the ribbon is pulled from the melt. A similar process is called the String Ribbon
technique, in which two high-temperature vertical strings are pulled vertically
through a shallow silicon melt. The molten silicon spans and freezes between the
strings, forming a long, thin single-crystal ribbon. The silicon ribbon is then cut
to length without interrupting the continuous growth of new ribbon.
A third ribbon technology was introduced by Siemens Solar in 1990, but was
never fully developed until the German company, Brandl AG, picked it up in
2000. The S-Web process utilizes a carbon-fiber net that is pulled horizontally
along the surface of a silicon melt. The silicon solidifies along the lower side of
the net, forming a crystal that can be drawn out into a continuous ribbon, which
can then be doped and cut into rectangular, cell-sized pieces. A sketch of the
process is shown in Fig. 8.50.