Monday, July 28, 2014

Proper Material Set Up is Key

Material set up is probably the most important thing you can do for your process to run smoothly. Everything about your deposition will derive from it.

I was asked to characterize a coating chamber with materials that were already in place. The materials had been premelted in the electron gun prior to my arrival. I started with the easy stuff first and everything was going well until I came to the Ta2O5.

I started evaporation manually to set power for soak and rate parameters. I set the initial O2 bleed based on rate and the size of the coating chamber. But when I ran an automatic process for a Ta2O5 layer to find the tooling factor and index, I saw some rate and pressure fluctuations that indicated a problem with the material set up.

I opened the chamber and removed the boule of Ta2O5 to find it hadn't been premelted thoroughly. The crucible was filled with Ta2O5 tablets and the top was melted leaving voids beneath the melted surface that is exposed to the vacuum where evaporation occurs.

Bad premelt of Ta2O5

If your material isn't premelted into a solid boule prior to evaporation the problems that will arise include inconsistent rate, spitting, inconsistent refractive index of deposited film, and inconsistent oxidation of deposited film. And of course, bad coatings - performance and quality.

Make sure the materials you start with are well prepared and your films will be well deposited.

Friday, July 18, 2014

Coaters Tech Videos on YouTube

All Coaters Tech videos are available on YouTube to watch at your convenience. Coaters Tech videos are geared towards everyone including engineers, technicians, operators and management.

You can find them all here - https://www.youtube.com/user/coaterstech/videos



Tuesday, July 08, 2014

Memories of a Coating Tech

Having worked in the coating lab for many years when I get together with other coaters there's always some good stories to tell.


Coating failure!
There's the obvious; forgot to put the shutter in, but have you ever forgotten to actually put the parts in? I did a full 3 hour deposition once and when I was done I turned to make room on the flow bench and son of a...! The optics I was supposed to have just coated were still sitting tooled up ready to go in the chamber! I had to stay late without booking the OT to get them coated like I was supposed to.

I once lobbied hard to use a different material for a prototype. I gave every good reason to set up and characterize the material in the chamber and run the tests. I got permission to do so and the results were as I expected and engineering was happy with the results. The day after testing concluded I received the $20K+ single optic to coat for the prototype device. Somewhere in the middle of a long process the new material I had successfully suggested and put into process exploded and spit molten material all over the part. That was not good! The damage to the polished surface was too much to polish out and the part had to be remade. Luckily management was very understanding. But we never used that material again.

Have you ever made a silly mistake? Or a very costly mistake? Let me know. Change the names to protect the innocent or make your tale anonymous if you like.