Invited Paper PS+AS-MoM3
Spatiotemporal Non-uniformity of CVD Plasmas and Film Qualities

Monday, October 30, 2017, 9:00 am, Room 23

Here we discuss great impact of nanoparticles formed in CVD plasma on uniformity of the plasma and film qualities [1-5]. Uniformity of thickness, composition, structure, and properties is a major concern of plasma CVD films. Multiple precursors including radicals, ions, and nanoparticles contribute to the film formation and hence their flux and flux ratio to the surface determine the film uniformity. Although most studies and text books describe film formation due to radicals and ions, such precursors are predominant only for very low pressure (< 5 Pa); in a pressure range of 10-500 Pa for most plasma CVD, contribution of nanoparticles to the film volume is 10-60% and cannot be disregarded [1-3]. CVD plasma tends to have inherently spatiotemporal non-uniformity of its internal parameters mainly because of nanoparticles. Nanoparticles have long time constant of their nucleation and growth. They tend to be charged negatively and are trapped in plasma. Nanoparticles act as loss sites of electrons, ions, radicals, and nanoparticles; and hence they have great influence on non-uniformity of plasma parameters, deposition rate, and film qualities. Particularly, they tend to give nonlinear response of CVD plasma, such as hysteresis, to discharge power and pressure. We show a model which reproduces well such non-linear response, and contribution of nanoparticles is one of keys to realize uniformity of high quality films [4, 5]. There is plenty of room to improve qualities of plasma CVD films by paying attention to contribution of nanoparticles to the films.

Work partly supported by JSPS KAKENHI grant numbers 26246036 and 16K13922.

[1] K. Koga, et al., J. Phys. D, 40, 2267 (2007).

[2] M. Shiratani, et al., Faraday Discussions, 137, 127 (2008).

[3] M. Shiratani, et al., J. Phys. D, 44, 174038 (2011).

[4] K. Keya, et al., Jpn. J. Appl. Phys., 55, 07LE03 (2016).

[5] S. Toko, et al., Suf. Coat. Technol., (2017) doi.org/10.1016/j.surfcoat.2017.01.034.