The precision with which the wafer stage, which carries the silicon wafers, is positioned is of critical importance in semiconductor exposure tools, since the wafer must be moved at high speed but very accurately during the exposure process. Etching a 130 nanometer-wide circuit requires an error factor of not more than (10 nanometers. To attain such precision, the wafer stages of Canon's semiconductor exposure tools employ a non-contact air guidance system that uses porous ceramic static pressure bearings and a linear motor, with the wafer stage being pneumatically floated. This eliminates friction, and enables high-speed, accurate positioning. This wafer stage can control wafer position in all three dimensions to within a few nanometers. In the future, circuits will be even further miniaturized, and wafer stages offering sub-nanometer precision will be required. Semiconductor exposure tools of the future will likely require a vacuum to boost circuit patterning precision further, and Canon is currently working on the development of vacuum air bearings technology to enable the use of air bearings in a vacuum.