Process-sensitive metrology systems and methods

Patent metadata

Field	Value
Publication number	US-10216096-B2
Application number	US-201615174111-A
Country	US
Kind code	B2
Filing date	Jun 6, 2016
Priority date	Aug 14, 2015
Publication date	Feb 26, 2019
Grant date	Feb 26, 2019

Abstract

A lithography system includes an illumination source and a set of projection optics. The illumination source directs a beam of illumination from an off-axis illumination pole to a pattern mask. The pattern mask includes a set of pattern elements to generate a set of diffracted beams including illumination from the illumination pole. At least two diffracted beams of the set of diffracted beams received by the set of projection optics are asymmetrically distributed in a pupil plane of the set of projection optics. The at least two diffracted beams of the set of diffracted beams are asymmetrically incident on the sample to form a set of fabricated elements corresponding to an image of the set of pattern elements. The set of fabricated elements on the sample includes one or more indicators of a location of the sample along an optical axis of the set of projection optics.

First claim

What is claimed:

1. A lithography system, comprising:
an illumination source including an off-axis illumination pole, wherein the off-axis illumination pole is separated from an optical axis by a known offset distance along an offset direction, wherein the pattern mask includes a first pattern element segmented with a focus-sensitive pitch along a segmentation direction and a second pattern element segmented with a focus-insensitive pitch along the segmentation direction; and
a set of projection optics configured to expose a sample with an image corresponding to the pattern mask based on illumination from the illumination source to generate exposed features, wherein the focus-sensitive pitch is selected based on the known offset distance such that illumination from the off-axis illumination pole diffracted by the pattern mask based on the focus-sensitive pitch is asymmetrically distributed in a pupil plane of the set of projection optics, wherein widths of segments of the first pattern element are selected such that at least some segments of the first pattern element along the segmentation direction are separated by a sub-resolution distance smaller than a resolution of the set of projection optics, wherein segments of the first pattern element separated by the sub-resolution distance are exposed as merged features, wherein exposed features on the sample corresponding to the first pattern element include one or more indicators of a focal position of the sample during exposure, wherein the focus-insensitive pitch is selected based on the known offset distance such that illumination from the off-axis illumination pole diffracted by the pattern mask based on the focus-insensitive pitch is symmetrically distributed in the pupil plane, wherein exposed features on the sample corresponding to the second pattern element are independent of the focal position of the sample during exposure, wherein differences between the first pattern element and the second pattern element along the segmentation direction with respect to the one or more indicators are indicative of the focal position of the sample during exposure.

2. The lithography system of claim 1 , wherein the offset direction is the segmentation direction.

3. The lithography system of claim 1 , wherein the segmentation direction is a first segmentation direction, wherein the first pattern element is further segmented with the focus-sensitive pitch along a second segmentation direction perpendicular to the first segmentation direction, wherein the offset direction is different than the first segmentation direction and the second segmentation direction.

4. The lithography system of claim 3 , wherein the one or more indicators of the focal position of the sample include one or more indicators measurable along the first segmentation direction and one or more indicators measurable along the second segmentation direction.

5. The lithography system of claim 1 , wherein the off-axis illumination pole is a first off-axis illumination pole, of wherein the illumination source further includes a second off-axis illumination pole symmetric to the first off-axis illumination pole along the offset direction, wherein illumination from the second off-axis illumination pole diffracted by the first pattern element is asymmetrically distributed in the pupil plane, wherein illumination from the second off-axis illumination pole diffracted by the second pattern element is symmetrically distributed in the pupil plane, wherein a combined distribution of illumination in the pupil plane associated with the first off-axis illumination pole and the second off-axis illumination pole is symmetric.

6. The lithography system of claim 5 , wherein the illumination from the first off-axis illumination pole diffracted by the first pattern element and illumination from the second off-axis illumination pole diffracted by the first pattern element are distributed in a non-overlapping pattern in the pupil plane.

7. The lithography system of claim 5 , wherein the one or more indicators of the focal position of the sample comprises:
at least one of sidewall angles or dimensions along the segmentation direction of the exposed features corresponding to segments of the first pattern element.

8. The lithography system of claim 1 , wherein at least some segments of the first pattern element comprise:
two or more sub-elements separated by the sub-resolution distance having different widths along the segmentation direction such that the two or more sub-elements are exposed as the merged features, wherein the merged features are asymmetric.

9. The lithography system of claim 1 , wherein the one or more indicators of the focal position of the sample comprise:
positions of the exposed features corresponding to segments of the first pattern element, wherein displacements along the segmentation direction of the exposed features corresponding to the first pattern element with respect to exposed features corresponding to the second pattern element are indicative of the focal position.

10. The lithography system of claim 1 , wherein the first pattern element is further segmented by the focus-insensitive pitch, wherein the first pattern element comprises:
two or more element groups distributed with the focus-insensitive pitch, wherein at least some element groups of the two or more element groups include two or more sub-elements distributed with the focus-sensitive pitch and separated with the sub-resolution distance such that the at least some element groups are exposed as the merged features.

11. The lithography system of claim 1 , wherein the pattern mask comprises:
a substantially transparent substrate; and
a substantially opaque material.

12. The lithography system of claim 11 , wherein the substantially opaque material includes a metal.

13. The lithography system of claim 1 , wherein the pattern mask comprises:
at least one of a binary pattern mask element or a patterned phase mask.

14. The lithography system of claim 1 , wherein the one or more indicators of the focal position of the sample during exposure comprise:
at least one of pattern placement, sidewall angles, or dimensions along the segmentation direction of the exposed features corresponding to segments of the first pattern element.

15. A metrology system, comprising:
a sample stage configured to support a substrate with a metrology target disposed upon the substrate, wherein the metrology target corresponds to an image of a pattern mask generated by a lithography system including an off-axis illumination pole, wherein the off-axis illumination pole is separated from an optical axis by a known offset distance along an offset direction, wherein the pattern mask comprises:
a first pattern element segmented with a focus-sensitive pitch along a segmentation direction, wherein the focus-sensitive pitch is selected based on the known offset distance such that illumination from the off-axis illumination pole diffracted by the pattern mask based on the focus-sensitive pitch is asymmetrically distributed in a pupil plane of the lithography system during exposure, wherein widths of segments of the first pattern element are selected such that at least some segments of the first pattern element along the segmentation direction are separated by a sub-resolution distance smaller than a resolution of the set of projection optics, wherein segments of the first pattern element separated by the sub-resolution distance are exposed as merged features, wherein features on the metrology target associated with the first pattern element include one or more indicators of a focal position

Assignees

• Kla Tencor Corp

Inventors

• Lee Myungjun
• Smith Mark D
• Kapasi Sanjay
• Pandev Stilian
• Sanko Dzmitry
• Subrahmanyan Pradeep
• Levy Ady

Classifications

• G03F7/70558 Primary

  Dose control, i.e. achievement of a desired dose · CPC title

• G03F7/70091

  Illumination settings, i.e. intensity distribution in the pupil plane or angular distribution in the field plane; On-axis or off-axis settings, e.g. annular, dipole or quadrupole settings; Partial coherence control, i.e. sigma or numerical aperture [NA] · CPC title

• G03F7/70641

  Focus · CPC title

• G03F7/70691

  Handling of masks or workpieces · CPC title

• G03F7/70383

  Direct write, i.e. pattern is written directly without the use of a mask by one or multiple beams (maskless lithography using a programmable mask G03F7/70291) · CPC title