Fusor Forums

The plate is biased; at those voltages and pressures the gas conducts and the ionized atoms "knock" off metal atoms that then move to and adhere to the glass. Your picture shows a rather badly "burned" film. It might just be the photo but if not, the issue of contamination looks to be a problem in your system. I don't bias my substrates but do use a DC voltage in the high hundreds (400 - 850 volts.) I've used higher voltage systems with magnetrons.

Also, your pressure is a bit on the low end. By the way, do you use air or argon? Air with oxygen can causes issues with your films.

Using an RCA cleaning process is over-kill for most sputtering systems (that is generally used only for semi-conductor systems and require ultra clean glassware ...); in any sputtering system the ionized gas will clean the substrate as long as you have first used alcohol to clean it of any minor contamination. For grossly contaminated glass surfaces using detergent and water, and then following this up by alcohol is ok.

I sputter films all the time and routinely make ultra-high quality films and I don't even bother to clean the substrates since standard slides are more than clean enough (you are using gloves to handle them?)

I'm using air, as I don't have access to argon yet. DC voltage you mean is just the magnetron sputtering voltage? Mine is probably something similar, I don't have any instrumentation. The power supply is a rectified OBIT.

I know the pressure is a bit low. One frustrating problem is that either higher pressures or the low pressures I mentioned work due to Paschen's Law, but intermediate pressures cause the plasma to leave the magnetron. But its my impression that sputtering works at a wide range of pressures and lowering the pressure makes it more radiant.

It is 110% the light in that last picture. My workspace is poorly lit and the surroundings are not of uniform color. Most of my films are pretty much white silver.

The last film i did, with the cross, is burned/contaminated and actually is the way that picture looks.

Yes, all my sputtering is done with DC.

Any good sputtered film will be a highly specular - that is, perfect mirror reflector on a piece of glass.

I sputter onto very thin plastic films (as thin as 20 microns) all the time with no trouble since sputtering and the plasma offer no significant heat load; that is not always the case for the grounding plate, however; and that can cause issues. So for thin plastic films I mount them above the ground plate using a plastic support.

Argon is popular for home based Tig welding and inexpensive (comparatively) gas systems are available in many locations. Argon is vastly superior for sputtering and allows for very high quality films to be deposited.

Scientific American has an excellent article on Sputtering in its Amateur Scientist back in the Oct 1967 issue.

Dennis sure is fast!
I was about to ask who else remembered that old Amateur Scientist column, from the era that I grew up with. Really cool projects, including plenty that could kill you if followed carelessly. And things that today would scare people for miles. Amateur glassblowers could work their way up to DIY mercury-vapor diffusion pumps. Bookstores were allowed to sell the magazine to just anybody!

Ian, do you live in the San Francisco Bay area?
My day job is across the street from a company called Meivac, where they manufacture industrial sputtering systems & similar vacuum gear. I got a tour & some free stuff once, years ago, when I was mentoring some science fair kids and first joined this forum. Could find my old contact info if you're interested.

Oh, cool!

I live in the south bay area bordering on Silicon Valley, and work at a company that makes MEMS devices (though I am not at all involved in microfabrication processes). I'd love to have that info.

I've been scheming to set up argon, but it costs money and I've not yet decided to spend it especially as the results on silver are so good without it.

My sputtered films are quite specular, though the exact specularity isn't totally uniform -- there's a very faint haze in the center. Of course, it's easy to sputter long enough that spalling starts and then it's not so nice.

I finally built a... very sloppy... demo fusor, thereby justifying my presence on the Fusor Forums, which are not really the Sputtering Forums. (I also dismounted my sputtering magnetron from my chamber)

It successfully forms a globule of plasma inside the grid, and also forms an impinging beam that must not be allowed to heat and crack/spall my glass.

Unfortunately I also managed to heat my grid (of the extremely easy and very sloppy spiral type) to incandescence and may have evaporated a small amount of copper oxide over the inside of the jar. Or maybe it's just the light.

Pictures are a series taken over the course of pumpdown. Power, as before, is provided by an oil burner ignition transformer with microwave oven diode rectifiers. This supply is capable of providing positive and negative outputs simultaneously but is capped at about 5kv, current-limited.

(unfortunately, I still don't really have the trick to properly photographing glow discharges.)

Regarding heating the grid to incandescence........Don't do that.

Richard Hull

Because of melting/evaporation, or for some other reason?

As you are noticing, metal is evaporating from your filament! That occurs when one over heats their cathode. This also tends to allow current to run along the walls reducing power to the cathode when metal is covering all the insulating surfaces in the system. A more serious issue (especially for home made systems) is that the support rod/conductor will heat up and this can weaken the feed thru sealant resulting sudden vacuum failure.

Your pictures are fine.

Glad you made your first demo fusor and got a plasma with it.

Yeah. I kinda want to try one of the tiny simple mass specs that people have posted here.

Feedthrough is probably a good point. My feedthroughs are sealed with epoxy and viton. So they don't want to get hot. Though I think they heatsink fairly well.

I'll need to clean the thing. Fortunately I have done this before (and it's nowhere near the level of total silver coatings I got when sputtering).

Acetone works very well with removing metal coatings from glass and even off of some metals like steel; do wear proper gloves and do it outside. While acetone isn't very toxic, it is best to minimize exposure. Do wear proper eye protective googles.

Interesting and not intuitive. How does it do that?

A proper sputtered film will not rub off with acetone or pull off with the scotch tape test
evaporated films may come off with either methods as mentioned above.
I clean our sputter system viewports @ work with aqua regia and if its being a bit slow i'll add some hydrogen peroxide to jazz it up
SEM techs use KOH solution to clean the apertures from tungsten deposits

And the KOH does not destroy the glass? Or etches it very slowly, while stripping tungsten quickly? What were you stripping with aqua regia?

aqua regia strip for Ag, Au, Mg, Ca, Bi alloys various, ZnO As, Cu, Ti, Al,W, WO, Sb and Sb alloys, Fe, Ni, Te, Zr, Gd, Sc, Pb, S, C, B, BN, ITO,Co, Dy, Si, SiO, TiN,Na,K,, and a few more I cannot remember at the mo.
usually there are several differing layers on the pyrex viewports
KOH will not attack glass in the short term.
For layers that are highly resistant to the aqua regia I drop a couple of mls of 70% HF on top but you have to be carful as this does etch the viewport and you must neutralize the acid before removing from the solution otherwise the viewport will go opaque (Frost)

OK, interesting. Thank you. I guess I need some acid.

Silver films must come out as silver chloride particles, I assume.

Do you have any advice on how to handle this stuff on a small scale without needing immersion?

Do realize HF (hydrofluoric acid) is an extremely powerful neurotoxin and at 70% or higher concentrations does not cause pain if it touches skin; it is bone seeking and a long-term chronic poison in such cases. It is very dangerous to breathe. Use only with proper equipment.

Mixing peroxide with acid has to be done carefully and the mix will heat up a great deal (depending on concentration, of course.) If you do that, do be careful and realize that the mix could splatter on its own; don't mix HF and peroxide except if using a vented hood and proper safety gear and after reading/learning proper use/safety first. HF is not a strong acid but extremely toxic to living creatures (so disposal is an issue.)

If you decide to get HF, here is a good paper on its dangers: https://web.utk.edu/~ehss/training/has.pdf

I've used HF before, but that was in a very well equipped university lab. Not going to do it with my current capabilities. It's just impossible. Maybe some of the fluoride-ion-containing consumer market glass etchants?

Hi
Tungsten deposits cleans well with molten sodium nitrite (NaNO2).
You can heat gently the other side of the window and place a few grains of the salt, that will melt easily. After the attack salts must be cleaned with warm water.
In case of windows in a metal-to-glass seal, heating can be risky. I would suggest to melt the sodium nitrite in a crucible and pick up a small quantity still molten and to rub the W deposit.

fluoride-ion-containing consumer market glass etchants?

I believe (and anyone with knowledge, please weigh in) these are just more dilute HF solutions;which still poses a similar risk. If you decide to try one, read ALL the safety data they provide, use proper chemical googles, acid resistant gloves, and work in a well ventilated area; as a OSHA warning stated - if you think you have smelled HF, you haven't! And I am sorry to say, I know from personal experience that statement is 100% accurate ... .

you could also use stainless steel weld pickle gel
this is a mix of nitric and HF acids in a convienient gel form
HF 10 - 30 % nitric around 40%
all welding supply places carry this
also very important for cleaning vacuum hardware after welding

The consumer glass etchants contain a fluoride salt, not true acid.

Yeah, I'm probably staying away from the F.

Quick image of a control box for the cheap Spellman supply ("Christmas Comes Early").

Two pots for voltage and current, one gauge (change between V and I with a switch), and a power switch with a missile cover in lieu of a Big Red Button. Most of the parts for this came from Halted.



(Why are electronic project enclosures so expensive almost everywhere?)

As for cost of those boxes - they are up their but most are well made so I expect it.

One reason I bought a useless (for fusion) large power supply (30 kV, 250 ma but positive!) was I got it for the cabinet and internal parts (meters, filtering system and cables.) The unit was cheap and so well worth the cost for just its components and large shielded case. A good idea to keep in mind when searching ebay; also, I was lucky - the company selling it was within a 100 miles so no shipping costs; otherwise, might not have been such a deal (but boy, was that thing heavy!)

Yeah, similarly I bought a spot welder (?) For a few dollars to House my variac, and got a high current xformer in the bargain.