Adsorption of Monomer on Substrate and Reactor Wall Surfaces

ADSORPTION OF MONOMER ON SUBSTRATE AND REACTOR WALL SURFACES 

Establishing a constant system pressure in a closed system or in a flow system with substrate materials in the reactor is not as simple and straightforward as it might appear. A gas is generally fed into the system by a constant flow rate controlled by 

It is important to recognize that the most critical stage of LCVD is the very early stage in which the depositing material interacts with the substrate and the critical interface is created. In the later stage, the luminous gas phase interacts with the deposited LCVD material. The critical initial stage is influenced by the sorbed monomer regardless of whether LCVD is carried out in a closed or a batch-operated flow system. This implies that the truly dependable LCVD operation could be obtained only by means of a continuous in-line operation, in which a steady state of a luminous gas phase is established and well-preconditioned substrates move into the luminous gas phase and out by a linear motion. 

It is important to recognize that all surfaces that contact with the luminous gas phase participate and influence LCVD operation. Therefore, in principle, in a batch operation, the first run with clean reactor wall could not be replicated in the second run with contaminated reactor wall. Thus, it is necessary to include the step for cleaning the reactor. If only hydrocarbons were used in an LCVD, the cleaning could be done by O2 discharge prior to the normal LCVD operation. (The influence of wall contamination was described in Chapter 10.) In this respect, the effort to minimize the deposition on nonsubstrate surfaces is important even in batch operation of LCVD. Magnetron discharge is quite effective in this respect, as described in Chapter 14. 

In the continuous processing, a steady-state flow of luminous gas is established and maintained for the duration of operation, e.g., 1 month, without interruption. Due to the factors described above, it takes some time, e.g., 30 min, to establish a steady-state flow of luminous gas. Once a steady state is established, it can be maintained it for sufficient time to allow continuous processing. Substrates are fed into the steady-state flow of luminous gas in a cross-flow pattern. The rate of transport of substrate and the length of the path in the luminous gas phase determine the treatment time. 

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