As design rules shrink below 180nm, most fab engineers are interested in the ability to monitor the particle additions of their process tools and related equipment to defect sizes far below the design rule. As a general rule of thumb for the critical defect size is 0.5x the design rule, it would be necessary to monitor defect additions at 90nm while running a device manufactured by 180nm design rules.
Historically, particle test wafers used for fabs have been grown by standard CZ techniques, which have resulted in high levels of COP ( crystal originated particles ). The COP typically have a physical size of 100-150nm, and are detected by laser scattering metrology equipment in the range of 80-120nm. The relatively high counts of COP on a 200mm wafer ( between 200 and 1000 COP per wafer ) make it more difficult to detect real fab defects while scanning these wafers.
Metrology equipment suppliers such as KLA-Tencor have created sophisticated algorithms to distinguish COP from "real" defects. While these techniques can be quite useful, it sometimes becomes necessary to use a "low COP" or "COP free" wafer as a particle test wafer.
SEH has several options for this application. This includes wafers processed from special COP free ingots, and also wafers manufactured with nitrogen doping. Nitrogen has the impact of dramatically reducing the size of COP in as-grown CZ silicon, and it is possible to reduce the size of the COP below the critical defect size of interest. For example, the COP density detectable at 90nm may be low enough that standard laser scattering techniques can detect very small shifts in "real" fab defects added.
Contact SEH with your specific fab particle monitoring requirements.