대면적 RF 플라즈마 내에서 더스트 파티클 제거 및 진단

Abstract

플라즈마 내에서 더스트 파티클(Dust Particles)은 플라즈마 발생 가스 종, Etching, Ashing, Deposition, Re-deposition등을 통하여 필수 불가결하게 발생된다. 이러한 더스트 파티클은 플라즈마의 전기적 특성에 의해 대전되며, 쉬스 포텐셜에 의해 공중에 뜬 상태로 플라즈마 내에서 부유하며 움직인다. 이러한 더스트 파티클은 전자의 부착(Electron attachment)에 의해 일반적으로 음 대전되며 배경 플라즈마의 전자 가뭄 상태(Electron depletion)를 발생, 플라즈마의 손실을 초래하므로, 플라즈마의 물성 변화 및 재료 표면의 오염을 일으킨다. 플라즈마 내에서 이러한 더스트 파티클의 제어 및 제거에 대한 연구를 수행하기 위해, 새로운 형태의 대면적 RF 플라즈마 장치 (DBD with ICP mode or CCP mode)를 개발하였다. 이 장치 내에 설치된 97 개의 바닥 전극에 3상 전기 커튼(5V with 0°, 120°, 240°)을 인가하는 물리적 방법을 이용하여 플라즈마 내의 더스트 파티클을 1 m 의 이동 거리를 제어∙ 제거하였다. 플라즈마 내에서 더스트 파티클의 양을 측정하기 위하여, 빛-전압 센서 시스템(Light-to-Voltage sensor)과 축전 막 진공 게이지(Capacitive Diaphragm Gauge: CDG)를 개조하여 플라즈마 내에서 더스트 파티클 측정 시스템을 개발하였다. 더스트의 분사 실험을 통하여 더스트 파티클이 배경 플라즈마에 미치는 영향을 직접적으로 조사하였으며, 전기 탐침을 이용하여 순수 헬륨 플라즈마와 더스트 헬륨 플라즈마의 물리적 특성(이온 밀도, 전자 밀도, 전자 온도, 플라즈마 포텐셜, 플로팅 포텐셜) 변화를 비교하였다. 이를 통하여 더스트 파티클의 대전 메카니즘과 배경 플라즈마에 미치는 영향을 플라즈마의 준-중성 특성과 쉬스와 더스트 표면의 전위차의 비율을 통하여 분석하였다. 1 이하 조건 시 더스트 파티클은 음 대전되며, 반면에 1 이상 조건 시 더스트 파티클은 양 대전된다.| Dust particles are mainly charged negatively in plasmas, and they change the plasma parameters by interacting with the background plasma, which directly leads to the change of heat and particles fluxes on the material surfaces of fusion and processing devices. A large rectangular RF plasma device has been developed for the study of dust transport and plasma diagnostics, whose dimensions are 1200 (L) x 500 (W) x 440 (H) mm3. Al2O3 dusts with size of 1~10 um are sprayed in helium plasma, where they are charged and levitated close to the bottom electrode consisting of 97 conductor bars. Dust particles are successfully transported to the place by one meter distance along the one-sided direction by sinusoidal electrostatic curtains (SEC) consisting of three different phase angles (5 V with 0°, 120°, 240°). Dust transport speed increases linearly up to 5 Hz of the SEC, and dust removal efficiency becomes largest at 1 Hz. For the real time observation of the accumulated dusts in vacuum vessel, a light-to-voltage sensor and a modified capacitive diaphragm gauge (CDG) have been developed. A light-to-voltage sensor can be measured the output voltages of the voltage sensor with the accumulated dusts, which show the exponential relation. Capacitances between the electrode membranes in the CDG are analyzed by considering the geometric deflection of the electrode, and the measurement values of modified CDG have been compared to the simulation values. Dusty plasma with spherical tungsten dusts (size 1.89 um) is measured by a planar electric probe with radius of 5 mm to compare those of pure helium plasma. Dust effects on the background plasma are observed by comparing the relevant parameters (ion density, electron density, electron temperature, plasma potential, floating potential, respectively) of dusty helium plasma to those of pure helium plasma. Depending upon the plasma pressure, energetic electrons determine not only the parameter of the background plasma, but also affect the charging mechanism of dusts. Charging dusts are to be explained in terms of quasi-neutrality and the potential difference of sheath and surface of dust, i.e., ratio of electron density to ion density, ratio of potential energy difference to electron energy. The dust particles are negatively charged for the conditions of <1, while the dust particles are positively charged for the conditions of >1.; Dust particles are mainly charged negatively in plasmas, and they change the plasma parameters by interacting with the background plasma, which directly leads to the change of heat and particles fluxes on the material surfaces of fusion and processing devices. A large rectangular RF plasma device has been developed for the study of dust transport and plasma diagnostics, whose dimensions are 1200 (L) x 500 (W) x 440 (H) mm3. Al2O3 dusts with size of 1~10 um are sprayed in helium plasma, where they are charged and levitated close to the bottom electrode consisting of 97 conductor bars. Dust particles are successfully transported to the place by one meter distance along the one-sided direction by sinusoidal electrostatic curtains (SEC) consisting of three different phase angles (5 V with 0°, 120°, 240°). Dust transport speed increases linearly up to 5 Hz of the SEC, and dust removal efficiency becomes largest at 1 Hz. For the real time observation of the accumulated dusts in vacuum vessel, a light-to-voltage sensor and a modified capacitive diaphragm gauge (CDG) have been developed. A light-to-voltage sensor can be measured the output voltages of the voltage sensor with the accumulated dusts, which show the exponential relation. Capacitances between the electrode membranes in the CDG are analyzed by considering the geometric deflection of the electrode, and the measurement values of modified CDG have been compared to the simulation values. Dusty plasma with spherical tungsten dusts (size 1.89 um) is measured by a planar electric probe with radius of 5 mm to compare those of pure helium plasma. Dust effects on the background plasma are observed by comparing the relevant parameters (ion density, electron density, electron temperature, plasma potential, floating potential, respectively) of dusty helium plasma to those of pure helium plasma. Depending upon the plasma pressure, energetic electrons determine not only the parameter of the background plasma, but also affect the charging mechanism of dusts. Charging dusts are to be explained in terms of quasi-neutrality and the potential difference of sheath and surface of dust, i.e., ratio of electron density to ion density, ratio of potential energy difference to electron energy. The dust particles are negatively charged for the conditions of <1, while the dust particles are positively charged for the conditions of >1.