1. Field of the Invention
The invention relates to a method and a device for comminuting and sorting highly pure polycrystalline silicon.
2. Background Art
Highly pure polycrystalline silicon, referred to below as polysilicon, is used, inter alia, as a starting material for the production of electronic components and solar cells. It is obtained by thermal decomposition of a gas containing silicon or a gas mixture containing silicon. This process is referred to as chemical vapor deposition (CVD). On a large scale, this process is carried out in so-called Siemens reactors. The polysilicon is thereby created in the form of rods, which are then generally comminuted by means of manual methods. The coarse polysilicon fraction thus obtained has an irreproducible size distribution, with hardly any smaller fraction sizes being created in large quantities. A range of machine-based methods are known, in which a manually pre-comminuted coarse polysilicon fraction is further comminuted by using conventional crushers. Mechanical crushing methods are described, for example, in EP 1 338 682 A2. Mechanical crushing methods in combination with an elaborate thermal pre-treatment of the polysilicon rods are also known, which are intended to allow simpler crushing of the polysilicon (for example EP 1 338 682 A2). The polysilicon fraction is subsequently classified by a screening method, for example a mechanical screening method as known from EP 1043249 B1, or optical sorting as is known for example from U.S. Pat. No. 6,265,683 B1.
In the past, sorting or “classifying” polysilicon fractions has always been decoupled from comminution. Thus, isolation of fractions with targeted particle size distributions may entail considerable waste, and adjustment of the crushing to minimize this waste is largely a trial and error process.