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 λLED is disclosed. The system includes the wafer. The wafer has a roughened alignment mark with a root-mean-square (RMS) surface roughness σS. 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 λA that is in the range from about 2σS to about 8σS. 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.

主权项

1. An alignment system for aligning a wafer when lithographically fabricating on the wafer a light-emitting diode (LED) having a wavelength λLED, comprising:
the wafer, with the wafer having at least one wafer alignment mark; a rough surface formed on or above the wafer alignment mark and on a layer having a refractive index n, the rough surface having a root-mean-square (RMS) surface roughness σS that is within one of the following ranges: i) from about 2λLED to about 8λLED; ii) from about (0.5)λLED/n to λLED/n; or iii) from about λLED/n to λLED; a light source that illuminates the at least one wafer alignment mark with alignment light having a wavelength λA that is in the range from about 2σS to about 8σS; a lens configured to form an image of the at least one wafer alignment mark at the alignment light wavelength λA; an image sensor configured to detect the image and form therefrom a digital alignment mark image; and an image processing unit electrically connected to the image sensor and configured to receive and compare the digital alignment mark image to an alignment reference to establish a wafer alignment with respect to the alignment reference.