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Changing vacuum conditions in PVD

Q. Hello,

At my workplace, we have a PVD machine capable of cathodic arc and sputter deposition methods. We rarely use the sputter method, so in an effort to make cleaning easier, we removed the sputter targets (post type, 100x1000mm cylinders). The sputter targets are water cooled, so we made some caps that allow the water to cycle through (as far as the pump 'knows', the targets got shorter). As expected this has affected the chamber pressure during runs (pressure has increased, likely because the pumps have to work harder to vacuum the effectively larger chamber volume).

I was on the verge of perfecting a new multicolour coating prior to removing the targets, but now the same program gives various shades of black instead of the expected colour. Initially, I tried lowering the gas flow values to reduce pressure, but to no avail. I tried raising the gas flow values (to values that we had previously used successfully with the sputter targets in place), but that resulted in the pressure rising to a point that the machine threw up an alarm.

The chamber is roughly a 1200 x 1200 mm cylinder. How should I adjust my coating programs to account for this change in volume?

The PVD machine doesn't give us any units on our MFCs, but 1700 in total seems to be about as high as we can go before the chamber exceeds 3 Pa (from a starting pressure of 1.2e-2 Pa). I suspect the unit would be sccm, but I can't be sure. One of my colleagues wonders if the magnets inside the sputter targets could also affect the coating colour, but I'm not so sure.

Thanks in advance.

Ben O'Shea
- Katikati, New Zealand
October 22, 2019