​Surface Analytical Technique



When manufacturing semiconductor devices, surface metallic contamination can result in process variation and defects, such as poor coverage, vacancies, voids, leakage, shorts, and overburdens.



With the increasing integration density and decreasing line widths of modern integrated circuits (ICs), trace metal contamination is becoming a detrimental factor.

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Consequently, greater control over contamination during the fabrication processes involved in device manufacturing is becoming increasingly crucial because of the growing complexity and miniaturization of ICs.

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Vapor phase decomposition (VPD) is a proven method of wafer preparation for subsequent measurement of trace metal contamination.

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In this technique the entire oxide layer of the wafer is decomposed and concentrated into a single droplet, which then can be measured by inductively coupled plasma mass spectrometry (ICP-MS).

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Pairing the VPD wafer preparation with ICP-MS analysis gives fab engineers increased sensitivity and lowers detection limits (into the mid E07 atoms/cm2 for most elements on a 300 mm silicon wafer).

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VPD wafer preparation allows for good sensitivity because it concentrates a large volume of the wafer area scanned into a single measurement.



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VPD Sample Preparation and Analysis

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VPD is a 3 step process.



• ƒ  Vapor phase decomposition
• ƒ  Wafer surface impurity collection using a scanning droplet
• ƒ  Scanning droplet metal analysis using ICP-MS

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The silicon wafer is placed in a VPD chamber, and exposed to HF vapor for 10 minutes to dissolve the SiO2 surface layer.

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The wafer surface is then scanned with a 250-µL extraction droplet. This can be done manually or with an automated wafer scanner.



​The extraction droplet picks up the contents of the dissolved silicon layer as it is moved across the wafer surface.

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The extraction droplet is then pipette from the wafer surface and analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). 



Keywords: Vapor phase decomposition (VPD), Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

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Reference:

Beebe, M., & Anderson, S. (2010). Monitoring wafer cleanliness and metal contamination via VPD ICP-MS: Case studies for next generation requirements. Microelectronic Engineering, 87(9), 1701-1705.



Maillot, P., Martin, C., & Planchais, A. (2011). Advanced monitoring of trace metals applied to contamination reduction of silicon device processing. Paper presented at the AIP Conference Proceedings.



Rip, J., Wostyn, K., Mertens, P., De Gendt, S., & Claes, M. (2012). Methodology for Measuring Trace Metal Surface Contamination on Pv Silicon Substrates. Energy Procedia, 27, 154-159.



Takahara, H., Mori, Y., Shimazaki, A., & Gohshi, Y. (2010). Method and mechanism of vapor phase treatment–total reflection X-ray fluorescence for trace element analysis on silicon wafer surface. Spectrochimica Acta Part B: Atomic Spectroscopy, 65(12), 1022-1028. doi: http://dx.doi.org/10.1016/j.sab.2010.11.006





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