Method and apparatus for controlling melt temperature in a Czochralski grower
In a Czochralski process for growing single crystal silicon ingots, a system is provided for adding solid material to the liquid silicon during crystal growth for the purpose of directly controlling the latent heat of fusion with respect to a crystal melt interface. In contrast to the standard method for controlling power to the crucible heaters, the present system has been found to be much more effective for controlling melt temperature in the crucible, especially in heavily insulated systems. The system provides the advantages of reducing the electric power required to operate a Czochralski grower, while increasing the speed with which the melt temperature can be raised or lowered in a controlled manner.
1 . A CZ system for growing a single crystal ingot from a molten material comprising:
a crucible including a base and side walls for holding a quantity of molten material at a melt/crystal interface with respect to a seed crystal for growing an ingot from the molten material;
a feeder for providing solid feedstock material to the crucible where it is melted;
heaters disposed beneath the base and around the sidewalls for providing heat to the crucible;
one or more sensors directed at the melt/crystal interface to provide an output signal representative of sensed temperature at the melt/crystal interface;
an insulated thermal environment surrounding the heater means to minimize energy loss through the process chamber walls; and
a controller responsive to the sensor output signal and having a control lead for activating the feeder, the controller including a lookup table containing values for optimal amounts of feedstock, the controller being programmed such that adding solid feedstock provides dominant control of the temperature of the molten material in the crucible.
2 . CZ system as in claim 1 , wherein the introduction of solid feedstock provides direct, immediate control of the latent heat of fusion with respect to the melt/crystal interface.
3 . A continuous CZ system for growing single crystal ingots from a molten material comprising:
a crucible including a base and side walls for holding a quantity of molten material at a melt/crystal interface with respect to a seed crystal for growing an ingot from the molten material;
a feeder for adding solid feedstock material to the crucible upon receipt of an activation signal;
heaters disposed beneath the base and around the sidewalls for providing heat to the crucible;
insulators surrounding the heater means to minimize energy loss to the process chamber; and
a controller responsive to temperature of the molten material and/or melt crystal interface, having a control output lead for activating the feeder, the controller programmed to add solid feedstock to the molten material to control the temperature of the melt/crystal interface by the latent heat of fusion to provide dominant control of the temperature of the melt/crystal interface in the crucible.
4 . (canceled)
5 . A CZ system as in claim 1 , wherein at least one of the one or more sensors includes a direct line of sight to one of the melt surface and the melt/crystal interface.
6 . A CZ system as in claim 1 , wherein the controller is programmed to add solid feedstock to the molten material to alter the rate of crystal solidification and/or the crystal diameter.
7 . A CZ system as in claim 1 , wherein the heaters are resistive heaters.
8 . A CZ system as in claim 7 , wherein the heaters are annular and fabricated from graphite.
9 . A CZ system as in claim 7 , wherein the controller is programmed to control the amount of current to each heater to adjust the adjust characteristics of the melt.
10 . A CZ system as in claim 1 , wherein the crucible is fabricated from quartz.
11 . A CZ system as in claim 1 , wherein one or more of the sensors are directed at the crystal to provide an output signal representative of sensed temperature at the crystal.
12 . A CZ system as in claim 3 , further comprising one or more sensors directed at the melt/crystal interface to provide an output signal representative of sensed temperature at the melt/crystal interface.
13 . A CZ system as in claim 3 , further comprising one or more sensors directed at the crystal to provide an output signal representative of sensed temperature at the crystal.
14 . A CZ system as in claim 12 , wherein at least one of the one or more sensors includes a direct line of sight to one of the melt surface and the melt/crystal interface.
15 . A CZ system as in claim 3 , wherein the controller is programmed to add solid feedstock to the molten material to alter the rate of crystal solidification and/or the crystal diameter.
16 . A CZ system as in claim 3 , wherein the heaters are resistive heaters.
17 . A CZ system as in claim 16 , wherein the heaters are annular and fabricated from graphite.
18 . A CZ system as in claim 16 , wherein the controller is programmed to control the amount of current to the each heater to adjust the thermal characteristics of the melt.
19 . A CZ system as in claim 3 , wherein the crucible is fabricated from quartz.