Lee Hohyoung, Lee Jeongbeom, Park Gijung, Han Yunseok, Lee Youngwook, Cho Gunhee, Kim Hanam, Chang Hongyoung, Min Kyoungwook
Department of Physics, Natural Science Building, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea.
PLASMART, 188 Tekeuno2-ro, Yuseong-gu, Daejeon 305-500, South Korea.
Rev Sci Instrum. 2015 Aug;86(8):083505. doi: 10.1063/1.4928121.
A high-speed impedance measurement system was developed, which enables the measurement of various characteristics of CW and pulsed plasmas with time resolution of less than a microsecond. For this system, a voltage and current sensor is implemented in a printed circuit board to sense the radio frequency signals. A digital board, which has a high-speed analog to digital converter and a field-programmable gate-array, is used to calculate the impedance of the signal. The final output of impedance is measured and stored with a maximum speed of 3 Msps. This sensor system was tested in a pulsed-plasma by applying it to the point between the matching box and the plasma chamber. The experimental equipment was constructed connecting the matching box, a 13.56 MHz generator, a 2 MHz generator that produced pulsed power, and a pulse-signal generator. From the temporal behavior of the measured impedance, we were able to determine the time intervals of transient states, especially of the initial active state. This information can be used to set the pulse frequency and duty for plasma processing.
