Monitoring method and apparatus for control of excimer laser annealing

An apparatus for evaluating a semiconductor layer, said apparatus comprising:

• a light source for generating a beam of light directed normal to a surface of the semiconductor layer to illuminate an area of the semiconductor layer crystallized by exposure to a plurality of laser-radiation pulses having an energy density on the layer, the crystallization producing a first group of periodic surface features on the semiconductor layer in a first direction, and a second group of periodic surface features in a second direction perpendicular to the first direction, wherein characteristics of the first and second groups of periodic surface features depend on the energy density of the laser-radiation pulses to which the semiconductor layer has been exposed;
• a two-dimensional array detector arranged to capture light diffracted from the illuminated area by both the first and second groups of periodic surface features, and generating output signals corresponding to variations in brightness, with the variations in brightness of the light corresponding to characteristics of the first and second groups of periodic surface features in the illuminated area of the semiconductor layer;
• and
• a processor that calculates the contrast in brightness based on the output signals that correspond to the variations in brightness along at least one of the first and second directions in order to evaluate the energy density of the laser-radiation pulses to which the semiconductor layer has been exposed.