Study Of Harmonic Probe For Plasma Diagnosis In Insulative Films Deposition

Low-temperature plasmas have been attractively applied in thin film deposition process. Generally, the deposition products correlate closely to plasmas state, moreover, the key to monitor plasma state is to diagnose plasma. Langmuir probe with simple structure and easy to operate, is commonly used to diagnose electron temperature Te and plasma densities (electron density ne and ion density ni) which represent plasma state. However, the Langmuir probe will fail to work for its surface insulative by film deposition.To solve the contamination problem of the probe, there have been researchers proposed a harmonic probe technique, which applying AC signal on the probe, using the nonlinear characteristic of the probe sheath, to detect harmonics of the probe current and then compute plasma density and electron temperature. Nevertheless, recent literatures have not systematically investigated the selection of the bias signal amplitude Vo and frequency f of the harmonic probe. In this study, we carried out investigation aimed at exploring the influence of Vo and f of the technique on diagnostic results. While the resultant electron temperature Te and ion density ni changed little with f within the range that form 1 kHz to 10 kHz, both of them showed considerable increase with Vo. The phenomena may be interpreted, for Te mainly by the non-negligible change of the ion current with Vo at low amplitudes, and for ni by the sheath expansion mechanism. By comparing with the result of a conventional Langmuir probe, it was found that consistency of them may be achieved by setting V0?2Te/e(or reading from the relatively stable region) for Te, and by extrapolating the linear part of the ni-Vo relation to V0=0 for niBased on the observation, an improved method of using the harmonic probe was proposed and tested in the plasmas circumstance for insulative films deposition. The films deposition included microwave electron cyclotron resonance plasma enhanced chemical vapor deposition (MW-ECR PECVD) of diamond-like carbon (DLC) films and MW-ECR plasma assisted radio frequency (RF) magnetron sputtering deposition of SiNx films. The correlation between the DLC film deposition rate and plasma parameter was also obtained.Finally, we redesigned the harmonic probe diagnosing system instrumentally, and modified the software program based on the previous one. The results from the improved method of harmonic technique can display real-timely on the new diagnosis system when diagnosing. Also, the new system was tested in ECR plasma of pure Ar discharge.