It has been experimentally confirmed in many chemical vapor deposition (CVD) processes that charged nanoparticles tend to be generated in the gas phase. In an effort to confirm and measure charged gas phase nuclei, that might be generated during the deposition of Si thin films by hot wire CVD, we performed an in-situ measurement using particle beam mass spectrometer (PBMS), which can measure a size distribution of nanoparticles at low pressure. The size distribution of positively and negatively charged Si gas phase nuclei generated during hot wire CVD under 1.5 torr could be firstly measured. The particle diameter at the peak of the size distribution is about 10 ∼ 13 nm. At a wire temperature of 1800• C, the number concentration of negatively charged Si nanoparticles was higher than that of positively charged ones. The size and number concentration of charged nanoparticles decreased with increasing wire temperature from 1800 to 2000• C and increased with increasing SiH 4 concentration from 3 to 6%.
The effect of process pressure on the deposition behavior of crystalline Si films during hot-wire chemical vapor deposition was approached by nonclassical crystallization, wherein crystals grow not by individual atoms, but by nanoparticles. The size distribution of charged nanoparticles generated in the gas phase was measured using a particle beam mass spectrometer, and the nanoparticles were observed by transmission electron microscopy (TEM) after being captured from the gas phase on a TEM grid membrane. This found that, as the pressure is increased from 0.3 to 2 Torr, it is not only the size and the number of captured nanoparticles that are reduced but also the rate of deposition. An increase in the distance at which nanoparticles were captured from the hot wires under 1.5 Torr also reduced the size and number of particles; however, this tendency decreased markedly at 0.3 Torr. These results imply that the Si-H system should have a retrograde solubility, whose tendency increases with increasing pressure. The pressure dependence of the deposition behavior can be explained by nonclassical crystallization. On the basis of this understanding, the microcrystalline Si could be deposited on a glass substrate at 370 °C with an amorphous incubation layer of ∼10 nm.
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