Method for determining trace metals in silicon

A method for determining an amount of metallic impurities within silicon, comprising the steps of:

• a) providing a rodlike silicon sample and a rodlike seed crystal in a zone melting apparatus;
• b) zone melting to form a single silicon crystal having a conical end region, with a droplike melt forming at the end of the single silicon crystal in a separation step;
• c) cooling of the droplike melt to form a solidified silicon drop;
• d) partial or complete dissolution of the silicon drop in an acid;
• and e) analyzing the solution obtained within step d) by a trace analysis technique;
• wherein the separation step further comprises the steps of:
• (i) remelting of the silicon sample to reduce its diameter, where for a first time interval the direction of movement of the silicon sample and of the seed crystal is reversed relative to its previous direction of movement, to form the conical end region;
• (ii) forming a droplike melting zone, where for a second time interval the movement of the seed crystal is halted and the direction of movement of the silicon sample is reversed again;
• and (iii) wherein during separation of seed crystal and silicon sample where the direction of movement of the silicon sample is reversed, and wherein said separation step occurs for a duration of 5 to 20 s, and has a speed of movement of 150 to 400 mm/min.