Particle Production in High Density Silane Plasma
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Particle Production in High Density Silane Plasma Z. Shen1 , T. Kim2 , U. Kortshagen2 , P. H. McMurry2 , and S. A. Campbell1 1 Dept of Electrical and Computer Engineering, 2 Dept of Mechanical Engineering University of Minnesota, Minneapolis, MN 55455 Abstract: To understand the mechanisms of nanoparticle formation and its potential applications, we have investigated silicon particles formed in various gasses in an inductive coupled plasma (ICP) system and have measured their structural properties by electron microscopy. Particle generation in pure SiH 4 and SiH 4 /H2 are reported. ICP silane plasmas are shown to be an interesting and versatile source of nanoparticles. Three regimes are mapped out: a regime of no observable particle growth at the lowest pressures, a regime of polydisperse and agglomerated particles at the highest pressures, and a regime yielding highly monodisperse particles at intermediate pressures. Conditions that generate these nonagglomerated, extremely monodisperse silicon particles are emphasized. For H2 dilutions less than 92%, the growth rate is almost independent of H2 partial pressure. Particle growth decreases steadily when the H2 dilution is increased further. TEM images, however, indicate that the addition of hydrogen decreases the particle density. At higher dilution ratios, polycrystalline particles are obtained. Under all other conditions the particles are amorphous. Reasons for this behavior are explored. I. Introduction: Low pressure, high density plasma (HDP) discharges are currently used for etching and depositing thin films used in the manufacture of integrated circuits. To obtain reasonable device yields, particle contamination is a serious concern. The controlled formation of nanoparticles could also open up new applications. Thus, studying particle formation in plasma processing is important, both for applications in which particle growth should be avoided, and for applications requiring the controlled deposition of nanoparticles. In contrast to capacitively coupled plasmas (CCP), HDP systems can maintain a high process rate using high ion fluence at low ion energy. Thus HDP systems are now being used extensively in the semiconductor industry. Although there has been a tremendous amount of work on particle formation in the CCP systems 1 , the studies on particle formation in HDP tools such as electron cyclotron resonance (ECR), helicon and inductively coupled plasma reactors are limited. Here we report gas phase processes for the synthesis of nanometer-sized silicon particles in an ICP system and studies of the particles’ structural properties by electron microscopy. Particle production in pure SiH 4 and SiH 4 /H2 are reported. Conditions that generate highly monodisperse silicon particles are emphasized. II. Experimental Setup The plasma is generated in a modified GEC Reference Cell reactor 2 . The top plate of the chamber is a fused silica disk which forms a vacuum- tight dielectric window. The RF field is generated by means of a 4 turn, flat spiral coil made of ¼
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