Abstract: A device manufacturing method includes projecting a patterned beam of radiation through an optics compartment and a channel that provides an open connection between the optics compartment and a substrate compartment onto a substrate, maintaining an ionized flush gas at a higher pressure in the channel than in the substrate compartment and in the optics compartment during the projecting, intercepting particles that emanate from the substrate with the ionized flush gas, pumping the flush gas carrying the intercepted particles from the substrate compartment using a pump coupled to a gas outlet coupled to at least one of the compartments, and establishing an electrical potential difference between a wall of the channel and the outlet and/or a rotor of the pump so that the outlet and/or the rotor of the pump attracts positively charged ions that stem from the flush gas in the channel.

Abstract: In an off-axis levelling procedure a height map of the substrate is generated at a measurement station. The height map is referenced to a physical reference surface of the substrate table. The physical reference surface may be a surface in which is inset a transmission image sensor. At the exposure station the height of the physical reference surface is measured and related to the focal plane of the projection lens. The height map can then be used to determine the optimum height and/or tilt of substrate table to position the exposure area on the substrate in best focus during exposure. The same principles can be applied to (reflective) masks.