Studies on effect of remote plasma on an in-tandem main inductively coupled discharge

Abstract

In this thesis, the effect of remote plasma on an in-tandem main inductively coupled plasma (ICP) was studied. To diagnose remote and main plasma source, the floating harmonic method (FHM) was also investigated. The FHM is facing a challenge, because the RF fluctuation distorts the current-voltage (I-V) curve and probe bias voltage oscillates the sheath. Firstly, the RF fluctuation leads to measurement error. When diagnosing RF plasma with FHM, measurement results were different depending on presence or absence of RF compensation. It was found that the FHM measured at the floating potential was influenced by the RF voltage, and that the plasma measurement error was caused by the distortion of the second harmonic component. On the other hand, the first harmonic current was not significantly affected by RF fluctuation. To prevent measurement errors, a method of obtaining the electron temperature by using only the first harmonic components without using the second harmonic components was proposed. Secondly, the oscillating sheath also leads to measurement error. In the case of FHM, the AC voltage was applied to the sheath, the sheath oscillated and time-varying ion collection area was created. The existence of ion harmonic current due to the oscillating sheath area was founded by analytically and experimentally. The result of the experimental showed that there is a large error in the measurement when using cylindrical type probe because the ion collection area is larger than the one of electron. Therefore, the ion harmonic current should be considered when diagnosing with the cylindrical probe. To overcome disadvantages of conventional plasma source, a tandem plasma source was proposed. It is composed of a main ICP and a remote ICP. When the power of the main ICP was fixed while varying the power of the remote ICP, the electron temperature and density of the main ICP did not change significantly. On the other hand, with of the electron energy possibility function (EEPF) measurements, the population of low energy electrons decreased while the one of high energy electrons increased. This results indicate that, the EEPF of the main ICP region could be controlled by varying the power of the remote ICP. The same results were obtained in the electronegative plasma. As the population of high energy electrons increased, the number of electrons capable of dissociating the gas increased as well. Therefore, with the tandem source, more fluorine radicals were observed and etch rate of SiO2 film was increased when using CF4 gas without varying electron temperatures and densities.|본 논문에서는 유도 결합 플라즈마에 직렬 연결된 원격 플라즈마가 미치는 영향에 관해 연구하였다. 또한 원격 플라즈마와 주 플라즈마를 진단하기 위하여 부유 고조파 방법(Floating harmonic method, FHM)을 연구하였다. FHM 진단방법으로 라디오 주파수(radio frequency, RF) 플라즈마를 진단 할 때에 RF 전압이 전류-전압 응답 곡선을 왜곡하며 프로브에 인가 전압이 쉬스를 진동하게 하기 때문에 정확한 플라즈마 변수 측정에 어려움을 겪는다. 첫 번째로, RF 전압에 의한 측정 오차에 관하여 연구하였다. FHM을 이용하여 RF 플라즈마를 진단 할 때, RF 보상의 여부에 따라 측정 결과가 다르다. RF 전압이 부유 전위에 영향을 미치고, 2차 고조파 성분에 왜곡을 야기하기 때문에 진단결과에 오차가 발생하게 된다. 반면 1차 고조파 전류는 RF 전압에 큰 영향을 받지 않음을 알 수 있었다. 측정 오차를 줄이기 위하여 1차 고조파 성분만을 사용하여 전자온도를 측정하는 방법을 제시하였다. 두 번째로, 쉬스 진동 역시 측정에 영향을 준다. FHM는 교류 전압을 쉬스에 인가하는 방식이기 때문에 쉬스가 진동하게 되고 따라서 이온 수집 영역이 시간에 따라 변한다. 이론과 실험을 통하여 쉬스 진동에 의한 이온 고조파 전류의 존재를 찾을 수 있었다. 실험 결과, 원통형 프로브 탐침을 이용하였을 때 진단 결과에 큰 오차가 있었는데, 이것은 이온 수집 영역이 전자 수집 영역보다 매우 크기 때문이다. 따라서 FHM와 원통형 프로브 탐침을 사용할 때에는 이온 고조파 전류를 반드시 고려해야한다. 기존 플라즈마 소스들의 단점을 극복하기 위하여 직렬 연결된 플라즈마 소스를 고안하였다. 이것은 주 ICP와 원격 ICP로 구성 되어있다. 주 ICP의 전력을 고정하고 원격 ICP의 전력을 가변 할 때, 전자온도와 이온밀도의 큰 변화가 나타나지 않았다. 반면 전자 에너지 확률 분포(electron energy possibility function, EEPF)를 측정 결과 낮은 에너지 전자의 개수는 감소하고 높은 에너지 전자의 개수는 증가하였다. 즉, 직렬 플라즈마 소스를 사용하여 주 ICP 영역의 EEPF를 원격 ICP의 전력 가변을 통하여 제어할 수 있음을 알 수 있었다. 전기적으로 음성인 플라즈마에서도 같은 결과를 얻을 수 있었다. 높은 에너지 전자 개수가 증가하면서 기체를 해리할 수 있는 전자의 개수가 증가한다. 직렬 플라즈마 소스를 사용한 CF4 기체 방전 결과 더욱 많은 양의 불소 라디칼을 확인 할 수 있었으며 SiO2 식각률이 증가함을 알 수 있었다.; In this thesis, the effect of remote plasma on an in-tandem main inductively coupled plasma (ICP) was studied. To diagnose remote and main plasma source, the floating harmonic method (FHM) was also investigated. The FHM is facing a challenge, because the RF fluctuation distorts the current-voltage (I-V) curve and probe bias voltage oscillates the sheath. Firstly, the RF fluctuation leads to measurement error. When diagnosing RF plasma with FHM, measurement results were different depending on presence or absence of RF compensation. It was found that the FHM measured at the floating potential was influenced by the RF voltage, and that the plasma measurement error was caused by the distortion of the second harmonic component. On the other hand, the first harmonic current was not significantly affected by RF fluctuation. To prevent measurement errors, a method of obtaining the electron temperature by using only the first harmonic components without using the second harmonic components was proposed. Secondly, the oscillating sheath also leads to measurement error. In the case of FHM, the AC voltage was applied to the sheath, the sheath oscillated and time-varying ion collection area was created. The existence of ion harmonic current due to the oscillating sheath area was founded by analytically and experimentally. The result of the experimental showed that there is a large error in the measurement when using cylindrical type probe because the ion collection area is larger than the one of electron. Therefore, the ion harmonic current should be considered when diagnosing with the cylindrical probe. To overcome disadvantages of conventional plasma source, a tandem plasma source was proposed. It is composed of a main ICP and a remote ICP. When the power of the main ICP was fixed while varying the power of the remote ICP, the electron temperature and density of the main ICP did not change significantly. On the other hand, with of the electron energy possibility function (EEPF) measurements, the population of low energy electrons decreased while the one of high energy electrons increased. This results indicate that, the EEPF of the main ICP region could be controlled by varying the power of the remote ICP. The same results were obtained in the electronegative plasma. As the population of high energy electrons increased, the number of electrons capable of dissociating the gas increased as well. Therefore, with the tandem source, more fluorine radicals were observed and etch rate of SiO2 film was increased when using CF4 gas without varying electron temperatures and densities.