DEPOSITION MECHANISM OF DLC FILMS

The properties of DLC films, which are similar to those of diamond, are attractive because of their extreme mechanical hardness, high electrical resistivity, low friction, stability against acids, uniformly flat surface and optical transparency over a wide area. DLC films are deposited on several kinds of substrates at room temperature. These advantages of the DLC films lead to many application in mechanical, electrical and medical fields.

A radio frequency (r.f.) plasma chemical vapor deposition (CVD) process widely used for DLC films deposition for large areas because the methodology is simple in construction compared with other techniques. The advantage of this method is its application for wide-area coating and its stability compared with that of d.c. plasma. In addition, the possibility of DLC film coating the insulating materials can be estimated. R.f. plasma discharge has been particularly widely used to produce amorphous carbon films, because this method can be applied not only for etching, but also for deposition. It is most important to prepare DLC films on insulating materials for medical application, and this technique was selected for this study.

However, the properties of DLC films are strongly depend on deposition conditions such as total gas pressure, input power supplied from a generator, gas flow rate and also substrate material. The hardness of DLC films is mainly determined by the number of the ionic species in the plasma and the bias voltage, which in turn depends on the positioning and shape of electrodes. Thus, the geometric configuration of the experimental equipment is very important and will be discussed in details.