GAS-PHASE SELECTIVE ETCHING OF NATIVE OXIDE

A dry cleaning technology for ULSI process with regard to native oxide film on a silicon surface using gas-phase anhydrous hydrogen fluoride (AHF) has been developed at room temperature and at normal pressure. A fluorine passivated system for a corrosion-free condition and a continuous monitoring system for reaction mechanism are employed, where a strictly moistureless hydrogen fluoride (HF) gas is used, which is evolved by the generation method with low-temperature equilibrium. Gas-phase reaction of AHF gas with various kinds of silicon oxide films is investigated in detail. Gas-phase selective etching of native oxide film from other oxide films is achieved under the exact control of the concentration of HF and moisture. After etching of native oxide by HF gas, fluorine remains on the bare silicon surface in a chemically combined state, i.e., a fluorine terminated silicon surface. This fluorine terminated silicon surface gives a negative influence on succeeding processes. Then chemically combined fluorine must be removed from the bare silicon surface before each succeeding process. Elimination of chemically combined fluorine was examined using various treatments and has been achieved with Xe lamp irradiation. The reaction mechanism of HF and silicon oxides is discussed in detail. © 1990 IEEE