A metal mask includes: a metal frame, the metal frame being provided with a hollow region; and an alignment metal strip, the alignment metal strip being located at the edge of one side of the metal frame and being provided with a first align mark and a first photographing mark. The first align mark and the first photographing mark are arranged in the extending direction of the edge, the metal frame is provided with a first hole, and an orthographic projection of the first photographing mark on the metal frame is located within the area in which the first hole is located.

A position detector includes a detection unit configured to detect light from a first diffraction grating including a first pattern disposed in a first direction, and light from a second diffraction grating including a second pattern disposed in the first direction, and a control unit configured to obtain a relative position between the first and the second diffraction gratings based on the light detected by the detection unit. The position detector has a third pattern formed in a second direction different from the first direction at edges of the first pattern of the first diffraction grating, the third pattern has a width smaller than a width of the first pattern of the first diffraction grating.

An alignment system includes: a light emitting device located on one side of an object to be aligned for emitting light towards the object to be aligned; a light receiving device located on the other side of the object to be aligned and at a standard position corresponding to an alignment mark disposed on the object to be aligned, the light receiving device being provided with a plurality of light sensors for sensing light emitting from the light emitting device on an end surface facing the object to be aligned; a processor configured to receive sensing signals transmitted from each of the light sensors and determine whether the object to be aligned is aligned accurately according to whether each of the light sensors sense the light emitted from the light emitting device. This alignment system shortens the processing time and enhances the processing efficiency.

A metrology target may include a first rotationally symmetric working zone with one or more instances of a first pattern and a second rotationally-symmetric working zone with one or more instances of a second pattern, where at least one of the first pattern or the second pattern is a Moiré pattern formed from a first grating structure with a first pitch along a measurement direction on a first sample layer and a second grating structure with a second pitch different than the first pitch along the measurement direction on a second sample layer. Centers of rotational symmetry of the first and second working zones may overlap by design when an overlay error between the first sample layer and the second layer is zero. A difference between the centers of rotational symmetry of the first and second working zones may indicate an overlay error between the first and second sample layers.

Measurement targets for use on substrates, and overlay targets are presented. The targets include an array of first regions alternating with second regions, wherein the first regions include structures oriented in a first direction and the second regions include structures oriented in a direction different from the first direction. The effective refractive index of the two sets of regions are thereby different when experienced by a polarized beam, which will act as a TM-polarized beam when reflected from the first set of regions, but as a TE-polarized beam when reflected from the second set of regions.

An overlay error measurement structure includes a lower-layer pattern disposed over a substrate, and an upper-layer pattern disposed over the lower-layer pattern and at least partially overlapping with the lower-layer pattern. The lower-layer pattern includes a plurality of first sub-patterns extending in a first direction and being arranged in a second direction crossing the first direction. The upper-layer pattern includes a plurality of second sub-patterns extending in the first direction and being arranged in the second direction. At least one of a pattern pitch and a pattern width of at least one of at least a part of the first sub-patterns and at least a part of the second sub-patterns varies along the second direction.

A method of transferring a flexible layer to a substrate makes use of a partial bulge in the flexible layer, which does not make contact with the substrate. The partial bulge advances to the location of an alignment marker on the substrate. When alignment adjustments are needed, they are made with the partial bulge in place so that more reproducible positioning is possible when fully advancing the flexible layer against the substrate.

Methods and structures for improving alignment contrast for patterning a metal layer generally includes depositing a metal layer having a plurality of grains, wherein grain boundaries between the grains forms grooves at a surface of the metal layer. The metal layer is subjected to surface treatment to form an oxide or a nitride layer and fill the surface grooves. The metal layer can be patterned using alignment marks in the metal layer and/or underlying layers. Filling the grooves with the oxide or nitride increases alignment contrast relative to patterning the metal layer without the surface treating.

A method includes projecting an illumination beam of radiation onto a metrology target on a substrate, detecting radiation reflected from the metrology target on the substrate, and determining a characteristic of a feature on the substrate based on the detected radiation, wherein a polarization state of the detected radiation is controllably selected to optimize a quality of the detected radiation.

A lithographic apparatus includes an alignment sensor including a self-referencing interferometer for reading the position of a mark including a periodic structure. An illumination optical system focuses radiation of different colors and polarizations into a spot which scans said structure. Multiple position-dependent signals are detected in a detection optical system and processed to obtain multiple candidate position measurements. Each mark includes sub-structures of a size smaller than a resolution of the optical system. Each mark is formed with a positional offset between the sub-structures and larger structures that is a combination of both known and unknown components. A measured position of at least one mark is calculated using signals from a pair of marks, together with information on differences between the known offsets, in order to correct for said unknown component of said positional offset.