Non-Optical Inspection Technology Detects the Unseen
Posted date : Oct 31, 2007

ChemetriQ® Inspection provides fast, full-wafer inspection for Non-Visual Residue (NVR) defects.

As manufacturers drive yield improvement and cost reduction programs, the ability to detect and mitigate non-visual residue (NVR) defects is just as important as historical efforts focused on physical defect inspection. Detecting submonolayer NVR defects is a challenge as they do not scatter light; thus they are invisible to existing optical techniques. To address this challenge, a novel non-optical technique has been developed for NVR defect inspection.

Fast, Full-Wafer Detection of NVR Defects

Qcept’s ChemetriQ Inspection System incorporates a patented scanning differential work function technology that is extremely sensitive to NVR defects, including submonolayer organic residues, inorganic residues, slurry residues, trace-level metal contaminants down to E9 atoms/cm² and process induced oxide charge (see Figure 1 for examples of NVR defects).

The system scans 100% of the wafer surface, including the top bevel edge, in just four minutes collecting 4.5 million data points on a 300mm wafer. ChemetriQ can inspect a range of substrates including bare silicon and SOI wafers, along with blanket deposited films and patterned wafers.

Figure 1. ChemetriQ Images – Examples of NVR Defects. (a) A large area NVR defect was detected on a 300mm DRAM wafer. TOF-SIMS measured ~5E11 atoms/cm² of copper residue on the surface. (b) A strong NVR signature defect was detected at the outer edges of a 200mm wafer. Grazing angle FTIR detected high levels of fluorocarbon residues due to an outgassing interaction with the cassette.

Spatial Signature of NVR Defects Key to Mitigation

Analytical tools (e.g. VPD/ICPMS; scanning TXRF; etc.) provide classification of NVR defects, but they lack the ability to provide fast, full-wafer spatial signatures with the sensitivity required for advanced processes.

For one customer, the lack of a spatial signature presented a challenge in determining the root cause of a backside aluminum contamination issue. VPD/ICPMS data indicated ~2E10 atoms/cm² levels of backside aluminum, above their specification limits, and the customer assumed the source to be chuck contact with the wafer for this process tool.

ChemetriQ scans detected multiple backside NVR defect signatures, including a strong ring signature ~20mm from the edge that the customer and tool vendor were unaware of (see Figure 2 for ChemetriQ Image). TOFSIMS analysis detected ~5E11 atoms/cm² levels of aluminum contamination on the ring, matching the area-adjusted VPD/ICPMS results, thus identifying the root cause of the contamination.

Figure 2. ChemetriQ Image. A strong NVR signature is observed ~20mm from the edge of the wafer, which TOF-SIMS confirmed as the primary source of aluminum contamination on the wafer backside.

To summarize: fast, non-destructive, full-wafer detection of NV defects enables manufacturers to lower costs (reduced test wafer usage, reduced chemical costs via optimized clean processes), higher uptime on process tools (results in just four minutes), and decreased yield excursion risks due to NVR defects.

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