Carbon-Nitride, Diamond-Like-Carbon and Silicon-Based Films Synthesized by Electron Cyclotron Resonance Chemical Vapor D
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by Liu and Cohen has not been realized by any of the research groups that have been attempting to synthesize P-C 3N4 . Experimentally determined values of hardness for amorphous carbon nitride films are comparable to or only slightly higher than values for diamond-like carbon (DLC) [1]. Results presented here show that a crystalline phase of chlorine-doped carbon nitride (CNx:Cl) can be deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD). Recent thermodynamic calculations by Hughbanks and Tian [3] show that the hexagonal P-C 3N4 structure proposed by Liu and Cohen may not be possible. A more likely structure involves a slightly buckled, planar arrangement of tetrahedral sp 3 and graphitic sp2 bonds. The composition of this most recently proposed structure would be C4N3 . In the structure proposed by Liu and Cohen, there are only CN bonds and no CC bonds [4]. In the structure proposed by Hughbanks and Tian, there are both CN and CC bonds. A layered structure like that observed in the stacked pyramidal CNx:Cl crystallites in this work is consistent with either of the proposed structures. High resolution electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared (FTIR) spectra show that the CNx:C1 films deposited in the ECR-CVD are a mixture of single- and double-bonded carbon and nitrogen centers with a very small amount of triple-bonded CN. The ESCA and FTIR data is consistent with either of the proposed structures. In addition, the data shows that the amount of Cl in the CNx:C1 films is less than a few percent. Amorphous hydrogenated carbon (a-C:H) films deposited from N 2 mixed with neopentane (C5H 12) are very similar to a-C:H films deposited from argon (Ar) mixed with ethylene (C2H4 ) or with C5H 12 . In other words, N2 does not react significantly with single-bonded C5H1 2 to form CN bonds. On the other hand, the FTIR and ESCA data will show that N 2 reacts effectively with double-bonded C2H 4 to form hydrogenated carbon nitride (CNx:H) films. The CNx:CI films were deposited from mixtures of N2 and C2C1 4 or mixtures of N2 , Ar and C2C14. If trichloroethylene (C2HC13) is used in place of C2 C14, the results are identical. Chlorinated instead of hydrogenated precursors were chosen for the ECR-CVD CNx:Cl films to eliminate hydrogen incorporation during the growth process. A double-bonded, chlorinated
precursor like
C 2 HC13 or C 2 C14
reacts with N 2 in the plasma to form single- and double-bonded
CN with little or no formation of CH and NH bonds. In contrast, a non-chlorinated precursor like C 2 H 4 reacts with N 2 to form single- and double-bonded CN along with a large amount of CH and NH bonds. The hydrogen bonds are associated with a more amorphous phase of carbon nitride. The absence of CH and NH bonds is associated with a more crystalline phase. However, the crystalline phase is a Cl-doped version of carbon nitride. The resulting CNx:Cl films are somewhat porous and unstable with respect to moisture. It is much easier to obtain stable, dense films using ch
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