Lithographic apparatus, device manufacturing method and device manufactured thereby
View Patent ↗The X, Y and Rz positions of a mask stage are measured using two optical encoder-reading heads measuring displacements of respective grid gratings mounted on the mask stage. The grid gratings are preferably provided on cut-away portions of the mask table so as to be coplanar with the pattern on the mask itself. Measurements of the table position in the other degrees of freedom can be measured with capacitive or optical height sensors.
1. A lithographic apparatus comprising:
a support structure configured to support a patterning device, the patterning device configured to pattern a beam of radiation;
a substrate table configured to hold a substrate;
a projection system configured to project the patterned beam onto a target portion of the substrate; and
a displacement measurement system having a first sensor unit and a second sensor unit and configured to measure a displacement of a moveable object in two degrees of freedom relative to a reference frame, the movable object comprising one of the support structure and the substrate table, wherein
the displacement measurement system further comprises two grid gratings mounted on the reference frame, each grid grating corresponding to one of the first and second sensor units; and
the first and second sensor units are mounted on the moveable object and configured to measure displacements of a respective one of the grid gratings.
2. The lithographic apparatus of claim 1 , wherein the reference frame comprises the projection system.
3. The lithographic apparatus of claim 1 , wherein each of the first and second sensor units comprises a pair of sensor heads.
4. The lithographic apparatus of claim 1 , wherein the measurement system further comprises a Z-sensor configured to measure at least another degree of freedom of the moveable object relative to the reference frame.
5. The lithographic apparatus of claim 3 , wherein each of the sensor heads includes an encoder.
6. The lithographic apparatus of claim 4 , wherein the Z-sensor comprises:
an interferometer system configured to co-operate with a reflective surface of a grid grating, or
a capacitive sensor system configured to co-operate with a conductive part of a grid grating.
7. A lithographic apparatus comprising:
a support structure configured to support a patterning device, the patterning device configured to pattern a beam of radiation;
a substrate table configured to hold a substrate;
a projection system configured to project the patterned beam onto a target portion of the substrate; and
a displacement measurement system configured to measure a displacement of a moveable object in at least two degrees of freedom relative to a reference frame, the movable object comprising one of the support structure and the substrate table, and the displacement measurement system having a first sensor head and a first sensor unit comprising a pair of sensor heads, wherein
the displacement measurement system further comprises a grid grating mounted on the moveable object; and
the first sensor head and the first sensor unit are mounted on the reference frame and configured to measure a displacement of the grid grating.
8. The lithographic apparatus of claim 7 , wherein each of the sensor heads includes an encoder.
9. The lithographic apparatus of claim 7 , wherein the measurement system further comprises a fourth sensor head.
10. A lithographic apparatus comprising:
a support structure configured to support a patterning device, the patterning device configured to pattern a beam of radiation;
a substrate table configured to hold a substrate;
a projection system configured to project the patterned beam onto a target portion of the substrate; and
a displacement measurement system having a first sensor unit and a second sensor unit and configured to measure a displacement of a moveable object in two degrees of freedom relative to a reference frame, the movable object comprising one of the support structure and the substrate table, wherein
the displacement measurement system further comprises two grid gratings mounted on the moveable object, each grid grating corresponding to one of the first and second sensor units; and
the first and second sensor units are mounted on the reference frame and configured to measure displacements of a respective one of the grid gratings, wherein at least one of the two grid gratings include a reference mark detectable by the respective sensor unit to define a reference position of the movable object.
11. A lithographic apparatus comprising:
a support structure configured to support a patterning device, the patterning device configured to pattern a beam of radiation;
a substrate table configured to hold a substrate;
a projection system configured to project the patterned beam onto a target portion of the substrate; and
a displacement measurement system configured to measure a displacement of a moveable object in at least two degrees of freedom relative to a reference frame, the movable object comprising one of the support structure and the substrate table, and the displacement measurement system having a first sensor head and a first sensor unit comprising a pair of sensor heads, wherein
the displacement measurement system further comprises a grid grating mounted on the reference frame; and
the first sensor head and the first sensor unit are mounted on the moveable object and configured to measure a displacement of the grid grating.