Surface Roughness Evolution of PECVD Cathodic and Anodic a-Si:H.

Abstract

Surface or interface roughness can impact optical, electronic, and MEMS applications of thin a-Si:H films. Deposition at lower temperatures can be advantageous for some applications of a-Si:H, but lower temperature deposition generally leads to rougher films. We have found that the evolution of surface roughness growth can be modified substantially by ion bombardment due to the self-bias of the plasma during Plasma-Enhanced Chemical Vapor Deposition (PECVD). Notable differences in the surface roughness evolution and deposition rate are shown for films deposited in “cathodic” versus “anodic” mode – where the substrate is placed on the powered and grounded electrode respectively. Suppression of surface roughness growth of a-Si:H can be achieved under conditions of relatively high ion bombardment even at deposition temperatures as low as 75 C. Atomic force microscopy (AFM) was used to measure the relative surface roughness profile as a function of deposition time. Analysis of the power spectral density of the roughness yielded important statistical surface parameter information. Based on these observations, insight is given into growth mechanisms under the two deposition conditions.

Surface roughness and structural aspects of anodic and cathodic plasma deposited a-Si:H at low temperature

“…We have previously observed cathodic deposition resulting in mirror smooth surfaces under different rare-gas/silane mixtures [4,5]. This study extends upon these studies by evaluating the effects of ion-assisted processing of a-Si:H with He and Ar ions on morphology and microstructure.…”

“…Zero surface roughness evolution has only been reported for a-Si:H processing at much higher deposition temperatures -greater than 300°C [11]. These just-mentioned studies are of films that are deposited on the anode to purposely avoid high-energy ions and electrical property degradation of the films [4]. Energetic helium and argon ions impinging upon the cathode clearly play a role in mass transport on the surface -sufficient to overcome surface growth instabilities to result in smooth surfaces.…”

Temperature dependence of the surface roughness evolution during hydrogenated amorphous silicon film growth

“…13 However, for a-Si:H growth by plasmas the reported ␣ and ␤ values are in the range 0.5-1.0 and 0.1-0.5 for ␣ and ␤, respectively. [3][4][5][6][7][8][9] In this letter, we report the scaling behavior of the a-Si:H roughness evolution for a broad range of growth rates R d and substrate temperatures T sub . The films have been deposited by the remote expanding thermal plasma ͑ETP͒ under conditions in which film growth is dominated by SiH 3 and in which ion bombardment is absent.…”

Plant-derived cis-β-ocimene as a precursor for biocompatible, transparent, thermally-stable dielectric and encapsulating layers for organic electronics

“…The roughness parameters were quantified and are summarized in Table 1. A reduction in roughness with increasing power is attributed to a higher ion bombardment at these power levels which has been shown to etch the surface56. At 10 × 10 μm, the skewness is a small positive value indicating the films contain more peaks than valleys.…”