Improvement of the Harmonic Technique of Probe for Measurements of Electron Temperature and Ion Density

摘要

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 Vo,and evaluated its accuracy by comparing with the conventional Langmuir probe.It was found that the measured electron temperature Te increased with Vo,but showing a relatively stable region when Vo ＞ Te/e in which it was close to the true Te value.This is contrary to the general consideration that Vo should be smaller than Te/e for accurate measurement of Te.The phenomenon is interpreted by the non-negligible change of the ion current with Vo at low Vo values.On the other hand,the measured ni also increased with Vo due to the sheath expansion,and to improve the accuracy of ni it needs to linearly extrapolate the ni-Yo trend to Vo=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.