Wafering

A silicon crystal must change shape several times before it winds up as the precisely calibrated wafers that form the foundations of photovoltaic cells.

Cutting off the tops and tails of the ingots

 

Cutting

First, a saw cuts off the crystal’s so-called top and tail, so that a crystal of uniform width remains. Typically, wafering saws draw thin wire bearing a liquid abrasive across the crystal’s surface. (Below, a machine mounted with a giant donut-like steel blade does the cutting.) Wire saws also cut the crystal into ingots measuring 2 feet or less. Steel holders are mounted on the ends of these ingots for the next step.

Squaring the ingots in a wire saw 

Squaring

Mounted ingots are placed standing on end in a rack bearing 16 at a time inside another wire slicing machine. There, wire running in a lattice configuration descends on the ingots to shear off four rounded segments, leaving flat sides. The result: The ingots now have a square cross-section, except for still-rounded corners.

Slicing the ingot into wafers with a wire saw Slicing

The next wire saw is more intricate yet. A wire winding hundreds of times between two cylindrical drums forms a web of parallel, tightly spaced segments. As the wire unspoil through the machine, ingots mounted sideways on glass and metal holders are pressed two at a time through the wire web, slicing them into the thickness of slim business cards. Each millimeter of crystal yields about 2 1/2 wafers. Detached from their holders, the wafers are loaded into carriers, or boats, for transport to the next step.