Plasma- and gas-surface interactions during the chemical vapor deposition of tungsten from H2/WF6

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Abstract
Ion and neutral species were sampled from a H2/WF6 tungsten deposition atmosphere (with and without plasma enhancement) by a line‐of‐sight quadrupole mass spectrometer and cylindrical mirror ion energy analyzer. These diagnostics were used to investigate the influence of neutral and ion flux on the resistivity and morphology of α‐ and β‐tungsten films. In all depositions, WF, WF2, and WF6 were the principle tungsten‐fluorine species while WF+5 was the primary plasma‐generated ion. Variation of α‐tungsten film properties with thickness was dominated by impurities and defects incorporated early in the deposition and by domain size. Plasma‐enhanced chemical vapor‐deposited films exhibited lower resistivity, and higher temperature coefficient of resistivity and domain size compared to low‐pressure chemical vapor deposition films. The variation of α‐tungsten properties with increasing ion‐bombardment energies was consistent with enhanced sputtering and damage production. Low‐resistivity small‐domain films were deposited at low frequencies while low‐energy high‐current bombardment conditions were conducive to domain growth. Nucleation and growth of β tungsten required oxygen rather than fluorine impurities.