Growth of Nanoparticles in TEOS rf Plasma with Amplitude Modulation

Silicon dioxide (SiO2) films are widely used as dielectrics and passivation layers in optoelectronic devices [1-4]. They are most often deposited by plasma-enhanced CVD (PECVD) using TEOS (tetraethylorthosilicate, Si(OC2H5)4) [5,6]. Whereas there are several reports on effects of amplitude modulated (AM) on SiH4 plasma [7], there are few reports on those of AM on TEOS plasma.[8] Especially, relationship between nanoparticle growth and AM discharge TEOS has not been clarified yet. In this study, we examined effects of AM discharge on growth of nanoparticles in TEOS plasma.<br/>Experiment were carried out with a capacitive RF discharge reactor [9]. A power electrode of 60 mm in diameter was installed at 6 mm above a ground electrode of 60 mm in diameter. TEOS (Si(OC2H5)4 was supplied at a flow rate of 40sccm with O2 at a flow rate of 180 sccm, and diluted with Ar at a flow rate of 160 sccm. The total gas pressure was 6 Torr. The frequency was 13.56 MHzd. The RF discharge power was 30W, and the discharge period was Ton = 8 s.<br/>To obtain information on nanoparticles, 2DLLS method was applied. In this method, a sheet laser beam of 532 nm was irradiated to the region between electrodes, and the light scattering intensity from nanoparticles was measured with a high-speed camera (Photron, 1000 fps). The LLS intensity is proportional to the density np of the nanoparticles and the sixth power of the size dp in the Rayleigh scattering regime. In order to investigate the relationship between nanoparticle growth and AM discharge plasma, LLS intensity and Ar I (λ=750.4nm) emission intensity were simultaneously measured using two high-speed cameras.<br/>A high LLS intensity was observed near the powered electrode, suggesting that nanoparticles are generated in the plasma/sheath region near the powered electrode. There are two peaks at AM levels of 30 and 50%, indicating that nanoparticles there oscillate in the direction perpendicular to the electrode surface. The higher modulation level, the greater the oscillating width of nanoparticles. The higher modulation level, growth of nanoparticles tends to be more suppressed. The amount of nanoparticles decreases by 18% at AM level of 10% and by 60% at AM level of 50%. AM discharge TEOS plasma is effective to suppress growth of nanoparticles in the plasma.<br/>References<br/>[1]T. Nam, <i>et al</i>., <i>Appl. Surf. Sci., </i><b>485</b>, 381 (2019).<br/>[2]L. Wang, <i>et al</i>., <i>J. Non-Cryst. Solids</i>, <b>482</b>, 203 (2018).<br/>[3]H. Liu, <i>et al</i>., <i>Vacuum, </i><b>148</b>, 258 (2018).<br/>[4]W.-J. Lee, <i>et al</i>., <i>Thin Solid Films</i>, <b>657</b>, 32 (2018).<br/>[5]T. S. Cale,<i> et al</i>., <i>Surf. Coat. Technol., </i><b>201</b>, 8873 (2007).<br/>[6]K. Kamataki, et al., J. Instrum., 7, 4, C04017 (2012).<br/>[7]N. Kashihara, <i>et al</i>., <i>J. Nano Res</i>. <b>8</b>, 395 (2006).<br/>[8]K. Kamataki, <i>et al</i>., <i>Appl. Phys. Express</i>, <b>4</b>, 105001 (2011).