REDUCED PRESSURE ETCHING OF THERMAL OXIDES IN ANHYDROUS HF ALCOHOLIC GAS-MIXTURES/

Reduced pressure etching of thermal oxide in anhydrous HF gas with thr ee different alcoholic solvent vapors is studied. Thermal oxide etch r ates as functions of temperature, pressure, time, and HF partial press ure are presented for methanol, ethanol-water azeotrope (95.6% ethanol , 4.4% water), and 2-propanol (isopropyl alcohol). The etch rates are interpreted in terms of alcohol vapor pressure, KF ionization, and rea ction product desorption. The efficient desorption of reaction product s compared to vapor HF/H2O is believed to be responsible for both the wider process window for alcoholic solvents and the alleviation of the solid residue formation problem. Among the alcoholic solvents studied , methanol has the best potential while 2-propanol can also be useful in selected applications.