Atlas Technologies' Aluminum Ultra High Vacuum UHV,
Frequently Asked Questions

Why change my vacuum system to aluminum?

“ Use Aluminum!” when you are:

1)  having trouble with long pump-downs,

2)  experiencing to much H 2 , H 2 O contamination,

3)  experiencing surface desorption of gases in a high energy photon environment,

4)  experiencing a & b particle damage on your substrate,

5)  in need of a light weight vacuum system,

6)  having Fe, Cr, C, CO, CO 2 contamination in a plasma environment,

7)  in need of a electrically isolating environment,

8)  in need of a large process tool with a small foot print,

9)  need a low magnetic environment,

10) experiencing synchrotron or process generated Bremsstrahlung radiation,

1) having trouble with long pump-downs?  Use Aluminum! Aluminum has 10 x the thermal conductivity and 21 x the thermal diffusivity of stainless steel. This means that It heats up faster and it heats more completely during bake out, and it cools off faster as well. Cycle time can be improve by hours or perhaps days.

2) experiencing to much H 2 , H 2 O contamination? Use Aluminum! Like stainless aluminum surfaces must be cleaned and prepared for vacuum. Environmentally compatible detergents can clean the machined surface of aluminum of thick porous oxides and lay down thin dense oxide layers. This thin 40-50 Å dense surface layer seals the aluminum from further oxide growth. Research suggests that after the first bake out and pump down aluminum desorbs less water vapor than stainless.

You cannot easily coat the surface of stainless! It must be machined and polished. But even the its' surface remains porous and as you know it holds water vapor and out gasses H 2 what seems forever. Outgassing rates of <10 -13 Torr liter/sec cm 2 may be achieved with aluminum.

3) experiencing desorption of gases in a high energy photon environment? Use Aluminum! That's what happens in a UV lithography environments and in process environments such as PVD, RTA, ashing etc or just bake out. Well … put a bigger pump on. The pump will only add a few tens of thousands of dollars to the system. Or …. learn from the particle accelerator people. They have built the largest vacuum systems in the world, so big they measure them in kilometers. They operate them in the -11s and they build them of aluminum. Research has shown that synchrotron radiation, x-ray and deep UV cause gasses desorbtion from stainless steel quenching the vacuum, aluminum is a superior material for such applications.

4) experiencing a & b particle damage on your devices? Use Aluminum! It has been observed since WW II, hundreds of above ground nuclear tests, and accidents like Chernobyl, that all mill product steels decay a , b particles and gamma radiation. It seems that steels have a component of recycled steel in them. This steel has been nuclear activated from the environment and through illegal scrap metal recycling. Steel has a very long nuclear half life ~ 500K years. If you want steel that doesn't have this problem you have to retrieve it from ships sunk in the ocean before the nuclear age.

When your building devices with feature sizes in the 100nm class, a & b particle contamination becomes and issue. Aluminum is considered nuclear transparent. When exposed to radiation, it passes through it leaving very little residual results. With this in mind, the decision to use aluminum process chambers is an easy one.

5) need of a light weight vacuum system?   Use Aluminum! Aluminum is 1/5 th the weight of stainless. When evaluating material thickness requirements you discover that the typical ratios of critical thickness of the two materials are near unity suggesting that aluminum systems can be made of materials as thin as stainless. Aluminum is also easy to machine, about 5 times the speed of stainless steel and although people say it is hard to weld, it welds fast, like every thing else one has to learn how to do it.

6) having Fe Cr, C, CO, CO 2 contamination in a plasma environment?  Use Aluminum! Iron is one of the major contamination sources in PVD and Etch process environments. The plasma excites the Fe and other alloy materials and you get contamination. Use a aluminum vacuum chamber that has been anodized with a high density thin ~ 1 mil coating.

7)  need of a electrically isolating environment?  Use Aluminum! Aluminum oxide (alumna) is a ceramic with a very high dielectric constant. The oxide can be easily applied to a chamber using the anodization process. A high density thin ~ 1 mil coating will serve to electrically isolate a chamber at the same time as provide a very strong chemical resistance.

8)  need of a large process tool with a small foot print?  Use Aluminum! Does tube and flange technology of the stainless steel era remind you of your Uncles heating plant. Now imagine a system carved from blocks of metal with flange to flange distances at their minimum. Imagine associated supports and wiring harnesses screwed in orderly way right to the chamber using a modular bracket system. Image zero length internal studs that allow gate valves to be flush mounted both sides. All this and more is possible with aluminum. Try it with stainless and hang on to your wallet.

9)  need a low magnetic environment?  Use Aluminum! Aluminum is not magnetic whereas stainless steel, being essentially an alloy of iron exhibits residual magnetism. For applications that involve charged particles such as ion milling and even PVD and plasma etch, etc. aluminum is of advantage because it implies that the system will not modify environment.

10)  experiencing synchrotron or process generated B remsstrahlung radiation? Use Aluminum! Produced by high energy electrons encountering mater, the rapid deceleration results in gamma-ray production, a shower of electron-positron pairs and other particles. Bremsstrahlung radiation is the dominant source of radiation in electron accelerators. This radiation can be harmful to the research or process being conducted and harmful to personnel. Because of the superior out gassing performance of aluminum,(i.e. lower Hydrogen and carbon) the vacuum levels can be maintained lower levels than stainless steel systems resulting in a lower overall level of Bremsstrahlung radiation.