Effects of surface preparation on the electrical and reliability properties of ultrathin thermal oxide

A new wafer cleaning procedure has been developed for ultrathin thermal oxidation process (/spl les/50 /spl Aring/). It consists of a conventional RCA clean and a two-dip step, first in diluted HF and then in a methanol/HF solution, with no final DI water rinse. The effectiveness of this cleaning process has been compared to other commonly used cleaning methods, based on the dielectric integrity of the ultrathin thermal oxide grown. It has been found that this two-dip method produces oxides with reduced leakage current and stress-induced leakage current, which are believed to be the critical parameters for ultrathin oxide. Furthermore, this new procedure increases dielectric breakdown field, E/sub bd/ and charge-to-breakdown, Q/sub bd/ (both intrinsic and defect-related values) of ultrathin oxides. The improvement is believed to be due to enhanced silicon surface passivation by hydrogen and the reduced surface micro-roughness.<>