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SILICON RIBBON AND FOIL PRODUCTION 237<br />

Filaments<br />

Seed<br />

Sheet<br />

crystal<br />

Meniscus<br />

melt<br />

Crucible<br />

Figure 6.24<br />

Schematic of String Ribbon (STR) growth system<br />

VI<br />

Shaping die<br />

VR<br />

Si melt<br />

Substrate<br />

Si ribbon<br />

Figure 6.25<br />

Schematic of Ribbon Growth on a Substrate (RGS) configuration<br />

of the foil. The thickness of the foil is controlled by the heat-removal capacity of the<br />

substrate, pull rate and surface tension. The direction of crystallisation and growth are<br />

nearly perpendicular. The area of the growth interface now can be very large compared<br />

to the foil thickness. The latent heat is extracted by conduction into the substrate. The<br />

thermal gradients near the interface are small, thus reducing thermally induced stress in

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