Previous Investigations of MOCVD Chemistry

Aleksandrov et al. were the first to suggest that the rate-limiting step occurs in the gas phase with the cleavage of a methyl group from TMT [56] Based on a mass-spectral analysis of the gas phase during deposition performed at reduced pressures (6000 Pa), they proposed the following mechanism  

On the surface, intermediates such as SnO, are assumed to be rapidly oxidized to Sn02. While the first step in this mechanism is reasonable, the remaining reactions do not represent true elementary processes (i.e., gas-phase reactions that occur in a single step). 

The initial step in the ZGG model, not shown in Fig. 3, is the pyrolysis of TMT, forming CH3 radicals. Since this reaction is highly endothermic 

The ZGG model also predicts that bromine-containing species and alkenes inhibit film growth, which agrees with experimental results [39]. The predicted product distribution agrees reasonably well with experiments, except for the specific concentrations of CO, CO2, and CH2O (Fig. 4). However, the predicted sum of the CO and CO2 concentrations does agree rather well with the experiments. This may be caused by the fact that tin oxide surfaces catalyse the oxidation of CO [58]. 

Adachi and Mizuhashi investigated the oxidation of dimethyltin dichloride (DMTC) in a cold wall reactor [30]. They reported that the order of reaction is about one half in both oxygen and DMTC, similar to what was found by Ghoshtagore for the oxidation of SnCU [32,33]. Like Ghoshtagore, they also proposed that the reaction was diffusion limited at higher temperatures and surface reaction-limited at lower temperatures. They found an activation energy of 34 kcal moC in the kinetically limited region. 

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