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W&L - The Coaxial Bladed Reactor (CBR) System
The Coaxial Bladed Reactor (CBR) System is an advanced microwave plasma-enhanced chemical vapor deposition (PECVD) system designed explicitly for single crystal diamond growth and the deposition of microcrystalline diamond layers over a 4-inch circular area. Central to its operation is an interrupted coaxial transmission line with a built-in abrupt impedance transformation housed within a non-resonant process chamber. The system is powered by a robust 15 kW, 2.45 GHz microwave generator, allowing for process pressures exceeding 180 hPa. This formidable setup can heat a molybdenum substrate carrier plate to over 1000°C, necessitating efficient water cooling for both the substrate and the microwave transmission line. The CBR system offers six optical viewports for visual and infrared inspection of plasma discharge, ensuring precise thermal control of the substrates. It features a motor-driven, PLC-controlled substrate stage for accurate substrate height adjustments, crucial for uniform microcrystalline diamond layers and single crystal growth. The system supports automation via Siemens PLC and a human-computer interface for remote operation, enabling prolonged single crystal diamond growth of up to two weeks. The system is designed for homogeneous plasma-enhanced chemical vapor deposition of diamond layers using 2.45 GHz microwave power, promising competitive costs against the use of 915 MHz power.15 kilowatts of microwave power sustaining a hydrogen-methane plasma which is capable of heating a molybdenum substrate carrier plate to a 1,000°C and more need adequate water cooling.
But the microwave transmission line with the impedance matched transition from rectangular waveguide to a coaxial line also requires efficient water cooling.
A total of 6 optical viewports enable visual access to the plasma discharge in the center – not only for visual inspection but also for an infrared camera which helps to control thermal equilibrium across the 4 inch substrates.
The entire substrate stage is motor driven and PLC controlled for adjusting the distance between substrates and the CBR microwave launcher. In addition to the main substrate height adjustment which may be sufficient for the uniform growth of microcrystalline diamond layers a much more precise secondary height adjustment system for single crystal growth is available within the main stage.
It allows selected areas of the 4 inch stage to be lowered at the deposition rate. It can be set to rates of micrometers per hour to make sure the growing surface of single crystal diamonds will remain under constant plasma properties over extended periods of time.
The CBR system is fully automated by a Siemens PLC and a suitable human computer interface for remote operation. The growth of single crystal diamonds can last as long as 2 weeks. The light intensity of the plasma discharge can be monitored very precisely and can be used to switch off the system should a plasma breakdown or any other unforeseen malfunction happen.