Apparatus and Method for Inspecting a Substrate

A substrate, comprising:

• at least two targets associated with each field of the substrate, wherein:
• a first one of the targets has at least a first grating and a second grating having respective predetermined offsets, the predetermined offset of the first grating being in an direction opposite the predetermined offset of the second grating;
• and
• a second one of the targets has at least a first grating.

A method of measuring properties of a substrate, comprising:

• printing targets onto corresponding fields of the substrate, wherein a first one of the targets has at least a first grating and a second grating having respective predetermined offsets, the predetermined offset of the first grating being in an direction opposite the predetermined offset of the second grating and a second one of the targets has at least a first grating;
• reflecting a radiation beam from the first one of the targets of corresponding fields of the substrate;
• detecting the reflected radiation beam from the first one of the targets to obtain an asymmetry value for the first one of the targets;
• determining an overlay value for the first one of the targets based on at least the obtained asymmetry value and the predetermined offsets;
• and
• determining a polynomial fit across the targets for the relationship between the obtained asymmetry value and the determined overlay value of the targets.

A lithographic apparatus, comprising:

• an illumination optical system configured to illuminate a pattern on a patterning device;
• a projection optical system configured to project an image of the pattern onto a substrate having multiple measurement fields;
• and
• an apparatus for measuring properties of a substrate, comprising:
• a radiation source configured to direct radiation onto targets of corresponding fields of the substrate, wherein a first one of the targets has at least a first grating and a second grating having respective predetermined offsets, the predetermined offset of the first grating being in a direction opposite the predetermined offset of the second grating;
• a detector configured to detect the radiation reflected from the first one of the targets and to obtain an asymmetry value for the first one of the targets from the detected radiation;
• and
• a controller configured to (i) determine an overlay value for the first one of the targets based on at least the obtained asymmetry value and the predetermined offsets and (ii) determine a polynomial fit across the targets for a relationship between the obtained asymmetry value and the determined overlay value of the targets.

A lithographic cell, comprising:

• a coater arranged to coat a substrate with a radiation sensitive layer;
• a lithographic apparatus arranged to expose images onto the radiation sensitive layer of the substrate coated by the coater;
• a developer arranged to develop images exposed by the lithographic apparatus;
• and an apparatus for measuring properties of a substrate, comprising:
• a radiation source configured to direct radiation onto targets of corresponding fields of the substrate, wherein a first one of the targets has at least a first grating and a second grating having respective predetermined offsets, the predetermined offset of the first grating being in a direction opposite the predetermined offset of the second grating;
• a detector configured to detect the radiation reflected from the first one of the targets and to obtain an asymmetry value for the first one of the targets from the detected radiation;
• and
• a controller configured to (i) determine an overlay value for the first one of the targets based on at least the obtained asymmetry value and the predetermined offsets and (ii) determine a polynomial fit across the targets for a relationship between the obtained asymmetry value and the determined overlay value of the targets.

A device manufacturing method, comprising:

• forming a pattern on a substrate;
• and
• determining a value related to a parameter of the formed pattern, comprises:
• printing targets onto corresponding fields of the substrate, wherein:
• a first one of the targets has at least a first grating and a second grating having respective predetermined offsets, the predetermined offset of the first grating being in an direction opposite the predetermined offset of the second grating;
• and
• a second one of the targets has at least a first grating;
• reflecting a radiation beam from the first one of the targets of corresponding fields of the substrate;
• detecting the reflected radiation beam from the first one of the targets to obtain an asymmetry value for the first one of the targets;
• determining an overlay value for the first one of the targets based on at least the obtained asymmetry value and the predetermined offsets;
• determining a polynomial fit across the targets for the relationship between the obtained asymmetry value and the determined overlay value of the targets.