From Review SEM to Review PiFM: Automated Nano-Defect Review

Key Takeaways:

• Review PiFM on the Vista 300 complements Review SEM by combining nondestructive measurement with sub-5 nm resolution chemical and morphology imaging.
• Review SEM/EDX cannot adequately identify sub-10 nm defects, even if they are metal based, due to low-energy X-ray peak overlap.
• Review PiFM provides height, shape, and chemical identity of small and organic wafer defects.

Review PiFM (Photo-induced Force Microscopy) complements current Review SEM analysis used in Automated Defect Review (ADR) by combining nondestructive measurement with sub-5 nm resolution spectro-chemical and morphology imaging, thus enabling Automated Nano-Defect Review (ANDR). Due to advances in semiconductor device structures defects as small as 10 nm are now considered killer defects. Worse yet, non-metallic defects are contributing more to yield reduction and are not chemically distinguishable by Review SEM/EDX, the current ADR workhorse. Review SEM/EDX cannot adequately identify sub-10 nm defects, even if they are metal based, due to low-energy X-ray peak overlaps for many metals used in semiconductor processes. This application note explores how Review PiFM on the Vista 300 fills the limitation gaps of Review SEM and fits into the ADR workflow for defects even smaller than 10 nm. 

How PiFM Complements Review SEM

PiFM complements current ADR tools by providing non-destructive measurement and chemically identifying defects that are too small (sub-10 nm) or organic in nature. Review SEM/EDX is used in wafer defect review, however, e-beam bombardment from SEM/EDX analysis is damaging to sub-20 nm and organic defects. Figure 1 shows two types of destruction observed with PiFM on wafer defects after SEM/EDX analysis. Destructive measurement prohibits the ability to revisit defects using other techniques and inhibits the user’s ability to obtain complete information sets. PiFM combines non-contact Atomic Force Microscopy (AFM) with Infrared (IR) spectroscopy. By operating in non-contact mode Molecular Vista tools maintain the AFM probe in the attractive regime of the van der Waals potential between the probe and sample surface, ensuring that the tip and surface remain undamaged and uncontaminated. Non-contact operation provides users with the opportunity to revisit defects of interest (DOI).

For defects less than 20 nm in size, electron beam energies less than 3 keV must be used to reduce the interaction volume in EDX measurements. However, at such energies the main peaks of the differentiating x-ray families are not resolved and only one main peak is present. Figure 2 shows an example of this failure mode directly: the characteristic peaks of Si, W, Rb, and other elements present sit close enough in energy to merge into a single unresolved feature, so no individual element can be assigned with confidence. As defects shrink to sub-20 nm size scale, composition by EDX becomes indeterminate. Finally, when the defect is organic in nature, elemental composition cannot provide enough information to identify compounds even if the defect were to survive the e-beam interrogation.

PiF-IR spectroscopy avoids the EDX limitations discussed above. Because photo-induced force detection is a near-field effect confined to the tip-sample junction, the probed volume is set by the tip apex rather than by electron beam penetration, so the resulting spectrum reflects only the particle itself and not the surrounding material. PiF-IR measures vibrational absorption rather than electronic transitions, enabling the identification of molecular species. Figure 3 shows the PiF-IR spectrum collected with a Vista series tool on a 15 nm particle and the underlying quarts substrate. Where EDX would return an ambiguous, composite signal, PiFM returns an unambiguous molecular identification, in this case a Teflon particle. PiFM combines three capabilities for ANDR that SEM/EDX cannot: non-destructive measurement, molecular identification, and high spatial resolution with height information.

The ANDR Workflow with PiFM

PiFM on the Vista 300 integrates with standard fab inspection workflows by accepting defect coordinate maps (e.g. KLARF) directly from inline inspection tools, auto-deskewing to wafer fiducials (usually a few larger defects), and visiting every defect-of-interest (DOI) to acquire topography and PiF-IR spectra in sequence. Figure 4 displays a workflow diagram for Review PiFM. 

Typical throughput on the Vista 300 is approximately 2 minutes per defectdepending on the accuracy of the coordinates from the inspection tool, enabling chemical-ID surveys of roughly 30 defects in an hour.

Given its low throughput, PiFM is not positioned as a wholesale replacement for SEM/EDX but operates adjacent to those tools. Current SEM/EDX tools enjoy an order of magnitude higher throughput than Vista 300 ANDR. Thus, when many larger inorganic/metallic defects need to be binned by shapes and elemental content, SEM/EDX can continue to be the workhorse. However, the defects that SEM/EDX cannot classify effectively should be routed to the Vista 300 ANDR for PiFM analysis. This approach would reduce the need for time-consuming and destructive follow-up with ToF-SIMS or TEM/EELS.

PiFM Distinguishes Identical Particle Defects

Like SEM, PiFM topography images can identify particles on the surface with excellent lateral resolution. However, morphology alone is not enough to determine a particle’s composition, and therefore the root cause of defectivity. To determine where a defect class originates one must be able to determine the chemical composition of the defect. Figure 5 displays an example from a study conducted with CT Associates. Two particles of identical size and shape are shown on the substrate. Without chemical analysis, one might mistakenly determine that these particles have originated from the same source. PiF-IR spectra collected on the particles quickly identify these as silica and polystyrene particles, clearly originating from distinct sources. In this case, Review PiFM analysis has provided information that Review SEM would not be able to: distinguish between identically shaped particles, enabling a faster move to the next step in a root cause analysis study. 

PiFM can also identify particles smaller than 10 nm. In Figure 6 PiFM analysis clearly shows a 5 nm particle sitting on the silicon substrate. The size and height of the particle are determined by PiFM topography images while the chemical composition is determined by collecting PiF-IR spectra and comparing to known FTIR spectra of the bulk material. In this case the 5 nm particle is identified as PSL, another example of the power of PiFM in defect review. Even the particles that sit well below the spatial resolution of EDX analysis can be identified with PiFM.

Summary of Review PiFM Capabilities

Review PiFM extends Automated Defect Review to sub 10-nm and organic defect types that matter for shrinking device structures and Review SEM/EDX cannot address. By combining non-contact AFM topography with IR spectroscopy, the Vista 300 reports the height, shape, and molecular identity of defects below 5 nm without damaging them. The examples shown above demonstrate capabilities beyond the reach of SEM/EDX: unambiguous identification of a 15 nm Teflon particle, discrimination between identically shaped silica and polystyrene particles, and chemical identification of a 5 nm PSL particle. Because SEM/EDX retains an order-of-magnitude throughput advantage, the two techniques are best deployed together, with defects that SEM/EDX cannot classify routed to the Vista 300 for PiFM analysis. Used this way, ANDR with Review PiFM shortens the path from defect detection to root cause and reduces reliance on speculative, destructive follow-up techniques.

References

1. CT Associates, Inc. https://www.ctassociatesinc.com/.
2. D. Nowak, W. Morrison, H. K. Wickramasinghe, J. Jahng, E. Potma, L. Wan, R. Ruiz, T. R. Albrecht, K. Schmidt, J. Frommer, D. P. Sanders, and S. Park, “Nanoscale chemical imaging by photoinduced force microscopy,” Sci. Adv. 2:e1501571 (2016).
3. Molecular Vista Application Note, “Root Cause Analysis for Semiconductor Wafer Contamination: Identifying Sub-20 nm Organic and Inorganic Defects with PiFM,” June 2026.
4. KnowItAll IR Spectral Database Collection — Wiley Science Solutions.