Method of measuring asymmetry in a scatterometer, a method of measuring an overlay error in a substrate and a metrology apparatus

• US 20080239318A1
• Filed: 03/30/2007
• Published: 10/02/2008
• Est. Priority Date: 03/30/2007
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Den Boef, Arie Jeffrey, Van Der Mast, Karel Diederick, Der Schaar, Maurits Van
• Granted Patent: US 7,656,518 B2
• Time in Patent Office: Days
• US Class Current: 356/369
• CPC Class Codes: G01N 21/4785 Standardising light scatter apparatus; Standards therefor
• CPC Class Codes: G03F 7/70516 Calibration of components of the microlithographic apparatus, e.g. light sources, addressable masks or detectors
• CPC Class Codes: G03F 7/70616 Monitoring the printed patterns
• CPC Class Codes: G03F 7/70633 Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching

Abstract

In a method of measuring asymmetry in a scatterometer, a target portion is illuminated twice, first with 0° of substrate rotation and secondly with 180° of substrate rotation. One of those images is rotated and then that rotated image is subtracted from the other image. In this way, asymmetry of the scatterometer can be corrected.

Claims

1. A method of measuring asymmetry in a scatterometer, the method comprising:

first illuminating a target pattern with radiation and measuring a first two-dimensional angular scatter spectrum of radiation reflected and/or scattered by the target pattern by using the scatterometer to measure intensity at a plurality of pre-determined angular positions relative to the target pattern;

relatively rotating the target pattern and the scatterometer by about 180°

in a plane substantially perpendicular to the optical axis of the scatterometer;

second illuminating the target pattern with radiation and measuring a two-dimensional angular scatter spectrum by using the scatterometer to measure intensity at the plurality of pre-determined positions relative to the target pattern and rotating that angular scatter spectrum by 180°

to produce a second two-dimensional angular scatter spectrum; and

producing a sensor correction value for each of the plurality of pre-determined angular positions by, for each of the plurality of pre-determined positions, subtracting the intensity at the respective pre-determined position of the first two-dimensional angular scatter spectrum from the intensity at the respective pre-determined position of the second two-dimensional angular scatter spectrum.

2. The method of claim 1, wherein each intensity at the pre-determined positions is measured over an integration time of at least about 200 milliseconds.

3. The method of claim 2, wherein each intensity at the pre-determined positions is measured over an integration time of at least about 400 milliseconds.

4. The method of claim 1, wherein the first illuminating, relatively rotating, second illuminating and producing are first carried out with radiation polarized in a first direction to obtain any asymmetry correction value for each of the plurality of pre-determined angular positions for radiation polarized in the first direction and then carried out with radiation polarized in a second direction to obtain a sensor correction value for each of the plurality of pre-determined angular positions for radiation polarized in the second direction.

5. The method of claim 1, further comprising updating the sensor correction value for each pixel by dividing it by two.

8. A method of measuring an overlay error in a substrate comprising:

projecting a beam of radiation onto a target pattern on the substrate;

measuring an overlay two-dimensional angular scatter spectrum of radiation reflected and/or scattered by the target pattern by using a scatterometer to measure intensity at a plurality of pre-determined angular positions relative to the target pattern;

computing a corrected two-dimensional angular scatter spectrum by subtracting, for each pre-determined position, a sensor correction value for a respective pre-determined position obtained using the method of claim 1 from the measured intensity at the respective position of the overlay two-dimensional angular spectrum; and

determining the overlay error from the corrected two-dimensional angular scatter spectrum.

6. A method of measuring asymmetry in a scatterometer due to illumination beam asymmetry, the method comprising:

first measuring with a detector of the scatterometer the intensity of radiation of an illumination beam at a plurality of pre-determined positions relative to the detector in a cross-section of the illumination beam to produce a first map of intensities;

relatively rotating the illumination beam and the scatterometer by about 180°

in a plane substantially perpendicular to an axis of the illumination beam;

second measuring with the detector the intensity of radiation of the illumination beam at the plurality of pre-determined positions relative to the detector and rotating the produced map of intensities by about 180°

to produce a second map of intensities; and

producing an illumination asymmetry correction value for each of the plurality of pre-determined positions by, for each of the plurality of pre-determined positions, subtracting the intensity at the respective pre-determined position of the first map of intensities from the intensity at the respective pre-determined position of the second map of intensities.

7. A method of measuring asymmetry in a scatterometer due to asymmetries in a microscope objective of the scatterometer, the method comprising:

(1) obtaining sensor correction values using a method including

first illuminating a target pattern with radiation and measuring a first two-dimensional angular scatter spectrum of radiation reflected and/or scattered by the target pattern by using the scatterometer to measure intensity at a plurality of pre-determined angular positions relative to the target pattern;

relatively rotating the target pattern and the scatterometer by about 180°

in a plane substantially perpendicular to an optical axis of the scatterometer;

second illuminating the target pattern with radiation and measuring a two-dimensional angular scatter spectrum by using the scatterometer to measure intensity at the plurality of pre-determined positions relative to the target pattern and rotating that angular scatter spectrum by 180°

to produce a second two-dimensional angular scatter spectrum; and

producing a sensor correction value for each of the plurality of pre-determined angular positions by, for each of the plurality of pre-determined positions, subtracting the intensity at the respective pre-determined position of the first two-dimensional angular scatter spectrum from the intensity at the respective pre-determined position of the second two-dimensional angular scatter spectrum; and

(2) obtaining illumination asymmetry correction values using a method including

first measuring with a detector of the scatterometer the intensity of radiation of an illumination beam at the plurality of pre-determined positions in a cross-section of the illumination beam to produce a first map of intensities;

relatively rotating the illumination beam and the scatterometer by about 180°

in a plane substantially perpendicular to the axis of the illumination beam;

second measuring with the detector the intensity of radiation of the illumination beam at the plurality of pre-determined positions and rotating the produced map of intensities by about 180°

to produce a second map of intensities; and

producing an illumination asymmetry correction value for each of the plurality of pre-determined positions by, for each of the plurality of pre-determined positions, subtracting the intensity at the respective pre-determined position of the first map of intensities from the intensity at the respective pre-determined position of the second map of intensities; and

(3) for each pre-determined position, subtracting the respective illumination asymmetry correction value from the sensor correction value to obtain a microscope objective asymmetry value for each respective pre-determined position.

9. A metrology apparatus configured to measure a property of a substrate, the apparatus comprising:

a radiation projector configured to illuminate a target pattern of a substrate with radiation;

a detector configured to measure an intensity of reflected and/or scattered radiation from the target pattern at a plurality of pre-determined angular positions relative to the target pattern;

a system configured to relatively rotate the target pattern and the scatterometer by about 180°

in a plane substantially perpendicular to the target portion; and

a controller adapted to

control illumination of the target pattern with radiation,

determine a first two-dimensional angular scatter spectrum of radiation reflected and/or scattered by the target pattern by using the detector to measure intensity at a plurality of pre-determined angular positions relative to the target pattern,

relatively rotate the target pattern and the scatterometer by about 180°

in a plane substantially perpendicular to an optical axis of the scatterometer,

control illumination of the target pattern with radiation and determine a two-dimensional angular scatter spectrum by using the detector to measure intensity at the plurality of pre-determined portions relative to the target pattern and rotate that angular scatter spectrum by about 180°

to produce a second two-dimensional angular scatter spectrum, and

produce a sensor correction value for each of the plurality of pre-determined angular positions by, for each of the plurality of pre-determined positions, subtracting the intensity at the respective pre-determined position of the first two-dimensional angular scatter spectrum from the intensity at the respective pre-determined position of the second two-dimensional angular scatter spectrum.

10. The metrology apparatus of claim 9, further comprising a system to store the sensor correction value for each of the plurality of pre-determined angular positions.

11. The metrology apparatus of claim 9, wherein the controller is further adapted to

project a beam of radiation onto a target pattern on a substrate;

measure an overlay two-dimensional angular scatter spectrum of radiation reflected and/or scattered by the target pattern by using the detector to measure intensity at the plurality of pre-determined angular positions relative to the target pattern,

compute a corrected two-dimensional angular scatter spectrum by subtraction, for each pre-determined position, a respective the sensor correction value for a respective pre-determined position from the measured intensity at the respective position of the overlay two-dimensional angular spectrum, and

determine the overlay error from the corrected two-dimensional angular scatter spectrum.