Level sensor, lithographic apparatus and device manufacturing method

A lithographic apparatus, comprising:

• an illumination system configured to condition a radiation beam;
• a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a patterned 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 level sensor that determines a height of a surface of the substrate, the level sensor including:
• (i) an emitter that is arranged to emit a signal directed to a predetermined position on the surface of the substrate such that the signal is at least partially reflected by the substrate to render a reflected signal;
• (ii) a receiver that is arranged to receive at least part of the reflected signal;
• and
• (iii) a processor that determines the height of the surface of the substrate with respect to the level sensor based on the emitted and received signal.

A lithographic projection apparatus arranged to project a pattern from a patterning device onto a substrate, wherein the lithographic projection apparatus includes a level sensor comprising:

• an emitter that is arranged to emit a signal directed to a predetermined position on the surface of the substrate such that the signal is at least partially reflected by the substrate to render a reflected signal;
• a receiver that is arranged to receive at least part of the reflected signal;
• and
• a processor that determines the height of the surface of the substrate with respect to the level sensor based on the emitted and received signal.

A method of determining a height of a surface of a substrate using a level sensor that includes an emitter and a receiver, the method comprising:

• emitting a signal directed to a predetermined position on the surface of the substrate such that the signal is at least partially reflected by the substrate to render a reflected signal;
• receiving at least part of the reflected signal;
• and
• computing the height of the surface of the substrate with respect to the level sensor based on the emitted and received signal.