Mechanisms for deposition and etching in fluorosilane plasma processing of silicon

Abstract

A variety of analytical tools have been used to examine the gas-phase and surface chemistry of SiF4 and SiF4/H2 plasmas interacting with Si substrates. The effect of rf power (P) and source gas ratios on film composition, gas-phase species densities, and plasma–surface interactions of SiF and SiF2 have been studied. Film characterization was performed using Fourier transfer infrared, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Using the imaging of radicals interacting with surfaces technique, spatially resolved laser-induced fluorescence images of SiFx radicals were collected and used to characterize both the plasma-surface interface and the gas phase. Additional gas-phase characterization was achieved using optical emission spectroscopy and mass spectrometry. From all of these data, three plasma types have been defined. In etching systems (type 1) (e.g., 100% SiF4 plasmas at P>20 W), no net deposition occurs, and SiF2 radicals are produced at the surface. When only F atom incorporation occurs with no net etching or deposition (type 2), SiF2 can exhibit either surface loss or surface production, depending on other plasma parameters. In a-Si:H,F film depositing systems (type 3), SiF2 is lost at the surface under most conditions. Gas phase and surface mechanisms to describe these three plasma types are proposed.