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Anonymous Poster #1

Silicon Substrate Cleaning Before Coating

04/03/2019 6:14 PM

I have some (6" long & 4" wide) odd shaped flat Si (silicon) substrates.

Need to coat (Thin Film AR) both sides.

Need to clean the substrate (both sides) before coating, but after coating, I'm getting bunch of stain marks.

I used RCA cleaning method. But without good result.

I'm in USA working in a sophisticated Lab.

Anybody has any idea?

Even, do not have to be a chemical cleaning process, could be an ion milling (Etching) process. Let me know.

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#1

Re: Silicon Substrate Cleaning before Coating

04/03/2019 8:02 PM

"I'm in USA working in a sophisticated Lab."

What does this have to do with the price of tea in China?

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#2

Re: Silicon Substrate Cleaning before Coating

04/03/2019 8:26 PM
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#3

Re: Silicon Substrate Cleaning before Coating

04/03/2019 9:57 PM

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#4

Re: Silicon Substrate Cleaning before Coating

04/04/2019 2:42 AM

Here's an idea. Contact a more <...sophisticated lab...> for advice.

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#6
In reply to #4

Re: Silicon Substrate Cleaning before Coating

04/04/2019 10:38 AM

Here's a golden lab, perhaps he can help.

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Re: Silicon Substrate Cleaning before Coating

04/04/2019 2:45 AM
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#7

Re: Silicon Substrate Cleaning Before Coating

04/04/2019 12:11 PM

Pack a bag and brings a sample of your defect.

Then attend ..The appropriate trade show to ask the question... coming soon to a venue near you.

July 9-11 San Fran

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#8

Re: Silicon Substrate Cleaning Before Coating

04/04/2019 1:19 PM

Clean the Silicon with ethanol but not denatured ethanol. This is what the vacuum technicians use to maintain UHV cleanliness. There will be some added legal paperwork you will have to obtain for a chemical company to sell you this product. You need this to prove an industrial need for pure ethanol and that you will not drink it or sell it as a beverage.

You might find the thin Anti-Reflective coating is actually showing surface irregularities and not cleanable contaminants.

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#9
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Re: Silicon Substrate Cleaning Before Coating

04/05/2019 4:11 AM

We clean optics for UHV use in IPA then demin water followed by a gentle bake at 50°C to ensure that everything is driven off. We do see surface irregularities which are in the AR coating, not the substrate.

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#10
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Re: Silicon Substrate Cleaning Before Coating

04/05/2019 9:09 AM

I'm not sure why our vacuum technicians don't use isopropyl alcohol (I doubt you meant India Pale Ale ). Isopropyl alcohol would also leave a very low residue once it has evaporated. I suspect that without a bakeout any remaining isopropyl will just take too long to pump out versus ethanol.

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#11
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Re: Silicon Substrate Cleaning Before Coating

04/05/2019 9:24 AM

You could be right, all of our products as part of the final processing get a 380°C bake for 2-3 days.

(Now I really want some India Pale Ale).

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#12
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Re: Silicon Substrate Cleaning Before Coating

04/05/2019 10:20 AM

380°C would certainly expedite vaporization for evacuation of most chemicals. But three days of machine downtime for every UHV repair would not be acceptable. Some of our in vacuum cryogenic systems would not be happy with that level of baking. Still, when the LN2 starts to flow the vacuum levels drop even further.

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#13
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Re: Silicon Substrate Cleaning Before Coating

04/05/2019 10:38 AM

I imagine ½ hour of downtime would have most manufacturers screaming. We need a long bake for other reasons.

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#14

Re: Silicon Substrate Cleaning Before Coating

04/05/2019 12:05 PM

first what are the spots made of.

Two ways of cleaning

1. wash with Diluted HF acid. this will lightly etch the silicon. Rinse with DI water, rinse again. dry with N2 jets. Now you have to deal with the HF residue. calcium carbonate will bind it up. the slight etch will help with adhesion of your coating.

2. clean with Methanol, not IPA, Rinse with DI water. repeat the rinse and then dry with N2 jets.

IPA will leave a residue, methanol does not.

to get rid of the water that is still hydrogen bonded to the silicon heat to 315C. then coat.

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