	US 12,105,433 B2
	Imaging overlay targets using moiré elements and rotational symmetry arrangements
Yoel Feler, Haifa (IL); Mark Ghinovker, Yoqneam Ilit (IL); Diana Shaphirov, Yoqneam Illit (IL); Evgeni Gurevich, Yokneam Illit (IL); and Vladimir Levinski, Nazareth Ilit (IL)
Assigned to KLA Corporation, Milpitas, CA (US)
Filed by KLA Corporation, Milpitas, CA (US)
Filed on Feb. 18, 2022, as Appl. No. 17/675,912.
Application 17/675,912 is a continuation of application No. 16/743,124, filed on Jan. 15, 2020, granted, now 11,256,177.
Claims priority of provisional application 62/898,980, filed on Sep. 11, 2019.
Claims priority of provisional application 62/954,256, filed on Dec. 27, 2019.
Prior Publication US 2022/0171297 A1, Jun. 2, 2022 Prior Publication US 2024/0210841 A9, Jun. 27, 2024
Int. Cl. G03F 7/00 (2006.01)

CPC G03F 7/70633 (2013.01)

6 Claims

1. A metrology system comprising:

an imaging system comprising:

an illumination source to generate illumination;

one or more illumination optics to direct illumination from the illumination source to a metrology target, the metrology target comprising:

a working zone including a single instance of a Moiré pattern, wherein the working zone is rotationally symmetric, wherein the Moiré pattern includes a grating structure with a first pitch (p₁) along a measurement direction on a first sample layer and a grating structure with a second pitch (p₂) along the measurement direction on a second sample layer, wherein the second pitch is different than the first pitch;

a detector to generate an image of the metrology target based on the illumination from the illumination source, wherein an optical configuration of the imaging system is configurable according to at least a first optical configuration and a second optical configuration, wherein the first optical configuration and the second optical configuration differ by at least one of a wavelength of the illumination, a polarization of the illumination incident on the metrology target, an angle of the illumination incident on the metrology target, or a focal position of the metrology target;

a controller configured to be coupled to the imaging system, the controller including one or more processors configured to execute program instructions causing the one or more processors to:

receive a first image of the working zone including the single instance of the Moiré pattern using the first optical configuration, wherein the first image includes first Moiré fringes associated with the Moiré pattern with a Moiré pitch related to a difference between the first pitch and the second pitch;

determine a first axis of symmetry of the working zone along the measurement direction based at least in part on positions of the first Moiré fringes the first image;

receive a second image of the working zone including the single instance of the Moiré pattern using the second optical configuration, wherein the second image includes second Moiré fringes associated with the Moiré pattern with the Moiré pitch;

determine a second axis of symmetry of the working zone along the measurement direction based at least in part on positions of the second Moiré fringes in the second image;

determine an optical overlay measurement based on a difference between the first axis of symmetry and the second axis of symmetry; and

calculate an overlay error along the measurement direction associated with the first sample layer and the second sample layer by adjusting the difference between the axes of symmetry in the first image and the second image by a Moiré gain based on pitches of the Moiré pattern.