Polycrystalline silicon is one of the purest materials manufactured by mankind. It is used as the charge material in the silicon ingot growth process and therefore dictates the purity of wafers.
Lara Chamness, Dan Tracy, SEMI, San Jose, CA USA
Polycrystalline silicon is one of the purest materials manufactured by mankind. It is used as the charge material in the silicon ingot growth process and therefore dictates the purity of wafers. As the raw material used in the production of Czochralski single crystal silicon wafers, polysilicon is the substrate upon which essentially all semiconductors are produced. Polysilicon is also a key component for silicon-based solar cells. Given the explosive growth of photovoltaics in recent years, a lot of attention has been given to polysilicon availability.
Historically, the semiconductor industry consumed two-thirds of the polysilicon supply, with the remaining one-third going to the photovoltaic industry. In the mid-2000s, the solar industry began to consume more than its traditional share of available polysilicon, prompting widespread concerns about potential polysilicon shortages. In response, established silicon suppliers announced ambitious capacity expansions, with at least 30 more new manufacturers announcing their intentions to enter the market. Many of these new facilities and expansions came online in 2009, just as the semiconductor and photovoltaic industries were experiencing severe downturns.
Polysilicon spot prices of over $400 per kg peaked in mid-2008 with pricing erosion throughout 2009. Long-term pricing contracts were also re-negotiated at this time. Even though the downturn is over, polysilicon spot prices are expected to remain below 2008 levels due to large capacity additions. 2010 worldwide polysilicon capacity was approximately 190,000 metric tons, representing a 90% increase in annual production from the year before (Fig. 1). New entrants represented over a third of 2010?s total polysilicon capacity with photovoltaic applications representing the largest end-market for polysilicon. By 2012, it is expected that global polysilicon capacity will surpass 300,000 metric tons, over half of which will be supplied by new entrants.
The production of polysilicon is very energy intensive. Yet, exhaustive technical studies on lower cost replacement methods for producing polysilicon over the past 25 years have failed to identify an alternative process. There are currently three methods commercially employed to produce polysilicon. The oldest method, the ?Siemens? process, was the only commercial route to polysilicon prior to 1980. It remains the dominant technology used in the production of prime quality polysilicon chunks. The second method was developed in the late 1970s by Union Carbide, embellished by Komatsu Electronic Metals and is called the monosilane process. Only one company uses this technology to produce polysilicon, Renewable Energy Corporation (REC) (formerly ASiMI). The third method was developed in the 1980s by Ethyl Corporation, which spun off the operation as Albemarle. It was acquired by MEMC Electronic Materials in the late 1990s. This third process also uses silane in a fluidized bed reactor that results in a product that is distinguished by pellets or granules of polysilicon, as opposed to rods.
|FIGURE 1. Polysilicon capacity trends.|
Historically, some wafer suppliers produced polysilicon captively to ensure a steady supply. Established suppliers of polysilicon are Hemlock Semiconductor (North America), MEMC Electronic Materials (North America), Mitsubishi Materials Polycrystalline Silicon (Japan), Osaka Titanium (Japan), REC (Norway), Tokuyama Corporation (Japan), and Wacker (Germany). New entrants include but are not limited to: OCI Chemical (South Korea), KCC (South Korea), Taiwan Polysilicon (Taiwan), GCL Silicon (China), LDK Solar (China), Daqo Group (China), and Renesola (China). New polysilicon manufacturing capacity is primarily intended for production of material for photovoltaic applications.
Coinciding with the growth in polysilicon production and with the overall strength in PV manufacturing, the silicon ingot and wafer segments of the supply chain are rapidly growing as well. This is especially true in China where there are an estimated 100 plus companies producing solar grade ingots and wafers; however, less than 20 suppliers account for over 70% of the production output. Dozens of other silicon suppliers have production scale capacity of less than 100 MW annually.
For solar silicon applications, companies are focusing on technological innovation, equipment upgrades, and process improvements, to reduce costs and improve quality. This will contribute to improving the cost-effectiveness of silicon-based photovoltaics.
Lara Chamness received her BA from UC Irvine, MS from UC Los Angeles, and MBA from Santa Clara U.; she is a senior market analyst at SEMI, 3081 Zanker Road, San Jose, CA 95134, USA; ph.: 1-408-943-6900; firstname.lastname@example.org
Dan Tracy received his BS from SUNY ESF, MS from the Rochester Institute of Technology, and PhD from Rensselaer Polytechnic Institute; he is a senior director at SEMI.
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