Certain processes cannot be performed under atmospheric pressures but rather require vacuum and extreme cleanliness. Production equipment, including any motion control components that are inside the vacuum chamber need to be engineered to not only withstand the low-pressure conditions of vacuum processing but also not to emit (outgas) substances that might interfere with processes, optics or other equipment. There are several pressure regimes relevant to motorized stages of this caliber:
- Rough vacuum – extending as low as 10-2 millibar (mbar) – refers to conditions where many gas / vapour molecules still exist within a chamber, but the bulk gas has been exhausted using a pumping system.
- Process vacuum conditions occupy the pressure range from approximately 10-2 – 10-4 mbar. Here, after initial evacuation the vacuum chamber can be back-filled with special process gasses
- High vacuum refers to the pressure range of 10-5 – 10-9 mbar, where the chamber is empty of all but residual species.
- Ultra-high vacuum is the lowest possible pressure regime achievable with current pumping equipment, extending below 10-9 mbar. UHV chambers are typically void of all but extremely light residual gas molecules like hydrogen.
Operating motorized stages in HV/UHV conditions is challenging for many reasons. At these pressures, trace contaminants on equipment surfaces can desorb in situ and contaminate the process. Mechanical bearings and components that require lubrication also pose a risk of contamination, rendering many conventional motorized stage designs unsuitable for use in HV/UHV processing. When designing motion systems for vacuum applications, it is important to start with the application. For the coating of optics, different vacuum levels can be required, such as for X-ray crystallography for example. The partial pressure of hydrocarbons is often more important than the absolute vacuum pressure. The use of plastics in encoders, cables, limit switches or lubricants with the wrong specifications can result in the excessive contamination of surfaces with hydrocarbons. UV laser light can break down hydrocarbons and destroy optics. Experience in selecting the right materials and handling processes is critical for delivering a solution that will satisfy the requirements of each individual application. Preferred materials for vacuum positioning stages are: stainless steel; titanium; bronze; aluminium; ceramic; sapphiere; Viton; Teflon; PEEK; Kapton; and Macor.