Seismic Isolation system, including microlithography system for submicron design rule.

摘要

An active inertial isolation system is disclosed generally for any inertial body, and also for bodies subject to structural resonance, and further particularly for a microlithography system (2) for processing semiconductor wafers (4) subject to a submicron design rule. Acceleration of a body or worktable (6) is sensed and fed back, independent of floor position or motion, or variance thereof, to linear forcers (74, 76) with feedback loop gain km to actively isolate the worktable (6), increasing its dynamic mass and reducing its resonant frequency. The sensed acceleration is also integrated to velocity and fed back with loop gain kc to the linear forcers to inertially derive and increase damping of the worktable. The worktable is also stabilized against tilting without increasing the spring constant of soft spring supports (8,32). Vertical and horizontal system loops (110, 104) feed back only high frequency components to respective vertical and horizontal linear forcers. The horizontal loop additionally feeds back low frequency components to vertical linear forcers, additively on one side of the center of mass, and subtractively on the other side of the center of mass, and subtractively on the other side of the center of mass of the system, compensating tilting upon lateral stage motion in a step and repeat system. The stepper command (40) may also apply a predictive correction signal to the vertical linear forcers knowing beforehand the direction and displacement of lateral stage movement. The soft spring supports (8,32) are augmented by linear forcers, but the latter may have substantially lower supporting capability. Various arrangements are disclosed for isolating a body against structural resonance.