New inspection tool addresses yield, solar cell classification

by Debra Vogler, senior technical editor, Solid State Technology

March 12, 2009 – KLA-Tencor Corp.’s latest inspection product, the PVI-6, designed for optical in-line dual-sided inspection of photovoltaic (PV) wafers and cells, provides the capability to inspect solar wafers and cells at the highest speed and accuracy for all stages of the production process, according to the company.

The PVI-6 consists of a family of modules designed to inspect solar cells throughout the production process, from bare wafer to silicon nitride (SiN) coating, metallization, and final classification. Improved analytical tools increase the overall yield of the solar cell production process.

Among the key features the new product offers, according to Pieter Vandewalle, director of marketing for the ICOS division at KLA-Tencor: higher accuracy and repeatability measurements, with up to 4× improvement in measurement accuracy. Additionally, a yield-improvement package allows end users to conduct simulation studies offline, evaluating the impact of changes in inspection parameters.

Figure 1: Non-penetrating crack validated by the PVI-6. (Source: KLA-Tencor)

Inspection accuracy also influences revenue. Vandewalle noted that revenue from a given solar cell production line can be improved using the new inspection modules by eliminating “overkill” errors in cell classification at the end of the line. “Errors in classification of cells have an immediate impact on the price for which a cell can be sold,” said Vandewalle. “We have done studies showing that up to 2%, and even more, of cells have been misclassified [to a lower class] — cells that should have been classified in the top-rated class.” The company’s studies found that overkill can be reduced by more accurate inspection, with attendant savings of up to $1M/year in additional revenue per production line.

A third feature of the new tool is easier calibration and setup, with calibration time decreased by ~80%. Furthermore, tool matching and central module management offers consistent results in large production environments, across multiple production lines.

Multiple end-user sites have completed beta testing, and the PVI-6 is available to order now. — D.V.

Figure 2: Yield for solar cell production lines requires not only solar wafer surface and solar cell inspection, but also anti-reflective coating (ARC) and print inspection, micro-crack and texturizing inspection, and end-of-line cell classification. (Source: KLA-Tencor)


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