Depth Profiling and Cross-Sectional Laser Ablation Ionization Mass Spectrometry Studies of Through-Silicon-Vias

Abstract

Through-silicon-via (TSV) technology enables 3D integration of multiple 2D components in advanced microchip architectures. Key in the TSV fabrication is an additive-assisted Cu electroplating process in which the additives employed may get embedded in the TSV body. This incorporation negatively influences the reliability and durability of the Cu interconnects. Here, we present a novel approach toward the chemical analysis of TSVs which is based on femtosecond laser ablation ionization mass spectrometry (fs-LIMS). The conditions for LIMS depth profiling were identified by a systematic variation of the laser pulse energy and the number of laser shots applied. In this contribution, new aspects are addressed related to the analysis of highly heterogeneous specimens having dimensions in the range of the probing beam itself. Particularly challenging were the different chemical and physical properties of which the target specimens were composed. Depth profiling of the TSVs along their main axis (approach 1) revealed a gradient in the carbon (C) content. These differences in the C concentration inside the TSVs could be confirmed and quantified by LIMS analyses of cross-sectionally sliced TSVs (approach 2). Our quantitative analysis revealed a C content that is ∼1.5 times higher at the TSV top surface compared to its bottom. Complementary Scanning Auger Microscopy (SAM) data confirmed a preferential embedment of suppressor additives at the side walls of the TSV. These results demonstrate that the TSV filling concept significantly deviates from common Damascene electroplating processes and will therefore contribute to a more comprehensive, mechanistic understanding of the underlying mechanisms.

Effect of Chloride Concentration on Copper Deposition in Through Silicon Vias

“…Indeed the incorporation maps point to strong spatial variations that includes preferential incorporation of the Cl − along the sidewall that is similar to recent scanning Auger microscopy that show the majority of C impurities are preferentially localized to feature sidewalls. 53 …”

Isotope abundance ratio measurements using femtosecond laser ablation ionization mass spectrometry

“…Mass calibration of the spectra, mass peak integration, and the spectra filtering procedure were discussed in details in our previous publications. 23,[35][36][37]…”

“…Our laboratory studies indicate that with a depth resolution in the sub-micrometer range, regions of interests, such as individual mineralogical grains or mineralogical layers, can be detected relatively easily within the sample illustrating the high sensitivity of our miniature LIMS system. 28,29,34,35,39…”

Novel 2D binning approach for advanced LIMS depth profiling analysis

“…The chemical depth proling studies of the Sn/Ag solder bumps were carried out using a LIMS system discussed in detail in earlier publications. 1,2,18,21,22 In the following, only a brief description about the measurement principle is given.…”

“…24 Technical description of the measurement protocol Chemical LIMS depth proling studies have successfully been carried out on various materials, ranging from, e.g., geological samples containing putative fossils 25 to materials of high interest to the semiconductor industry. 1,18 Usually, these studies are performed by continuously ring a dened number of laser pulses at a given single surface location at a time before moving to a next surface location (named herein "single crater approach"). To further improve the LIMS chemical depth proling, we went from the conventional measurement protocol to a layer-by-layer removal of sample material.…”