Cross-sectional TEM Observations of Si Wafers Irradiated With Gas Cluster Ion Beams

Irradiation by a Gas Cluster Ion Beam (GCIB) is a promising technique for precise surface etching and planarization of Si wafers. However, it is very important to understand the crystalline structure of Si wafers after GCIB irradiation. In this study, the near surface structure of a Si (100) wafer was analyzed after GCIB irradiation, using a cross‐sectional transmission electron microscope (XTEM). Ar‐GCIB, that physically sputters Si atoms, and SF6‐GCIB, that chemically etches the Si surface, were both used. After GCIB irradiation, high temperature annealing was performed in a hydrogen atmosphere. From XTEM observations, the surface of a virgin Si wafer exhibited completely crystalline structures, but the existence of an amorphous Si and a transition layer was confirmed after GCIB irradiation. The thickness of amorphous layer was about 30 nm after Ar‐GCIB irradiation at 30 keV. However, a very thin (< 5 nm) layer was observed when 30 keV SF6‐GCIB was used. The thickness of the transition layer was the same both Ar and SF6‐GCIB irradiation. After annealing, the amorphous Si and transition layers had disappeared, and a complete crystalline structure with an atomically smooth surface was observed.