Heater electrode melting prevention e.g. in Czochralski apparatus

摘要

Equipment is claimed for preventing heater electrode melting in a single crystal pulling device which has a heater, surrounding a melting crucible, and a pair of metal electrodes, each of which has a water cooling channel and is joined by a threaded joint to an intermediate graphite electrode connected to the heater. The equipment comprises (a) a switch in a circuit between at least one of the metal electrodes and a voltage supply for the metal electrode pair; (b) a measuring device for measuring current passage through the heater; and (c) a controller which receives measurements from the measuring device and which switches off the switch to interrupt current flow when current fluctuations, beyond a tolerance range, last for a first predetermined time period of shorter duration than that required to cause melting of the metal electrode.