How do you achieve ultra-high vacuum levels?

In order to achieve ultra high vacuum conditions, special materials and pumping procedures are needed. Seals and gaskets used between components in a UHV system must prevent even trace leakage. Therefore, nearly all such seals are all metal, with knife-edges on both sides cutting into a soft gasket, typically copper. These all-metal seals can maintain integrity to UHV ranges.

Tips for achieving ultra-high pressure include:

1. Use a small chamber size (to minimize surface area);
2. High pumping speeds using multiple vacuum pumps in series and/or in parallel;
3. High conductance tubing to the pumps — large diameter, short runs with minimal obstructions (valves, etc.);
4. Use of low outgassing materials (stainless steel, aluminum, titanium, etc.);
5. Avoid creating pits of trapped gas behind bolts, welding voids, etc.;
6. All internal metal parts should be electropolished after machining or welding;
7. Use low vapor pressure materials (ceramics, glass, metals, Teflon if unbaked);
8. Bake the system to remove water or hydrocarbons adsorbed to the walls;
9. Chill chamber walls to cryogenic temperatures during use;
10. Use gloves to avoid all traces of hydrocarbons, including skin oils in fingerprints.

Source: VAC AERO International – Pumps for High and Ultra-High Vacuum