Study On The Time Evolution Of DC-pulsed Plasma

DC-pulsed plasma is widely used for surface treatment, such as ion nitriding, film deposition and surface modification. During the process of surface treatment, the parameters of the plasma influence the results of surface treating process. So it is helpful to understand the mechanism of how the plasma affects the results of process that investigating the time evolution of the parameters of plasma during a pulse period.A diagnostic system based on Langmuir probe theory which was used to investigate the pulsed-plasma has been developed. Consisting of a high-speed analog-to-digital converter which was use to sample the current of the probe, this system was able to measure the parameters of pulsed-plasma with the time resolution of 20 ns. The results of experiment indicated that this system is feasible to measure the parameters of the pulsed-plasma.The frequency of the pulsed power is 1 kHz and it's duty cycle is 15%. Air, ammonia and argon were used as discharge gas respectively. The pressure was fixed at 109Pa and each type of gas been discharged with the voltage of 600V, 700V and 800V respectively. The area of the probe is 16.5 mm2 and distance between two probes is 1.7 mm. The plane of the double probe is parallel to that of the cathode; the distance between them is 20mm. And the following are the phenomena those discovered from the experiments.1. When air or ammonia was used as discharge gas, about 2μs after the rising edge of the power pulse, the waveform electron density was narrow-pulse like, this pulse last for about 5μs and its mid-peak-value width was about 2μs. Some time after the'narrow-pulse'plasma, electron density decreased to a stationary regime and this state last until the power pulse was off, named it'steady'plasma. The electron temperature of the'narrow-pulse'plasma was found to oscillating with a period of about 1.3μs. When argon was used as discharge gas, there was only'steady'plasma found during one power pulse period.2. Under different conditions of the voltage of power pulse and discharge gas type, the delay time between the rising edge of the power pulse and the moment that'steady'plasma was detect varies from more than 10μs to 100μs. Under the same conditions of the voltage of power pulse and discharge gas type, with the increasing of the voltage of power pulse, the electron density was increasing but the electron temperature didn't vary apparently There were still some new phenomena can not be well explained. With the developing of diagnostic technique and the enhancing of the performance, this diagnostic system will be an effective instrument for diagnosing plasma which parameters vary rapidly.