EXPOSURE METHOD

1 . A method for exposing a surface of a target in a system comprising a projection lens for focusing one or more beams onto the surface for exposing the target, and a set of sensors mounted in a fixed relationship to the projection lens for measuring distance to the target, the method comprising:

clamping the target to a moveable table;

moving the target to a plurality of positions in which one or more of the sensors are positioned above the target;

receiving signals from one or more of the sensors positioned above the target;

calculating one or more tilt correction values based on the signals received from the sensors;

adjusting the tilt of the table based on the one or more tilt correction values in advance of the exposure;

exposing the target; and

adjusting the vertical position of the table during the exposure based on signals received from the sensors.

2 . The method of claim 1 , further comprising deriving a height map of height variations over the surface of the area of the target to be exposed, from the signals received from the sensors and wherein the adjustment of the vertical position of the table during the exposure is based on the height map.

3 . The method of claim 1 , wherein the tilt of the table is adjusted once per exposure of the target based on the one or more tilt correction values.

4 . The method of claim 1 , wherein multiple sets of tilt correction values are calculated for different areas of the target, and the tilt of the table is adjusted more than once per exposure of the target based on the multiple sets of tilt correction values.

5 . The method of claim 1 , wherein the step of calculating one or more tilt correction values comprises determining local gradients of the target at several pre-determined positions.

6 . The method of claim 5 , wherein the predetermined positions include positions at equidistant spacing around the periphery to the target.

7 . The method of claim 1 , wherein the one or more tilt correction values comprise a correction in the x-direction and a tilt correction in the y-direction, where the x- and y-directions are perpendicular to each other and generally perpendicular to the beam or beams used to expose the target.

8 . The method of claim 1 , wherein the adjustment of the vertical position of the table during the exposure is based on interpolation between measured values from the sensors.

9 . A lithography system for exposing a target, the system comprising:

a projection lens arrangement for projecting one or more beams onto the target for exposing the target;

a moveable table for carrying the target clamped to the table;

a plurality of sensors each sensor for measuring a distance between the sensor and the surface of the target at a sensing position; and

a processing unit for receiving signals from sensors and calculating one or more tilt correction values based on the signals received from the sensors;

wherein the table further comprises a tilt mechanism for adjusting the tilt of the table based on the one or more tilt correction values, and wherein the system is further configured to adjust the tilt in advance of exposure of the target and adapt for variation in the distance between the projection lens and the wafer surface during exposure of the target.

10 . The lithography system of claim 9 , wherein each of the sensors comprise a thin film structure, the thin film structure comprising a sensor having a first insulating layer and a first conductive film comprising a sensing electrode formed on a first surface of the first insulating layer, a second conductive film comprising a back guard electrode, the back guard electrode formed in a single plane and comprising a peripheral portion in the same plane, the back guard electrode disposed on a second surface of the first insulating layer and a first surface of a second insulating layer or protective layer, wherein the peripheral portion of the back guard electrode extends beyond the sensing electrode to form a side guard electrode which substantially or completely surrounds the sensing electrode.

11 . A method for measuring a topology of a surface of a target in a system comprising a set of sensors for measuring distance to the target, the method comprising:

moving the target to a first position in which a measurement point on the target coincides with a first subset of the sensors;

measuring a distance between each sensor of the first subset of sensors and the target and storing one or more values based on the first measurements;

moving the target to a second position in which the measurement point on the target coincides with a point under a projection lens and with a second subset of the sensors;

measuring a distance between each sensor of the second subset of sensors and the target, and storing one or more values based on the second measurements; and

calculating a value for distance to the target at the point under the projection lens based on the stored values of the first and second measurements.

12 . The method of claim 11 , wherein the value for distance to the target at the point under the projection lens is determined by interpolating between stored values of the second measurements based on stored values of the first measurements.

13 . The method of claim 11 , further comprising determining a topology of the target t the measurement point on the target based on the first measurements.

14 . The method of claim 1 , further comprising determining an amount of bow of the target at the measurement point of the target based on the first measurements.

15 . The method of claim 14 , wherein the value for distance to the target at the point under the projection lens is determined by interpolating between stored values of the second measurements based on the amount of bow of the target at the measurement point of the target.

16 . The method of claim 11 , further comprising measuring tilt of the target based on stored values of the first and second measurements.

17 . The method of claim 16 , wherein stored values used to determine the tilt derive from measurements of at least three sensors arranged in a triangular arrangement.

18 . The method of claim 11 , wherein the set of sensors comprise an array of sensors.

19 . A lithography system for exposing a target, the system comprising:

a projection lens arrangement for projecting one or more beams onto the target for exposing the target;

a moveable stage for carrying the target, the stage being moveable in at least a first direction;

a plurality of sensors, each sensor for measuring a distance between the sensor and the target at a sensing position, the plurality of sensors comprising:

at least a first sensor with a sensing position aligned with and spaced from the projection lens arrangement in a direction parallel to and opposite to the first direction;

a first subset of one or more sensors, each sensor of the first subset aligned with the first sensor in a direction perpendicular to the first direction;

a second subset of one or more sensors, each sensor of the second subset aligned with and spaced from the projection lens in a direction perpendicular to the first direction; and

a calculation unit for calculating a value dependent on a distance between the projection lens arrangement and the target, the value based on the measurements from the first subset of sensors and the measurements from the second subset of sensors.

20 . The lithography system of claim 19 , further comprising at least one thin film structure, the thin film structure comprising a sensor having a first insulating layer and a first conductive film comprising a sensing electrode formed on a first surface of the first insulating layer, a second conductive film comprising a back guard electrode, the back guard electrode formed in a single plane and comprising a peripheral portion in the same plane, the back guard electrode disposed on a second surface of the first insulating layer and a first surface of a second insulating layer or protective layer, wherein the peripheral portion of the back guard electrode extends beyond the sensing electrode to form a side guard electrode which substantially or completely surrounds the sensing electrode.