Wafer Whoppers

Microchip manufacturers etch their chips, more than 100 at a time, on large, round silicon wafers. The bigger the wafer, the greater the number of chips-and the lower the per-chip cost. The problem is that silicon crystals-from which wafers are harvested-cannot be grown to diameters larger than about 30 centimeters without being riddled with defects. Now, Juergen Werner and his colleagues at the University of Stuttgart, Germany, have found a way to get large wafers by joining smaller ones. They lay two wafers side by side and crystallize silicon vapor between their edges to close the gap. In early work, Werner connected two one-by-three-centimeter wafers; the technique should work to seal together larger wafers as well. The same method should also work with germanium-whose crystal growth is limited to 15 centimeters-to produce large wafers for more efficient solar cells and electronic displays.