Wafer Slicing

The crystal becomes an "ingot" only after the seed-end (the top) and the tapered-end (the bottom) are removed using an inner-diameter (ID) saw. These ends are sometimes discarded; however, to avoid a complete material loss, some ends are re-melted and used in future crystal specifications. After the ends are cut-off, the ingot is cut into shorter sections in order to optimize the slicing operation that will follow later. Next, each section is ground to the specified diameter on a mechanical lathe. A thick "slug" is taken at the end of each ingot for quality control and testing. This includes measurement of resistivity, oxygen, carbon, and bulk defects. The whole ingot is then x-rayed to confirm crystal (atomic structure) orientation.

Following x-ray, the ingot is mounted on a carbon "block" using an epoxy resin. It is carefully mounted according to its orientation. The resin is allowed to cure before the ingot proceeds to slicing.

Silicon wafers are sliced from the ingot using both ID and Wire type saws. The ID saw can produce only single wafers at a time. The Wire saws are more efficient because we are able to slice the entire ingot at once. After the epoxy has cured, the ingot section is inverted and mounted into the 10-ton Wire saw. The ingot is gradually lowered into a "web" of fast moving, ultra-thin wire. The cutting action is created by pouring an abrasive slurry on the wire web, which is actually a single wire being fed from one spool to another. Immediately after slicing, the "as-cut" wafers are cleaned in a series of chemical baths to remove any residual slurry. From here, the wafers proceed into a series of refining steps to make them stronger and flatter.

First, the sharp, fragile edges are rounded or "profiled" to provide strength and stability to the wafer. This will ultimately prevent chipping or breakage in subsequent processing. Next, each wafer is laser-marked with very small alphanumeric or bar code characters. This laser-mark ID gives full trace-ability to the specific date, machine, and facility where the wafers were manufactured. The wafers are then loaded into a precision "lapping" machine that uses pressure from rotating plates and an abrasive slurry to ensure a more uniform, simultaneous removal of saw damage present on both front and backside surfaces. This step also provides stock removal and promotes flatness uniformity - a critical foundation for the polishing manufacturing process.

Now the wafers must go through an "etching" cycle. Chemical etching is necessary for the removal of residual surface damage caused by lapping; it also provides some stock removal. During the etching cycle, wafers progress down another series of chemical baths and rinse tanks with precise fluid dynamics. These chemical solutions produce a flatter, stronger wafer with a glossy finish. All wafers are then sampled for mechanical parameters and for process feedback.