Effects of Radical Species on Structural and Electronic Properties of Amorphous Carbon Films Deposited by Radical-Injection Plasma-Enhanced Chemical Vapor Deposition

• Published in: Plasma processes and polymers Vol. 13; no. 7; pp. 730 - 736
• Main Authors: Jia, Lingyun, Sugiura, Hirotsugu, Kondo, Hiroki, Takeda, Keigo, Ishikawa, Kenji, Oda, Osamu, Sekine, Makoto, Hiramatsu, Mineo, Hori, Masaru
• Format: Journal Article
• Language: English
• Published: Weinheim Blackwell Publishing Ltd 01.07.2016; Wiley Subscription Services, Inc
• Subjects: Amorphization; Carbon; Chemical vapor deposition; Deposition; Electronic properties; Electronic structure; Nanotubes; Optical properties; Plasma; plasma-enhanced chemical vapor deposition (PECVD); Radicals; residence time; structural properties
• ISSN: 1612-8850; 1612-8869
• DOI: 10.1002/ppap.201500229

Amorphous carbon (a‐C) films are deposited using a radical‐injection plasma‐enhanced chemical vapor deposition (RI‐PECVD) system employing a mixture of H2 and CH4 gases. Variations in the structural and electronic properties of the resulting films with changes in the residence times of radical species and molecules are investigated by varying the total gas flow rate from 50 to 400 sccm. With decreasing residence time, the deposition rate is found to gradually increase, reaching a maximum value at a residence time of 6 ms, after which a decrease was observed. Optical emission spectra showed that the relative intensity of the CH emission increased with decreasing residence time. These results indicate a change in the dominant radical species resulting from suppression of the dissociation of radicals and molecules. Increasing amorphization and an obvious increase in the Tauc gap from 0.6 to 0.9 eV are found with decreasing residence time, while there is little change in the hydrogen content of the films. From these data, it is evident that control over the structural properties and optical bandgap of a‐C films can be realized by optimizing the distribution of radical species. Amorphous carbon (a‐C) films are deposited using a radical‐injection plasma‐enhanced chemical vapor deposition (RI‐PECVD) system employing a mixture of H2 and CH4 gases. With decreasing residence time from 18 to 2 ms, Tauc gap Eg increases from 0.6 to 0.9 eV, and Raman spectra indicate an increasing amorphization of structure in the film. It is considered that the change in electronic structure and structural properties are essentially correlated with the variation in radical species in plasma, which can be seen from the revolution of deposition rate and optical emission spectra of monitored radical species. It is anticipated that the knowledge obtained in this study will allow precise control of the structural properties and electronic structure of a‐C films, and hence lead the way to various device applications.