Patent ID: 9091945
Filing Date: 2015-07-28
Classification: G02B,G03F

Abstract:
1. An illumination system having a pupil surface, comprising: a spatial light modulator configured to vary an intensity distribution of light in the pupil surface of the illumination system, the spatial light modulator comprising an array of reflective elements configured to reflect impinging light into variable directions; a beam folding unit configured to direct the light toward the spatial light modulator, the beam folding unit comprising a prism having a surface on which the light impinges a first time and a second time, the first time being when the light leaves the prism and before the light is reflected by the reflective elements, the second time being when the light enters the prism after the light has been reflected by the reflective elements; and a pupil perturbation suppressing mechanism configured to: a) reduce reflections of the light when the light impinges on the surface the first time; and/or b) prevent reflections of the light when the light impinges on the surface the first time from contributing to the intensity distribution of the light in the pupil surface, wherein the illumination system is a microlithographic illumination system.