Monitoring method and apparatus for control of excimer laser annealing
A method is disclosed evaluating a silicon layer crystallized by irradiation with pulses form an excimer-laser. The crystallization produces periodic features on the crystallized layer dependent on the number of and energy density ED in the pulses to which the layer has been exposed. An area of the layer is illuminated with light. A microscope image of the illuminated area is made from light diffracted from the illuminated are by the periodic features. The microscope image includes corresponding periodic features. The ED is determined from a measure of the contrast of the periodic features in the microscope image.
1. 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.
2. The apparatus of claim 1 , wherein the two-dimensional array detector generates an image and wherein the image is formed from rows and columns of pixels and the contrast is determined by measuring an amplitude of one of all rows and all columns of pixels in the image and taking a standard deviation from an average amplitude as a measure of the contrast of the periodic surface features.
3. The apparatus of claim 1 , wherein the two-dimensional array detector generates an image and wherein the image is formed from rows and columns of pixels and the contrast is determined by measuring an amplitude of one of all rows and all columns of pixels in the image and taking a difference between highest and lowest measured amplitude as a measure of the contrast of the periodic surface features.
4. The apparatus of claim 1 further including a means for blocking at least a portion of zero order light from reaching the two dimensional array detector.
5. The apparatus of claim 4 , wherein the means for blocking the portion of zero order light is defined by a combination of a polarizer and an analyzer set at 90-degree relative rotation.
6. The apparatus of claim 4 , wherein the means for blocking the portion of zero order light is defined by a stop positioned along the central axis of the captured light.
7. The apparatus of claim 1 further including a blue filter located in front of the two-dimensional array detector.
8. The apparatus of claim 1 further including a green filter located in front of the two-dimensional array detector.