Active edge control of a crystalline sheet formed on the surface of a melt
An optical sensor is configured to detect a difference in emissivity between the melt and a solid ribbon on the melt, which may be silicon. The optical sensor is positioned on a same side of a crucible as a cold initializer. A difference in emissivity between the melt and the ribbon on the melt is detected using an optical sensor. This difference in emissivity can be used to determine and control a width of the ribbon.
1 . An apparatus for controlling a thickness of a crystalline ribbon grown on a surface of a melt, the apparatus comprising:
a crucible configured to hold the melt;
a cold initializer configured to produce a cooling jet that is directed toward the surface of the melt;
an optical imaging device comprising a camera or a CCD camera configured to, in part, produce an image of at least a portion of the melt and the crystalline ribbon;
a processor comprising electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, analog or digital controls/switches, microcontrollers, or computing systems, the processor configured to determine, based at least in part on the image, a location of an edge of the crystalline ribbon relative to the melt surface using differences in emissivity and vibration, and to adjust a width and a thickness of the crystalline ribbon on the melt by varying a gas flow or heat of one or more of a plurality of segments based on the determined edge location; and
a segmented thinning controller that includes the plurality of segments that are each configured to output the gas flow or heat, wherein the segmented thinning controller is configured to adjust the width and the thickness of the crystalline ribbon on the melt based on signals received from the processor.
2 . The apparatus of claim 1 , wherein the segmented thinning controller is below the crucible and includes a uniform melt back heater that includes a heater that is configured to be controlled by the processor based on the image.
3 . The apparatus of claim 1 , wherein the processor is in electronic communication with the optical imaging device and the segmented thinning controller, and wherein the processor is configured to control the segmented thinning controller based on a detected width of the crystalline ribbon in the image.
4 . The apparatus of claim 3 , wherein the processor is configured to adjust the gas flow or heat output from at least one outermost segment among the plurality of segments of the segmented thinning controller.
5 . A method comprising:
providing a melt in a crucible;
forming a ribbon on a surface of the melt using a cold initializer configured to produce a cooling jet that is directed toward the surface of the melt, wherein the ribbon is a single crystal;
pulling the ribbon at a rate of ribbon formation;
applying heat to the ribbon through the melt using a heater disposed below the melt;
thinning the ribbon with a segmented thinning controller that includes a plurality of segments that are each configured to output a gas flow or the heat;
using at least one optical imaging device comprising a camera or a CCD camera to capture an image of at least a portion of the melt and the ribbon;
based at least in part on the image, determining a location of an edge of the ribbon relative to the melt surface using differences in emissivity and vibration between the melt and the ribbon;
controlling a width of the ribbon by varying the gas flow or the heat output of one or more of the plurality of segments of the segmented thinning controller based on the determined edge location; and
separating the ribbon from the melt at a wall of the crucible where a stable meniscus forms.
6 . The method of claim 5 , further comprising determining a width of the ribbon based on the image.
7 . The method of claim 5 , wherein the melt includes silicon.
8 . The method of claim 5 , wherein the segmented thinning controller is below the crucible and includes a uniform melt back heater that is configured to be controlled based on the image.
9 . The apparatus of claim 1 , further comprising a viewport positioned over and perpendicular to the melt, wherein the optical imaging device is positioned to view the melt and the crystalline ribbon via the viewport.
10 . The apparatus of claim 1 , further comprising a pyrometer focused on an edge of the crystalline ribbon and configured to provide pyrometer signals to the segmented thinning controller.
11 . The method of claim 5 , further comprising providing a view for the optical imaging device of the melt and the ribbon via a viewport that is positioned over and perpendicular to the melt.
12 . The method of claim 5 , wherein determining the difference in the emissivity is further based, at least in part, on pyrometer signals generated by a pyrometer that is focused on an edge of the ribbon.
13 . The method of claim 5 , wherein the ribbon is a single crystal.