Going green gives new life to reclaimed silicon

by Debra Vogler, senior technical editor, Solid State Technology

July 27, 2009 – ATMI latest “green” product, RegenSi 74, released at SEMICON West, is an improved and more environmentally friendly extension of its advanced test wafer recycle and reclaim products. The line of all-wet process materials is used by semiconductor manufacturers to strip away films from test wafers while limiting damage to the underlying silicon.

The new process, designed to operate at room temperature, is able to rapidly remove aluminum and copper stacks and can be implemented on wet-bench platforms to replace existing two- or three-chemical process steps (see Figures 1 and 3). Tod Higinbotham, EVP, process solutions at ATMI, told SST that standard processes use commodity chemistry (e.g., dilute HF) which doesn’t work as well on newer, more advanced films being used, so higher concentrations are needed which then eat away at the silicon. As test wafer usage goes up with increasingly complex processes now being used, the reclaim process also becomes more difficult.

Figure 1. Overall costs per test wafer cycle (individual results will vary). (Source: ATMI)
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Conversely, the new chemistry is highly selective and strips away a wide variety of films, yet will not touch the silicon, “leaving a passivated, very smooth surface that can be reused for another test,” said Higinbotham. By using the new chemistry, test wafers require little or no grinding and polishing to restore their surface to a reusable condition (see Figures 2 and 4).

Figure 2. Test wafer reclaim cycle sustainability (individual results will vary). (Source: ATMI)

Furthermore, by using the new chemistry, end users have reduced waste volumes, and greatly reduced rinse water volumes. The product was designed using the Twelve Principles of Green Chemistry, explained Higinbotham. “When you use less chemical, you use less tool time and less pump time, and that translates to less energy usage,” said Higinbotham. So while performance chemistries are more expensive than commodity chemistries, they attack the COO issues (i.e., tool utilization, less hazardous waste, less disposal cost) that end users care about.

Figure 3. Si surface condition after industry-standard, three-chemical process. (Source: ATMI)
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The company has said that its new solution can cut film removal cycle times in half and greatly reduce the amount of chemicals required for wafer reclamation. And in some end user trials, silicon loss has been reduced by as much as 75% compared to traditional reclaim methods. According to the company, the new chemistry can provide an overall carbon footprint 18× lower than existing three-step processes. In one case, the company said its new process was shown to require up to 85% less energy and save up to 20 tons of de-ionized rinse water per day. — D.V.

Figure 4. Si surface condition after RegenSi 74 process. (Source: ATMI)
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