The feature correlation matrix (Figure ) depicts the quality of linear correlations between each of the model's input and output (the denotion of each feature is provided in Table ). In the input feature group, three features have high Spearman's rank correlation with a coefficient above 0.85, i.e., the precursor flow rate, the spray cone angle and the sprayer nozzle diameter. Specifically, the correlation between the precursor flow rate and the other two input features is -0.89 and 0.91, respectively. The correlation between the spray cone angle and the sprayer nozzle diameter is -0.89.