 |
| Figure 1. GlobalFoundries encountered yield loss caused by a cleaning tool in a 45-nm logic production line and had to take it offline. NVD inspection determined that process-induced charging was the source of the yield loss. As a result, GlobalFoundries was able to make adjustments to the cleaning process, which eliminated the charge problem and allowed it to bring the cleaning tool back online. |
Ralph Spicer, VP, marketing, Qcept Technologies, describes the company’s technology for detecting discontinuities in the workfunction at the surface of wafers – such discontinuities cause non-visual defects (NVDs). NVDs are primarily surface chemical defects caused by organic and metallic residues and process induced charge. Because NVDs do not scatter light, they are not detectable by optical inspection tools. Based on the well known principle of contact potential difference (the actual probe does not contact the wafer, however), the method used by Qcept is able to detect sub-monolayer contaminants – at the millivolt level − that can impact device performance (Figs. 1-2). As the number of new materials increases at advanced semiconductor manufacturing nodes concurrent with shrinking process windows, it is becoming increasingly more critical to be able to detect such NVDs.
 |
| Figure 2. Soitec encountered yield loss in its advanced silicon-on-insulator (SOI) wafer production process. Using NVD inspection, Soitec determined that the SOI donor wafer (at left) was contaminated by an edge-handling metrology tool. After the wafer was flipped and bonded to the substrate, the metallic contamination migrated, causing defects in the final SOI layer that. Soitec was able to have the metrology tool fixed, which caused the yield issue to disappear (right). |
