Nanomechanical characterization of amorphous hydrogenated carbon thin films
Introduction
Recently, amorphous hydrogenated carbon (a-C:H) thin films, also called diamond-like carbon (DLC) films, have attracted extensive attention because of their physical properties for applications in optical, microelectronic productions and various engineering systems [1], [2], [3], [4], [5].
Many deposition methods have been developed to prepared DLC thin films, including ion-beam deposition, sputtering systems, plasma enhanced chemical vapor deposition and pulsed laser deposition [6], [7], [8], [9], [10]. Each method has its relative advantages for certain applications. Among these, electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD) is a promising technique because of its superior plasma species production rate and low substrate temperature during deposition [11], [12], [13].
Structurally, a-C:H thin films vary from films dominated by a diamond-like tetrahedral (sp3) structure to films dominated by a graphite-like trihedral (sp2) structure. The films structure has been found to depend strongly on the source gases and deposition methods. Erdemir et al. [14] studied the influences of various sources gases, such as methane (CH4), ethane (C2H6), ethylene (C2H4) and acetylene (C2H2), had on the friction and wear mechanics of DLC thin films. They concluded that the addition of H2 to the methane source gas improved the film's frictional behavior [14]. However, understanding the film's characterizations such as hardness, Young's modulus and surface morphology is important for achieving industrial applications.
In this study, a-C:H thin films deposited using different mixtures of methane–hydrogen by ECR-MPCVD were investigated. Influences of the addition of H2 to the methane source gas on the microstructures, surface morphologies and mechanical properties of a-C:H films are presented using Raman spectroscopy [15], atomic force microscopy (AFM) and nanoindentation technique [16].
Section snippets
Experimental details
Amorphous hydrogenated carbon thin films were produced on a silicon substrate by ECR-MPCVD with a RF bias applied to the substrate holder. The films were prepared in an ASTeX AX2115 ECR-MPCVD system, with reactant gases of methane and hydrogen. Upon introducing a mixture of methane and hydrogen to the chamber, the plasma for the film deposition was excited in the ECR zone by microwaves at 2.45 GHz. The electric field vector of the microwaves was perpendicular to the magnetic field line. A 13.56
Results and discussion
Raman spectroscopy is widely utilized to analyze the structural contents of deposited films and also measures the ratio of the sp3- and sp2-bonded states in DLC films. Fig. 1 shows the Raman spectra results using various mixtures of methane–hydrogen gas. The two peaks of the curve correspond to the peaks for sp2 (G-peak) and sp3 (D-peak), centered at approximately 1590 and 1350 cm−1, respectively. The Raman spectra showed an increase of the sp3 bonding carbon clusters when increasing the
Conclusion
The properties of a-C:H thin films deposited by ECR-MPCVD with methane–hydrogen gas mixtures were improved. From the viewpoint of microstructure, the hydrogen in a-C:H thin films acts as a promoter/stabilizer of the sp3-bonded carbon phase [14], [25]. Clearly, the presence of hydrogen is better to the structural and mechanical properties for a-C:H films. Summarizing, the structural and mechanical properties of a-C:H thin films that were prepared by ECR-MPCVD using different mixtures of H2 and CH
Acknowledgements
The authors would like to thank Sheng-Rui Jian for technical assistance and this work was partially supported by the National Science Council of Taiwan, under Grant Nos. NSC94-2212-E-150-045 and NSC94-2212-E-168-004.
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