Article

Compositional characterization of electrically isolated solder bumps by Scanning Auger Electron Spectroscopy (AES)

Surface Analysis Spotlight: AES

	by Juergen Scherer Sr. Staff Scientist

Key Takeaways

• AES can provide surface-sensitive analysis of electrically isolated solder bumps and non-conductive substrates
• Micro-area analysis reveals surface composition including trace contaminants
• Proper analysis conditions allow for analysis without charging artifacts

Background

As semiconductor devices continue to scale toward higher density and performance, the reliability of interconnect structures—particularly solder bumps—has become increasingly critical. Even minor changes in surface composition or chemistry can impact electrical performance, leading to increased resistance, poor contact, or long-term reliability issues. A detailed understanding of bump surface composition is therefore essential for identifying the root causes of electrical failures and ensuring consistent device performance. Scanning Auger Electron Spectroscopy is well suited to this challenge by combining high spatial resolution with high surface sensitivity.

Results

The PHI 710 Auger Nanoprobe was used for the analysis, comparing two regions shown in Figure 1: the surface of an electrically isolated solder bump (Area 1) and the surrounding polyimide (Area 2). Beam conditions were carefully selected to eliminate charging artifacts.

Information obtained from the spectrum:

• Area 1 (bump surface) shows strong signals associated with Sn, as expected for a solder bump, along with detectable levels of C, O and S.
• The presence of oxygen suggests surface oxidation, which is commonly observed and can influence contact resistance.
• Carbon contamination is also evident, likely originating from environmental exposure or processing residues.
• Notably, trace sulfur is detected, which may indicate contamination that could impact wetting behavior or long-term reliability.
• Area 2 (surrounding polyimide) exhibits a distinctly different composition, with signals from C, N and O, as well as a trace of Si.

Overall, the results highlight how even small amounts of surface contamination—such as sulfur or carbon—can be detected and evaluated, enabling more informed failure analysis and process optimization.

Fig.1 Secondary electron image of an electrically isolated Sn solder bump (left) and AES spectra acquired on the surface of the bump and the surrounding polyimide (right)

Conclusion

In this study, electrically isolated solder bumps and adjacent insulating substrate regions were analyzed using AES. The results demonstrate how high-resolution, surface-sensitive analysis enables the identification of both major constituents and trace-level contaminants on bump surfaces, even on electrically isolated or non-conductive surfaces. By targeting micro-scale regions, AES provides a sensitive and efficient way to detect subtle compositional variations that can directly impact electrical performance. This level of insight is particularly valuable for understanding failure mechanisms and improving interconnect reliability.

Overall, this study establishes cryo‑XPS as a necessary tool for reliable SEI characterization, revealing true interfacial chemistry and heterogeneity that are obscured by conventional RT‑XPS. These insights enable more accurate interpretation of structure–performance relationships and provide a foundation for rational design of advanced lithium metal batteries.

This approach of targeting micro-scale regions is broadly applicable across semiconductor workflows, supporting:

• Product evaluation
• Process monitoring and optimization
• Failure and defect analysis

As packaging technologies continue to advance, high-precision analytical methods such as scanning AES nanoprobe analysis play an increasingly important role in ensuring the reliability and performance of next-generation electronic devices.