Rapid Photo-Thermal Chemical Vapor Deposition of Amorphous Carbon From Diiodomethane
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ABSTRACT A novel approach to deposit amorphous carbon from the precursor CH 212 at low cost and high efficiency is reported. The combination of thermal and quantum photo effects shows new interesting growth behaviour. The radiation of a halogen-lamp was used to heat the substrate material and to split photolytically the precursor molecules above the substrate surface. The deposition process was investigated as a function of lamp power, gas phase partial pressures and substrate materials. The films were analysed by Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photon spectroscopy, transmission electron microscopy and atomic force microscopy. INTRODUCTION Amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) have many interesting properties [1] such as high hardness, low friction and low chemical reactivity. This unique combination of properties suggests potential practical applications as biocompatible coating or protection coatings for cutting tools and against corrosion [2]. While most methods of production use ion beams, sputter and plasma techniques or laser ablation, the present technique allows a low cost and rapid deposition of high quality films at fairly low temperatures. This
method combines thermal and photolytical activation of the carbon precursor. EXPERIMENTAL The experiments were performed in a cold wall CVD reactor. Fig. la shows the experimental set-up. The water-cooled reactor was made out of stainless steel and was sealed with 0-rings. The carbon precursor CH 212 was fed into the reactor from a refluxer unit using argon as a carrier gas. The partial pressure of CH 212 could be varied by changing the temperature of the cooling unit of the refluxer. To achieve even flow conditions, the gas mixture could bypass the reactor before starting the deposition. Deposition on the inlet window was avoided due to the low power density close to the lamp front surface, see Fig. Ib. The argon line was adjusted with a mass flow controller (MFC). A halogen lamp with a spectrum ranging from UV to NIR [3] was used to activate the deposition process. The lamp had a fixed focal length of 19 mm and a beam waist diameter of about 5 mm. In all experiments the lamp-substrate-distance was kept at the focal length and the direction of radiation was perpendicularly to the substrate surface. The leaking rate of the vacuum system was less than 5x 107 torr 1/s. The purity of CH 212 and of argon was 99 % and 99.9999 %, respectively.
279 Mat. Res. Soc. Symp. Proc. Vol. 593 ©2000 Materials Research Society
Quartz window(s)
Watetcooling Gasintlet
Substrate
Radiatio
-ub-t--t-
F
Substrate holder
Quartz windowjj r Gasinlet
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- Gasoutlet
Sealing(s)
Reflector Latnp
Fig. Ia. Experimental set-up.
Fig. lb. Lamp configuration
In all the experiments the carrier gas flow and the refluxer temperature were kept constant at 10 sccm and at 15'C, respectively. An additional reactor-purge of the same quantity was supplied for improvement of the flow and pressure conditions
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