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As in silicon ingot processing, the crystalline structure of the GaAs ingot is determined by the use of an x-ray diffraction unit. The ends of the single-crystal ingot are then cropped using a water-lubricated single-bladed diamond saw, with various coolants added to the water.
The following are potential hazards of ingot evaluation and machining. Arsenic
The gallium arsenide ingots are wax-mounted to a graphite beam and sawed into individual wafers with the use an automatic inner diameter blade saw. Lubricants used in this operation generate a gallium arsenide slurry, which is collected, centrifuged, and recycled.
The wafers are then dismounted from the wax and graphite beam to prepare for cleaning. Cleaning consists of sequentially dipping the wafers in wet chemical baths containing methanol, de-ionized water, and an acid mixture of sulfuric acid, hydrogen peroxide, and water, in a 5:1:1 concentration. A visual inspection is also performed at this stage.
After cleaning, the wafers are wax-mounted to a lapping machine. The lapping machine operates at a set rotational speed and pressure and uses a lapping slurry containing aluminum oxide, glycerin, and water. After lapping, the wafers are dismounted on a hot plate, rinsed in a soap solution, and wiped dry.
Finally, the wafers are physically mounted to a mechanical polishing machine, and polished using a slurry consisting of sodium bicarbonate, 5 percent chlorine, water, and colloidal silica slurry.
The following are potential hazards of wafer preparation. Arsenic