RegenSi™: Low Carbon Footprint Alternative Wafer Reclaim Solution for Extending Life Cycle of Silicon Test Wafers
Korzenski, Michael ; Jiang, Ping
( Advanced Technology Development, Advanced Technology Materials, Inc. Danbury, CT )
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Semiconductor manufacturers typically use test wafers to optimize and monitor their manufacturing processes. A large fab might spend $2 million/month on test wafers, which cost >$100 each. Because of the large volumes of test wafers used, silicon remains by far the greatest material expense in semiconductor manufacturing fabs. More than 27 million test wafers are used annually across the industry, and as a result, chip makers are now focusing on extending the usable life of test wafers by attempting to re-use them as many times as possible through a reclaim process. A wafer reclamation process involves three steps: chemically stripping unwanted films from the wafer surface, mechanically polishing to remove any surface damage, and cleaning to ensure that customers’ ultra low defect requirements can be met. Currently, the number of times a wafer may be reclaimed is limited, as the combination of strip and polish steps physically reduces the thickness of the substrate by tens of microns. Eventually, the test wafers become too thin to be reclaimed and are then scrapped and replaced. Therefore, the need for a cost effective method of efficiently reclaiming test wafers is highly desired. RegenSi™ is a novel all-wet single step process used to strip away most films from the test wafer while limiting damage to the underlying silicon, thus eliminating or reducing the need for wafer surface planarization following the film stripping step, which is both energy intensive, uses high volume of consumables, and is expensive. After implementing RegenSi for internal processing of test wafers, a Taiwanese manufacturer reported that yields rose to 85% and silicon loss was reduced by 75%, enabling them to achieve four times more life from each test wafer. This combination of higher yields, greater productivity and increased re-use leads to significant overall cost savings, energy savings and waste reduction.