An efficient wet-cleaning of SiGe virtual substrates and of thick, pure Ge layers on Si(0 0 1) after a chemical mechanical planarization step

Abstract

The aim of this study is to propose an efficient wet cleaning of the surfaces of the SiGe virtual substrates just after a chemical mechanical polishing step. We have first of all studied the chemical compatibility of miscellaneous solutions, such as the standard cleaning 1 (SC1), the Standard Cleaning 2 (SC2), the CARO one etc with SiGe. A definite, logarithmic-like increase of the etch rate with the Ge content has been obtained for the SC1, the SC2 and the CARO solutions (with values 1000–10,000 those of Si evidenced for pure Ge), making them unsuitable for Ge contents above 30%. We have thus investigated the efficiency of new cleaning sequences (named “DDC-SiGe” for SiGe and “HF/O 3” for pure Ge) that call upon diluted HF and ozone solutions spiked with HCl, on SiGe and pure Ge. The overall material consumption of those cleaning sequences, which increases from 10 Å for pure Si up to 130 Å for pure Ge, is quite low. The particle removal efficiency of such cleanings is around 99% for Si 0.8Ge 0.2 and Si 0.7Ge 0.3. It drops down to 83% for Si 0.5Ge 0.5 and to 65% for pure Ge. This is most probably due to pre-existing epitaxy defects which are revealed during the wet cleaning then wrongly assimilated to particles by our surface inspection tool. The metallic contaminants present on the surface after the use of our wet cleaning sequences have a surface density lower than 10 10 atoms cm −2, this whatever the Ge content of the underlying layer.