Laser beam micro-smoothing
The present invention provides laser beam micro-smoothing for laser annealing systems. Laser beam micro-smoothing comprises shifting a laser beam in the direction perpendicular to the scanning direction (y) of a laser annealing system, while holding the laser beam fixed in the direction of scanning (x). The shifting may be accomplished, for example, with a pair of micro-smoothing mirrors. The shifting smoothes out small-scale inhomogeneities in the profile of the laser beam and prevents microscopic stripes associated with prior art laser annealing systems. Because the shifting occurs only in the direction perpendicular to the scanning direction (y), the laser annealing process in not adversely affected.
1. A method for smoothing effects caused by inhomogeneities in a laser beam, comprising the steps of:
positioning a line of focus of said laser beam at a first position on a surface of a work piece, with the long axis of the line focus being in the y-direction;
processing said first position of said work piece with said laser beam by applying a plurality of laser beam pulses to said first position; and
during said processing of said first position, shifting said laser beam in the y-direction only between the applications of said pulses by a predetermined distance.
2. The method of claim 1 , wherein said step of shifting said laser beam comprises moving said laser beam between each of said laser beam pulses in the y-direction by a distance substantially equal to the average width of small-scale inhomogeneities of said laser beam.
3. The method of claim 1 , wherein said step of shifting said laser beam comprises moving said laser beam in the y-direction in a substantially sinusoidal motion.
4. The method of claim 3 , wherein the frequency of the sinusoidal motion is approximately a fifteenth to a tenth of said laser beam's pulse repetition frequency.
5. A method of treating a workpiece with a pulsed laser beam, said beam having a beam spot with an elongated footprint having a long axis and a short axis, said method comprising the steps of:
(a) directing the beam to the workpiece;
(b) dithering the beam in a first direction only, said first direction being parallel to the long axis of the beam spot to cause multiple pulses to impinge upon the workpiece at different positions;
(c) translating the workpiece with respect to the beam spot in a second direction perpendicular to the long axis of the beam spot; and
(d) repeating steps (b) and (c) to treat the workpiece in a manner to compensate for inhomogeneities in the long axis of the beam.
6. A method as recited in claim 5 , wherein the workpiece is continuously translated with respect to the beam spot at a velocity such that a plurality of pulses overlap in the scanning direction.