System and method for suppression of tool induced shift in scanning overlay metrology

An overlay metrology system comprising:

• an illumination sub-system comprising:
• an illumination source configured to generate an illumination beam;
• a collection sub-system comprising:
• one or more detectors;
• and
• an objective lens configured to collect measurement light emanating from a sample in response to the illumination beam as the sample is scanned along a scan direction, wherein the sample comprises an overlay target according to a metrology recipe, wherein the overlay target comprises two or more cells comprising structures with periodicity along the scan direction;
• and
• a controller communicatively coupled to the collection sub-system, the controller comprising one or more processors configured to execute program instructions causing the one or more processors to execute the metrology recipe by:
• receiving first detection signals from the one or more detectors from a first cell of the two or more cells;
• receiving second detection signals from the one or more detectors from a second cell of the two or more cells;
• generating an overlay measurement of the first cell based on the first detection signals;
• generating an overlay measurement of the second cell based on the second detection signals;
• generating an overlay measurement associated with the overlay target based on a value indicative of an average of the overlay measurement of the first cell and the overlay measurement of the second cell,
• wherein the first cell is defined as a first cell type characterized by an order of the structures in layers, the order characterized by pitches of the structures in the layers, wherein the second cell is defined as a second cell type characterized by a second order of second structures in the layers, the second order characterized by second pitches of the second structures in the layers,
• wherein the first cell includes a first layer of structures having a first pitch and a second layer having a second pitch, wherein the second cell includes a first layer of structures having the second pitch and a second layer having the first pitch such that the pitches of structures within layers of the second cell are reversed relative to the first cell, wherein the order of structures in layers of the first cell type and second cell type are configured to suppress tool induced shift (TIS) error by averaging overlay measurements of cells with reversed pitch orders,
• wherein the receiving the first detection signals and the receiving the second detection signals comprises receiving time-varying interference signals as the overlay target is scanned while the overlay target is in motion;
• extracting at least one of intensity or phase information associated with the received time-varying interference signals using a phase locking technique;
• and
• determining an overlay error between the first and second layers of the overlay target based on at least one of intensity or phase information.

An overlay target comprising:

• four cells aligned in a row comprising:
• a first cell and a third cell comprising periodic structures at plus 45 degrees from a scan direction;
• and
• a second cell and a fourth cell comprising periodic structures at minus 45 degrees from the scan direction,
• wherein the first cell and the second cell are of a first cell type, and the third cell and the fourth cell are of a second cell type,
• wherein the first cell type is characterized by an order of structures in layers, the order characterized by pitches of the structures in the layers, wherein the second cell type is characterized by a second order of second structures, the second order characterized by second pitches of the second structures in the layers,
• wherein the first cell includes a first layer of structures having a first pitch and a second layer having a second pitch, wherein the second cell includes a first layer of structures having the second pitch and a second layer having the first pitch such that the pitches of structures within layers of the second cell are reversed relative to the first cell, wherein the first cell type and second cell type are configured to suppress tool induced shift (TIS) error by averaging overlay measurements of cells with reversed pitch orders,
• wherein time-varying interference signals of the overlay target are obtained when the overlay target is in motion;
• wherein at least one of intensity or phase information associated with the received time-varying interference signals is extracted from the overlay target using a phase locking technique;
• and
• wherein overlay error between layers of the overlay target is determined based on at least one of intensity or phase information.

A method comprising:

• receiving first detection signals from one or more detectors from a first cell of two or more cells of an overlay target of a sample comprising structures with periodicity along a scan direction;
• receiving second detection signals from the one or more detectors from a second cell of the two or more cells;
• generating an overlay measurement of the first cell based on the first detection signals;
• generating an overlay measurement of the second cell based on the second detection signals;
• generating an overlay measurement associated with the overlay target based on a value indicative of an average of the overlay measurement of the first cell and the overlay measurement of the second cell,
• wherein the first cell is defined as a first cell type characterized by an order of the structures in layers, the order characterized by pitches of the structures in the layers, wherein the second cell is defined as a second cell type characterized by a second order of second structures in the layers, the second order characterized by second pitches of the second structures in the layers,
• wherein the first cell includes a first layer of structures having a first pitch and a second layer having a second pitch, wherein the second cell includes a first layer of structures having the second pitch and a second layer having the first pitch such that the pitches of structures within layers of the second cell are reversed relative to the first cell, wherein the order of structures in layers of the first cell type and second cell type are configured to suppress tool induced shift (TIS) error by averaging overlay measurements of cells with reversed pitch orders,
• wherein the receiving the first detection signals and the receiving the second detection signals comprises receiving time-varying interference signals as the overlay target is scanned while the overlay target is in motion;
• extracting at least one of intensity or phase information associated with the received time-varying interference signals using a phase locking technique;
• and
• determining an overlay error between the first and second layers of the overlay target based on at least one of intensity or phase information.