Method and apparatus for selecting wafer alignment marks based on film thickness variation

A method for aligning wafers, comprising:

• providing a wafer having at least a first and a second alignment mark formed thereon, each alignment mark comprising a grating structure;
• illuminating the grating structure of the first alignment mark with a light source;
• measuring light reflected from the grating structure of the first alignment mark to generate a first reflection profile;
• illuminating the grating structure of the second alignment mark with the light source;
• measuring light reflected from the grating structure of the second alignment mark to generate a second reflection profile;
• comparing the first and second reflection profiles to a library of reference reflection profiles, each reference reflection profile having an associated degradation rating;
• selecting a first reference reflection profile closest to the first reflection profile;
• selecting a second reference reflection profile closest to the second reflection profile;
• selecting the one of the first and second alignment marks corresponding to the one of the first and second reference reflection profiles having a lower associated degradation rating;
• and
• configuring a stepper to align the wafer using the selected one of the first and second alignment marks.

A method for aligning wafers, comprising:

• providing a wafer having at least a first and a second alignment mark formed thereon, each alignment mark comprising a grating structure;
• illuminating the grating structure of the first alignment mark with a light source;
• measuring light reflected from the grating structure of the first alignment mark to generate a first reflection profile;
• illuminating the grating structure of the second alignment mark with the light source;
• measuring light reflected from the grating structure of the second alignment mark to generate a second reflection profile;
• comparing the first and second reflection profiles to a target reflection profile;
• quantifying the degradation of the first and second alignment marks based on the comparisons between the first and second alignment marks and the target reflection profile;
• selecting the one of the first and second alignment marks having the lesser quantified degradation;
• and
• configuring a stepper to align the wafer using the selected one of the first and second alignment marks.

A processing line, comprising:

• a stepper adapted to align a wafer;
• a metrology tool adapted to receive a wafer having at least a first and a second alignment mark formed thereon, each alignment mark comprising a grating structure, the metrology tool being further adapted to illuminate the grating structure of the first alignment mark with a light source, measure light reflected from the grating structure of the first alignment mark to generate a first reflection profile, illuminate the grating structure of the second alignment mark with the light source, measure light reflected from the grating structure of the second alignment mark to generate a second first reflection profile, compare the first and second reflection profiles to a library of reference reflection profiles, each reference reflection profile having an associated degradation rating, select a first reference reflection profile closest to the first reflection profile, and select a second reference reflection profile closest to the second reflection profile;
• and
• a process controller adapted to select the one of the first and second alignment marks corresponding to the one of the first and second reference reflection profiles having a lower associated degradation rating, and configure the stepper to align the wafer using the selected one of the first and second alignment marks.

A processing line, comprising:

• a stepper adapted to align a wafer;
• a metrology tool adapted to receive a wafer having at least a first and a second alignment mark formed thereon, each alignment mark comprising a grating structure, the metrology tool being further adapted to illuminate the grating structure of the first alignment mark with a light source, measure light reflected from the grating structure of the first alignment mark to generate a first reflection profile, illuminate the grating structure of the second alignment mark with the light source, measure light reflected from the grating structure of the second alignment mark to generate a second first reflection profile, and compare the first and second reflection profiles to a target reflection profile to determine a degradation rating for each of the first and second alignment marks;
• and
• a process controller adapted to select the one of the first and second alignment marks corresponding to the one of the first and second reference reflection profiles having a lower associated degradation rating, and configure the stepper to align the wafer using the selected one of the first and second alignment marks.

A processing line, comprising:

• means for aligning a wafer having at least a first and a second alignment mark formed thereon, each alignment mark comprising a grating structure;
• means for illuminating the grating structure of the first alignment mark with a light source,
• means for measuring light reflected from the grating structure of the first alignment mark to generate a first reflection profile;
• means for illuminating the grating structure of the second alignment mark with the light source;
• means for measuring light reflected from the grating structure of the second alignment mark to generate a second reflection profile;
• means for quantifying degradation of the first and second alignment marks based on the first and second reflection profiles;
• and
• means for selecting one of the first and second alignment marks for aligning the wafer based on the quantified degradations of the first and second reflection profiles.