Apparatus for growing silicon crystals

An apparatus for growing silicon single crystals by the Czochralski technique, comprising:

• (a) a crucible for holding a silicon melt;
• (b) pulling means for pulling a seed crystal immersed in said silicon melt;
• (c) a furnace having an upper wall for housing said crucible, said upper wall having an opening located directly above said crucible;
• (d) a cooling shell located above said crucible for cooling said silicon single crystal, which is being pulled, from a temperature of 1,050.degree. to 850.degree. C. in no more than 140 minutes, said cooling shell being disposed around said silicon single crystal which is being pulled, and having an upper end and a lower end, said lower end being spaced apart from the melt in said crucible;
• (e) a secondary heater to heat said silicon single crystal, which is being pulled, such that the dwelling time of said single crystal in a temperature zone of 800.degree. to 600.degree. C. is at least two hours, said secondary heater being fixed at said furnace opening and coaxial therewith and disposed above said cooling shell and arranged so as to define a space between said secondary heater and said cooling shell;
• and
• (f) means located at said opening for introducing an argon gas flow through said secondary heater into the cooling shell whereby said gas flow traverses said space between said secondary heater and said cooling shell.