Coaters - what's worth considering

[Malcolm Roberts]

Folks......
I have been given the unenviable task of taking over management of our coating facility. We have a variety of different bits of kit - some in better condition than others and all set up for specific jobs. One of these is a very old Edwards unit, which still sees plenty of use because of the shear number of thin sections one can load inside. It does a good job, but it showing signs of age and is probably best put out to stud. I've been surfing around, and most of the products I have seen such as Cressington and similar are all small volume units - the Cressington we have will take three thin-sections or four 1 inch mounts. I see one large volume unit available from China - turbo and at a price of between US$6-9k.
Who else has been through a similar situation? What did you find out was the best solution?
Cheers,
malc.

[Probeman]

Folks......
I have been given the unenviable task of taking over management of our coating facility. We have a variety of different bits of kit - some in better condition than others and all set up for specific jobs. One of these is a very old Edwards unit, which still sees plenty of use because of the shear number of thin sections one can load inside. It does a good job, but it showing signs of age and is probably best put out to stud. I've been surfing around, and most of the products I have seen such as Cressington and similar are all small volume units - the Cressington we have will take three thin-sections or four 1 inch mounts. I see one large volume unit available from China - turbo and at a price of between US$6-9k.
Who else has been through a similar situation? What did you find out was the best solution?
Cheers,
malc.

Hi Malcolm,
I have to say: those old Edwards 306A coaters are built like the proverbial "brick sh*t house". They are very robust- yes the roughing/backing valve mechanism is a nightmare to try and repair (just ask our machine shop!), but they can be rebuilt.

We have three of them, one for carbon coating, one for metal evaporation and another as an emergency spare that is left turned off most of the time!

We've replaced a few parts such as the carbon rod holders with some stainless steel designs of our own and they just keep chugging along. 

If I were you I would repair your Edwards coater and/or buy another surplus unit.
john

[jon_wade]

hhv now make the 306 under licence in both diff pumped and turbo variants. I've just bought one, sight unseen, which is always a bit risky but its identical to the old 306. Parts are all named manufacturers  - Edwards turbo's and gauges, Eurotherm controllers and thyristor (the new e fit variant for those that care) and touch screen with pumping schematic.  Nicely, parts are interchangeable with the old 306's so bell jars are being re-used.  So far, I'm pleased with it.

jon

[Malcolm Roberts]

Thanks Jon. I had a look at their website and it is remarkably similar. Would you be willing to divulge how much you paid for said thing?
Cheers,
malc.

[Michael Lance]

Reading the Goldstein book and the User Forum, it is clear that getting uniform carbon coatings with the same thickness for unknowns and standards is critical for Quant EPMA. We have a Cressington Vacuum Coating System from Ted Pella  that sputter coats using carbon rods. We have horrible results from this. Often times we get no coating at all depending on the shape of the tip so I don’t think there is much control with it.
 
Could someone here recommend an evaporation carbon coater that would produce uniform and consistent carbon layers on samples? What are the issues involved with the different coating approaches? What is the optimal approach?
 
Thanks,
 
Michael

[JonF]

We've got a Cressington 208c carbon coater and we're generally happy with it, so as you already have one, it might be worth investigating what's wrong with the one you have.

Regarding rod shape, we have the special sharpener that produces long, thin profile rod rather than like a pencil as seen here : http://www.agarscientific.com/sem/vacuum-coating-materials/hand-tool-for-carbon-rod-shaping

We also use our rotating Planetary tilting stage that also helps as we're able to get closer to the carbon source without getting a gradient, and use brass blocks to monitor thickness (I've found this method more reliable than the thickness monitor). We also have good control over thickness.

I've recently refurbished ours with new ceramics, new copper braid and new spring and it's like new again, so very pleased. The coater seems particularly sensitive to the spring being worn.

[UofO EPMA Lab]

I concur with Jon Fellowes. The color change on brass from red to blue (violet = 20 nm) is thicker than one normally needs for conductivity on smooth samples, but it's a very reproducible transition.

I'm glad to hear about a modern carbon sputter coater that works well, because I'd always seen large gradients in thickness in other models.  That said we're still using a venerable Edwards 306A diff pumped evaporater, which is a real workhorse.

The re-manufactured version of the 306A mentioned by Jon Wade is interesting:

https://probesoftware.com/smf/index.php?topic=623.msg3807#msg3807

[JonF]

I'm glad to hear about a modern carbon sputter coater that works well, because I'd always seen large gradients in thickness in other models.  That said we're still using a venerable Edwards 306A diff pumped evaporater, which is a real workhorse.

From playing around with it, the gradient seems a function of distance from the carbon rod contact.
I think of this as a point source with a hemisphere of carbon coming from it: if the sample is close to the rods then there is a sharp gradient across it (as the thin section is tangental to the hemisphere) but covers a large solid angle, so gets coated very quickly.
Move the sample to the other extreme covers a very small area of the hemisphere and gets much less gradient but is likely to need multiple goes coating.

The rotary planetary stage lets you spin the sample round on two vertical axes and lets you put the sample close up to the carbon rods, giving you the best of both worlds with a nice even coat that gets put down quickly!

From putting the samples in to the coater to taking them back out again with a nice even coat is typically less than 10 minutes. You can usually get 4 (or 8 if you're brave) 1" rounds on to the RPT stage, otherwise you'll only get 2 thin sections without them colliding with each other in the chamber. You can get more thin sections in (5 or 6 plus brass block) if you settle for the rotating rather than RPT stage, but then you need to drop away from the source...

[UofO EPMA Lab]

I'm glad to hear about a modern carbon sputter coater that works well, because I'd always seen large gradients in thickness in other models.  That said we're still using a venerable Edwards 306A diff pumped evaporater, which is a real workhorse.

From playing around with it, the gradient seems a function of distance from the carbon rod contact.

I think of this as a point source with a hemisphere of carbon coming from it: if the sample is close to the rods then there is a sharp gradient across it (as the thin section is tangental to the hemisphere) but covers a large solid angle, so gets coated very quickly.

This makes sense.  Our Edwards 306A coater has a rotary stage which evens out the carbon distribution from the (point) source. I was thinking of our sputter coater which has heads for Au, Ag and C. But even though the target of that sputter coater is over 50mm in diameter, it still always laid down a very narrow radial distribution.  Probably due to the magnetic field which concentrates the deposition area. 

I've always hoped that newer sputter technologies would somehow provide a more even coating deposition over a large area, but I agree that a rotating stage is still probably the most important aspect of coating deposition whether it's evaporation or sputtering.

Do you see any problems from samples that are non ideally flat using sputtering? For example, higher rates of deposition where the surfaces are rough or pointy, because the electric field gets preferentially concentrated there?

[JonF]

Hang on, maybe crossed wires but the carbon coater is an evaporation source, not sputter?

We don't do a huge number of non-flat samples at any rate, the EPMA samples are flat and the majority of samples for the SEM that aren't are usually run in variable pressure mode.

[UofO EPMA Lab]

Hang on, maybe crossed wires but the carbon coater is an evaporation source, not sputter?

We don't do a huge number of non-flat samples at any rate, the EPMA samples are flat and the majority of samples for the SEM that aren't are usually run in variable pressure mode.

Yes, our Edwards 306A is evaporation.

Just curious about sputter coaters, because in principle one would only need to replace the sputter target every few years or so.

[Beamsys]

With due disclaimer that (a) I've been doing C coatings mostly for charge mitigation on FIB Circuit Edit samples, and (b) below are personal impressions and not a conclusion from any kind of comparative study:

The best (perceived as smoothest, cleanest, and most uniform) carbon coatings I've seen were produced by Gatan's PECS system, using ion sputtering. I haven't operated PECS myself, but coatings made in it for me were just perfect.

Overall impression is that good cord and rod evaporation coatings typically come from turbo-pumped systems run by an operator with enough patience to wait for a full pump-down.

I have been using high-vacuum version of Safematic, and despite of my initial skepticism am very pleased with it. Automated exchange of evaporation cord is oh so convenient..

No vested interest in Gatan/AMETEK or Safematic here....

Valery

P.S. I concur that most of old Gatan and Edwards coaters were very well made are worth restoring and rebuilding - providing that skills, time, and resources are available.

Valery Ray (also with REFINE Lab, UCONN)
==========================================
MEO Engineering Company, Inc. DBA "PBS&T"
290 Broadway, Suite 298, Methuen MA 01844
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E-mail: vray@partbeamsystech.com
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