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Summary
Using the concepts of an optical cavity furnace, scientists at the National Renewable Energy Lab have created a low power, high throughput (1,200-2,000 wafers/hr) wafer screening machine with the capacity to operate at throughput levels required by high speed solar cell manufacturers. This cavity furnace should reduce the overall cost of standard crystalline solar module production by efficiently identifying high failure cell candidates during manufacturing.

Technical Description:
Using the concepts of an optical cavity furnace, scientists at the National Renewable Energy Lab have created a low power, high throughput (1,200-2,000 wafers/hr) wafer screening machine which would sit quietly on top of any existing line, use far less energy than the traditional system, and meet throughput levels required by high speed solar cell manufacturers. In the traditional process, the wafer is transported underneath reflectors via conveyor belt. Light sources are directed into one small area to optically induce the maximum thermal stress the wafer would be subject to during manufacturing. While this process allows solar manufacturers to screen potentially bad wafers, the water-cooled lamps and reflectors require a tremendous amount of energy and the time required to scan does not offer the required throughput.

The proposed method of screening wafers takes advantage of the concepts of an optical cavity furnace to build a high throughput wafer screening machine with low power requirements. In much the same manner as the traditional method, the wafer in the improved system is transported through the process via conveyor belt. However, in the improved system, an optical cavity is formed by placing optical sources within the reflecting walls of the furnace. This design ensures that all energy coming from the light sources is transferred to the wafer only, resulting in substantial energy savings over the traditional method. After the wafer exits the cavity furnace, it is then subjected to a jet of cold air. This dynamic temperature profile of the wafer produces a predetermined time-dependent stress in the wafer, which corresponds to the highest stress the wafer can experience during solar cell processing.

Benefits
There exists a need in the industry for a wafer screening process with low power requirements that can offer the throughput needed by the photovoltaic industry (1200-2000 wafers/hr). For crystalline silicon based manufacturers, almost one half of the installed cost of a silicon cell solar module is driven by the cost of the silicon wafer. Wafer breakage is a very serious problem in the PV industry because 5%–10% of wafers break during cell/module fabrication. Wafers that break during the manufacturing process decrease the effective yield and increase the manufactured cost per watt. This technology would reduce total manufacturing costs to crystalline silicon based manufacturers by providing a wafer screening machine with improved throughput (1,200-2,000 wafers/hr) and reduced energy consumption.

Progress Status
A research scale prototype has been fully developed in an in-line prototype created with speeds approaching 1,200 wafers/hr.

IP Status: Patents Included
NREL 04-07 11/722,981
NREL 06-23 US 12/919,433,
CHINA CN102027581A
EP 09 758 841.2
NREL 10-31 PCT/US11/24584

If you would like to be considered for the Industry Lead Role, please put the project in the subject line and email your resume to Eric@BoulderInnovationCenter.com.