Device and process for producing poly-crystalline or multi-crystalline silicon; ingot as well as wafer of poly-crystalline or multi-crystalline silicon produced thereby, and use for the manufacture of solar cells

Abstract

A process and a device for producing crystalline silicon, particularly poly- or multi-crystalline silicon are described, wherein a melt of a silicon starting material is formed and the silicon melt is subsequently solidified in a directed orientation. A phase or a material is provided in gaseous, fluid or solid form above the melt in such a manner, that a concentration of a foreign atom selected from oxygen, carbon and nitrogen in the silicon melt and thus in the solidified crystalline silicon is controllable, and/or that a partial pressure of a gaseous component in a gas phase above the silicon melt is adjustable and/or controllable, the gaseous component being selected from oxygen gas, carbon gas and nitrogen gas and gaseous species containing at least one element selected from oxygen, carbon and nitrogen. The formation of impurity compound precipitations or inclusions, in particular of silicon carbide affecting electric properties of solar cells, can be effectively inhibited and prevented according to the present invention.