Friday, March 30, 2007
It's Shiny and Glittery, and Covered With Aluminum Foil!
One of the most common comment that I get when I show our deposition system to visitors is "What's with all the aluminum foil?" In fact, as you can see from the picture, you can't even see the vacuum chamber since it is almost completely covered by it.
Anyone who has done any work in trying to get to ultra-high vacuum (UHV) can tell you that one of the things we have to do after we vent and close our system is to do a "bake-out" during pumping. While all the vacuum pumps are running, we want to reach the vacuum system to above 100 C to drive out moisture and gases that may have been absorbed (or adsorbed) into the walls of the vacuum system. So the outer part of the vacuum chamber is often wrapped with heating tapes. To reduce heat loss and increase the heating efficiency, we also cover the vacuum chamber with aluminum foil. Thus, the presence of aluminum foil in many systems that go down to UHV level.
For the system in the picture, we usually do a bake-out for about 2 to 3 days, and after cooling, we can consistently get down to as low as 2.5 x 10^-10 Torr using a combination of ion and turbo pumps. Since we do have to vent the system pretty often, it is a lot easier to just leave the heating tapes and the aluminum foil "wrappings" on the chamber. So we haven't actually seen the whole chamber underneath all that aluminum foil for about a year (I'm guessing it's still there!).