Systems and methods for reducing pulsed laser beam profile non-uniformities for laser annealing
View Patent ↗Systems and methods for reducing pulsed laser beam profile non-uniformities for laser annealing are disclosed. The methods include directing an initial pulsed laser beam along an optical axis, and imparting to each light pulse a time-varying angular deflection relative to the optical axis. This forms a new laser beam wherein each light pulse is smeared out over an amount of spatial deflection δ sufficient to reduce the micro-scale intensity variations in the laser beam. The new laser beam is then used to form the line image, which has better intensity uniformity as compared using the initial laser beam to form the line image.
1. A method of reducing micro-scale intensity variations in a laser beam used for laser annealing of a semiconductor wafer, comprising:
generating from a laser source a laser beam having a wavelength λ and including light pulses, wherein the laser beam has an amount of the micro-scale intensity variations with a modulation period p s between λ/4 and 40λ;
imparting a time-varying spatial deflection δ to each light pulse to form a deflected light beam by passing each light pulse through a beam-redirecting element that is activated in synchrony with the laser source, wherein p s ≤δ; and
forming from the deflected light beam a line image at an image plane.
2. The method according to claim 1 , wherein δ≤100 μm.
3. The method according to claim 1 , wherein the light pulses have a repetition rate of f rep , and wherein imparting the time-varying spatial deflection δ includes driving the beam-redirecting element at a repetition rate f a _ rep that is equal to or a harmonic of the repetition rate of the light pulses.
4. The method according to claim 1 , wherein the beam-redirecting element is either acoustic-based or electro-optic based.
5. The method according to claim 1 , wherein the modulation period p s is between λ/2 and 20λ.
6. The method according claim 1 , further comprising performing beam conditioning of the laser beam either before or after imparting the time-varying spatial deflection δ.
7. The method according to claim 1 , wherein forming the line image using the deflected light beam includes passing the second laser beam through a relay optical system.
8. The method according to claim 1 , wherein the micro-scale intensity variations occur in two orthogonal directions, wherein the light pulses travel along an optical axis, and wherein the act of imparting the time-varying spatial deflection δ to each light pulse is performed using the beam-redirecting element that is oriented at an angle relative to the optical axis such that the micro-scale intensity variations are reduced in the two orthogonal directions.
9. The method according to claim 1 , wherein forming the line image includes passing the deflected light beam through a knife-edge aperture while imaging the knife-edge aperture onto the image plane with a relay optical system.
10. The method according to claim 9 , wherein the micro-scale intensity variations have a root-mean square (RMS) value, and wherein the RMS value of the micro-scale intensity variations in the deflected light beam as measured at the knife-edge aperture is decreased by at least a factor of between 1.5× and 5× as compared to an undeflected laser beam as measured at the knife-edge aperture.
11. A method of reducing micro-scale intensity variations when performing laser annealing of a semiconductor wafer with a line image, comprising:
directing along an optical axis a first laser beam having light pulses and first micro-scale intensity variations;
imparting to each light pulse in the first laser beam a time-varying angular deflection relative to the optical axis, thereby smearing out each light pulse over an amount of spatial deflection δ to form a second laser beam having second micro-scale intensity variations that are less than the first micro-scale intensity variations; and
using the second laser beam to form the line image.
12. The method according to claim 11 , wherein the first micro-scale intensity variations have a root-mean square (RMS) value, and wherein the RMS value of the micro-scale intensity variations in the second laser beam is decreased by at least a factor of between 1.5× and 5× as compared to the first laser beam.
13. The method according to claim 11 , wherein δ≤100 μm.
14. The method according to claim 11 , wherein the micro-scale intensity variations in the laser beam are reduced by a factor of at least 1.5× root-mean square (RMS) as compared to no time-varying spatial deflection.
15. The method according claim 11 , further comprising performing beam conditioning of the laser beam either before or after imparting the time-varying angular deflection.
16. The method according to claim 11 , wherein forming the line image using the second laser beam includes passing the second laser beam through a relay optical system.
17. The method according to claim 11 , wherein the micro-scale intensity variations occur in two orthogonal directions, and wherein the act of imparting the time-varying angular deflection to each light pulse is performed using a beam-redirecting element that is oriented at an angle relative to the optical axis such that the micro-scale intensity variations are reduced in the two orthogonal directions.
18. The method according to claim 11 , wherein the micro-scale intensity variations in the laser beam are reduced by a factor of at least 1.5× root-mean square (RMS) as compared to no time-varying angular deflection.
19. The method according to claim 11 , wherein the first micro-scale intensity variations have a modulation period p s , and wherein p s ≤δ.
20. The method according to claim 19 , wherein the first laser beam has a wavelength λ and λ/4≤p s ≤40λ.
21. The method according to claim 20 , wherein λ/2≤p s ≤20λ.