A method for optically testing semiconductor devices or wafers using a
holographic optical interference system with an infrared or thermal light
source providing a light beam of coherent wavelength with a wavelength to
which the semiconductor material is transparent, splitting the light beam
into a reference beam and an object beam, imposing the object beam on the
semiconductor material to generate a reflected object beam reflected from
interior structures of the semiconductor material, adjusting the angle of
the reference beam relative to the object beam between a plurality of
angles with the semiconductor material being a different state for each
angle of the reference beam, imposing the reflected object beam and the
reference beam onto a detection device to create a plurality of
interference patterns, one for each of the reference beam angles, and
comparing the interference patterns to one another to determine and
display characteristics within the semiconductor material.