Rubicon Technology, Inc. (NASDAQ:RBCN), a leading provider of sapphire substrates and products to the LED, semiconductor, and optical industries, today announced that the United States Patent and Trademark Office (USPTO) has granted a patent to Rubicon entitled, “Asymmetrical Wafer Configurations and Method for Creating the Same,” U.S. Patent No. 8,389,099. The patent covers the creation of visual and tactile indicators to make sapphire wafers asymmetric according to their crystalline orientation.
Sapphire wafers have specific orientation that is invisible to the naked eye. Rubicon has developed a simple, yet elegant, process to make wafers appear asymmetrical via visual or tactile inspection. This is important as LED and semiconductor manufacturers process sapphire wafers using specific crystalline orientations. The patent helps manufacturers in the LED and SoS/RFIC industries eliminate costly and unnecessary steps to determine orientation of sapphire wafers during processing, such as x-ray crystallography.
Epitaxy-ready wafers have either an orientation flat or an orientation notch, but this provides insufficient information: the wafer could be flipped front-to-back and still look the same yet be unusable in that state crystallographically. Only through repeated x-ray inspections could the manufacturer ensure that no wafers are reversed. If the wafers are made asymmetrical, operators at each stage of production can verify surface orientation quickly and economically, and will be confident that the wafers have been handled correctly.
Rubicon’s patent demonstrates several different solutions for making sapphire wafers asymmetric. In one solution, a rounded corner on the orientation flat or notch allows a user to easily determine that the wafer has not been reversed. In another solution, both corners of the flat are rounded to different radii. These differences are enough to determine orientation by touch or visual inspection. The technique can be applied to other substrates including silicon, silicon oxide, aluminum nitride, germanium, silicon carbide, gallium arsenide, gallium phosphide, gallium nitride, and amorphous analogs.