System for continuous growing of monocrystalline silicon
View Patent ↗An improved system based on the Czochralski process for continuous growth of a single crystal ingot comprises a low aspect ratio, large diameter, and substantially flat crucible, including an optional weir surrounding the crystal. The low aspect ratio crucible substantially eliminates convection currents and reduces oxygen content in a finished single crystal silicon ingot. A separate level controlled silicon pre-melting chamber provides a continuous source of molten silicon to the growth crucible advantageously eliminating the need for vertical travel and a crucible raising system during the crystal pulling process. A plurality of heaters beneath the crucible establish corresponding thermal zones across the melt. Thermal output of the heaters is individually controlled for providing an optimal thermal distribution across the melt and at the crystal/melt interface for improved crystal growth. Multiple crystal pulling chambers are provided for continuous processing and high throughput.
1. A system for achieving improved level control for continuously replenishing a melt of crystalline feedstock in a crucible for continuous CZ crystal growth, wherein an ingot is pulled from a respective seed crystal positioned at a melt/crystal interface in the crucible comprising:
a weight sensor means attached for weighing the crucible and for converting a load or weight exerted by the crucible into output signals representative of that sensed load or weight;
a controller communicatively linked with the weight sensor means for receiving output signals from the weight sensor representative of the weight of the crucible, for determining the weight of the growth crucible both empty and with a desired depth of melt at the crystal growth interface, and for providing activation signals over a second communication link to a dispenser for selectively providing silicon feedstock to the crucible, wherein the controller further comprises a computer means for determining activation of the dispenser based on a desired depth D of melt in the crucible according to the following relationship:
D =( W−Wt )/(π* R exponent 2 *r );
where W is the total weight of the crucible containing melt; Wt is the weight of the crucible measured empty; R is the internal radius of the crucible; and r is the density of liquid silicon; and
a source of silicon feedstock connected to the dispenser, such that the dispenser, in response to the output signals from the controller, releases a predetermined amount of solid silicon feedstock into the crucible to maintain the melt level at the growth/crystal interface at a desired depth.
2. A system for achieving improved level control for continuously replenishing a melt of crystalline feedstock in a crucible for continuous CZ crystal growth as in claim 1 , wherein the weight sensor means further comprises one or more load cells, each having an arm, coupled with the crucible, capable of deflection in response to an applied load, such that weight of silicon melt in the crucible produces a deflection that in turn produces an electrical resistance change proportional to the load.
3. A system for achieving improved level control for continuously replenishing a melt of crystalline feedstock in a crucible for continuous CZ crystal growth as in claim 1 , wherein the communication links between the weight sensor, controller and dispenser comprise electrical cable, fiber optic cable, wireless or infra red links to provide stable high temperature operation.