Patent ID: 7616290

Claim:
An exposure apparatus comprising: (a) a projection optical system for projecting a pattern of a reticle onto a plate to be exposed, via a liquid that is filled in a space between the projection optical system and the plate, the projection optical system including a plurality of lenses; (b) a supply pipe for supplying the liquid to the space between a final surface in the projection optical system and the plate; (c) a recovery pipe for removing the liquid from the space between the final surface in the projection optical system and the plate; and (d) a measuring apparatus for measuring a refractive index of the liquid, wherein said measuring apparatus comprises: (i) a cell for accommodating the liquid and transmitting light, wherein the cell is connected to the recovery pipe, and is disposed apart from the space between the final surface in the projection optical system and the plate, and the cell has an accommodating part and a plurality of openings, and each of the openings is connected to the recovery pipe, so that the liquid is recovered through the accommodating part of the cell from the space between the final surface in the projection optical space and the plate; (ii) a detector for detecting an incident position of the light refracted by the liquid in the cell, wherein the light is emitted from a light source and is exposure light used for exposure of the plate, (iii) a beam splitter for splitting the light from the light source; and (iv) a spatial filter arranged between the beam splitter and the cell.