Rudolph focuses on increasing average cell efficiency

by Meredith Courtemanche, contributing editor, PV World

Jan. 12, 2009 — With the economy and oil prices plummeting, the solar cell industry is fighting to retain the interest, investment, and production volumes it gained as a result of the recent energy crisis and environmental awareness. Rudolph Technologies Inc. introduced a software package targeting the still-troublesome area of photovoltaic cell efficiency, hoping to bring solar cells closer to grid parity through reduced costs and inefficiencies.

Rudolph pulls product value from a mature production field — semiconductors — for its Discover Solar software package. The company asserts that cell efficiencies still have significant room for improvement, while competitions and attention to costs have escalated. Discover Solar is designed to automate process control and perform root cause analysis closer to real time.

Discover Solar is a fab management software tool designed to help photovoltaic (PV) manufacturers increase cell efficiency and reduce costs. Rudolph claims that the software, which operates with in-line data, reduces scrap and downtime by identifying root-causes of yield issues. For a PV cell manufacturer producing 7,500,001 30-MWp line wafers per year, the Discover Solar tool can cut out $495,000 in scrap, $90,000 in inefficiencies, and $87,600 in engineering costs, according to Rudolph, citing cost analysis data from a PV fab.

While Discover Solar is based on Rudolph’s semiconductor manufacturing process control software, the company acknowledged that they had to consider “everything differently” when designing software for PV lines, primarily due to the high volume of silicon wafers and the varying degrees of raw material quality. Discover Solar incorporates a re-engineered database structure and analysis engine optimized for the requirements of high-volume photovoltaic production. “Not a lot of in-line metrics are available in PV facilities, as compared to the semiconductor world,” states Mike Plisinski, VP and GM of Rudolph’s data analysis and review business unit. Root causes of useless solar cells or those with poor energy conversion efficiency are less easily tracked, he added. Using in-line metrology, equipment, and cell test data, the software’s path analysis equations allow for faster and more automated correlation between a problem and a specific line, line tool, or batch of wafers.

Discover Solar automatically identifies specific tool or process issues. (Source: Rudolph Technologies)

Discover Solar allows engineers to pinpoint a problem on the process tools (e.g., chambers, tubes, zones, or print tables), inline metrology (resistivity, thickness, color), tool input parameters (temperature, pressure, gas flow), and cell test data, by showing out-of-spec results after a particular process during PV manufacturing. The software can also call out a bad batch of wafers by identifying variations between wafers run over the same recipe in the same tools. Finally, it can alert users to “hidden” correlations between scrap or inefficient cells and multiple errors at different steps, resolving or preventing “second-order effects,” Plisinski asserts.

To accommodate the throughput volume at PV facilities, these path analyses are performed in seconds, according to Rudolph. Discover Solar also has alarming functions, which can be set to report out-of-spec operation automatically. It replaces slow, engineer-intensive statistical process control methods, such as SAS JMP or Excel programs, says Plisinski.

Rudolph is targeting process optimization and health monitoring with the software release. Discover Solar has been tested at a manufacturer, and testing is underway with different applications within the product’s scope. — M.C.


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