Level sensor, a method for determining a height map of a substrate using a selected resolution, and a lithographic apparatus

A method for determining a height map of a substrate for use in a lithographic process using a level sensor, comprising:

• determining a height level of a measurement subarea or a combination of measurement subareas within a measurement area comprising:
• projecting a measurement beam on the substrate by a projection unit,
• receiving a reflected beam by a detection unit,
• determining a resolution for the measurement area,
• calculating a height level of the measurement subarea based on a measurement signal of one detection element associated with the measurement subarea in response to determining a high resolution for the measurement area, and
• calculating a height level of the combination of multiple measurement subareas within the measurement area based on measurement signals of multiple detection elements associated with the combination of multiple measurement subareas in response to determining a low resolution for the measurement area.

A lithographic apparatus comprising:

• an illumination system configured to condition a radiation beam;
• a support configured to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
• a substrate table configured to hold a substrate;
• and
• a projection system configured to project the patterned radiation beam onto a target portion of the substrate,
• wherein the lithographic apparatus comprises a level sensor configured to determine a height level of a surface of the substrate supported on the substrate table, comprising:
• a projection unit configured to project a measurement beam on a measurement area of the substrate,
• a detection unit configured to receive the measurement beam after reflection on the substrate, wherein the detection unit comprises an array of detection elements and each detection element is arranged to receive a part of the measurement beam reflected on a measurement subarea of the measurement area, and is configured to provide a measurement signal based on the part of the measurement beam, and
• a processing unit configured to:
• determine a resolution for the measurement area,
• calculate a height level of the measurement subarea based on the measurement signal of one detection element associated with the measurement subarea in response to determining a high resolution for the measurement area, and
• calculate a height level of a combination of multiple measurement subareas within the measurement area based on measurement signals of multiple detection elements associated with the combination of multiple measurement subareas in response to determining a low resolution for the measurement area.

A level sensor configured to determine a height level of a surface of a substrate, comprising:

• a detection unit configured to receive a measurement beam, wherein the measurement beam results by reflection of a beam off a measurement area of the substrate, the beam being projected by a projection unit, wherein the detection unit comprises an array of detection elements and each detection element is arranged to receive a part of the measurement beam reflected on a measurement subarea of the measurement area, and is configured to provide a measurement signal based on the part of the measurement beam;
• and
• a processing unit configured to:
• determine a resolution for the measurement area,
• calculate a height level of the measurement subarea based on the measurement signal of one detection element associated with the measurement subarea in response to determining a high resolution for the measurement area, and
• calculate a height level of a combination of multiple measurement subareas within the measurement area based on measurement signals of multiple detection elements associated with the combination of multiple measurement subareas in response to determining a low resolution for the measurement area.

A method for determining a height level of a subarea or a combination of subareas within a measurement area of a substrate, comprising:

• projecting a measurement beam on the substrate by a projection unit;
• receiving a reflected beam by a detection unit;
• determining a resolution for the measurement area,
• calculating a height level of each measurement subarea based on a measurement signal of one detection element associated with the measurement subarea in response to determining a high resolution for the measurement area, and
• calculating a height level of the combination of multiple measurement subareas within the measurement area based on measurement signals of multiple detection elements associated with the combination of multiple measurement subareas in response to determining a low resolution for the measurement area.