Systems and method for optimization of laser beam spatial intensity profile
View Patent ↗In a thin beam directional Crystallization System configured anneal a silicon layer on a glass substrate uses a special laser beam profile with an intensity peak at one edge. The system is configured to entirely melt a spatially controlled portion of a silicon layer causing lateral crystal growth. By advancing the substrate or laser a certain step size and subjecting the silicon layer to successive “shots” rom the laser, the entire silicon layer is crystallized. The lateral crystal growth creates a protrusion in the center of the melt area. This protrusion must be re-melted. Accordingly, the step size must be such that there is sufficient overlap between successive shots, i.e., melt zones, to ensure the protrusion is melted. This requires the step size to be less than half the beam width. A smaller step size reduces throughput and increases costs. The special laser profile used in accordance with the systems and methods described herein can increase the step size and thereby increase throughput and reduce costs.
1. A method of processing a liquid crystal display, comprising:
shaping a laser beam profile in a short axis so as to have steep sides at both edges, an increasing linear gradient between both edges, and an intensity peak near one edge of the profile that corresponds to a protrusion in a silicon film to which the beam is applied; and
scanning a laser beam that includes the laser beam profile over the silicon film using a step size near a maximum step size,
wherein the shaping the laser beam short axis profile further comprises correlating the intensity profile of the laser beam to a melting temperature of the silicon film,
wherein the width of the laser beam in the short axis is dimensioned to produce, responsive to the laser beam firing, a single protrusion in the silicon film, and
wherein the edge of the profile having the intensity peak is a trailing edge of the laser beam with respect to relative movement between the silicon film and the laser beam.
2. The method of claim 1 , further comprising shaping the long axis profile of the laser beam to produce a long, thin beam.
3. The method of claim 2 , wherein the laser beam profile is approximately 5 microns wide in the short axis.
4. The method of claim 3 , wherein the beam profile is 730 mm long.
5. The method of claim 3 , wherein the beam profile is approximately as wide as a glass substrate.
6. The method of claim 3 , wherein a glass substrate moves at a constant velocity under the beam profile.
7. The method of claim 6 , wherein the beam profile is triggered to fire after a translation of 0.5 to 4 microns.
8. The method of claim 5 , wherein the beam profile is triggered to fire after a translation of approximately 2.5 microns.
9. The method of claim 1 , wherein the beam has a wave length of 351 nm.
10. The method of claim 1 , wherein the beam has a wave length of 308 nm.
11. The method of claim 1 , wherein the protrusion extends above the surface of the silicon film by an order of a thickness of the silicon film.
12. The method of claim 1 , wherein the short axis of the beam profile has a first edge having a minimum beam intensity and a second edge having the peak beam intensity, and the gradient in intensity maintains a constant slope between the first edge and second edge.
13. The method of claim 1 , wherein the short axis of the beam profile has a first edge having a minimum intensity and a second edge having the peak intensity of the profile, and the gradient in intensity maintains an increasing slope between the first edge and the second edge.
14. The method of claim 1 , wherein maximum step size is equal to one-half the width of the melt region generated by the beam application.
15. The method of claim 1 , wherein maximum step size is equal to the lateral growth distance of the silicon film between beam applications minus the width of the protrusion.