| In this work, particle nucleation and growth during thermal chemical vapor deposition (CVD) of SiO2 films and inductively-coupled plasma CVD of poly-Si films are investigated using particle beam mass spectrometer (PBMS) and transmission electron microscopy (TEM) measurements. To improve the ease of PBMS operation, a new electron gun with thoria-coated iridium filaments, which has longer lifetime (∼3 months) than the previous electron gun with zirconium filament (∼2 hours), was adopted. Also, a new design criterion for the deflector was established to ensure that the deflected particle beam would reach the Faraday detector. For thermal CVD of SiO2 films, particle size distributions were measured using the PBMS at pressures and temperatures ranging from 0.5 to 2.0 torr and 200 to 800°C, using an O2/SiH4 ratio of 20. We found that within this parameter space, there are three different particle formation regions (explosion, unsteady, and steady) and a particle free region. The measured particle size distributions in the steady region are bimodal with one mode around 7 nm in diameter and the other around 20 nm, which is in reasonable agreement with TEM measurements. These results are consistent with predictions of numerical model, which was developed by Song-Moon Suh to simulate particle nucleation and growth in this system. It is also found that there is a correlation between particle concentration and film surface morphology, dielectric constant, and current-voltage characteristics of the film. During inductively-coupled plasma CVD of poly-Si films, PBMS measurements at 200 mtorr confirmed that most of the particles are trapped inside the plasma because they are negatively charged. At 10 and 12 mtorr, TEM measurements were performed and the results show that particle sizes are highly uniform with relative standard deviations much less than 0.2. Furthermore, the surface morphology of particles changed from smooth to rough as particles grew. A similar evolution in the surface structures of thin films grown by CVD has been reported. These observations suggest that particle growth occurs by surface deposition of molecules (or ions). It was found that particle concentrations are approximately constant, which supports particle growth by surface deposition, not by coagulation. |
