Single pass lithography overlay technique

A lithography method comprising:

• exposing a first mask having:
• a pattern for a first grating;
• exposing a second mask having:
• a pattern for a second grating, and
• the pattern for the first grating;
• and
• determining alignment of the first and second masks based on the first and second gratings formed on a wafer after exposing the first and second masks.

A structure formed on a wafer used to determine mask misalignment in a lithography process, comprising:

• a first grating having periodic lines and spaces;
• and
• a second grating having periodic lines and spaces,
• wherein the first and second gratings were formed using:
• a first mask having a pattern for the first grating, and
• a second mask having a pattern for the first and second gratings, and
• wherein a difference in the width of the periodic lines or spaces of the first and second gratings indicate misalignment between the first and second masks.

A system for adjusting a lithography process, comprising:

• a lithographic track;
• a stepper;
• at least one metrology tool:
• wherein the at least one metrology tool-measures the magnitude of a misalignment in masks based on gratings formed by exposing the masks, and
• wherein the at least one metrology tool measures the direction of a misalignment in masks based on alignment direction target elements formed by exposing the masks;
• and
• a controller, wherein the controller adjusts the stepper based on the magnitude and the direction of the measured misalignment.

An integrated circuit fabrication system using a lithography process to fabricate a wafer, the system comprising:

• a first mask having:
• a first pattern for a first grating having lines and spaces, and
• a second pattern for a second grating having lines and spaces, wherein the lines and spaces of the second pattern are orthogonal to the lines and spaces of the first pattern;
• a second mask having:
• the first and second patterns,
• a third pattern for a third grating having lines and spaces,
• a fourth pattern for a fourth grating having lines and spaces, wherein the lines and spaces of the fourth pattern are orthogonal to the lines and spaces of the third pattern,
• a lithography cluster configured to expose the wafer through the first mask and through the second mask, the exposure forming the first, second, third, and fourth gratings on the wafer;
• and
• a metrology system configured to measure the width of the lines or spaces of the first, second, third, and fourth gratings on the wafer to determine an alignment error between the first and second masks in a first direction and a second direction.

A method of detecting misalignment between masks used in a lithography process, the method comprising:

• forming a grating having lines and spaces on a wafer using a first mask;
• measuring the width of the lines or spaces of the grating formed on the wafer;
• exposing the grating formed on the wafer a second time using a second mask having a pattern for the grating;
• measuring the width of the lines or spaces of the grating after the grating formed on the wafer is exposed a second time;
• and
• determining if the first and second masks were misaligned based on a difference in the width of the lines or spaces measured after the grating is formed on the wafer and measured after the grating formed on the wafer is exposed a second time.