An optical measurement system for evaluating a sample has a azimuthally
rotatable measurement head. A motor-driven rotating mechanism is coupled
to the measurement head to allow the optics to rotate with respect to the
sample. In particular, a preferred embodiment is a polarimetric
scatterometer (FIG. 1) for measuring optical properties of a periodic
structure on a wafer sample (12). This scatterometer has optics (30)
directing a polarized illumination beam at non-normal incidence onto the
periodic structure. In addition to a polarizer (8), the illumination path
can also be provided with an E-O modulator for modulating the
polarization. The measurement head optics also collect light reflected
from the periodic structure and feed that light to a spectrometer (17) for
measurement. A polarization beamsplitter (18) is provided in the
collection path so that both S and P polarization from the sample can be
separately measured. The entire measurement head can be mounted for
rotation of the plane of incidence to different azimuthal directions
relative to the periodic structures on the wafer. The instrument can be
integrated within a wafer process tool in which wafers may be provided at
arbitrary orientation.
