Laser beam micro-smoothing

Abstract

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art laser annealing system.

FIG. 2 illustrates a substrate processed by the prior art laser annealing system of FIG. 1.

FIG. 3 illustrates a first embodiment of an apparatus for laser beam micro-smoothing consistent with the present invention.

FIG. 4 illustrates a second embodiment of an apparatus for laser beam micro-smoothing consistent with the present invention.

FIG. 5 illustrates an overhead view of the apparatus for laser beam micro-smoothing of FIG. 4.

FIG. 6 illustrates a simulation of a substrate processed by a laser annealing system consistent with the present invention.

Claims

1. An apparatus for smoothing effects caused by inhomogeneities in a laser beam, said laser beam being configured for use with a laser annealing system that scans a substrate in a scanning direction by applying a series of laser beam pulses to contiguous positions on a surface of said substrate, comprising: means for moving a line focus of said laser beam on said surface of said substrate in a direction substantially perpendicular to said scanning direction by a predetermined distance between individual pulses of said series of pulses

2. The apparatus of claim 1, wherein said moving means is configured such that movement of said line focus of said laser beam in said scanning direction is minimized.

3. The apparatus of claim 1, wherein said means for moving comprises a mirror and an actuator for tilting said mirror.

4. The apparatus of claim 3, wherein said actuator comprises a piezoelectric actuator.

5. The apparatus of claim 3, wherein said actuator is configured to tilt said mirror in a substantially sinusoidal motion.

6. The apparatus of claim 5, wherein the frequency of the sinusoidal motion is approximately a fifteenth to a tenth of said laser beam's pulse repetition frequency.

7. The apparatus of claim 1, wherein said predetermined distance is approximately equal to the average width of small-scale inhomogeneities in said laser beam.

8. The apparatus of claim 1, wherein said means for moving comprises first and second mirrors having first and second actuators configured to move said first and second mirrors in opposite directions to minimize acceleration forces associated with movement of said mirrors.

9. 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;processing said first position of said work piece with said laser beam by applying a plurality of laser beam pulses to said first position; andduring said processing of said first position, shifting said laser beam in the y-direction between the applications of said pulses by a predetermined distance.

10. The method of claim 9, 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.

11. The method of claim 9, wherein said step of shifting said laser beam comprises moving said laser beam in the y-direction in a substantially sinusoidal motion.

12. The method of claim 11, wherein the frequency of the sinusoidal motion is approximately a fifteenth to a tenth of said laser beam's pulse repetition frequency.

13. A laser annealing system, comprising: a laser for generating a laser beam for scanning a substrate in a scanning direction by applying a series of laser beam pulses to contiguous positions on a surface of said substrate; andmeans for moving a line of focus of said laser beam on said surface of said substrate in a direction substantially perpendicular to said scanning direction by a predetermined distance between individual pulses of said series of pulses, while holding said line of focus of said laser beam substantially fixed in said scanning direction.

14. The laser annealing system of claim 13, wherein said means for moving comprises a mirror and an actuator for tilting said mirror.

15. The laser annealing system of claim 14, wherein said actuator comprises a piezoelectric actuator.

16. The apparatus of claim 14, wherein said actuator is configured to tilt said mirror in a substantially sinusoidal motion.

17. The apparatus of claim 16, wherein the frequency of the sinusoidal motion is approximately a fifteenth to a tenth of said laser beam's pulse repetition frequency.

18. The laser annealing system of claim 13, wherein said means for moving comprises first and second mirrors having first and second actuators configured to move said first and second mirrors in opposite directions to minimize acceleration forces associated with movement of said mirrors.

19. An optical system for delivering a pulsed laser treatment beam to a workpiece, said laser treatment beam having a beam spot with an elongated footprint, and wherein said workpiece is translated in a first (x) direction with respect to the optical system, said first direction being perpendicular to the longitudinal axis of beam spot, said optical system comprising: a movable optical element for dithering the beam spot with respect to the workpiece in a second direction (y) perpendicular to the first direction and parallel to the longitudinal axis of the beam spot, with the translation speed of the workpiece and the frequency and extent of the dithering of the beam spot being arranged to compensate for inhomogeneities in the longitudinal axis of the beam.

20. An optical system as recited in claim 19, wherein the movable optical element is a movable mirror.

21. An optical system as recited in claim 20, further including a second movable mirror which cooperates with the first movable mirror to dither the beam spot.

22. An optical system as recited in claim 19, wherein the optical element is moved in a substantially sinusoidal pattern.

23. A method of treating a workpiece with a pulsed laser beam, said beam having a beam spot with an elongated footprint comprising the steps of: (a) directing the beam to the workpiece;(b) dithering the beam in a direction parallel to the longitudinal 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 direction perpendicular to the longitudinal 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 longitudinal axis of the beam.

24. A method as recited in claim 23, 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.