Method for achieving sustained anisotropic crystal growth on the surface of a silicon melt

A method for growing a crystalline sheet from a melt, the method comprising:

• providing a first cold block proximate a melt surface, the first cold block that confronts the melt surface and defines a first cold area having a first width in a first direction, the first cold area operable to provide localized cooling of a first region of the melt surface proximate the first cold block;
• determining that a crystalline layer attached to a crystalline seed has formed on the melt;
• pulling the crystalline seed along a path in a second direction perpendicular to the first direction so as to form a ribbon extending in the second directing and having a width in the first direction;
• and
• providing a second cold block proximate the melt surface, the second cold block located downstream from the first cold block along the path and defining a second cold area confronting the melt surface, the second cold area having a width in the first direction that increases from the first width to a second width, the second cold area operable to provide localized cooling of a second region of the melt surface proximate the first second block to widen the ribbon and form the crystalline sheet;
• wherein a vertical distance between the melt surface and the lower surface of the second cold block varies in the first direction to position outer regions of the lower surface of the second cold block along the first direction at a greater vertical distance from the melt surface than inner regions of the lower surface of the second cold block.