Influence of the source gas ratio on the hydrogen and deuterium content of a-C:H and a-C:D films: Plasma-enhanced CVD with CH4/H2, CH4/D2, CD4/H2 and CD4/D2

Effect of incorporation of deuterium on vacancy-type defects of a-C:H films prepared by plasma CVD

“…2a, the D concentration of the film increases linearly with increasing CD 4 /(CH 4 + CD 4 ) source gas ratio, reaching 23.4 at.% at 100% CD 4 /(CH 4 + CD 4 ), and the H concentration linearly decreases. In our previous study, the film produced from CH 4 /D 2 under the same processing pressure and total gas flow rate contained a lower D concentration compared with that of the film produced from CH 4 /CD 4 in this study [14]. For example, in this experiment, the D concentration of the film from CH 4 /CD 4 at 80% CD 4 /(CH 4 + CD 4 ) was 19.8 at.%, which is approximately double that of the film from CH 4 /D 2 at 80% D 2 /(CH 4 + D 2 ) (11 at.%) in our previous study.…”

“…2b, the D concentration of the film increased with increasing D 2 partial pressure and reached 7.8 at.% at P D2 = 7 Pa (or P D2 /(P CH4 + P D2 ) = 41%). In our previous study of CH 4 /D 2 source gas, the D concentration of the film was approximately 4.8 at.% at a 40% D 2 /(CH 4 + D 2 ) flow ratio [14], which shows a tendency of a smaller D concentration than that in the present study. This difference might be due to the difference in the total gas pressure.…”

“…Another study agreed with this hypothesis; it was reported that there was no difference in the film hardness produced between CH 4 /H 2 and CH 4 /D 2 . That is, the film hardness did not depend on which additional source gas, H 2 or D 2 , was used with CH 4 [14]. During deposition of the a-C:D film from CD 4 , the C D bonds in CD 4 should dissociate into C and D atoms in the plasma, and the dissociated C atoms should produce C C bonds to grow the film.…”

“…In our previous study and another study examining the properties of a-C:D films, the hardnesses of the a-C:D films were lower than that of the a-C:H film even if the sp 2 /sp 3 ratios of these films were the same, suggesting that the void structures of these films might be different [13][14][15]. However, the void structures of the a-C:D and a-C:H films have not been investigated.…”