Comparison of plasma properties in normal and multiple holes hollow cathode RF PECVD and their utility in a-SiNx:H thin film deposition

Conventional and multiple-hole hollow cathode (MHHC) showerhead electrodes of an RF capacitively coupled plasma (CCP) source were experimentally studied to investigate their capability of plasma generation and suitability of plasma application like PECVD. The plasma characteristics of the CCPs were critically examined for the PECVD plasmas produced by various showerhead configurations. The optimum performance in terms of high-density plasma generation and high emission intensity of excited species was observed for the operation using MHHC discharge. The MHHC discharge is characterized by an anode glow and a strong low-frequency fluctuation in the range of similar to a few kHz that is measured by the Langmuir probe (LP). The LP measurements in a broad pressure range revealed the scenario of hollow cathode discharge characterized by the enhanced electron temperature and the highest plasma density around 120 mTorr. It is realized that the bulk plasma intrusion inside the hole of the electrodes of the showerhead and the enhanced ionization in the plasma sheath regions of each hole facilitated the generation of high-density plasmas when the hole diameter is slightly bigger than twice or thrice the sheath length. The effectiveness of MHHC PECVD for high rate and low-temperature deposition of a-SiNx:H thin films is realized.