METHOD OF REDUCING CYCLIC ERROR EFFECTS IN A LITHOGRAPHIC PROCESS, PROJECTION SYSTEM AND LITHOGRAPHIC APPARATUS COMPRISING A PROJECTION SYSTEM

摘要

It is an object of the invention to provide a method of reducing cyclic error effects in a lithographic process. Further, it is an object of the invention to provide a projection system that is arranged to reduce cyclic error effects and a lithographic apparatus comprising such projection system. According to an aspect the invention there is provided method of reducing cyclic error effects in a lithographic process having a projection phase and an idle phase, wherein the method comprises controlling in a first control loop a first position of a first module, the first module being a position controlled mirror of a projection system, the first control loop having a first bandwidth and comprising a first position measurement system having a first cyclic error, wherein controlling the first position comprises continuously moving the first module at least during the projection phase, such that a first main frequency of the first cyclic error will be above the first bandwidth of the first control loop. According to an aspect the invention there is provided projection system to project a beam, comprising: a first module having a first movement range, the first module being a position controlled mirror of the projection system arranged to reflect the beam. a first position measurement system to measure a first position of the first module, a control system comprising a first control loop to control the first position of the first module, the first control loop having a first bandwidth, wherein the control system is arranged to continuously move the first module at least during a projection phase of a lithographic process, such that a first main frequency of a first cyclic error of the first position measurement system will be above the first bandwidth of the first control loop. According to an aspect the invention there is provided a method lithographic apparatus comprising the projection system of any of the claims 15-28.