Hi Jose-Maria,

For plasma ignitiion you can of course use power as a variable but plasma ignition is very much dependent on the combination voltage, pressure, electrode spacing and the sort of sputtering gas. Playing with the pressure is the easiest to get a plasma started at lower power levels. There is an optimum for ignition which relates the breakdown voltage to the product of pressure and electrode spacing. look for Paschen curve on the Internet. Another very important effect has the magnet strength. The stronger these magnets are the better it is for good ignition and sustainigng of the plasma. It is known that magnet strengths can degrade through the years (depending on the type of magnet). I would first play with the pressure to see if you can get the plasma started al lower power levels. In a DC-magnetron a plasma should normally start easy around 20-25 mT. If you don't succeed to do this with pressure think about changing the electrode distance (don't know if you can change this, very often this is fixed). If this does not work check the magnets.

Hi, do you mean that 3kW is the maximum or the minimum power necessary to ignite or sustain the plasma? As far as I understand your question : Mo can be by DC sputtered and the power should be adapted to the area of your target and to the cooling system.

What is the Ar pressure that you are using to ignite the plasma at 3kW?

power must be calculated from the current density which is influenced by the target sample surface area

I concur with Enrique. You can apply 10-15 W/cm2 power levels on your target if the target is well cooled and bonded by a good metal bond. If it is bonded by conducting polymer bond be careful with power levels as mensitoned above.

@ Peter Knapen: thanks for your answer. I tried different process pressure but max. power in any case is limited to 4kW meanwhile power supply is able to achieve 5 kW.

@ Enrique: considering our target area, max. power I can apply is 7 W/cm2, which means lower values than expected

Hi Jose-Maria,

I would plot the I-V curve at different pressures and have a look if I or V is saturating of showing unusual clipping. This might give an indication of the problem. Can you adjust the electrode distance? 

Hi Peter, thanks again. Current is the limitation factor in my case. Any suggestion? Target distance is fixed, sorry

Hi Jose-Maria,

This could be a number of things. First of all, at what pressure do you get most power into the system? Usually this is at higher pressures since you have more molecules which can be ionized. But not getting enough current through the system might also be an indication of resistance problem. First thing you should do is check the generator itself by hooking up a Watt meter between generator and reactor to check if you get the exact powerlevel. It is my experience that this can differ from what you see on the monitor of your system. This is a real important check to verify your power supply is ok.

If the power supply is ok than you might have a resistance problem in your circuit, limiting the current going through your plasma. The best way to check this to use an ohmmeter and measure by putting 1 pin on the Mo target and the other one on the cable end which hooks up to the generator. This should only read a few ohms. If that's not the case you might have a cable problem or you target is not well bonded. To check if the bonding is ok you can measure on the surface of the Mo-target and on the electrical connection of the target. This usually is a few ohm's. It also could be leakage between target and ground. This you can easily check by measuring with one pin on the electrical target conncetion and one pin on the body of the reactor. This should read at least 1Mohm. If this is not the case, you either have a resitacne leak because of bad isolation between target and reactor wall (check o-rings or ceramic isoalation on contamination or you loose powee cooling system. If the latter is the case check on the conductivity of the water. This might be to high.

Finally and as mentioned before there could be a problem with your magnets. To check these you can use a gaussmeter. If you have your target assembly with the magnets on top you can put the sensor of the gaussmeter on the Mo-surface. Try the find the maximum value. This should at least read 300-500 Gauss. This can vary because of the different magnets which are being used (AlNiCo, FeNbB, SmCo). Best thing to do is measure all target assemblies. If they all read similar values you should be ok.