Room-Temperature Si Etching in NO/F2 Gases and the Investigation of Surface Reaction Mechanisms

Abstract

We have been investigating a plasmaless Si chemical dry etching in NO/F2 gas mixtures using the F produced by the exothermic reaction of F2 + NO → FNO + F at room temperature. The effect of the change in the flow rate ratio of NO and F2, fNO/fF2, on the etch rate, the chemical bonding structures, and the surface morphology was measured by laser microscopy, Fourier transform infrared spectrometer, scanning electron microscopy, and scanning white light interferometry and results were compared with the calculated F flux. Total energy variations and their changes in chemical bonding structures before and after the reactions of molecules in the gas phase and the Si surface were considered using the molecular orbital (MO) method. On the basis of the MO calculation using a Si(100)-2×1 cluster model, F was necessary to form a dangling bond at the surface of Si that would trigger subsequent chemical reactions of Si with F2, NO, F, or FNO. The etch rate and surface roughness increased with the addition of NO up to the fNO/fF2 = 1.0 to 1.5 and then decreased due to the reduction of F flux in the gas phase together with the presence of the Si-NO and the Si-FNO bonds that would block the interaction of Si with F2 and F.