Glow discharge operational modes

The continuous operation of noncontinuous substrates, e.g., contact lenses, video disks, microsensors, etc., is performed by placing a certain number of substrate in an evacuation/transfer chamber, in which the evacuation is carried out and samples are transferred to the adjacent sample holding chamber in vacuum. The evacuated sample holders are placed on a conveyer one by one and pass through glow discharge zones. The coated substrates follow the reverse process at the downstream end of a reactor to be taken out in the ambient environment. Thus, the substrate charge is done in butch mode, but the LCVD process is done continuously. 

The potential use of the secondary plasma is closely tied to the chemical reactivity of the gas used. Oxygen glow discharge, which does not form polymer, can be used in both the primary and the secondary plasmas. In this case, the use of the secondary plasma is well justified particularly when the substrate to be treated is sensitive to photoirradiation. On the other hand, in glow discharge of Ar, of which excited species do not exist beyond the glow region, the secondary plasma mode operation could not be used. 

The primary glow discharge reactor in this configuration could be used for plasma coating in a low-pressure regime, in principle however, in consideration of flow pattern in such a multiple shelves reactor and electrical field in multiple electrodes, it is difficult to achieve uniform coatings in such a mode of operation. 

It is also important to note that the same glow discharge treatment could be achieved in the primary glow if the conditions are tailored for such a surface treatment by a very short exposure, e.g., a few seconds in contrast to a few hours of treatment time in the secondary plasma treatment. However, depending on the size and shape of substrate surface to be treated, a very short treatment is difficult to practice by a batch mode operation. This is where the merit of secondary plasma or remote plasma treatment is recognized. 

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