Automated Surface Analysis of Metal Contaminants in Silicon Wafers by Online VPD-ICP-MS/MS

Importance of the topic

Ultratrace metal contamination on silicon wafers critically affects device yield and reliability in semiconductor manufacturing. Vapor phase decomposition coupled with ICP-MS/MS enables high-sensitivity surface analysis under automated conditions, meeting the demand for continuous contamination control.

Objectives and overview of the study

This work evaluates a fully automated VPD-ICP-MS/MS workflow combining the IAS Expert PS system with the Agilent 8900 ICP-QQQ. Key goals include assessing detection limits, quantitative accuracy, and integration for 24/7 wafer monitoring in advanced fabrication environments.

Methodology and instrumentation

Contaminants were extracted from the native or thermal oxide layer of 300 mm Si wafers using HF vapor in a VPD chamber. A scanning droplet of dilute HF/H₂O₂ (or aqua regia for precious metals) collected the released metals. Automated Standard Addition Systems delivered calibration standards and internal standards (Be, In). The droplet was introduced to an Agilent 8900 ICP-QQQ operated in MS/MS mode with multiple tune conditions to remove spectral interferences.

Used instrumentation

• IAS Expert PS automated VPD system with two ASAS modules for calibration and ISTD addition
• Agilent 8900 ICP-QQQ with PFA sample kit, C-Flow nebulizer, platinum cones
• High-stability RF generator and fast-switching reaction cell gases (H₂, He, O₂)

Main results and discussion

Detection limits ranged from 2.3×10^5 to 3.0×10^7 atoms/cm² (<1 pg/mL) across 30 elements. Spike recoveries in HF/H₂O₂ exceeded 98% for most elements; Cu showed 81% recovery due to strong substrate affinity. Aqua regia scans for precious metals achieved recoveries within 86–96%. The robust plasma tolerated up to 5000 ppm Si matrix, ensuring reliable quantification at ultratrace levels.

Benefits and practical applications of the method

• Automated operation reduces manual handling and contamination risk
• Continuous 24/7 wafer monitoring within fab computer-integrated manufacturing
• High sensitivity for both light and heavy metals supports advanced process control

Future trends and potential applications

Integration with next-generation fab automation and expansion to other substrates (e.g., SiN, high-k dielectrics) will drive broader adoption. Continued improvements in detection limits and throughput will enable real-time control of emerging device architectures such as 3D NAND and advanced logic nodes.

Conclusion

The IAS Expert PS and Agilent 8900 ICP-QQQ VPD-ICP-MS/MS system delivers robust, ultratrace surface analysis of metal contaminants on silicon wafers. Proven in leading fabs worldwide, this automated solution ensures reliable, high-throughput contamination control essential for modern semiconductor manufacturing.

Reference

1. Measuring Inorganic Impurities in Semiconductor Manufacturing, Agilent, 5991-9495EN.
2. Bohling C.; Sigmund W., Self-Limitation of Native Oxides Explained. Silicon 2016, 8, 339–343.
3. International Analytical Solutions Inc., Expert Auto Scanning System, 2023.
4. IAS Inc., Automated VPD-ICP-MS, application note.
5. IAS Inc., Automated Standard Addition System (ASAS II), technical note.
6. Sakai K.; Mizobuchi K.; Kobayashi R., Automated Analysis of Ultratrace Elemental Impurities in Isopropyl Alcohol, Agilent 5994-0273EN.