In recent years, the development of three-dimensional large-scale integration (3D-LSI) has been accelerated to overcome the limitations of the classical 2D integration approach, which has begun to deviate from the ideal scaling trends¹. Ever increasing complexity of these novel structures that assemble a great variety of materials with distinct physical properties pose new challenges for fabrication and subsequent composition analysis of microchips. In this context, metal electrodeposition plays a crucial role in the manufacturing of the interconnect networks inside the devices. Since these metallic interconnects are manufactured by an additive-assisted metal electrodeposition process, incorporation of the employed additives in the metallic matrices in trace amounts might heavily influence their performance and durability². Herein we present case studies that analyze two key components of state-of-the-art integrated circuits (ICs), namely through-silicon-vias (TSV)² and lead-free solder interconnects³ (Sn-Cu). In the former case, accurate targeting and chemical composition analysis of TSVs was addressed by means of three complementary techniques: femtosecond laser ablation ionization mass spectrometry (LIMS technique; τ ~ 190 fs, λ = 775 nm, laser crater diameter Ø ~ 15 µm)⁴, Auger electron spectroscopy and focused ion beam. Top-down laser ablation analysis of the TSVs allowed qualitative depth profiling that showed a decreasing trend of the C content with depth. This indicates preferential incorporation of organic impurities from the employed plating additives on the top level of the TSV feature. Quantitative C content analysis inside the copper lines was enabled by an alternative experimental approach, in which the chemical composition of the copper structures was analyzed over the feature cross-sections. In agreement with top-down profiling this approach revealed a 1.5-fold increased embedment of C in the upper part of the TSV with respect to the bottom section.

Regarding the second case study, we focused on enabling quantitative depth profiling investigations of Sn-Cu bilayers as representative model system of the target Sn solder bumps deposited on Cu pillars. We report a dedicated study on the quantification of side-walls contributions in the course of fs-laser ablation mass spectrometry depth profiling experiments using the LIMS technique. We identified the prerequisites for quantitative depth profiling of multi-layer systems similar to these Sn/Cu solder bumps and compared different general approaches. Preliminary LIMS results on Sn/Cu solder bumps will be discussed.

Overall, these investigations shed light on the spatial chemical distribution of contaminants in metal films that might enable further improvements of additive-assisted electrodeposition processes.

1 Motoyoshi, M. Through-Silicon Via (TSV). Proceedings of the IEEE 97, 43-48, (2009).

2 Gambino, J. P., Adderly, S. A. & Knickerbocker, J. U. Microelectronic Engineering 135, 73-106, (2015).

3 Bigas, M. & Cabruja, E. Microelectronics Journal 37, 308-316, (2006).

4 Grimaudo, V. et al. Anal. Chem. 87, 2037-2041, (2015).