Patent ID: 7733459

Claim:
A lithographic projection apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to hold a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a liquid supply system configured to at least partly fill a space between the projection system and the substrate with a liquid, the liquid supply system comprising a liquid purifier configured to purify the liquid and to maintain optical properties of the liquid in the space substantially constant, wherein the liquid is water or an aqueous solution and the liquid purifier is configured to purify the water or aqueous solution such that it has the following properties (a) to (c) in the space for exposure: (a) a particle content of no more than 2 particles having a dimension of 50 nm or greater per ml of liquid; (b) a dissolved oxygen concentration of 15 ppb or less; and (c) a silica content of 500 ppt or less.