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polysilicon products from Poly Plant ProjectsPolysilicon Products

A supplier may classify the polysilicon produced into 50 or more different grades with different specifications specific to the user and the application. In general, the supplier may offer:

  • Float Zone Grade, poly rods designed for very high purity single crystal float zone growth of silicon ingots for semiconductor power devices
  • Electronic Grade (Prime Grade, VLSI Grade, Virgin Poly, Semiconductor Grade), poly chunks designed for high purity single crystal Czochralski growth of silicon ingots for advanced IC applications
  • IC Grade or Standard Grade, poly chunks designed for single crystal Czochralski growth for standard, less advanced IC applications
  • Secondary or Test Wafer Grade, poly chunks with lower purity values for Czochralski growth of silicon test wafers or solar cell applications
  • Solar Grade or Casting Grade, poly chunks and rod sections with lower purity values for silicon cast crystal growth for solar cell applications
  • Reject or Scrap Grade, poly chunks, rod sections, small chips, with lower purity values often sold to the recycling/recovery companies

polysilicon rodsWithin each product grade are detailed specifications for rod size (diameter, length), chunk size (large, medium, small), acceptor/donor/carbon purity, bulk and surface metals purity, surface texture, and appearance. Sales prices are based on industry demand, product quality, and cost of production.

When supply and demand have been in balance, prices range from ~$100/kg for high purity fabricated Float Zone poly rods to ~$ 5/kg for waste/scrap polysilicon. In general, polysilicon products are identified by form (rod, chunks, chips) and purity. Purity specifications for solar-grade (SOG) polysilicon are much lower than for Electronic Grade (EG) poly. Table 1 lists general purity specifications for SOG and EG poly.

User A, B, and C are summaries from dozens of user specifications for solar cell applications. Standard Cz and Advanced IC are summaries from dozens of user specifications for Electronic Grade polysilicon. Acceptor elements, primarily boron, and donor elements, primarily phosphorus, are measured in parts per billion, atomic. Carbon and oxygen are measured in parts per million, atomic. Bulk metals and surface metals are measured in parts per billion, by weight.

Most solar cells are fabricated on silicon wafers that have been cut from ingots at about 0.1 ohm-cm p-type, so the polysilicon can have relatively large amounts of boron, compared to EG poly. An important difference between SOG and EG poly is the metals content. Reduction of metals content increases production costs. Metals content is not usually specified for SOG.


General Purity Specifications for SOG and EG Polysilicon

Element

PV Map SOG

User A, SOG

User B, SOG

User C, SOG

Std. Cz EG

Adv. IC EG

B, ppba 500 < 200 <3 0.8 0.3 0.15
P, ppba 50 <1 <2 0.8 0.3 0.15
C, ppma 0.5 – 10 <1 <2 <1 0.5 0.4
O, ppma 10 --- --- --- --- ---
Blk Mtls 100 <10 < 300 <30 100 10
Srf Mtls
Fe, ppbw
--- --- --- --- 20 0.8
Cr, ppbw --- --- --- --- 8 0.2
Ni, ppbw --- --- --- --- 8 0.2
Na, ppbw --- --- --- --- 8 0.2

   
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