Non-contact autofocus height detector for lithography systems

Details Non-contact autofocus height detector for lithography systems Non-contact autofocus height detector for lithography systems

1999-03-22

2001-06-12

Nguyen, Kiet T. (Department: 2881)

Radiant energy

Calibration or standardization methods

C250S491100, C250S492200

Reexamination Certificate

active

06246053

ABSTRACT:

FIELD OF THE INVENTION
The field of the invention is that of lithography, in particular the use of particle beams to write a pattern in a photoresist.
BACKGROUND OF THE INVENTION
Modern steppers for semiconductor lithography and micromachining have a depth of focus that is only a few microns. Since the vertical position of a wafer or other workpiece can easily move by more than that (because of irregularities in the wafer stage motion, irregularities in the wafer exposure surface such as bowing, and thermal expansion of the system components), it is known to measure the position of the wafer and, if necessary, change the wafer height or readjust the focus. Prior art systems have suffered from the limitation that the position sensors can not be allowed to block the beam, so that fixed position sensors must measure the height at a position considerably removed from the actual exposure location.
In the case of e-beam exposure systems, there are additional problems such as evaporation of the photoresist during exposure and subsequent contamination of the sensors and restrictions on the materials of the measurement system (non-magnetic and non-insulating) in order to avoid interference with the beam.
SUMMARY OF THE INVENTION
The invention relates to an apparatus for measuring the distance between the final lens (or other reference surface) in the optical train of a lithography system and the top surface of the wafer at the area being exposed, in which a support arm moves from a calibration position well away from the beam to a measurement position on the optical axis of the system.
An advantageous feature of the invention is the insensitivity of the measurement to mechanical construction and alignment differences between the calibration subsystem and the environment of the measurement.
Another advantageous feature of the invention is the ability to calibrate the sensors as often as desired in order to compensate for thermal and other changes.
Yet another advantageous feature of the invention is the ability to select sensors and other materials without regard to whether they would interfere with the beam.
Yet another advantageous feature of the invention is that the sensor is not subjected to contamination, which could affect performance, generated by exposure of photoresist by the electron beam.


REFERENCES:
patent: 4885472 (1989-12-01), Young

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