I am trying to rf sputter FeGa, onto glass slides and have made a number of attempts, with no film forming.
I have adjusted the power between 80W to 150W , adjusted the distance of the target to the substrate and have sputtering times up to 40 minutes. And still no trace of anything forming on the glass.
The plasma forms, although it is tricky to get it started sometimes. I am using Argon gas in the chamber.
Has anyone had this problem of the plasma forming and things seeming to work as expected, but no film ends up forming on the substrate?
Or any suggestions as to what may be the problem here?
Is there a stable formation of plasma in the chamber? what is your substrate Bias? Pressure in the chamber?
It has nothing to do with the FeGa target.
and is related more to your electrode arrangement, and target thickness.
Increase your pressure a little bit more, and try striking the plasma, and wiat
for the pressure in the chamber to get stabilised well enough.
Also check the ground shield, it should be maintained with an appropriate gap all around the electrode and on top of the target. the gap is critical maybe around1.5 to 2 mm.
K. Sreenivas
What is your base pressure, working pressure and argon pressure.
The main thing is if you keep on increasing the power alone it may affect the electrons to bombard within them and the film growth will be affected. The ionisation depends mainly on the pressure in the chamber rather than the power (pls dont ignore the power it also plays a major role but to a lesser extent)
The plasma appears stable, when it gets going, but is not as bright as from other targets used. And I need to increase Ar pressure beyond what is normally used for sputter other targets to get the plasma to strike.
The voltage bias auto adjusts and has ranged between 454V to 554V.
The pressure in the chamber is brought down to 2.5 x 10-5 mb, and when Ar is introduced the pressure is brought up to 6 x 10-3 mb.
A colleague had trouble with a target, similar to me, apparently an oxide layer had formed on the surface of the target and prevented the sputtering from occurring. And by sanding down the surface of the target that fixed his problem.
I thought I might try this, and then increasing the Ar pressure in my next attempts.
It's RF magnetron sputtering system, just to be clear
No luck with increasing the Ar pressure, or sanding down the surface of the target. Still no deposition.
I am thinking of trying a copper seed layer now.
Strange ! What are the target-substrate distance and the target size ?
I use quite same pressure of Ar and a power of typically 1W/cm²; target-substrate of 4 cm and get a deposition rate of around 3 nm/min.
Distance I'm using currently is 10 cm, between target and substrate before it was 15 cm. I tried moving it to 5 cm, but I could not get the plasma to strike. Most people using the system here have a 15 cm distance between their targets and substrate.
Target size is 50.8 mm diameter, 6.36 mm height
Do you think I should keep trying at the closer distance? Have you tried sputtering FeGa with larger distances between your target and substrate?
In my case, the target-substrate distance was fixed to 4 cm. As it works, I did not try other distances, Yes, I believe you should try a closer distance, but I don't know if it will solve your problem (but it can help) ! Perhaps you should also increase a little bit the Ar pressure to 0.01 mBar (after reducing target-substrate the distance) ?
Good luck !
Just another remark : my target is only 2 mm height, if you have the possibility to try such thinner target it would perhaps help (I started with a more thicker target and had also very low deposition rate).
Thanks Gilles for the suggestions.
I was just speaking with somebody else who came to the similar conclusion about the target height. Saying that the magnetic flux shunts through the magnetic target. So a thinner target may be the solution.
Dear Dr. David in case you had mentioned that you are using a magnetron sputtering, and using a magnetic target like galfenol. The answer and solution were simple and straightforward.
Even I faced problems with sputtering of magnetic materials.
For example in order to sputter Nickel, I normally use thin Ni foil targets. Nce to learn from your discussion and interactions, and hopefull the problem is solved.
K. Sreenivas
Thank you K.Sreenivas for your comment.
I believe the we have found the solution, although it will be a couple weeks before I can actually try this, I feel confident that this is the way forward.
And thank you to everyone who contributed to the discussion, and helped me find my way.
In case any one was curious as to what happened, and the results of the applied suggestions.
I thinned my target to ~1 mm and did start to see some deposition, but it was a depositing at a very slow rate, and I was not getting a usefully thick film down.
The sputter gun then died, and became unusable, and irreparable, despite much effort to revive it.
We were able to replace the sputter gun, and from speaking with the manufacturers they recommended a "strong" magnetic set for the magnetron sputter gun for magnetic materials, with thinner targets.
With this "strong" magnetic set and my target of ~1 mm thickness, with a separation of approximately 6.5 cm between target and substrate, I have now been able to deposition FeGa at a rate of around 15 nm/min.
With increased power the rate has been 28 nm/min, but it moves away from the desired composition at higher power.
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Still adjusting parameters to move towards the desired FeGa composition for the film. Typically I have been getting a higher Fe content than I would like, and results so far seems to indicate a lower RF power and higher Ar pressure, give me an increase in Ga content (lower Fe) in my films.
Based on the colour of the plasma I am seeing with adjustment to the Ar pressure, (with RF power constant) as I increase pressure the colour shifts from a violet to a blue, which indicates a change in the power density of the plasma from my understanding. Blue light being of a lower energy than violet, the increase in Ar pressure appears to lower the energy of the plasma, which comes about from there being more gas in the chamber to ionise fir the fixed RF power.
This is my understanding of what is happening based on what I have seen and tried, and from some discussions. So for my case it seems that I need a lower energy than I am currently using to get the film ratio of Fe:Ga that I would like.
I figure it is most likely trial and error, but I am curious to find out whether what studies may exist on depositing alloys and their composition based on the sputtering plasma density energies and path length (substrate to target).
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