Patent ID: 8691598

Claim:
A method of annealing with a laser a wafer having a melt temperature and a surface that supports an array of dies with each die having a varying emissivity, comprising: scanning an annealing laser beam from the laser over the array of dies, wherein the laser has laser noise and is adjustable to control an amount of power in the annealing laser beam, wherein the annealing laser beam creates an annealing temperature at the wafer surface that does not exceed the wafer melt temperature; measuring and controlling the amount of power in the annealing laser beam using a first control loop that measures the amount of power and operates at a first frequency f 1 to control the laser noise in the laser; and controlling the amount of power in the annealing laser beam using a second control loop that operates at a second frequency f 2 <f 1 by measuring thermal emission radiation from the wafer, including averaging the thermal emission radiation over at least one die and determining therefrom a corresponding average measured temperature, and using the average measured temperature and an annealing temperature set point to adjust the laser to control the amount of power in the annealing laser beam.