[Stuttgart, Germany]

Upgraded Metallurgical Silicon (UMG-Si) development continues towards a 100% UMG feedstock.
New monosilane production facility is on track to begin supply in early 2011.

As foreshadowed in Of Silicon Metal, Solar Grade, and PV-1201, Dow Corning Corporation did deign to provide a UMG project Update at PHOTON’s 8th Solar Silicon Conference.

Dow Corning Solar Solutions Global Industry Director Dr. Gaëtan Borgers said UMG production was stopped as a result of decreased demand in 2009. Although 3000 MT (Metric Tons) of capacity remain in place, the assets have been redirected but the pilot line is still running. Restart of production and capacity additions will be contemplated per customer demand and appear to hinge on the successful development of PV-1501 slated for the 2012 timeframe.

Low cost polysilicon in excess supply has raised the quality bar for solar grade silicon. I also note a change to the UMG roadmap slide with the PV-1201 Boron concentration increased to 2.5 ppmw (part per million by weight) from the 2 ppmw shown in 2009. The specification change may have contributed to the production stop.

Committed to continuing UMG development, Dow Corning decided to skip intermediate steps on their UMG roadmap and focus on the ultimate goal, PV-1501, a product that can be used without blending for 100% UMG silicon solar cells. Dow Corning’s targets for PV-1501 purity are below 0.5 ppmw Boron and below 0.5 ppmw Phosphorus tighter than mentioned at PHOTON’s 7^th Solar Silicon Conference. In addition, UMG goals of scalability, consistency, and a sustainable process that does not generate more byproducts than the main product were reiterated. The UMG manufacturing cost goal is well below $15 per kg (kilogram), and CAPEX (capital expenditures) must be below 20% of the Siemens process used for polysilicon production.

Dr. Borgers discussed the Research and Development status of the two main UMG process steps.

Dopant Purification
Dow Corning is continuing to explore two technical paths to reach the required purity levels. Technical option 1 achieves “Out of arc furnace ladle: B < 1.5 ppm (roadmap to cut this by 2) P < 13 ppm (roadmap to cut this by 5).” The more promising Technical option 2 utilizes a batch 200-kg pilot unit to obtain “B < 0.5 ppm P < 1.2 ppm (target is <0.5).”

Directional Crystallization
Dr. Borgers said:

Here I am very happy to announce that we have demonstrated a breakthrough high yield directional solidification technology. It’s a technology that positions our cost structure at a fraction of what would be an ATM furnace to do similar processes.

With capital cost well below the target budget, the new directional solidification technology’s segregation coefficient almost matches the theoretical coefficient, and the process facilitates the integration of an additional purification step if needed to further improve quality.

Combining the two steps, Dow Corning believes their UMG efforts are on credible path to deliver a PV-1501 class UMG Silicon.

Monosilane
On the status of the monosilane plant of undisclosed capacity, Dr. Borgers said:

And I am glad to report that we are on track with that project. Right now we are completing the building of the manufacturing plant, and we are planning to start delivering material early 2011.

Dow Corning’s aspiration is to become a leader in monosilane production. Recent developments in the amorphous silicon (a-Si) thin film space a la Applied Material’s SunFab weigh on their plans for increasing monosilane supply next year.

Dow Corning is a member of the Silicon Solar Consortium, “a global partnership for photovoltaic research, development and education” including photovoltaic silicon materials.