Advantages:

Atlas Technologies specializes in aluminum vacuum chambers.  We strongly believe that aluminum is a superior vacuum material to stainless steel.  It is easy to see by reading the following description of aluminum why the high and ultra high vacuum industry is rapidly embracing aluminum. 

Atlas Aluminum vacuum chambers have excellent ultra high vacuum (UHV) properties and for most applications aluminum is a superior UHV vacuum chamber material.  Aluminum has 10,000,000 x (7 orders of magnitude) less less Hydrogen permeation than stainless steel.   Consequently aluminum chambers have far less H2, H2O, & hydrocarbon vapor at high vacuum and ultra high vacuum levels (references). Aluminum also has less carbon than stainless steel which reduces the amount of carbon based gas contamination in vacuum Atlas Technologies manufactures ultra high vacuum (UHV) aluminum vacuum chambers with a thin dense aluminum oxide this serves as a resistive barrier reducing diffusion and desorption of high vacuum & ultra high vacuum contaminates (Hydrogen, Oxygen & Carbon).  Once baked Atlas' aluminum vacuum chambers generally cycle to high vacuum and ultra high vacuum levels faster than stainless chambers and require less pumping.

The following phyical properties of aluminum describe why it is an excellent vacuum material:

Mechanical properties. Typical elastic modulii for aluminum alloy 6061 T6 and stainless steel alloy 304 [9] are 7470 kgf/mm2 and 19700 kgf/mm2, respectively. If these values are used in mechanical formulae for standard geometries, the ratios of critical thickness for the two materials are [10]: Here, tAS(flat plate), tAS(long cylinder), and tAS(short cylinder) are the minimum thickness ratios to avoid buckling in flat plates, long cylinders, and short cylinders, respectively.

Note that the ratios are close to unity. An aluminum vacuum system will not require parts that have appreciably greater thickness than similar ones manufactured from stainless steel.

Thermal conductivity: Aluminum`s thermal conductivity, depending on the alloy, ranges between 170 W/mK and 230 W/mK. Stainless steels, by contrast, have thermal conductivities that are between 14 W/mK and 16 W/mK (aluminum is 10x stainless). High thermal conductivity is an advantage when designing systems that require temperature cycling. This is the case for vacuum systems that must be baked to reach UHV levels. An aluminum chamber may be baked and then cooled much more rapidly than a stainless chamber. Furthermore, aluminum`s high conductivity allows a complete bakeout without recondensation of gases on local cool spots, a common problem in stainless steel systems.

Due to aluminum's superior thermal conductivity aluminum vacuum chambers bake-out faster, and more uniformly even at lower temperatures (150 C).  

CF Flanges For Aluminum: Atlas Technologies manufactures robust demountable, all-metal-seal, Atlas Flanges tm and Atlas AT-VCR tm face seal fittings which have a stainless steel knife edge or sealing face on a aluminum body for weld-up to an aluminum vacuum chamber.  Browse our Atlas CF Flange tm, Atlas Quick Disconnect Flange or our Atlas AT-VCR tm pages for aluminum vacuum chamber sealing options.

Weight: Aluminum is roughly 1/3 the weight of stainless steel (2.8 g/cm3 [Al] vs. 8.0 g/cm3 [stainless steel alloys]). The cost burden associated with excess weight begins when the raw materials are handled and progresses throughout the manufacturing process. It affects all production steps, including shipping, installation, and even the architectural engineering and construction of the environment surrounding a process tool. Magnetic properties. Aluminum is not magnetic, whereas stainless steel, being essentially an alloy of iron, exhibits residual magnetism. The absence of magnetic properties in aluminum is advantageous for applications involving charged particle beams, because the vacuum chamber will not modify the fields from the beam control magnets.  

Radioactivity: Aluminum, in comparison to stainless steel, has a much more rapid decay of induced radioactivity. If both types of materials are bombarded with the same flux of charged particles, the residual radioactivity will typically be one to two orders of magnitude less for an aluminum sample than for an identical stainless steel sample [13]. The nuclear half-life of elements that make up stainless steel suggests that a-particle contamination is always present in stainless steel and a possible source of circuit damage.

Corrosion: The corrosion of both aluminum and stainless steel alloys in reactive gasses is complicated. Experimental work performed on various alloys in different reactive gaseous environments shows that both aluminum and stainless steel are subject to attack by reactive gasses; halogen-containing species are typically the most damaging; and the corrosion of any given compound is usually no worse than that of its halogen component alone [9, 10]. 

 Aluminum is not a worse corroder than stainless steel. It simply has different reaction dynamics that do not serve as a source of iron and nickel contamination, one of the most significant yield-limiting factors for silicon IC production. Outgassing properties. One of the most important properties of a vacuum material is the outgassing rate, as this determines the ultimate pressure that may be obtained in the vacuum chamber. Repeatable outgassing rates of <10-13 Torr liter/sec cm2 are now possible in aluminum UHV systems [13], comparable to the best outgassing rates obtainable with stainless steel [14]. This improvement in outgassing performance has been one of the principal breakthroughs that has allowed aluminum to become a competent material for the construction of UHV systems. 

Conclusion: Atlas Technologies aluminum vacuum chambers offer extraordinary UHV performance. Surface treatment, automated welding processes, and metal-sealed flange technologies have made this possible. The impact of UHV environments for contamination-free manufacturing processing has yet to be determined in a quantitative fashion. Current studies, however, indicate that they will be essential components of semiconductor materials processing and control and key aspects of 300-mm processing systems.

To learn more about other Atlas' expertise with other vacuum chambers follow this link.

Aluminum is recognized more and more for its superior vacuum properties and lower cost.  Contact Atlas to find out how to make our aluminum technology work for your vacuum application.