iLS-W2 PL inspection tool from BT Imaging offers quasi-mono wafer grading

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Updated: Video interview attached: BT Imaging has launched the next-generation iLS-W2 for on-the-fly photoluminescence (PL) inspection of wafer quality; the all-new iS-G1 for inline cast mono grain inspection; a new automation unit, the iQ, that houses the iLS-W2 and/or iS-G1 so that existing production lines can be upgraded; and, the QS-W2, a fully integrated inspection tool that can automatically sort wafers. With this suite of tools, wafer makers and fully integrated PV manufacturers can inspect every wafer in production and understand its electrical performance before they make it into a cell, thereby commanding premium pricing for wafers and cells.


In the drive to higher cell efficiency, cast mono silicon PV wafers are being seen as a major technology for the future of wafer manufacturing in the solar industry. As wafer producers migrate capacity to quasi-mono or cast mono, they have to contend with new yield challenges. The main benefit of the mono-like wafer is that an alkaline texture process can be used which increases the cell efficiency by about 0.5% absolute—a significant gain. Thus, the current industry practice is to manually sort wafers based on the fraction of mono-crystalline area in a wafer. Grade A wafers sell at up to a 50% premium (to standard multi) since the 0.5% efficiency gain can be achieved from the alkaline texture.


Even though the Grade A wafers look optically perfect, there is often a wide efficiency spread due to defects like dislocations that go undetected by standard optical inspection technologies. With BT Imaging’s new suite of tools, manufacturers can efficiently grade cast mono wafers. The iS-G1 is an optical inspection module, which grades wafers based on mono area fraction. The iLS-W2 is a PL module, which grades mono-like wafers based on dislocation count. Both of these modules can inspect wafers on the fly at the end of the wafer manufacturing line or beginning of a cell line, and sort wafers according to their electrical quality and value. The iLS-W2 offers on-the-fly inspection at 3,600 wafers per hour—a 2x increase over the iLS-W1. Together the iS-G1 and iLS-W2 provide a complete grading solution for cast mono wafers.


The iLS-W2 inspects and grades the electrical quality of silicon PV wafers at full wafer line speeds using PL imaging and integrated image processing algorithms.  The iLS-W2 is capable of grading as-cut multi-crystalline and cast mono wafers, with the ability to grade CZ mono silicon PV wafers being added in the near future.


Existing production lines can easily integrate the iLS-W2 with any wafer inspection system. The new iQ automation unit can be retrofitted into existing wafer lines to enable grading with the iS-G1 and the iLS-W2. This compact automation unit contains an internal belt which moves the wafer under the iLS-W2 for inspection. The iQ has adjustable belt height, flexible handshaking, and supports any communication protocol, enabling it to be easily installed between any wafer inspection system and sorter system in a factory. The QS-W2 is a stand-alone sorter which automatically loads and sorts wafers with the iS-G1 and iLS-W2.


Tools are shipping from July 2012. BT Imaging is accepting orders now.

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