The broadband brightfield/darkfield wafer inspection system provided
receives broadband brightfield illumination information via a defect
detector, which signals for initiation of darkfield illumination. The
defect detector forms a two dimensional histogram of the defect data and
a dual mode defect decision algorithm and post processor assess defects.
Darkfield radiation is provided by two adjustable height laser beams
which illuminate the surface of the wafer from approximately 6 to 39
degrees. Each laser is oriented at an azimuth angle 45 degrees from the
orientation of the manhattan geometry on the wafer, and 90 degrees in
azimuth from one another. Vertical angular adjustability is provided by
modifying cylindrical lens position to compensate for angular mirror
change by translating an adjustable mirror, positioning the illumination
spot into the sensor field of view, rotating and subsequently moving the
cylindrical lens. A brightfield beamsplitter in the system is removable,
and preferably replaced with a blank when performing darkfield
illumination. Light level control for the system is provided by a dual
polarizer first stage. Light exiting from the second polarizer passes
through a filter which absorbs a portion of the light and comprises the
second stage of light control. The beam then passes through a polarizing
beamsplitter. The second channel is further reflected and polarized and
both beams thereafter illuminate the substrate.