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. A method for evaluating a semiconductor layer at least partially 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 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 features depend on the energy density of the laser-radiation pulses to which the semiconductor layer has been exposed, the method comprising:
illuminating an area of the crystallized semiconductor layer with a beam of light directed normal to the surface of the layer;
recording an image of the illuminated area with a detector aligned to capture light centered on an axis normal to the layer and arranged to capture light diffracted from the illuminated area by the first and second groups of periodic features, with the variations in brightness within the recorded image corresponding to the characteristics of the first and second groups of periodic features in the illuminated area of the layer; and
determining the energy density from a measure of the contrast in brightness along at least one direction of the image corresponding to one of the first or second directions of the layer.
2. The method of claim 1 , wherein the image is a transmission microscope image.
3. The method of claim 1 , wherein the image is formed from rows and columns of pixels and the contrast is determined by measuring the amplitude of one of all rows and all columns of pixels in the image and taking the standard deviation from an average amplitude as a measure of the contrast of the periodic image features.
4. The method of claim 1 , wherein the image is formed from rows and columns of pixels and the contrast is determined by measuring the amplitude of one of all rows and all columns of pixels in the image and taking the difference between the highest and lowest measured amplitude as a measure of the contrast of the periodic image features.
5. The method of claim 1 , wherein the image is green-filtered image.
6. The method of claim 1 , wherein the image is a blue filtered image.
7. The method of claim 1 , wherein a minimum of the measured contrast indicates an optimum energy density for the crystallization.
8. The method of claim 1 , wherein at least a portion of zero order light is blocked from reaching the detector.
9. The method of claim 8 , wherein the zero order light is blocked from reaching the detector using a combination of a polarizer and an analyzer set at 90-degree relative rotation.
10. The method of claim 8 , wherein the zero order light is blocked from reaching the detector by a stop positioned along central axis of the captured light.