Low-Energy Sputtering Yields by Resonance Absorption and Emission Spectroscopic Methods

Abstract

Low-energy sputtering yields for a (110)-oriented gold single crystal are determined by means of a resonance or atomic absorption technique wherein the sputtered atoms absorb the resonance radiation from an external gold, hollow cathode source. If the square root of the relative yield is plotted vs target voltage, a linear portion is found between 40 and 70 V. The extrapolation of the linear portion of the curves gives rise to an average intercept energy EE of 29 eV at low pressures. The discharge chamber is specially designed to permit consecutive measurements of the sputtering yields by the absorption and by a previously employed emission technique under identical chamber geometry and discharge conditions. In the direct comparison of results possible thereby, the average value of EE from the emission curves is 29.5 eV which is approximately equal to the above absorption value of 29 eV. The plasma potential for these experiments is found to be about 12 eV. Moreover, the curves themselves are proportional over the range of 40 to 100 V. These results strongly indicate that EE is an experimental invariant from which reliable threshold energies can be obtained. This coincidence of curves also indicates that the variation of excitation probability of the Au atoms with different ion and correspondingly different atom energies does not affect the emission yield curves. The sensitivity of the absorption method with the present hollow cathode is slightly poorer than that of the emission method. The observed increase in the slope of the absorption square root yield curve with increased discharge current is attributed to imperfect resonance which may be due to the difference in argon pressures and discharge currents within the gold, hollow cathode source and those within the sputtering single-crystal target chamber.