of etch time.