US 5,552,888 AGranted

Apparatus for measuring position of an X-Y stage

AssigneeNikon Precision Inc.

InventorsMichael R. Sogard, Martin E. Lee

Life of this patent

Estimating the term…

Loading patent…

Abstract

An interferometer used to measure distance to an object is provided with a laser sheath. The sheath encloses a substantial part of the measurement beam's path to provide a controlled environment which reduces environmental influences on the measured distance. The sheath is of variable length and responsive to a follower so as to maintain a sheath end nearest the object at a small distance from the object. An environmental controller controls the environment within the sheath. The environment within the sheath can be a vacuum or a suitable gas or gas mixture. A corrector can be used to compensate the interferometer's measured-distance signal for detected environmental characteristics to produce a corrected signal which indicates distance between the interferometer and the reflective surface. The apparatus and methods can be used to measure and control stage position in a projection-type wafer exposure system which is affected by variations in its atmospheric environment.

Claims29

Dependent claims

Apparatus for measuring position of an XY stage, comprising:

a. a stage movable along mutually-orthogonal X and Y axes, the stage having an X-axis mirror and a Y-axis mirror;
b. a first laser interferometer for directing an X-axis measurement beam along an X-axis beam path toward the X-axis mirror and for producing a first measured-distance signal indicative of an optical path length between the first laser interferometer and the X-axis mirror;
c. a sheath enclosing the X-axis measurement beam along substantially the entire X-axis beam path to define a volume of controlled environment for the X-axis measurement beam, the sheath including an X-axis sheath portion having an effective length which varies in response to a follower system as the X-axis mirror changes position;
d. a second laser interferometer for directing a Y-axis measurement beam along a Y-axis beam path toward the Y-axis mirror and for producing a second measured-distance signal indicative of an optical path length between the second laser interferometer and the Y-axis mirror;
e. a sheath enclosing the Y-axis measurement beam along substantially the entire Y-axis beam path to define a volume of controlled environment for the Y-axis measurement beam, the sheath including a Y-axis sheath portion having an effective length which varies in response to a follower system as the Y-axis mirror changes position;
f. an X-axis follower system for varying the effective length of the X-axis sheath portion so that substantially the entire X-axis beam path remains enclosed as the X-axis mirror changes position relative to the first laser interferometer, wherein the X-axis follower system comprises a follower which follows movement of the stage while remaining out of contact with the stage, and wherein an end of the X-axis sheath portion nearest the X-axis mirror is mounted for movement with the follower such that said end of the X-axis sheath remains at a substantially constant spacing from the X-axis mirror;
and
g. a Y-axis follower system for varying the effective length of the Y-axis sheath portion so that substantially the entire Y-axis beam path remains enclosed as the Y-axis mirror changes position relative to the second laser interferometer.

5 more elements

Apparatus for measuring position of a stage movable along mutually-orthogonal first and second axes, the stage having a first reflector substantially normal to the first axis, comprising:

a. a first-axis laser interferometer for directing a first-axis measurement beam along a first beam path parallel to the first axis toward the first reflector and for producing a measured-distance signal indicative of an optical path length between the first-axis laser interferometer and the first reflector;
b. a first-axis follower system having a first-axis follower which follows movement of the stage along the first axis while remaining out of contact with the stage;
and
c. a first-axis sheath enclosing the first-axis measurement beam along a substantial part of the first beam path to define a volume of controlled environment for the first-axis measurement beam, the first-axis sheath including a movable sheath portion carried by the follower such that the sheath has an effective length which varies with movement of the stage along the first axis while remaining out of contact with the stage.

1 more element

Dependencies are inferred from the claim text.

Facts

Application: 08/349,733Filed 2 Dec 1994
Granted: 3 Sep 1996
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

G01B 9/0207
Reduction or prevention of errors; Testing; Calibration: error reduction by correction of the measurement signal based on independently determined…
G01B 9/02021
With multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations: contacting…
G01B 9/02027
Characterised by the beam path configuration: two or more interferometric channels or interferometers
G01B 9/02052
Characterised by particular mechanical design details: protecting, e.g. shock absorbing, arrangements