Particle formation during low-pressure chemical vapor deposition from silane and oxygen: Measurement, modeling, and film properties

Particle generation in thermal chemical vapor deposition (CVD) processes can lead to the formation of contaminant particles that affect film properties and eventually device performance. This article reports on measurements of particle formation during low-pressure CVD of SiO2 from silane and oxygen. Measurements of aerosol size distributions were made using a particle beam mass spectrometer (PBMS) and were carried out at pressures and temperatures ranging from 0.5 to 2.0 Torr (67-267 Pa) and 200-800 deg. C, using an O2/SiH4 ratio of 20. We found that within this parameter space, there are three different particle formation regions and a particle-free region. The particle formation regions include an explosion region [200-300 deg. C, P(greater-or-similar sign)1.0 Torr (∼80 Pa)], an unsteady region [400-600 deg. C, P(greater-or-similar sign)0.8 Torr (∼107 Pa)], and a steady region [700-800 deg. C, P(greater-or-similar sign)0.6 Torr (∼67 Pa)]. PBMS size analysis in the steady region shows that the size distributions are bimodal with one mode around 7 nm in diameter and the other around 20 nm, which is in reasonable agreement with transmission electron microscopy measurements. A numerical model was developed to simulate particle nucleation and growth in this system. The model predicts that for a given temperature, there exists a critical pressure above which abundant particle formation occurs and below which particle production is insignificant. The pressures for which particle formation was measured with the PBMS are in good agreement with model predictions, and measured and calculated particle sizes are in reasonable agreement. 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