Glow-Discharge Microwave Plasma Deposition

A glow-discharge (non-isothermal) plasma is genereited in a gas by a high-frequency electric field such as microwave at relatively low pressure. In such a plasma, the following events occur  

The most common frequencies in diamond deposition are the microwave (MW) frequency at 2.45 GHz and, to a lesser degree, radio frequency (RF) at 13.45MHz (the use ofthese frequencies HHistcomplywithfederal regulations). 

Deposition Process. A typiceil microwave plasma for diamond deposition has an electron density of approximately 10 electrons/m and sufficient energy to dissociate hydrogen. A microwave-deposition reactor is shown schematically in Fig. 13.2.P M 1 The substrate (typically a silicon wafer) is positioned at the lower end of the plasma. Gases are introduced at the top of the reactor, flow around and react at the substrate, and the gaseous by-products are removed into the exhaust. The substrate must be heated to 800 - 1000°C for diamond to form. This can be done by the interaction with the plasma and microwave power but this is difficult to regulate and, more commonly, the substrate is heated directly by radiant or resistance heaters which provide more accurate temperature control. 

Incident Power Substrate Temp. Gas mixture H2/CH4 Pressure  

The morphoiogy and properties of the deposited coating vary as a function of substrate temperature, gas ratio, and the intensity of the piasma atthe deposition surface. Deposition rate is iow, averaging 1 -3 rn/h. This may be due to the iimited amount of atomic hydrogen available in the deposition zone (estimated at 5%). 

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Handbook of Chemical Vapor Deposition 9.3 Glow-Discharge (Microwave) Plasma... 

The cold plasma is most often generated in laboratories and industry by an electric glow discharge xmder low pressure using various frequencies of the applied electric field audio frequencies (AF, mainly in the range of 10-50 kHz), radio frequencies (RF, mainly 13.56 MHz), and microwave frequencies (MW, mainly 2.45 GHz). Sometimes, a direct current (DC) discharge is also used. An example of typical parallel plate plasma reactor, one of those being used in our laboratoiy for deposition of thin films, is sketched in Fig. 2. 

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