Optical alignment systems for forming LEDs having a rough surface

摘要

An alignment system for aligning a wafer when lithographically fabricating LEDs having an LED wavelength λ_LED is disclosed. The system includes the wafer. The wafer has a roughened alignment mark with a root-mean-square (RMS) surface roughness σ_S. The system has a lens configured to superimpose an image of the reticle alignment mark with an image of the roughened alignment mark. The roughened alignment marked image is formed with alignment light having a wavelength λ_A that is in the range from about 2σ_S to about 8σ_S. An image sensor detects the superimposed image. An image processing unit processes the detected superimposed image to measure an alignment offset between the wafer and the reticle.