Practical silicon deposition rules derived from silane monitoring during plasma-enhanced chemical vapor deposition
We clarify the difference between the SiH4 consumption efficiency eta and the SiH4 depletion fraction D, as measured in the pumping line and the actual reactor of an industrial plasma-enhanced chemical vapor deposition system. In the absence of significant polysilane and powder formation, eta is proportional to the film growth rate. Above a certain powder formation threshold, any additional amount of SiH4 consumed translates into increased powder formation rather than into a faster growing Si film. In order to discuss a zero-dimensional analytical model and a two-dimensional numerical model, we measure eta as a function of the radio frequency (RF) power density coupled into the plasma, the total gas flow rate, the input SiH4 concentration, and the reactor pressure. The adjunction of a small trimethylboron flow rate increases eta and reduces the formation of powder, while the adjunction of a small disilane flow rate decreases eta and favors the formation of powder. Unlike eta, D is a location-dependent quantity. It is related to the SiH4 concentration in the plasma c(p), and to the phase of the growing Si film, whether the substrate is glass or a c-Si wafer. In order to investigate transient effects due to the RF matching, the precoating of reactor walls, or the introduction of a purifier in the gas line, we measure the gas residence time and acquire time-resolved SiH4 density measurements throughout the ignition and the termination of a plasma. (c) 2015 AIP Publishing LLC.