Patent ID: 7948607
Filing Date: 2011-05-24
Classification: G03F

Abstract:
1. An immersion lithography apparatus comprising: an optical system for projecting a pattern onto a part of a surface of a wafer, the optical system having a liquid delivery unit arranged to dispose, when in use, a quantity of an immersion liquid for filling a space between the optical system and the surface of the wafer, the liquid delivery unit having a lower horizontal surface defining a clearance between the lower horizontal surface and the surface of the wafer, the liquid delivery unit including a first port for deploying the quantity of the immersion liquid and including a second port for deploying a quantity of a barrier liquid, the second port to dispense into the clearance; a carrier unit for carrying the wafer, the carrier unit being arranged to move, when in use, relative to the optical system for exposing different parts of the surface of the wafer to the pattern; and a source of the barrier liquid arranged to provide through the second port, when in use, the quantity of the barrier liquid adjacent and in contact with the quantity of the immersion liquid, thereby preventing ingress to the quantity of the immersion liquid of a gas external to the quantity of the barrier liquid, wherein the barrier liquid is hydrophobic and non-aqueous and has a density between about 700 kgm