LIGHTING DEVICE FOR SEMICONDUCTOR EXPOSURE DEVICE

摘要

PROBLEM TO BE SOLVED: To provide the lighting device which can prevent speckle formation without making an optical path difference arising means large in size for a light source having long coherent length and reduce a place where an optical thin film is formed. SOLUTION: An incident beam 1 is made incident on the incidence/projection surface 2 of a prism 3 at an angleθ. The incident beam 1 is split by a means such as the optical thin film on the incidence surface 2 into reflected light and refracted light 5 at a specific ratio. The refracted light 5 travels in the prism 3 and is totally reflected by reflecting surfaces 6 and 8 where the thin film is absent and reflected by a reflecting surface 7 to return to nearby the incidence position. The returned circulation light is split into projection light which is parallel to the starting reflected light and travels to outside the prism 3 and reflected light which travels into the prism 3. The reflected light which is reflected by the incidence/projection surface 2 into the prism 3 is repeatedly circulated in the prism 3. Almost all of the incident beam 1 comes together as the reflected light and following projection light to become a projection beam 4. Speckles are reduced since the difference in length between optical paths that respective projection light beams of the projection beam 4 have passed is set to more than the half of a coherence distance.