Abstract: A gas manifold to direct a gas flow between two plates of an optical component of a lithographic apparatus, the gas manifold having an inlet, a diffuser downstream of the inlet, a flow straightener downstream of the inlet, a contractor downstream of the flow straightener, and an outlet downstream of the contractor.

Abstract: In a lithographic method, a characteristic of a projection system is measured before and after periods of heating (exposures) and cooling to provide data to calibrate a model of lens heating. The model has a part modeling the effect of cooling and a part modeling the effect of heating on the characteristic.

Abstract: A thick pellicle is allowed to have a non-flat shape and its shape is characterized to calculate corrections to be applied in exposures to compensate for the optical effects of the pellicle. The pellicle may be mounted so as to adopt a one-dimensional shape under the influence of gravity to make the compensation easier.

Abstract: The projection system of a lithographic apparatus has a plurality of pupil planes and at least two irises provided in respective pupil planes each optimized to provide a high degree of NA uniformity over a respective NA range so that a high degree of NA uniformity can be provided over a wide range of NA settings.

Abstract: In a projection system a pattern plane on a reticle is illuminated to have a projection image focussed on an image plane. The presence of a pellicle in the optical path causes a virtual shift of the position of the pattern plane on the reticle. Depending on the presence or absence of the pellicle the image plane of the projection image needs to be adapted for proper focussing. A compensator counteracts the virtual shift of pattern plane due to the pellicle, by shifting the position of the pattern plane.

Abstract: In, for example, an immersion lithography apparatus, a sensor that would normally be provided on the substrate table is replaced by a retro-reflector on the substrate table and a sensor at, for example, patterning device level. This may avoid the need to make the sensor compatible with the immersion liquid and also make incoupling of radiation easier since the numerical aperture may be less at, for example, patterning device level.

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.

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.

Abstract: In a projection system a pattern plane on a reticle is illuminated to have a projection image focussed on an image plane. The presence of a pellicle in the optical path causes a virtual shift of the position of the pattern plane on the reticle. Depending on the presence or absence of the pellicle the image plane of the projection image needs to be adapted for proper focussing. A compensator counteracts the virtual shift of pattern plane due to the pellicle, by shifting the position of the pattern plane.

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.