Method and apparatus for repetitively projecting a mask pattern on a substrate, using a time-saving height measurement

A product manufactured by a lithography technique using a method of projecting a mask pattern on a plurality of substrate fields of a substrate provided with a radiation-sensitive layer, by a projection beam and a projection system, wherein prior to introducing a substrate holder with the substrate into the projection beam and underneath the projection system, a surface profile of the substrate is determined for each substrate field, the method comprising:

• measuring a height of the substrate field in a direction parallel to an axis of the projection beam while moving at least one of a first height sensor and said substrate field with respect to the other in a direction perpendicular to the axis of the projection beam;
• measuring a height of a reference plane of the substrate holder with a second height sensor separate from the first height sensor;
• establishing a relation between the height of the substrate field and the height of the reference plane of the substrate holder and determining an ideal height of the reference plane of the substrate holder based on an ideal height of the substrate field;
• storing the ideal height of the reference plane of the substrate holder for the substrate field in memory;
• and
• after the substrate has been introduced into the projection beam, determining the height of the reference plane of the substrate holder for each substrate field by using a third height sensor separate from the first and second height sensors, and adjusting the height of the substrate holder based upon such determination and the stored ideal height of the reference plane of the substrate holder for each substrate field.

A lithographic projection apparatus suitable for performing a method of projecting a mask pattern on a plurality of substrate fields of a substrate provided with a radiation-sensitive layer, by a projection beam and a projection system, wherein prior to introducing a substrate holder with the substrate into the projection beam and underneath the projection system, a surface profile of the substrate is determined for each substrate field, said apparatus comprising:

• a measuring station for measuring a height of each substrate field and a height of a reference plane of the substrate holder, the measuring station comprising a first height sensor and a separate second height sensor, the first height sensor measuring said height of each substrate field in a direction parallel to an axis of the projection beam, the second height sensor measuring said height of the reference plane of the substrate holder;
• means for establishing a relation between the height of the substrate field and the height of the reference plane of the substrate holder and determining an ideal height of the reference plane of the substrate holder based on an ideal height of the substrate field;
• a memory for storing the ideal height of the reference plane of the substrate holder for each substrate field;
• and
• a projection station for projecting a mask pattern on the plurality of substrate fields of the substrate arranged on the substrate holder, the projection station comprising a third height sensor for measuring the height of the reference plane of the substrate holder after the substrate has been introduced into the projection beam, the third height sensor being separate from the first and second height sensors, wherein the height of the substrate holder is adjusted based upon the measurement by the third height sensor and the stored ideal height of the reference plane of the substrate holder for each substrate field.