Characterization of oxide etching and wafer cleaning using vapor phase anhydrous hydrofluoric acid and ozone

A cleaning process using anhydrous hydrofluoric acid/methanol (AHF) and ozone was carried out in a vapor phase cleaning module (VPC). The dependence of the AHF vapor phase etch rate of thermally grown silicon dioxide on different process parameters, such as etch time, AHF-flow and temperature was studied. The optimized etch process is attained at a temperature of 40 degrees C and a pressure of 50 mbar. To demonstrate the feasibility of this cluster tool for advanced gate dielectric formation, investigations on surface properties after AHF vapor cleaning, such as contact angle measurement and atomic force microscopy (AFM) were carried out. Using XPS, the surface binding states of HF-vapor treated silicon surfaces were studied. Traces of fluorine and low oxygen coverage were monitored. An ozone treatment immediately after AHF cleaning increases significantly the fluorine concentration on the silicon surface. A beneficial impact of AHF and ozone on the electrical characteristics of 4 nm oxide films grown in oxygen by RTP in a cluster tool immediately after cleaning without breaking the vacuum was found