Conventional Langmuir probe techniques usually face the difficulty of being used in processing plasmas where dielectric compounds form,due to rapid failure by surface insulation.A solution to the problem,the so-called...Conventional Langmuir probe techniques usually face the difficulty of being used in processing plasmas where dielectric compounds form,due to rapid failure by surface insulation.A solution to the problem,the so-called harmonic probe technique,had been proposed and shown effectiveness.In this study,the technique was investigated in detail by changing bias signal amplitudes V_0,and evaluated its accuracy by comparing with the conventional Langmuir probe.It was found that the measured electron temperature Teincreased with V_0,but showing a relatively stable region when V_0〉Te/e in which it was close to the true Tevalue.This is contrary to the general consideration that V_0should be smaller than Te/e for accurate measurement of Te.The phenomenon is interpreted by the non-negligible change of the ion current with V_0at low V_0values.On the other hand,the measured nialso increased with V_0due to the sheath expansion,and to improve the accuracy of niit needs to linearly extrapolate the ni-V_0trend to V_0=0.The results were applied to a diagnosis of the plasmas for chemical vapor deposition of diamond-like carbon thin films and the relationship between plasma parameters and films deposition rates was obtained.展开更多
文摘Conventional Langmuir probe techniques usually face the difficulty of being used in processing plasmas where dielectric compounds form,due to rapid failure by surface insulation.A solution to the problem,the so-called harmonic probe technique,had been proposed and shown effectiveness.In this study,the technique was investigated in detail by changing bias signal amplitudes V_0,and evaluated its accuracy by comparing with the conventional Langmuir probe.It was found that the measured electron temperature Teincreased with V_0,but showing a relatively stable region when V_0〉Te/e in which it was close to the true Tevalue.This is contrary to the general consideration that V_0should be smaller than Te/e for accurate measurement of Te.The phenomenon is interpreted by the non-negligible change of the ion current with V_0at low V_0values.On the other hand,the measured nialso increased with V_0due to the sheath expansion,and to improve the accuracy of niit needs to linearly extrapolate the ni-V_0trend to V_0=0.The results were applied to a diagnosis of the plasmas for chemical vapor deposition of diamond-like carbon thin films and the relationship between plasma parameters and films deposition rates was obtained.
