Hello ResearchGate community. I am facing a problem that puzzles me. I am trying to make two targets work on a DC sputter system that has become my primary dep tool.
- I am having issues with Cu and Ti targets, while other 2 (the tool has 4 guns) work fine (W and Sn).
- Ti target only strikes plasma at high pressures (~30 mTorr). If I try to strike at lower P (or try to decrease P after strike), the voltage runs away and hits the power supply hard limit of 1 kV, current drops to zero - end of journey. Otherwise, at high pressure the target behaves correctly - FDBK voltage in the range 300-400 V and stable, nice bright plasma - just what it should behave like. In my practice, Ti targets have always been the simplest to deal with, and they always did strike at = non-bonded). Previous target worked perfectly fine, no issues whatsoever. The new one also strikes at high pressure only. Voltage is high (~500 V at 100 W and 600+ V at 200 W on a 4-inch target) and extremely sensitive to pressure - opening the shutter leads to voltage go through the roof. I am doing its burn-in - cycling power at small increments (sometimes as small as 10 W to avoid voltage runaway), ramping up - soaking - ramping down and up again... The process is pretty slow but again, one thing I don't understand is why it requires such a high pressure.
- Both guns are in the working condition. The Ti gun works fine with another target (W), so gun isn't a source of problem here. The Cu gun worked fine just before the target was replaced by a new one.
I am no stranger to sputtering but never have seen such a target behavior. Why can't I work at reasonably low pressures (5-10-15 mTorr, or even 3 mTorr), why would the voltage run away? What is the reason for an erratic behavior of the Cu target? Am I doing the burn-in conditioning incorrectly? It's even more embarrassing since it happens with Cu and Ti that are supposed to be the simplest targets to work with.
Any ideas are welcome. Thank you!
It seems to me that your targets are floating up to high potential indicating that they are poorly grounded. Since they work at higher pressure, that indicates that they do have some path to ground, but it is too resistive. Obviously the resistance won’t be in the ingot itself, but somewhere there’s excess resistance.
In semiconductor, DC sputtering uses a direct current to maintain a glow discharge, resulting in energetic ions (usually Ar⁺). These ions move towards the target, and their momentum transfer causes the target's surface atoms to be ejected (sputtering). The sputtered atoms then deposit on the substrate. The DC current can be adjusted to regulate plasma density and ion energy.
Your new Ti and Cu target surfaces may be slightly oxidised. just take a fine blade and skim off the oxide layer, and take a fine emery/sand paper, and polish them, and clean thoroughly with acetone, dry them and load them into the chamber. paper
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