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Microwave Plasma Assisted Chemical Vapour Deposition (MW-CVD)


The Applied Science and Technology (ASTeX) type reactor consists of a cylidrical chamber attached to a microwave generator via a rectangular waveguide, with a mode converter. The microwave generator operates at a frequency of 2.45 GHz. The three ASTeX reactors can operate at powers up to 1.5 kW, 3 kW and 5 kW, respectively. The plasma is generated above a substrate, remote from all reactor surfaces. The distance between the position of the substrate table and the microwave transparent – quartz window is adjustable allowing further tuning of the microwave circuit (adjusting the cylindrical resonant cavity geometry). The substrate table can be heated inductively (upto a temperature of 1000°C) and / or biased independent of the plasma generation. The gases are admitted to the reactor via stainless steel canulas and their flow rates are adjusted with controlable mass flow meters. An MKS gas control unit is used with the possiblity of controlling and using various gas systems. Examples of gases that could be processed are H2, CH4, C2H2, Ar, N2, O2, Tetramethyl Borane (TMB), Tetramethyl Silane (TMS) etc. Special bubbler systems are attached to the feed gas line for the usage of solid and liquid precursors.The working pressure of the reactor ranges from few – to few hundreds Torr and is controlled with a MKS- vacuum gauge controller with a base pressure of 10-3 Torr.

The reactor body features view ports at several positions allowing a variety of external and in-situ measurements, e.g. external temperature measurements using remote IR-pyrometers, in-situ stress measurement via a bending substrate method, attachement of a Molecular Beam Mass Spectrometry (MBMS) unit for plasma chemistry diagnostics.

In our institute the ASTeX reactors are used for a variety of applications and reasearch areas. For example, the deposition of high quality CVD diamond films for a wide variety of applications as well as diamond doping for semiconductor applications, the deposition of various nanocrystalline gradient composite thin film systems like diamond/ß-SiC, diamond/WC etc on metallic and ceramic substrates, synthesis of carbon based nanostructures such as carbon nanotubes, carbon nanohelices, tubular graphitic cones etc.