| AVS 66th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Tuesday Sessions |
| Session PS-TuM |
| Session: | Plasma Diagnostics and Sources I |
| Presenter: | Chenhui Qu, University of Michigan |
| Authors: | C. Qu, University of Michigan J. Brandon, North Carolina State University C. Smith, North Carolina State University S.C. Shannon, North Carolina State University D. Coumou, MKS Instruments S. White, MKS Instruments M.J. Kushner, University of Michigan |
| Correspondent: | Click to Email |
During pulsed operation of inductively coupled plasmas (ICPs) using radio frequency (RF) power, the resistance of the plasma can change by factors of 10-100 while the reactance can change sign (from negative to positive during an E-H transition). These changes in impedance add to the intrinsic impedance of the reactor. The components in the impedance matching network (IMN) hat interface the reactor to the power supply typically cannot be changed rapidly enough to track the plasma transients and maintain a match. The IMN is then tuned to match at a specified time during the plasma pulse, a process called set-point-matching. With feedback control systems and wideband amplifiers, it is possible to make a real-time adjustment of the frequency of the RF oscillator to provide a real-time impedance matching.
In this work, impedance matching to a pulsed ICP plasma was computationally and experimentally investigated using set-point-matching and frequency tuning. The Hybrid Plasma Equipment Model (HPEM) was used for the computational investigation with results compared to experiments performed on the ICAROS reactor, consisting of a four-turn solenoidal coil powering a cylindrical ICP having a 5 cm radius and 15 cm height. The ICPs were operated in Ar at pressures of 1-50 mTorr. The RF power (frequencies from 10-14 MHz) was pulsed modulated at 10 kHz pulsed power with 50 W amplitude and 50% duty cycle.
Set-point-matching early during the pulsed cycle produces more rapid rise in the plasma density while having high reflective power late in the pulse. Set-point-matching late during the pulsed cycle produces a slow rise in the plasma density while having low reflective power late in the pulse. Frequency tuning is able to functionally match during the entire pulsed cycle. For example, when the IMN was set to match in the early period during the pulse, frequency tuning within a range of ±2 MHz is able to maintain reflected power to be less than 10%, and functionally zero late in the pulse. Combinations of set-point-matching and frequency tuning are able to match pulsed-operation over a wide range of power, pressure, pulse repetition frequency and duty cycle.
* Work supported by Samsung Electronics, National Science Foundation and the DOE Office of Fusion Energy Science.