Method and apparatus for setting the gap distance between a mask and a wafer at a predetermined distance

A method for setting the gap distance between first and second objects at a predetermined distance so that the respective sample surfaces of the first and second objects are parallel to each other, by means of an apparatus which comprises a first moving stage mobable along an imaginary reference plane defined as a plane parallel to the transferring direction of the first object an supporting the first object, said first moving stage including means for tilting the first object and a first displacement sensor, and a second moving stage supporting the second object and including means for tilting the second object and at least two second displacement sensors, comprising steps of:

• (a) scanning the sample surface of the second object by means of the first displacement sensor in response to the movement of the first moving stage along the reference plane, thereby measuring an error in the parallelism of the sample surface of the second object with respect to the reference plane;
• (b) tilting the second object so as to eliminate the error in the parallelism, thereby keeping the sample surface of the second object parallel to the reference plane;
• (c) measuring distances between the second displacement sensors and at least two points on the sample surface of the first object by means of the second displacement sensors;
• (d) subtracting the distances between the sample surface of the second object and the second displacement sensors from the measured distances, individually, thereby obtaining the gap distances between the sample surface of the second object and the at least two points on the sample suface of the first object, so that an error in the parallelism of the sample surface of the first object with respect to the sample surface of the second object and the gap distance between the respective sample surfaces of the first and second objects are calculated;
• and
• (e) tilting the first object so as to eliminate the calculated error in the parallelism, thereby keeping the respective sample surfaces of the first and second objects parallel to each other, and adjusting the gap distance between the respective sample surfaces of the first and seond objects so that the gap distance is set at the predetermined distance.

An apparatus for setting the gap distance between first and second objects at a predetermined distance so that the respective sample surfaces of the first and second objects are parallel to each other, comprising:

• a first moving stage movable along an imaginary reference plane defined as a plane parallel to a direction in which the first object is transferred and supporting the first object;
• a second moving stage supporting the second object;
• a first displacement sensor disposed on the first moving stage and adapted to scan the sample surface of the second object in response to the movement of the first moving stage along the imaginary reference plane, thereby measuring an error in the parallelism of the sample surface of the second object with respect to the reference plane;
• tilting means attached to the second moving stage and adapted to tilt the second object so as to eliminate the error in the parallelism, thereby keeping the sample surface of the second object parallel to the reference plane;
• at least two second displacement sensors disposed on the second moving stage and adapted to measure distances form at least two points on the sample surface of the first object;
• arithmetic means for subtracting the distances between the sample surface of the second object and the second displacement sensors from the measured distances, individually, thereby obtaining the distances between the sample surface of the second object and the at least two points on the sample surface of the first object, so that an error in the parallelism of the sample surface of the first object with respect to the sample surface of the second object and the gap distance between the respective sample surfaces of the first and second objects are calculated;
• tilting means attached to the first moving stage and adapted to tilt the first object so as to eliminate the error in the parallelism, thereby keeping the respective sample surfaces of the first and second object parallel to each other;
• and
• adjusting means for adjusting the gap distance between the respective sample surfaces of the first and second objects on the basis of the calculated gap distance so that the gap distance is set at the predetermined distance.