Damage assessment of a wafer using optical metrology

A system for assessing damage of a dual damascene structure, comprising:

• a transfer system configured to obtain a wafer after the wafer has been processed using a dual damascene process;
• an integrated metrology module configured to perform a first damage-assessment procedure on the wafer, wherein an optical metrology process is used to gather damage-assessment data for a first set of measurement sites on the wafer, wherein, for each measurement site in the first set of measurement sites, the optical metrology process determines an amount of damage of a damaged area of a periodic grating in the measurement site, wherein the damage-assessment data includes the amount of damage determined by the optical metrology process, wherein the optical metrology process includes defining a hypothetical profile of the periodic structure, wherein the hypothetical profile is divided into multiple effective medium layers, each effective medium layer having an undamaged portion, which corresponds to an area of a first material in the periodic structure undamaged by the dual damascene process, and a damaged portion, which corresponds to an area of the first material in the periodic structure damaged by the dual damascene process, wherein the undamaged portion and the damaged portion have different properties associated with them, and wherein the optical metrology process includes generating a simulated diffraction signal using the hypothetical profile of the periodic structure;
• and
• a controller configured to create a first damage-assessment map for the dual damascene process, the first damage-assessment map including the damage-assessment data and the locations of the first set of measurement sites on the wafer, and for comparing one or more values in the damaged-assessment map to damage-assessment limits established for the dual damascene process to identify the wafer as a damaged or undamaged wafer.

A computer readable storage medium containing computer executable code for assessing damage of a dual damascene structure by instructing a processing system to operate as follows:

• obtain a wafer after the wafer has been processed using a dual damascene process;
• perform a first damage-assessment procedure on the wafer, wherein an optical metrology process is used to gather damage-assessment data for a first set of measurement sites on the wafer, wherein, for each measurement site in the first set of measurement sites, the optical metrology process determines an amount of damage of a damaged area of a periodic grating in the measurement site, wherein the damage-assessment data includes the amount of damage determined by the optical metrology process, wherein the optical metrology process includes defining a hypothetical profile of the periodic structure, wherein the hypothetical profile is divided into multiple effective medium layers, each effective medium layer having an undamaged portion, which corresponds to an area of a first material in the periodic structure undamaged by the dual damascene process, and a damaged portion, which corresponds to an area of the first material in the periodic structure damaged by the dual damascene process, wherein the undamaged portion and the damaged portion have different properties associated with them, and wherein the optical metrology process includes generating a simulated diffraction signal using the hypothetical profile of the periodic structure;
• create a first damage-assessment map for the dual damascene process, the first damage-assessment map including the damage-assessment data and the locations of the first set of measurement sites on the wafer;
• and
• compare one or more values in the damaged-assessment map to damage-assessment limits established for the dual damascene process to identify the wafer as a damaged or undamaged wafer.