Producing polycrystalline silicon ingots/blocks, by placing a crucible in a process chamber, and heating a solid silicon material in the crucible above a melting temperature of the silicon material to form molten silicon in the crucible

The process comprises placing a crucible (6) in a process chamber (4), heating a solid silicon material in the crucible above a melting temperature of the silicon material to form molten silicon in the crucible, cooling the silicon material in the crucible below a solidification temperature of the molten silicon, blocking any direct gas flow from the crucible to a diagonal heater by unit of a foil curtain, which is provided adjacent to the side of the diagonal heater that faces the crucible, and lowering a plate element located in the process chamber. The process comprises placing a crucible (6) in a process chamber (4), heating a solid silicon material in the crucible above a melting temperature of the silicon material to form molten silicon in the crucible, cooling the silicon material in the crucible below a solidification temperature of the molten silicon, blocking any direct gas flow from the crucible to a diagonal heater by unit of a foil curtain, which is provided adjacent to the side of the diagonal heater that faces the crucible, lowering a plate element located in the process chamber and passively heated via the diagonal heater, directing a gas flow to the surface of the molten silicon in the crucible during a time segment of a time period of solidification of the molten silicon, fixing additional solid silicon material to the plate element before heating of the silicon material in the crucible in such a way that a part of the additional silicon material is immersed into the molten silicon in the crucible during the lowering of the plate element for melting, where the filling level of the molten silicon in the crucible is raised, directing a top-bottom gas flow over a side of the diagonal heater facing the crucible during a section of the heating and/or cooling step of the silicon material, and providing two stacked diagonal heaters. The crucible is filled with the solid silicon material or is filled with silicon material in the process chamber. The crucible is arranged with respect to the diagonal heater in such a way that the diagonal heater is laterally offset and is above the silicon ingot to be produced. A temperature distribution in the silicon material during the cooling step is controlled partially via the diagonal heater. The gas flow is directed to the surface of the molten silicon partially via the passage in the plate element. The plate element comprises a passage for a gas supply. The diagonal heaters are controlled during the step o