Power And Cooling

Home » Power And Cooling

Power Requirements

Power and cooling requirements are critical considerations in magnetron operation, and the two are inextricably intertwined.

The power level directly affects the deposition rate. But approximately 80% of the power in the plasma is

converted to heat, which must be removed by the cooling system. Otherwise, it may damage the target,

the magnet array, and perhaps the substrate as well.

We provide two types of magnetron cooling designs:

Direct Cooling

In this approach, the cooling water is brought into direct contact with the target, or with the target’s backing plate when a brittle target material must be bonded. This is the most efficient method of cooling, but it requires that target changes be made carefully to avoid allowing excess coolant into the chamber.
Indirect Cooling

In this approach, the coolant is not brought into direct contact with the target itself, but with the cathode body, to which it is clamped. Cooling is thereby achieved via conduction through the cathode body. Because this is less efficient than direct cooling, an indirectly cooled magnetron has a lower maximum power limit, and hence a lower maximum sputtering rate.

The following table is a useful guide to maximum power limits, and selection of the appropriate power supply. Note that the power limit for indirectly cooled magnetrons can be increased by about 10% by using a thermally conductive paste or foil to enhance heat transfer.

	Max. DC Power (watts/ in²)	Max. DC Power (watts/ cm²)
Direct	250	39
Indirect	100	16

Pulsed or Medium Frequency -MF- maximum power is the same as the DC level.
Maximum RF power is 1/3 the values in the above table.

Cooling Requirements

We strongly suggest that the magnetron power supply be interlocked with a fluid flow switch placed in the exit line of the magnetron. That way, power cannot be applied to a magnetron unless coolant is flowing through the cathode. The coolant should be supplied at or slightly below room temperature, and the flow rate should be .25 gal/min (1L/min) for every kilowatt of applied DC power. The inlet pressure should be maintained at less than 60 psi (4 bar), to prevent leakage or distortion of the cathode body. Outlet pressure should be 0 psi or into an open drain. Open Drain Diagram Operation manual will have actual specifications.


Coolant Flow:	.25 gallon per minute (1 liter per minute)/1 kW Power.
Coolant Temperature:	68°F (20°C) inlet recommended. Range 55 - 75°F (13 - 24°C). Rise in outlet should not exceed 22°F (12°C). Inlet temperature should remain above local dew point to prevent condensation on target surface.
pH Level:	Range 6 to 8.
Coolant Pressure:	Unless otherwise specified, 60 PSI (4 bar) maximum inlet. 0 PSI maximum outlet, open to drain.
Resistivity:	Greater than 100k Ohms (relative to ground).
Conductivity:	Less than 10 micro Siemens/cm.
Particulate:	Water should be filtered to less than 50 microns, especially for magnetic particles, which can build up on magnets and impede cooling water flow.

The chart below represents the maximum flow rate possible when using that sized tubing on a magnetron.

For example, this means that the max flow rate through any cathode with ¼” convoluted tubing will be no

more than 1 gallon/minute. All these tests were done with a water inlet pressure of 60 psig (4 bar) and an

outlet to an atmospheric drain.

Straight Wall	GPM	Convoluted	GPM
3/16" O.D. x .040 Wall	0.75	N/A	-
1/4" O.D. x .040 Wall	1.25	1/4" O.D. x .030 Wall	1
3/8" O.D. x .060 Wall	3	3/8" O.D. x .030 Wall	2.8
1/2" O.D. x .060 Wall	6.4	1/2" O.D. x .030 Wall	5.7