K. B. Chai

Role of hydrogen in evolution of plasma parameters and dust growth in capacitively coupled dusty plasmas

The temporal behavior of naturally produced dust parameters (radius and density) and plasma parameters (electron temperature and ion flux) was investigated in radio frequency SiH4/H2/Ar plasmas. As a result, the electron temperature and ion flux were shown to be strongly correlated with the three-step dust growth pattern. In addition, the generation of dust particles was suppressed by mixing more hydrogen gas due to the plasma chemistry, and consequently, the dust growth rate in the molecular accretion growth, which is known to be proportional to the growth rate of thin film deposition, increased.

Charge dependence of nano-particle growth in silane plasmas under UV irradiation

The controlled generation of nano-particles has been an important issue for the nano-structure formation in processing plasmas. We observed that the particle growth under UV irradiation was enhanced due to electric charge reduction of the particles, suggesting that the variation of particle charges could be a control parameter for the particle growth. The particle growth variation 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.

Electron temperature and pressure dependences of nonlinear phenomena in dust particle oscillation in dc plasmas

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 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 amplitude of the subharmonic resonance peak was large and the frequency shift of the primary resonance peak was observed to be more significant in the case of high electron temperature. The force profile near the particle trap position was calculated in order to understand the dependence of the oscillation spectra on the electron temperature and the electron density. The electron temperature dependence of the particle oscillation was well explained from the calculated force profile. In addition, it was experimentally shown that the amplitudes of both the subharmonic resonance and the primary resonance became large as the pressure was decreased, which was consistent with the calculation.

Electron Temperature and Density Variation Due To Temporal Evolution of Nano Particle Growth in RF Silane Plasma

Nano particles, generated in various processing plasmas, have been extensively studied for applications in the fabrication of microelectronics devices. However, studies to find the relation between the particle parameters (particle size and density) and the plasma parameters (electron temperature and density) have been limited because of the availability of the appropriate diagnostic method. The utilization of Langmuir probes are limited in many cases due to the probe tip contamination and the presence of abundant negative ions and particles. In this work, measurements of electron temperature and ion density were performed in rf silane plasmas using a floating probe, which allows an accurate measurement even under harsh plasma environments. The size and density of nano particles were measured by the laser light scattering and the laser extinction method at various gas pressures. It was found that the temporal evolution of the particle growth played a significant role in changing the plasma parameters due to the electron and ion fluxes to the particles. The relation between the plasma parameters and the particle parameters was described by a power balance equation including the power loss to the particle surface.

Plasma Parameter Dependence of Critical Particle Size at the Moment of Void Formation in RF Silane Plasmas

Although dust‐free voids are frequently observed in many dusty plasmas, experiments regarding the critical particle size for the void formation have not been reported much. In this work, the dust particle size measurement at the critical moment of the void formation was performed by the polarization‐sensitive laser light scattering method (PSLLS) as the input rf power was varied in the silane plasmas in which particles were created and grown. The electron temperature and ion density were also measured by a floating probe, and the relation between the parameters was studied. The results show that the critical particle size was decreased from 50 nm to 35 nm as the rf power was increased from 30 W to 100 W. In addition, the electron temperature and ion density were increased from 4.7 eV to 6.2 eV and from 7.0×109 cm−3 to 1.4×1010 cm−3, respectively. To investigate the mechanism of the void formation, we calculated the critical particle size for the void with measured plasma parameters using a simple one‐dime...

Multi Optical Passes Method for Measuring 2-D Particle Size Distribution in Plasmas

The laser light scattering (LLS) is a powerful method for size measurement of dust particles in plasmas. Several two dimensional measurement tools have recently been developed, but measurement of particle size < 100 nm was limited because of the weak incident beam intensity attributed from implementing a sheet beam as the incident laser beam. In this work, multi optical passes were adopted using two spherical mirrors, which enabled detection of small particles as small as about 50 nm. Vertical multi passes could be obtained by tilting the two mirrors, and the 2-D detection was realized using a CCD camera as a detector. The 2-D particle size distribution was obtained in various operating conditions in low pressure capacitively-coupled silane plasmas. Experiments showed that particles near the sheath boundary had almost constant size, while particles above the sheath grew in size and diffused repetitively. The geometrical center of the particle trap was found through a 2-D contour plot.

Effects of UV Irradiation on the Particle Growth in Low Pressure Silane Plasmas

Summary form only given. The effects of UV irradiation on the particle growth were studied in low pressure capacitively-coupled silane plasmas. The growing speed of the particles increased when UV was irradiated on the plasmas. The particle growth was monitored two dimensionally by the laser light scattering method. The particles grew about 100 nm in diameter and dragged out toward the chamber wall by the ion drag force. The growth and disappearance process of the particles were faster in the discharge with the UV irradiation than that without the UV irradiation. The experiments were performed with various discharge conditions; the operating RF power range of 50 -100 W and the pressure range of 30 -100 m-Torr. For example, at 80 mTorr and 70 W, the particles grew up to approximately 70 nm in time about 3 seconds faster with the UV irradiation than the case without the UV irradiation. This result is attributed to the particle coagulation mechanism. The particle growth speed increases when the positive ion density increases in the silane plasmas. The photoemission from the initially-formed several nm size particles is responsible for particles having positive charges, which results in the increase of the particle growth speed. These results were also confirmed by the SEM photographs.