SYSTEMS AND METHODS FOR USING WHITE LIGHT INTERFEROMETRY TO MEASURE UNDERCUT OF A BI-LAYER STRUCTURE
Systems and methods for using white light interferometry to measure undercut of a bi-layer structure are provided. One such method involves performing a first scan of a first bi-layer structure with a microscope using a first scan range, where the microscope is configured for white light interferometry, generating a first interferogram using data from the first scan, performing a second scan of the first bi-layer structure with the microscope using a second scan range, generating a second interferogram using data from the second scan, determining a first distance between features of the first interferogram, determining a second distance between features of the second interferogram, and calculating a width of the undercut based on the first distance and the second distance. One such system involves using the microscope and/or a computer to perform one or more actions of this method.
1 . A system for measuring an undercut of bi-layer structures on a wafer, the system comprising:
a microscope configured for white light interferometry, wherein the microscope is configured to:
perform a first scan of a first bi-layer structure using a first scan range;
perform a second scan of the first bi-layer structure using a second scan range;
generate a first interferogram using data from the first scan; and
generate a second interferogram using data from the second scan; and
a computer coupled to the microscope and configured to:
determine a first distance between features of the first interferogram;
determine a second distance between features of the second interferogram; and
calculate a width of the undercut based on the first distance and the second distance.
2 . The system of claim 1 , wherein the first scan range is less than the second scan range, wherein the first and second ranges extend in a direction that is about normal to a top surface of the first bi-layer structure.
3 . The system of claim 2 :
wherein the features of the first interferogram comprise two edges each corresponding to a portion of the first interferogram having a maximum slope; and
wherein the features of the second interferogram comprise two peaks each corresponding to a point of the second interferogram having a peak amplitude.
4 . The system of claim 3 :
wherein the first bi-layer structure comprises an upper layer on a lower layer, where an area of the lower layer is less than that of the upper layer;
wherein the two edges of the first interferogram correspond in position to outer edges of the upper layer; and
wherein the two peaks of the second interferogram correspond in position to outer edges of the lower layer.
5 . The system of claim 3 :
wherein the first bi-layer structure comprises an upper layer on a lower layer, where an area of the lower layer is less than that of the upper layer;
wherein the first bi-layer structure comprises a centrally disposed hole extending through both the upper layer and the lower layer;
wherein the two edges of the first interferogram correspond in position to edges of the upper layer defining the hole; and
wherein the two peaks of the second interferogram correspond in position to edges of the lower layer defining the hole.
6 . The system of claim 2 :
wherein the features of the first interferogram comprise four edges each corresponding to a portion of the first interferogram having a maximum slope;
wherein the features of the second interferogram comprise four peaks each corresponding to a point of the second interferogram having a peak amplitude;
wherein the microscope is configured to perform the first scan of the first bi-layer structure and a second bi-layer structure using the first scan range; and
wherein the microscope is configured to perform the second scan of the first bi-layer structure and the second bi-layer structure using the second scan range.
7 . The system of claim 6 :
wherein the first bi-layer structure comprises an upper layer on a lower layer, where an area of the lower layer of the first bi-layer structure is less than that of the upper layer of the first bi-layer structure;
wherein the second bi-layer structure comprises an upper layer on a lower layer, where an area of the lower layer of the second bi-layer structure is less than that of the upper layer of the second bi-layer structure;
wherein a first two edges of the four edges of the first interferogram correspond in position to outer edges of the upper layer of the first bi-layer structure;
wherein a second two edges of the four edges of the first interferogram correspond in position to outer edges of the upper layer of the second bi-layer structure;
wherein a first two peaks of the four peaks of the second interferogram correspond in position to outer edges of the lower layer of the first bi-layer structure; and
wherein a second two peaks of the four peaks of the second interferogram correspond in position to outer edges of the lower layer of the second bi-layer structure.
8 . The system of claim 2 :
wherein the features of the first interferogram comprise four edges each corresponding to a portion of the first interferogram having a maximum slope;
wherein the features of the second interferogram comprise four peaks each corresponding to a point of the second interferogram having a peak amplitude;
wherein the first bi-layer structure comprises an upper layer on a lower layer, where an area of the lower layer of the first bi-layer structure is less than that of the upper layer of the first bi-layer structure;
wherein the first bi-layer structure comprises a first hole and a second hole, each extending through both the upper layer and the lower layer;
wherein a first two edges of the four edges of the first interferogram correspond in position to edges of the upper layer of the first bi-layer structure defining the first hole;
wherein a second two edges of the four edges of the first interferogram correspond in position to edges of the upper layer of the first bi-layer structure defining the second hole;
wherein a first two peaks of the four peaks of the second interferogram correspond in position to edges of the lower layer of the first bi-layer structure defining the first hole; and
wherein a second two peaks of the four peaks of the second interferogram correspond in position to edges of the lower layer of the first bi-layer structure defining the second hole.
9 . The system of claim 1 , wherein the second scan range is less than the first scan range, wherein the first and second ranges extend in a direction that is about normal to a top surface of the first bi-layer structure.
10 . The system of claim 1 , wherein if the width of the undercut is outside of a preselected range, then a fabrication process for forming the first bi-layer structure is modified.
11 . The system of claim 10 , wherein the fabrication process is modified by adjusting a duration of a development sub-process used in forming the undercut of the first bi-layer structure.