Hot cathode direct current plasma chemical vapor deposition equipment (DCCVD)

Hot cathode direct current plasma chemical vapor deposition equipment (DCCVD)

Hot cathode direct current plasma chemical vapor deposition equipment (DCCVD) is developed on the basis of conventional cold cathode glow discharge, and is mainly used for the deposition and growth of diamond single crystal or polycrystalline film

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The composition area and basic characteristics of hot cathode glow discharge：

The glow discharge of the hot cathode direct current plasma chemical vapor deposition equipment can be divided into four areas along the axis of the cathode to the anode: cathode glow layer, Faraday dark zone, positive column glow plasma ball, and anode glow layer. Among them, the cathode glow layer is a thin light-emitting layer close to the cathode, where the huge wave discharge occurs, which plays an important role in the glow discharge process; the Faraday dark zone is the transition zone between the cathode zone and the positive column zone. The electrons collide in the cathode region and lose energy, and the slow electrons are not enough to cause ionization and excitation, so they present a dark area that does not emit light; the glow plasma ball in the positive column area is at the most obvious position of the glow discharge, and its width is about the cathode The anode spacing is about 4/5, and the length changes with the change of the anode and cathode spacing; compared to the bright positive column area, the anode glow layer emits slightly darker light.

Hot cathode, high gas pressure and high current density are the basic characteristics of hot cathode glow discharge which are different from conventional cold cathode glow discharge. During discharge, there is a distribution of glow intensity, color, and brightness between the electrodes, which are divided into four obvious areas. The glow discharge covers the entire cathode surface, and the discharge voltage increases with the increase of the discharge current; the cathode electron emission is combined by the thermal emission and the γ process, and the degree of bias between the two is mainly determined by the cathode temperature; the cathode drop zone is to maintain the glow The indispensable part of the light discharge, the thickness of this area is very thin, there is a high potential drop, so the field strength in this area is very high, and generate a huge wave discharge. The current density of hot cathode glow discharge is much greater than that of cold cathode glow discharge.

DCCVD technical parameters of hot cathode DC plasma chemical vapor deposition equipment:

Deposition chamber	Stainless steel water-cooled interlayer	Design the appropriate cavity size according to the electrode size to ensure that there is no discharge between the cavity wall and the electrode
	Open cavity way	Lift to open the cavity or open the door in front, convenient for lofting and cleaning
	Observation window	Set up multiple observation windows to ensure that the cathode, anode and deposition table can be observed
Vacuum system	Vacuum pump	Vacuum is pumped by mechanical pump, no need to configure molecular pump
	Ultimate vacuum	0.1~1Pa
	Pump down time	5~15min
	Vent setting	Ensure uniformity of pumping
	Air pressure adjustment range	0.1Pa~30KPa
	Release valve	Can be restored to the atmosphere
	Vacuum gauge	High-precision vacuum gauge accurately measures the pressure value of the cavity
Gas distribution system	Air source configuration	5 gas sources of hydrogen, methane, nitrogen, argon, and oxygen, with an additional one reserved for backup
	Gas flow control	The volume flow is controlled by MFC, and a flow meter with a suitable range is selected according to the size of the cavity. Different flow sizes will affect the pressure rise time. In general, the flow rate of hydrogen: methane: nitrogen: argon: oxygen is 40:1:1:40:1
	Air intake setting	Reasonable air inlet setting to ensure air inlet uniformity
Water cooling system	Water cooler power	The cooling power and head of the water chiller should match the heat generation of the equipment and the cooling water flow, and the temperature should be adjustable, generally set at about 20°C
	Valve	The deposition chamber, cathode, and anode all need to be cooled, and a water separator needs to be installed, and manual valves are set at the inlet and outlet of each branch on the water separator.
	Operating temperature	The anode working temperature is 600-1100℃, the cathode working temperature is 700-1100℃
Power	Operating Voltage	600~1200V, adjustable output voltage
Power	Working current	6~15A
Control System	1) Gas flow control; 2) Electrode lifting control, real-time display of cathode and anode distance, control accuracy 1mm; 3) Monitoring and display of cathode, anode and substrate temperature; 4) Some functions can be adjusted manually, such as air pressure; 5) Fault alarm to prevent misoperation;
Electrode	1) The anode diameter is 60mm, and the material is copper 2) The diameter of the cathode is 80~100mm, and the material is molybdenum. After long-term use, carbon is easy to deposit on the surface of the cathode and the discharge is unstable. Therefore, it needs to be designed as a replaceable structure; 3) The distance between the cathode and anode is adjustable, the range is 10~60mm, the distance is displayed in real time, and the adjustment accuracy is 1mm; 4) The edges of the cathode and anode can be rounded to prevent edge discharge; 5) The anode can be negatively biased, and the bias voltage range is 0~400V; 6) The edge of the electrode is insulated to prevent edge discharge;