A method of measuring machine alignment offset of an optical machine having an
alignment system, so that subsequent processing of substrates on set of optical
machines can be performed in a machine-independent manner. The optical machine
forms overlayed images of first and second patterns formed on either one or two
reticles onto a substrate at respective first and second levels. The method of
the invention includes forming a virtual zero-offset alignment pattern and a virtual
zero-offset metrology pattern and imaging first and second metrology patterns on
the substrate at the first and second levels, respectively. The second metrology
pattern is aligned to the first metrology pattern using the zero-offset alignment
pattern so that the exposures are performed in an overlayed manner. The first and
second metrology patterns are based on the virtual zero-offset metrology pattern.
An image of the overlayed first and second metrology patterns formed on the substrate
is obtained using the alignment system of the optical machine. The virtual zero-offset
metrology pattern is compared to corresponding portions of the image of the overlayed
metrology patterns to deduce an offset from an idea alignment of the first and
second metrology patterns. Zero-offset alignment patterns for one or more jobs
may also be created so that the jobs can be run without an extra step of determining
the job-dependent offset for each job.
