My sputtering system

[Joe Jarski]

This is the second sputtering chamber that I built. The first was a 1pt. mason jar just to check the feasibility. I'll post and update with chamber number 3 when it's complete. The cap on this chamber includes a water cooled gun that holds 2 inch targets.

The lower power supply was the first one that I used for sputtering. It's a 25W vacuum tube test bench bench power supply that I built from the book "Beginner's Guide to Tube Audio Design". It worked fine with silver, but didn't have enough power to do aluminum. The second power supply that I tried was a 500V 1.25A electrophoresis supply that I picked up cheap, unfortunately it only lasted about 30 seconds while sputttering. Apparently the the solid state components didn't like the voltage spike from the huge inductor when the plasma went into oscillation. That's probably a lesson for for "It almost worked!". On to power supply #3. Having success with PS#1 & the tubes, I decided to cannibalize #2 for the transformer, choke and other goodies to build #3, which is the supply on top. It's somewhat power limited by the scavenged transformer, but has been working well so far. It's also makes a nice heater for the shop in the winter!

[johnf]

Joe

Aluminium does not sputter well
so don't worry if your results are a bit off on it

I did put up a list of elements in sputtering order on Fusor.net about a year ago.

We use Al for apertures on our ion sources as it is better than tantalum for not being sputtered.

However if you raise the energy of your argon ions to 10-20kV then Al will sputter albeit with a lot of argon in the layer.

Al evaporates very well so that is the most common way of putting up an Al film although it has a problem with the 3M test when evaporated.

all for now dinner calling

[Joe Jarski]

Thanks John. I did find that sputtering order list a while back. I've had good results with aluminum on several materials so far. The tricky one that I'm still trying to figure out is getting good second surface reflectivity from aluminum. Plastics always come out dark, but I'm sure its because of moisture in the plastics. The results on glass have been somewhat spotty, always better than plastic, but not always good. Probably a contamination issue there, which I should be able to cure with this next go 'round.

I've noticed a strange characteristic with aluminum in my system that you may have some insight on. I've been sputtering Al at around 600V and on start up it'll pull about 300mA without sputtering. After some period of time, sometimes a second, sometimes up to a minute, the current will drop to about 90mA with a slight change in the color of the plasma then the sputtering starts. I could only do Al at the limits of my old vacuum system, so maybe it's related to the mean free path. My other thought was maybe target temperature, but I don't think it is. Or maybe single vs multiple ionization?

[Doug Coulter]

I'll second John on that -- here I get absolutely great results with Al, but evaporating it onto just about anything, not sputtering. It comes out very nicely shiny on both sides, but is
soft as heck so you can't touch it much. The process is so fast that the substrate doesn't get very hot at all -- so fast it's a problem to get some exact thickness without having a fast shutter on the source. Lesker sells chromium coated evaporation heaters for mirror uses....much harder stuff and nearly as good a reflector. That's what they use on sunglasses.

Your Al might be getting an oxide layer, it happens here even in pretty good vacuum...and that's a pretty good insulator. You can see it by the sparkles that happen in the holes in the oxide, instead of a uniform glow all over it.

I'm sure John knows better, newer stuff, but John Strongs old "Procedures in Experimental Physics" has a good section on sputtering, and for that he was using a lot higher volts and much lower pressures. More like a few kV. He also mentions that putting a thin coat of silica or CaF on top makes the Al a better reflector and tougher too. He talks about adjusting the pressure
so the substrate is about at the edge of the cathode dark space. This was before magnets were used....so take it for what it's worth, but that works here. I've sputtered some nice
things with copper doing it his way.

Some materials seem to sputter better with RF or pulses, you might investigate that. Lesker's catalog has a bunch of very useful data on deposition in the back, and it's free -- not to mention accurate in so far as I've tested it, very nice. You just sign up for one on their website.

Evaporation is real easy, I should put up some info, and will when I recover from my recently busted toe -- dropped a 180kv multiplier stack on my foot yesterday, which also needs to get pictures up here, it's going to put the "kill" in kilowatt fer sure.

I love this book. I've learned a lot from duplicating the interesting parts of it. What was rocket science then is easy now.

http://www.amazon.com/Procedures-Experi ... 0917914562

[johnf]

Joe /Doug


Yes the Al is getting an oxide layer just a minutes exposure to air will see to that.
So when you start the plasma, ions have to sputter the Al2O3 (not a trivial task) to expose fresh Al.

What we have noticed @ work is if you bombard your target to near its melting point the sputtering yield goes down to zero

easy to explain when you think of the target as a solid block of ice to bounce a basket ball off against trying to bounce it off a water bed.

[Joe Jarski]

My new chamber is set up to be fairly flexible, so although I've only done DC sputtering so far, I'd like to to be able to do evaporation, RF sputtering and maybe electron beam if I find the need. I recently picked up a RF signal generator thinking that I can modify my power supply into a large amplifier and just feed it whatever signal I want to output, be it DC or RF. I've been mulling over essentially the same modular approach for induction heating.

Good point on the oxide layer. My current sputtering gun doesn't have a cathode shield because it just didn't fit in the small chamber and opening the chamber up would definitely expose the Al to air/oxidation. I didn't even think about going back to put the shields in on the new system, but I'll have to do it (there's plenty of space). Keeping the purge gas on during substrate changeout should help reduce the oxide layer problem.

Thanks for the book recommendation - I'll add that one the list. BTW, I've just started getting into the book by Halliday (different topic if you're following along).

[Doug Coulter]

I think you need to just try evap on Al with a simple spiral tungsten filament, you'll be impressed with that. You need a really stiff low volt source for that, like a rewound microwave oven xfrmr or I rewound a spot weld transformer (way overkill!). Else it's just too hard to control during the ramp up of the tungsten heater resistance. I used #6 wire, a few turns...and taps at half-turns.
When Lesker says this heater can take 8 volts at 80 something amps, that's true, but rarely do you run one near its limit. Here it's more like 3.5-4.5 volts for Al, for example, on an 8v rated heater. Amps are huge of course, and I use a fat SSR and big snubbers in the primary of the transformer to control that. And short #2 wire to the 1/4" copper rod feedthroughs.

What John didn't mention, but I will, is that Al picks up O and N even in a pretty good vacuum and that makes troubles in sputtering it along with the high valence -- it's just hard to knock off there. The stuff is a great getter according to my vacuum gages. For that reason, both sputtering and evap do better if you can have a shutter, and start up the process awhile before you start the real deposition -- cook the crud out of the system right before you do the depo, and it all just works better (much!). John may not run into this as much as he's working with some real superior vacuum gear already, in a very clean lab.


Halliday rocks, I think much better than most other books. Where he makes any predictions of what's to come, the guy was careful, but prescient. Most anything you need to know to do fusors is on the first 30 pages or so -- nice. I think there was some low hanging fruit in the merely nuclear field when the race to high energy and sub-nuclear stuff started up in earnest, and that books from this era are more useful to us than some others. And that low hanging fruit might still be there for us. For the bucks, that's the one book to have first. Next might be those "fast neutron physics" books out of Rice. Kohl is expensive, but more expensive to NOT have...the techniques in there will save anyone a ton of money when they homebrew -- not to mention hassle. I hate recommending high price tomes from ripoff publishers, but...there are exceptions, and Kohl is one of those. Kohl and Halliday are just good expositors of useful information, standouts in their respective fields, very accessible to us mostly mere mortals. Strong was one from a couple generations back, but the facts are still the same -- and his approach is practical and worth having in your mind as much as the info there is.

Though I'm a big fan of hands-on (more than anything else) I guess I'm revealing I'm also a good-book-freak. So be it, these are worth it, they are the giant shoulders we can stand on.
If it saves me a year of work, who gives a .... what the book costs? All these are in that class.

[Joe Jarski]

Doug, you're probably right - I may have to just stick with evaporation for the Al and save the sputtering for some of the other materials. Once the new chamber is done I'll have to start working on the evap. Thanks for the tips on the setting up the system!

More books to look for - I'm going to need another wing on my library!

[johnf]

Joe
One of the reasons for bad Al films sputtered by Argon is that alot of Argon gets trapped in the film

after some time the argon aggregates then bursts through the Al surface to escape

pic of surface below normal light microscope used

[Joe Jarski]

Wow, thanks for the picture! Those craters are impressive, but in a bad way. Is that a unique characteristic of Al/Ar sputtering or is that something that just happens with Al using any gas? I assumed that compact discs were sputtered. Are they evaped or is it another process and/or material?

Sorry to be picking your and Doug's brains so much, but I've found little useful information on the internet. So I've just been working with my own experimentation on mediocre equipment. Going from one of the easiest materials to one of the hardest probably wasn't the best approach either. Hopefully Doug's book recommendations will help me along. Evaporation sounds pretty straight forward, especially with lower melting temperature metals.