Companies Expanding Use of Reclaimed Silicon
Efficient and sustainable re-use of silicon is needed across both the photovoltaic and semiconductor industries. The key to recycling used wafers is to verify and sort material by dopant and impurity levels. Both p-doped and n-doped waste wafers can be reprocessed to manufacture solar cells. Panel performances made from such materials are used to satisfy the market demand for solar energy in Europe.
SEMI, San Jose -- PV Society, 6/11/2009
Silicon is a critical strategic material for both the semiconductor and photovoltaic industries. Historically, the PV industry has relied on excess silicon from the IC industry. Given the tremendous growth of the PV industry over the past few years, demand for silicon has outstripped supply. This has led PV companies to search for alternative silicon sources, and reclaimable silicon has proven to be a vital source of material to meet PV demand.
The PV market uses reclaimable silicon in the form of semiconductor wafers, broken ingots, pot-scraps, and ingot tops and tails. It has been shown that PV companies with advanced expertise can reclaim IC silicon without impacting the final cell efficiency, and contributing to reducing the cost-per-watt of solar modules. Several PV wafer producers are using reclaimable silicon, but only the most experienced companies are able to use a feedstock mix with up to 80% of reclaimable silicon without impacting the final cell efficiency. Thus, these reclaimed materials are a very attractive alternative to PV vendors.
In light of the growing demand for silicon, many semiconductor and electronics manufacturers are expanding their activities into reselling or trading reclaimable silicon. Of particular importance to the reclaimable silicon market is the trading and selling of reclaimable and reclaimed wafers.
In using reclaimable wafers for PV applications, these are the main challenges:
• Setting up reliable machines for wafer testing.
• Testing wafers for purity throughout the reprocessing steps.
• Minimizing labor and additional processing costs.
• Two techniques are used in wafer reprocessing for PV applications: a chemical etching process to remove circuit patterns; and mechanical stripping techniques (grinding, lapping, sanding).
The key to recycling used wafers is to verify and sort material by dopant and impurity levels. Both p-doped and n-doped waste wafers can be reprocessed to manufacture solar cells. Panel performances made from such materials are used to satisfy the market demand for solar energy in Europe.
For device makers, intellectual property is an important concern as companies do not want patterned wafers released to the outside world. An investment of $50,000 to $80,000 in equipment to remove circuit patterns and grind down the surface prevents the release of IP, yet allows device makers an opportunity to receive compensation for their unused or broken wafers — wafers that would otherwise be discarded. For cell makers, pre-processed wafers sorted by type (dopant and metallization) are ideal to improve efficiencies and lower costs.
So while the main interest in reclaimable silicon originated with the tight silicon supply issue, the topic is essential in light of sustainable concerns. Repurposing of reclaimable silicon provides an opportunity for both the semiconductor and PV industries to work together to minimize waste and use resources in an efficient manner. A global network for silicon re-use, improving communication from manufacturer to manufacturer, would raise awareness to develop mutually beneficial efficiencies in the silicon reclaimable supply chain.
Synergies naturally exist between the semiconductor and PV industries. As silicon production consumes a lot of energy, working together, the semiconductor and PV industries can realize value in the efficient recycling of silicon and thus increase sustainable business practices.
This article is based on a presentation that was given by Steven Zhu, vice president of procurement and business development at Trina Solar, at the Silicon Manufacturers Group meeting at SEMICON Japan 2008. If you or your company is interested in further discussion on this subject, please contact the SEMI PV Group.
