Pulsed laser deposition of nanocrystalline SiC films
Introduction
SiC is a ceramic material possessing outstanding mechanical, optical, and electronic properties that have been exploited in many applications such as in microelectronics, hard and protective coatings or in nuclear industry. However, it is rather difficult to obtain high quality thin films for property investigations since SiC exhibits low sputtering rates, high crystallization temperature, and high affinity for oxygen. Various thin films deposition techniques, such as CVD [1], laser-assisted CVD [2], and rf sputtering [3] were used to obtain thin SiC films. Pulsed laser deposition technique has many key advantages allowing to quickly obtain small area films for characterization purposes [4], [5], [6], [7]
Previous work showed that films deposited at lower to moderate substrate temperatures were amorphous [7]. A substrate temperature as high as 1200 °C was necessary to grow high quality crystalline or epitaxial films [8]. Recently, we explored the deposition of thin carbide films using a high repetition excimer laser [9]. The results indicated that the deposition of high quality carbide films required very low residual vacuum, high purity gases, high laser fluences and high repetition rates. A similar approach has been applied to the deposition of thin SiC and the results are presented below.
Section snippets
Experimental details
The PLD experimental set up used to deposit films uses a KrF excimer laser (λ = 248 nm, pulse duration τ = 25 ns, 8 J/cm2 fluence, 40 Hz repetition rate) to ablate SiC polycrystalline targets (Angstrom Sciences) in a stainless steel chamber. The ultimate pressure in the deposition chamber was in the low 10−6 Pa. Films were deposited on p++ (1 0 0)Si substrates (MEMC Electronic Materials, Inc.) at nominal substrate temperatures from 400 to 1000 °C under a high purity atmosphere of CH4. After deposition,
Results and discussion
Several XRR curves acquired from SiC films deposited at 400 °C are displayed in Fig. 1. Simulations of such curves using a commercially available software (Reflectivity from Panalytical) indicated that the density of these films was between 3.10 and 3.20 g/cm3, very close to tabulated values for bulk SiC. The higher density values were obtained for films deposited at 850 and 1000 °C. It is also worth mentioning that a 3.21 g/cm3 density value was obtained from the XRR curve recorded for a single
Conclusions
Thin SiC films were grown by the PLD technique on Si substrates using high fluence-high repetition rate. The films were dense, polycrystalline, and exhibited a slight texture. XPS investigations showed a low oxygen contamination in bulk, while nanoindentation results indicated very high hardness values. These results confirmed that PLD of SiC could produce good quality films required for properties investigations or application testing.
Acknowledgements
We would like to thank the Major Analytical Instrumentation Center-University of Florida for help with samples characterization. This work was supported by the IFA-CEA C3-03 grant and CNCS – UEFISCDI project Nucleu 2013.
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