Old Silicon Wafers Shine in New Role

Michael A. Greenwood

What do you do with old computer-chip wafers? Throwing them out is no longer the answer.

IBM Corp. began a program at its Burlington, Vt., plant in early 2007 to recycle cast-off silicon wafers and sell them to companies that manufacture solar panels. The company plans to expand the program to its East Fishkill, N.Y., facility in 2008.

A process to recycle discarded computer-chip wafers into material for solar panels has been started by IBM Corp. The computer-chip wafer (left) is shown as it looks before the process begins and as it appears at different stages until its conversion into a solar panel (right) is complete. Courtesy of IBM.

What used to be regarded as scrap material and crushed now is being used to convert photons into usable electricity. Silicon is the most widely used material in the construction of photovoltaic arrays, but its supply has been crimped in recent years because of increased demand for the material. The shortage threatens to curtail the growth of solar power.

The computer company said that if the estimated 3 million silicon wafers (weighing about 187.5 tons and covering an area of ~22.5 acres) that are discarded each year are instead transformed into solar power arrays, up to 13.5 MW of usable power could be generated. That would be enough to meet the energy needs of as many as 6000 homes at 9500 kWh per house per year.

Preparing the encoded wafers for use by solar manufacturing companies is relatively simple. The company’s patented reclamation process involves removing any circuit patterns printed on the wafer by placing it onto a polishing machine that has a rotating abrasive pad lubricated with deionized water. The process entirely removes any programming or intellectual property printed on the wafer without damaging the valuable silicon underneath.

Other methods for cleaning used wafers involve chemicals that strip away the circuitry.

The problem is that they also strip away some of the silicon. The company said that it plans to make its abrasion process available to other semiconductor manufacturers.

The reclamation program will result in about $1.5 million in savings annually. It was honored with the 2007 Most Valuable Pollution Prevention Award from the National Pollution Prevention Roundtable.