Rail system for wafer transportation

A method, comprising:

• receiving a first rail plan;
• assembling an overhead raceway module comprising a plurality of installation positions for a rail assembly;
• after the assembling of the overhead raceway module, installing the overhead raceway module to a ceiling;
• installing the rail assembly to one of the plurality of installation positions according to the first rail plan;
• after the installing of the rail assembly, receiving a second rail plan different from the first rail plan;
• and
• reinstalling the rail assembly to another of the plurality of the installation positions according to the second rail plan without uninstalling the overhead raceway module from the ceiling.

A method, comprising:

• installing a pre-assembled overhead raceway module to a ceiling, the pre-assembled overhead raceway module comprising:
• a plurality of first level raceways extending along a first direction, each of the plurality of first level raceways being fastened to a plurality of hangers configured to be mounted on the ceiling, and
• a plurality of second level raceways extending along a second direction perpendicular to the first direction, each of the plurality of second level raceways being fastened to the plurality of first level raceways;
• installing a rail assembly to a first position on the plurality of second level raceways;
• and
• shifting the rail assembly from the first position to a second position on the plurality of second level raceways,
• wherein the second position is spaced apart from the first position along the second direction.