The removal of the particles out of the plasma processing ambient has become more important as the feature size of the integrated circuit rapidly decreases. In other aspects, the inclusion of nano crystalline silicon particles in the amorphous hydrogenated silicon (a-Si:H) films results in the photovoltaic cell with better electronic properties and enhanced stability against light-induced defect creation. For the applications of nano-particles, in-situ monitoring and control of the particles are essential. In this thesis work, the diagnostics of particles was improved, and the particle dynamics was analyzed. In addition, the control of particle growth by UV irradiation was also studied.
At first, the dynamics of macroscopic particles was investigated, and the relation between the particle dynamics and the plasma parameters were studied. Firstly, the 2-D distribution of macroscopic particles was analyzed, and the various forces on a particle was discussed. Secondly, the oscillatory motion of the trapped 3.09 $\mu$ m particles was investigated. Experiments and calculations were performed to study the dependence of the nonlinear dust oscillatory motion on electron temperature and gas pressure in direct current plasmas. The frequency spectra of the dust particle oscillations induced by an excitation wire (1-100 Hz, 1-10 V AC voltage) were measured in different discharge conditions. At higher electron temperature in accordance with the higher cathode voltage, the nonlinear phenomena of the oscillation spectra became more prominent. The electron temperature dependence of the particle oscillation was well explained from the calculated force profile.
From understanding of the dynamics of macroscopic particles, the study on the nano-particles was performed. To achieve this aim, at first, the diagnostics of nano-particles was implemented. The polarization sensitive laser light scattering (PSLLS) method was used for the measurement of particle sizes. For two-dimensional measurement, the multi-pass of laser beam was implemented. Conventional laser light scattering methods used for 2-D particle size measurement in plasmas have detection limit under 50 nm (radius) due to the weak incident beam intensity attributed from the sheet beam. In this letter, however, small particle of about 15 nm (radius) was successfully measured in two-dimension with a low power He-Ne laser (30 mW), two spherical mirrors providing vertical multi-pass, and charge coupled device as a detector.
Measurement of the time evolution of the particle number density was also investigated in rf silane plasmas by using the multi-pass laser extinction method. A He-Ne laser beam underwent multiple reflections on one horizontal plane of the plasma. The extinction signal increased in proportion to the beam pass numbers. A $10^{11}cm^{-3}$ density of 8 nm radius particles was measured at 10 s in a 32 mTorr 50 W discharge using 9 passes.
Using the size measurement of growing particles in silane plasmas, the particle growth and the transport was studied. The particle movement was also observed from LLS measurement. The particles (about 100 nm diameter) were dragged toward chamber wall, due to the ion drag force. The particle movement was well described by ambipolar diffusion model.
From understanding particle dynamincs, the control of particle growth and electric charge was investigated. Using the focused UV light, the photo-emission from particles was induced, and the variation of electric charge and the particle growth was observed. In silane plasmas, we observed that the particle growth under UV irradiation was significantly enhanced due to electric charge reduction of the particles, suggesting that UV irradiation could be an excellent control parameter for the particle growth. The particle growth enhancement by UV irradiation is well described by the particle coagulation model with time-dependent particle charges in consideration, where predator particles grow by adsorbing a few nanometer-sized proto-particles.
본 논문에서는 플라즈마 내 티끌입자의 거동이해를 바탕으로, 실제 반응성 플라즈마 내 나노입자의 성장과 거동제어를 위한 연구를 수행하였다. 본 논문에서 구현한 나노입자의 진단법은 기존의 진단법에 비해 그 측정한게와 공간적인 측정범위가 개선된 것이었다. 이를 바탕으로 성장하는 나노입자에 자외선을 조사하여 입자 전하량 및 성장 속도가 제어될 수 있음을 보였다. 또한 나노입자들의 거동은 다양한 플라즈마 변수와 매우 밀접한 상관관계에 있음을 알 수 있었다.
먼저 직류(DC) 플라즈마 내 외부에서 크기를 알고 있는 티끌입자(직경 3.09μm)를 삽입하고, 입자의 진동운동이 플라즈마 내 전자온도, 전자밀도 등과 어떠한 상관관계가 있는 지를 조사하였다. 높은 방전전압의 경우 전자온도가 높았으며, 이 때 진동 스펙트럼의 비선형성이 매우 잘 나타났다.
수 μm입자에 대한 연구결과를 바탕으로 사일레인 플라즈마 내 발생돈 나노입자의 성장과 거동에 대한 연구를 수행하였다. 입자들의 성장은 고속 성장단계와 성장 둔화단계의 두 단계를 보였으며, 입자들이 정지해 있는 것이 아니라, 입자들의 위치가 시간에 따라 바뀌는 것을 확인할 수 있었다. 또한 이온끌이힘에 의해 입자들은 챔버벽으로 빠져 나가는 것을 관찰할 수 있었다. 이를 이론적으로 설명하기 위해 쌍극확산(ambipolar diffusion)모델을 적용하여 입자가 빠져나가는 부유 속도(drift velocity)를 계산할 수 있었고, 실험결과와 일치하는 것을 확인할 수 있었다.
마지막으로 사일레인 플라즈마 내 성장 입자에 자외선 조사 실험을 수행하였다. 렌즈를 이용하여 포커싱된 자외선 빛을 입자에 조사하여 입자의 광전효과를 유도하였으며, 이로 인한 입자의 전하량 변화와 성장 속도 증가를 확인할 수 있었다. 이를 통해 자외선 조사가 입자 성장 제어에 있어서 좋은 수단이 될 수 있음을 알 수 있었다. 자외선 조사에 의한 입자 성장속도 증가는 Lemons의 입자 엉김 현상 모델에 의해 잘 기술할 수 있었다. 엉김 현상 모델은 작은 초기 입자가 성장하는 입자에 붙으면서 입자가 성장하는 모델로, 본 논문에서는 엉김현상모델에 입자 전하량을 고려하여 수정된 엉김 현상 모델을 사용하였다.
