BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a lithography system for processing a target, such as a wafer, and a method for operating a lithography system for processing a target, such as a wafer.

2. Description of the Related Art

Systems for processing a target are known in the art, usually comprising a final projection system for projecting a pattern on the target surface and a system for determining the position of a wafer with respect to the final projection system. In general, these systems may use position marks on the wafer. Between a first and a second session of projecting a pattern, it may be required to remove the wafer from the lithography system. In that case, it may be required that the position of the pattern of the second session is matched with the position of the pattern of the first session and that the position of the wafer with respect to the final projection system (or the patterning beam) may have to be determined twice, at the beginning of each session. However, it may be difficult to determine the position of the wafer with respect to the final projection system with a high reproducibility.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved lithography system and method for processing a target, such as a wafer. The invention includes a method for operating a target processing system for processing a target on a chuck, the method comprising providing at least a first chuck position mark and a second chuck position mark on the chuck; providing an alignment sensing system arranged for detecting the first and second chuck position marks, the alignment sensing system comprising at least a first alignment sensor and a second alignment sensor; moving the chuck to a first position based on at least one measurement of the alignment sensing system; and measuring at least one value related to the first position of the chuck.

The relative position of the first chuck position mark with respect to the second chuck position mark may be substantially the same as the relative position of the first alignment sensor with respect to the second alignment sensor. The alignment system may be arranged for measuring of the chuck position marks in a substantially horizontal direction (x, y direction). The method may further comprise providing a final projection system arranged to project a patterning beam onto the target, and wherein the first alignment sensor is arranged at a distance from the final projection system in a first direction and the second alignment sensor is arranged at distance from the final projection system in a second direction. In this way, the alignment sensors may be arranged along perpendicular x- and y-axes to provide a faster determination of position of the chuck position marks in both dimensions.

The method may comprise projecting a patterning beam onto the target to form a beam grid on the target, wherein the first alignment sensor is arranged for detecting a position mark at a distance from the beam grid in a first direction and the second alignment sensor is arranged for detecting a position mark at a distance from the beam grid in a second direction. In this arrangement, the alignment sensors are arranged along perpendicular x- and y-axes with respect to the beam grid projected onto the target, to provide a faster determination of position of the chuck position marks in both dimensions.

The method may comprise projecting a patterning beam onto the target to form a beam grid on the target, wherein the alignment sensing system comprises one or more alignment sensors arranged for detecting a position mark at distance from the beam grid, and wherein the method further comprises determining a spatial relationship between the one or more alignment sensors and the beam grid. The step of determining a spatial relationship between the one or more alignment sensors and the beam grid may comprise determining a vector for each alignment sensor describing the position of the alignment sensor relative to the beam grid in a substantially horizontal direction (e.g. an x, y direction).

The alignment sensing system may comprise at least one alignment sensor for detecting a position mark on a surface of the target and/or the chuck, and the alignment sensor may comprise a light source arranged for providing an alignment light beam; a light intensity detector arranged for determining a light intensity of a reflected alignment light beam, wherein the reflected alignment light beam is generated by reflection of the alignment light beam by the surface; and an optical system arranged for focusing the alignment light beam on the surface and for guiding the reflected alignment light beam on the light intensity detector.

The step of measuring at least one value relating to the first position of the chuck may comprise moving the chuck to align the chuck position marks with the alignment sensors, and measuring at least one value related to the current position of the chuck. The step of moving the chuck to align the chuck position marks with the alignment sensors may comprise moving the chuck in two horizontal axes (e.g. x- and y-axes) and rotating the chuck about a vertical axis (e.g. Rz direction) as necessary to achieve the alignment.

Aligning the chuck position marks with the alignment sensors may comprise performing a minimum least squares fit of the alignment of a first chuck position mark with a first alignment sensor, and a second chuck position mark with a second alignment sensor.

A chuck position measurement system may be provided comprising at least two interferometers, wherein measuring at least one value related to the first position of the chuck comprises measuring an output of the interferometers. The method may further comprise initializing the interferometers with the chuck located at the first position. The method may further comprise storing the at least one measured value related to a first position of the chuck as a chuck initialization position.

A level sensing system may be provided comprising a plurality of level sensors, and a reference surface may be provided on the chuck, the method further including measuring at least one value relating to the orientation of the reference surface with respect to the level sensors. The method may further comprise moving the chuck to align the reference surface with a level sensor plane of the level sensors prior to measuring at least one value relating to orientation of the beam grid. This enables the tilt of the chuck to be corrected or aligned to simply subsequent measurements and processing. The step of moving the chuck to align the reference surface with a level sensor plane of the level sensors may comprise measuring a distance from the first level sensor to the reference surface and measuring a distance from the second level sensor to the reference surface, and moving the chuck as necessary so that the reference surface coincides with the level sensor plane. The level sensing system may be arranged for measuring a distance to the surface in a substantially vertical direction (e.g. a z direction). The level sensing system may comprise a differential capacitive sensing system. The level sensing system may comprise at least a first level sensor arranged at a distance from the final projection system in a first direction and a second level sensor arranged at distance from the final projection system in a second direction.

The alignment sensing system may comprise at least one alignment sensor and the level sensing system may comprise at least one level sensor, and the at least one alignment sensor may be arranged to detect a position mark on the surface at a first point and the at least on level sensor may be arranged for measuring distance to the surface at the first point or adjacent to the first point.

The method may further comprising measuring a position of a nominal target center for a target loaded directly or indirectly on the chuck with respect to the alignment sensing system. The method may further comprise moving the chuck to a second position based at least in part on the measured value related to the first position of the chuck, and measuring at least one value related to the second position of the chuck. The method may further comprise providing a reference target having a target position mark at a center position of the reference target; moving the chuck to align the center position with at least one of the alignment sensors; and measuring a current position of the chuck. The method may include determining a relative position of the center position of the reference target with respect to each of the alignment sensors, e.g. by calculating a vector.

The invention also relates to a method, which may be performed additionally to or separately from the above-described method, the method comprising the steps of generating a patterning beam, the patterning beam having a focal length on a focal plane, moving the chuck to position the beam position sensor under the patterning beam, the patterning beam forming a beam grid on the beam position sensor, and measuring at least one value relating to orientation of the beam grid on the beam position sensor. The step of generating the patterning beam may comprise generating a plurality of sub-beams, the sub-beams being arranged in a grid formation. The method may further comprise providing at least one blocking feature on the beam position sensor, and the step of measuring at least one value relating to orientation of the beam grid on the beam position sensor may comprises sweeping the patterning beam across the at least one blocking feature of the beam position sensor.

The step of generating the patterning beam may comprise generating a plurality of sub-beams arranged in a grid formation, the step of providing at least one blocking feature on the beam position sensor may comprise providing a plurality of blocking features arranged on the beam position sensor at relative spatial positions corresponding to the nominal relative spatial positions of the sub-beams, and the step of sweeping the patterning beam may comprise sweeping the plurality of sub-beams across corresponding ones of the plurality of blocking features.

The target may have a first pattern and target position marks formed on a surface, the method further comprising aligning the chuck and the beam grid based on the at least one measured value relating to orientation of the chuck and the at least one measured value relating to orientation of the beam grid. The step of aligning the chuck and the beam grid may comprise rotating the chuck about a vertical axis (e.g. the Rz direction). The step of measuring at least one value relating to orientation of the chuck with respect to the alignment sensors may comprise determining a substantially horizontal chuck axis, wherein the step of generating the patterning beam comprises generating a plurality of sub-beams arranged in a grid formation, the sub-beams being arranged relative to a substantially horizontal beam grid axis, and wherein the step of aligning the chuck and the beam grid comprises aligning the chuck axis parallel to the beam grid axis.

The invention further relates to a method, which may be performed additionally to or separately from the above-described methods, the method comprising the steps of aligning the surface of the target with the focal plane of the patterning beam. The step of aligning the surface of the target with the focal plane of the patterning beam may comprise moving the chuck substantially horizontal in two dimensions (x, y directions) as necessary to position an origin of the chuck under an origin of the beam grid, and moving the chuck in a substantially vertical direction (z direction) as necessary to position the origin of the chuck in the focal plane of the final projection system. The method may further comprise rotating the chuck about a substantially horizontal axis (Rx, Ry direction) as necessary to align the reference surface to a level sensor plane.

The method may further comprise rotating the chuck about a substantially vertical axis (Rz direction) as necessary to align an axis of the chuck with an axis of the beam grid, and may comprise calibrating the level sensors to a level sensor plane coinciding with the focal plane. The method may further comprise measuring at least one value relating to orientation of a first pattern formed on the target.

The invention further relates to a method, which may be performed additionally to or separately from the above-described methods, the method comprising the steps of measuring an offset of a center position of the first pattern on the target with respect to a nominal center position for the target, and calculating at least one value relating to a position of the target position marks with respect to the alignment sensing system based on the offset and the position of the target position marks with respect to the target.

The step of measuring at least one value relating to orientation of the first pattern beam grid in the above-described methods may further comprise moving the chuck to position a center position of the first pattern on the target under the first alignment sensor; moving the chuck to position a first target position mark under a first alignment sensor; and determining a position of the first target position mark with respect to the beam grid. The method may further comprise moving the chuck to position the center of the target under the second alignment sensor; moving the chuck to position a second target position mark under a second alignment sensor; and determining a position of the second target position mark with respect to the beam grid.

The above-described methods may further comprise aligning the first pattern formed on the surface with the beam grid based on the at least one measured value relating to orientation of the first pattern and the at least one measured value relating to orientation of the beam grid. The methods may include rotating the target to align an axis (y-axis) of the first target pattern with a corresponding axis (y-axis) of the beam grid, and may further include forming a second pattern on the surface with the patterning beam.

The invention also relates to a method for forming a second pattern on a target with a patterning beam, the second pattern being aligned with a first pattern previously formed on a surface of the target, the method comprising providing a lithography system for generating the patterning beam, the lithography system comprising a final projection system for projecting the patterning beam onto the surface, and further comprising an alignment sensing system and a level sensing system; and providing a chuck, the chuck comprising chuck position marks and a beam position sensor. The method includes the steps of moving the chuck to a first position based on at least one measurement of the alignment sensing system and measuring at least one value related to the first position of the chuck; measuring a position of a nominal center of a target loaded directly or indirectly on the chuck with respect to the alignment sensing system; generating the patterning beam, the patterning beam having a focal length on a focal plane; moving the chuck to position the beam position sensor under the patterning beam, the patterning beam forming a beam grid on the beam position sensor; and measuring at least one value relating to orientation of the beam grid on the beam position sensor. The method may further include the steps of positioning the target directly or indirectly on the chuck, the target having a surface and having a first pattern and target position marks formed on the surface; aligning the chuck and the beam grid based on the at least one measured value relating to orientation of the chuck and the at least one measured value relating to orientation of the beam grid; aligning the surface of the target with the focal plane of the patterning beam; measuring at least one value relating to orientation of the first pattern; aligning the first pattern formed on the surface with the beam grid based on the at least one measured value relating to orientation of the first pattern and the at least one measured value relating to orientation of the beam grid; and forming the second pattern on the surface with the patterning beam.

The invention further relates to a method for determining a spatial relationship of a pattern with respect to a beam grid, wherein the pattern is formed on a surface of a target and the target is positioned directly or indirectly on a chuck, and wherein the beam grid is formed by projecting a patterning beam onto the surface. The method comprises moving the chuck to a first position and measuring at least a first value relating to a spatial relationship of the chuck with respect to a reference coordinate frame; moving the chuck to a second position, the chuck movement based at least in part on the first value, and measuring at least one value relating to a spatial relationship of the target with respect to the reference coordinate frame; moving the chuck to a third position, the chuck movement based at least in part on the first value, and measuring at least one value relating to a spatial relationship of the beam grid with respect to the reference coordinate frame; moving the chuck to a fourth position, the chuck movement based at least in part on the first value, the second value, and the third value, and measuring at least one value relating to a spatial relationship of the pattern with respect to the reference coordinate frame.

In yet another aspect, the invention relates to a target processing system for processing a target on a chuck, the system comprising: a moveable chuck including at least a first chuck position mark and a second chuck position mark; an alignment sensing system arranged for detecting the first and second chuck position marks, the alignment sensing system comprising at least a first alignment sensor and a second alignment sensor, an actuator arranged for moving the chuck to a first position based on at least one measurement of the alignment sensing system; and a measurement system arranged for measuring at least one value related to the first position of the chuck.

The relative position of the first chuck position mark with respect to the second chuck position mark may be substantially the same as the relative position of the first alignment sensor with respect to the second alignment sensor. The alignment system may be arranged for measuring of the chuck position marks in a substantially horizontal direction (x, y direction). The system may further comprise a final projection system arranged to project a patterning beam onto the target, and wherein the first alignment sensor is arranged at a distance from the final projection system in a first direction (y-axis) and the second alignment sensor is arranged at distance from the final projection system in a second direction (x-axis).

The system may further comprising a final projection system for projecting a patterning beam onto the target to form a beam grid on the target, wherein the first alignment sensor is arranged for detecting a position mark at a distance from the beam grid in a first direction (y-axis) and the second alignment sensor is arranged for detecting a position mark at a distance from the beam grid in a second direction (x-axis).

The system may further comprise a final projection system for projecting a patterning beam onto the target to form a beam grid on the target, wherein the alignment sensing system comprises one or more alignment sensors arranged for detecting a position mark at distance from the beam grid, and wherein the system further comprises a measurement system for determining a spatial relationship between the one or more alignment sensors and the beam grid.

The measurement system may be arranged to determine a spatial relationship between the one or more alignment sensors and the beam grid by determining a vector for each alignment sensor describing the position of the alignment sensor relative to the beam grid in a substantially horizontal direction (x, y direction). The alignment sensing system may comprise at least one alignment sensor for detecting a position mark on a surface of the target and/or the chuck, the alignment sensor comprising a light source arranged for providing an alignment light beam; a light intensity detector arranged for determining a light intensity of a reflected alignment light beam, wherein the reflected alignment light beam is generated by reflection of the alignment light beam by the surface; and an optical system arranged for focusing the alignment light beam on the surface and for guiding the reflected alignment light beam on the light intensity detector.

The chuck may comprise at least two chuck position marks on the chuck, and wherein the measurement system is arranged for measuring at least one value relating to the first position of the chuck including moving the chuck to align the chuck position marks with the alignment sensors; and measuring at least one value related to the current position of the chuck. The measurement system and chuck actuator may be arranged for moving the chuck to align the chuck position marks with the alignment sensors including moving the chuck in two horizontal axes (x, y-axis) and rotating the chuck about a vertical axis (Rz direction) as necessary to achieve the alignment.

The system may be arranged for aligning the chuck position marks with the alignment sensors, comprising performing a minimum least squares fit of the alignment of a first chuck position mark with a first alignment sensor, and a second chuck position mark with a second alignment sensor. The system may further comprising a chuck position measurement system comprising at least two interferometers, and wherein measuring at least one value related to the first position of the chuck comprises measuring an output of the interferometers. The system may be arranged for initializing the interferometers with the chuck located at the first position. The measurement system may be arranged for storing the at least one measured value related to a first position of the chuck as a chuck initialization position.

The system may further comprise a level sensing system comprising a plurality of level sensors, and a reference surface on the chuck, the system arranged for measuring at least one value relating to the orientation of the reference surface with respect to the level sensors. The measurement system and actuator may be arranged for moving the chuck to align the reference surface with a level sensor plane of the level sensors prior to measuring at least one value relating to orientation of the beam grid.

The level sensing system may be arranged to measure a distance from the first level sensor to the reference surface and measuring a distance from the second level sensor to the reference surface; and the actuator is arranged to move the chuck as necessary so that the reference surface coincides with the level sensor plane. The level sensing system may be arranged for measuring a distance to the surface in a substantially vertical direction (z direction). The level sensing system may comprise a differential capacitive sensing system. The level sensing system may comprise at least a first level sensor arranged at a distance from the final projection system in a first direction (y-axis) and a second level sensor arranged at distance from the final projection system in a second direction (x-axis).

