Abstract: A level sensor for a lithographic projection apparatus includes a light source configured to direct light onto a substrate to be measured, a detector configured to detect light reflected from the substrate, and a processor configured to calculate a difference between measurements made with the filter in the first configuration and in the second configuration. The sensor is adjustable between a first configuration, in which the light is given a first property, and a second configuration, in which the light is given a second property. The sensor may include a polarizing filter, such that the first and second properties are different polarization states.

Abstract: A level sensor for a lithographic projection apparatus according to one embodiment of the invention includes a light source, a first reflector, a second reflector and a detector. The first reflector is positioned to direct light from the light source towards a wafer surface, and the second reflector is positioned to direct light reflected from the wafer surface to the detector. The first and second reflectors are selected to incur a minimal process dependent apparent surface depression.

Abstract: According to one embodiment, a method of calibrating level sensors of at least two lithographic projection apparatus to correct machine to machine level sensor process dependency includes using a first lithographic projection apparatus to measure a first set of leveling data for a reference substrate and a second set of leveling data for a substrate processed according to a selected process, and using a second lithographic projection apparatus to measure a third set of leveling data for the reference substrate and a fourth set of leveling data for the processed substrate. The method also includes calculating, based on the first, second, third and fourth sets of leveling data, a set of level sensor parameters corresponding to machine to machine level sensor differences for the selected process, wherein the machine to machine level sensor differences are measured and stored as intrafield values.

Abstract: A method of calibrating level sensors of at least two lithographic projection apparatus to correct machine to machine level sensor process dependency includes measuring a first set of leveling data using a first lithographic projection apparatus for a reference substrate, measuring a second set of leveling data using the first apparatus for a substrate processed according to a selected process, measuring a third set of leveling data using the second apparatus for the reference substrate, measuring a fourth set of leveling data using the second apparatus for the processed substrate, and using the first, second, third and fourth sets of leveling data to calculate the set of level sensor parameters corresponding to machine to machine level sensor differences for the selected process.

Abstract: A level sensor for a lithographic projection apparatus according to one embodiment of the invention includes a light source, a first reflector, a second reflector and a detector. The first reflector is positioned to direct light from the light source towards a wafer surface, and the second reflector is positioned to direct light reflected from the wafer surface to the detector. The first and second reflectors are selected to incur a minimal process dependent apparent surface depression.

Abstract: A method of calibrating level sensors of at least two lithographic projection apparatus to correct machine to machine level sensor process dependency includes measuring a first set of leveling data using a first lithographic projection apparatus for a reference substrate, measuring a second set of leveling data using the first apparatus for a substrate processed according to a selected process, measuring a third set of leveling data using the second apparatus for the reference substrate, measuring a fourth set of leveling data using the second apparatus for the processed substrate, and using the first, second, third and fourth sets of leveling data to calculate the set of level sensor parameters corresponding to machine to machine level sensor differences for the selected process.