A test structure includes a plurality of lines and a plurality of contact
openings defined in the lines. A method for determining contact opening
dimensions includes providing a wafer having a test structure comprising a
plurality of lines and a plurality of contact openings defined in the
lines; illuminating at least a portion of the contact openings with a
light source; measuring light reflected from the illuminated portion of
the contact openings to generate a reflection profile; and determining a
dimension of the contact openings based on the reflection profile. A
metrology tool adapted to receive a wafer having a test structure
comprising a plurality of lines and a plurality of contact openings
defined in the lines includes a light source, a detector, and a data
processing unit. The light source is adapted to illuminate at least a
portion of the contact openings. The detector is adapted to measure light
reflected from the illuminated portion of the contact openings to generate
a reflection profile. The data processing unit is adapted to determine a
dimension of the contact openings based on the reflection profile.
