Thermal CVD Hot Filament

In the processes described above, the plasma is generated by an electric current. A plasma can also be generated by high temperature which, in the case of diamond deposition, is obtained by a resistively heated wire or tube made of tungsten or tantalum.I i K J A schematic of the equipment is shown in Fig. 13.6. 

The metal temperature is maintained at 2000°C or slightly higher. Atomic hydrogen is formed and the carbon species become activated in the vicinity of the hot metal. The deposition rate and the composition and morphology of the deposit are functions of the temperature and the distance between the hot meted emd the substrate. This distance is usually 1 cm or less. Much beyond that, most of the atomic hydrogen recombines and no diamond is formed. 

Diamond is grown in air with a simple unmodified oxy-acetylene brazing/welding torch.l l Substrates such as silicon can be rapidly coated when exposed to the reducing portion of the flame but uniformity in structure and composition is not readily achieved. 

The high gas temperature ( 2000°C) makes it mandatory to cool the substrate. As a result, large thermal gradients are produced which are difficult to control. The deposition efficiency is extremely low with a nucleation rate of 1/10. This means high gas consumption, high energy requirements, and high cost. The deposition mechanism is not clearly understood at this time. 

CVD dianx nd has been produced from the single carbon isotope, As a reminder, normal diamond is composed of98.89% and 1.108% 

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