An experimental and modelling investigation on the application of a structured showerhead to improve the process uniformity in plasma enhanced chemical vapour deposition*

In this research, we demonstrate the application of a structured showerhead electrode in improving the film thickness uniformity across large-diameter substrate processing using plasma enhanced chemical vapor deposition (PECVD). The modelling and experimental investigations are conducted at an intermediate pressure regime of 1-2.5 Torr in the Oxford Instruments PlasmaPro-100 PECVD reactor. The fluid-kinetic simulations are carried out using the Hybrid Plasma Equipment Model (HPEM) accessed via the Quantemol Virtual Tool (Q-VT) interface. The simulation model indicates a substantial role played by the showerhead cavity ring in controlling the radial plasma distribution in the discharge gap. The modelling results are verified with the optical actinometry in Ar/O₂ plasma to capture the cavity ring effect on the radial profile of the measured atomic oxygen concentration. The simulation model is further extended to investigate the performance of the multi-cavity structured showerhead in the process relevant SiH₄ chemistry. It has been observed that the uniformity of SiH₃ radical flux across large-diameter substrates can be significantly improved with the use of multiple cavity rings in the showerhead electrode as compared to the conventional planar case. Finally, the observed improvement in the quality of the plasma assisted deposition resulting from the structured showerhead is reported for SiO₂ process and the results are characterised against the planar showerhead electrode.