OTS (February 2007) -- Internal recycling of test wafers using FSI’s ZETA^® spray processor can save millions of dollars compared to the cost of new wafers or externally reclaimed wafers. A high volume production fab may consume 500 to 1000 test wafers every day. With new 300mm wafers costing about $200 each, the cost of test wafers is very significant. 200,000 new wafers per year—548 wafers per day—cost $40 million. Most manufacturers mitigate this cost by recycling wafers, usually through a third party reclaim service. Reclaimed wafers from these services are usually about half the cost of new wafers.

Assuming that a wafer can be recycled an average of three times, the average cost per wafer use over the wafer lifetime drops to $125 ([200+100+100+100]/4) and the annual cost for test wafers drops to $25 million, a savings of $15 million compared to using all new wafers. Many manufacturers are now realizing that by moving the recycle operation in house they can reduce the cost of recycled wafers dramatically—to as little as $1 per wafer. At that rate the average cost per wafer use drops to $50.80, and the annual cost is reduced by almost another $15 million.

A number of major semiconductor manufacturers have built in-house recycling programs around FSI’s ZETA^® batch spray processor. The ZETA^® G3 system is the third generation of this production proven line—FSI has shipped over 1000 spray cleaning systems. The ZETA^® system’s flexible chemistries allow a single system to run multiple recipes, effectively substituting one system for many. In-line blending with inputs for up to 8 fresh chemicals and 2 recirculated chemicals delivers fresh mixtures directly to the wafer and saves on the cost of specialty chemicals by permitting multiple custom blends. Closed-loop process controls ensure repeatable performance. Wafers enter and leave the controlled environment of the nitrogen purged process chamber dry. The ZETA^® system’s centrifugal technology enhances mass transfer at the wafer surface to remove heavy contaminants.

These capabilities make the ZETA^® system an excellent tool for recycling test wafers. It’s programmability and flexibility allow a single system to remove a wide range of materials with minimal setup or operator interaction. Fresh chemical delivery with precise mixing and dispensing controls insures consistent, reliable recycling while minimizing the consumption of chemicals and DI water. Table 1 lists a selection of materials and removal chemistries that can be implemented on the ZETA^® tool. Some critical operations may require segregation of wafers, or even dedicated tools, but in general a single tool can recycle test wafers from many different processes.

Table 1: A selection of materials and chemistries that can be implemented on the ZETA^® tool

All reclaim operations cause a gradual accumulation of defects, but careful management of recycled wafers can extract the maximum useful life from each one. Correct recipe construction can minimize crystal damage. Wafers that have been through multiple reclaim cycles can be used in less critical operations. Even wafers that have been recycled four times or more can still be useful in monitoring some processes.

Over the years, FSI has built considerable expertise in configuring tools and recipes for wafer reclaim operations. Call us, we’ll be happy to help you set up a reclaim program for your fab.

If you would like to receive more information on reclaiming test wafers with the ZETA^® system, click here.