Discharge turn on and turn off

Summary form only given, as follows. RF discharges of various sorts are being used and investigated extensively for semiconductor processing. In addition, the use of an amplitude modulated or pulsed RF excitation has been the subject of considerable investigation and debate. One of the advantages in using pulsed excitation is that the discharge characteristics can be altered by changing the pulse width and duty cycle. For example, the discharge characteristics at turn off will be emphasized by using a very small duty cycle. A very large duty cycle, on the other hand, emphasizes the characteristics of the glow at steady state. Effecting a change in the discharge conditions is one thing; but, determining whether or not the differences between plasma turn on, steady state, and turn off are significant for processing is another question. This question is only partly answered today because of limited measurements and modeling of pulsed discharges compared to their continuous counterparts. Since the steady state conditions are generally understood, I will present an overview of discharge turn on and turn off for capacitively coupled discharges in a variety of gases. Time resolved power and plasma measurements taken at UTD indicate how the sheaths form, the electron density rises and the electron collision frequency changes during turn on as well as the amount of time required to reach the approximate steady state condition. Time resolved measurements and models also indicate how the sheaths disintegrate, the electron density decreases and the charges move at plasma turn off.