Towards Structural Analysis of Polymeric Contaminants in Electrodeposited Cu films

Abstract

ABSTRACT:The incorporation of plating additives into Cu films was studied by means of preferential inclusion and accumulation of contaminants at grain boundaries inside the Cu deposit whereas the Cu grains remain largely contamination-free. A novel LIMS desorption approach is presented which allows for a molecular structure analysis of the polymeric additive ensembles preferentially embedded at grain boundaries of the Cu deposit. Our LIMS analysis confirms a recently discussed mechanism on the action of these hybrid additives which relies on their interaction with thiolate-stabilized Cu(I) intermediates.

Review—Laser Ablation Ionization Mass Spectrometry (LIMS) for Analysis of Electrodeposited Cu Interconnects

“…4b shows sharp grain boundaries (emphasized by dashed yellow lines) that constrain well-recrystallized Cu domains and spatially coincide with the potential oscillations observed in panel a. 60 Standard depth profiling analyses by SIMS presented in Fig. 4c exhibit a periodic modulation of the C, N, O, S and Cl signals within the Cu deposit whose peak center correlate with the grain boundaries revealed by the SEM images.…”

“…As listed in Table II the contamination stoichiometry from the horizontal grain boundaries (regime I) differs from that of the randomly distributed boundaries inside the recrystallized Cu domains (regimes II and III). 60 The fraction of C is substantially larger in the horizontal grain boundaries, indicating that they are mainly constituted of plating additives. The relative N/S ratio in this region is ∼1.5, referring further to the embedment of the suppressor ensemble with a non-stoichiometric contribution of leveler (IMEP) and antisuppressor (MPS), imposing that only a fraction of the leveler's OH-groups are effectively coordinated to MPS-Cu(I) ligands (Fig.…”

“…Figure 4a displays the potential transient of a 15.4 μm thick test sample galvanostatically deposited at j = −6 mAcm −2 from plating bath 4 in Table I. 60 The ordinate of the plot corresponds to the nominal measured potential and the abscissa to the charge transferred upon Cu electroplating. According to the proposed reaction mechanism, the dark-red sections of the transient curve are observed when the suppressor network is effectively floating on top of the surface, whereas the sharp potential transitions highlighted by orange appear when the suppressor network collapses and gets embedded inside the growing Cu deposit.…”

“…4c exhibit a periodic modulation of the C, N, O, S and Cl signals within the Cu deposit whose peak center correlate with the grain boundaries revealed by the SEM images. 60 However, in contrast to the manifest sharpness of these grain boundaries, the impurity intensities recorded by SIMS expand over a broader depth range and attenuate with progressive ion erosion. This is a SIMS instrument artifact and can be attributed to the surface roughening induced by the ion sputtering of the SIMS measurement, which smears and dilutes the embedded contaminants in the subjacent Cu layers (layer mixing).…”

Novel 2D binning approach for advanced LIMS depth profiling analysis

“…5,14 To increase the lateral resolution, which is primarily limited by the diameter of the induced ablation crater, deconvolution models were developed for the analysis of measurement campaigns where laser ablation craters overlapped with each other. 16 In the past few years, substantial effort has been made in our laboratory to develop sophisticated measurement protocols for the LIMS technique [17][18][19][20] dedicated to the chemical analysis of electrochemically fabricated samples, e.g. through-silicon-vias 1 or lead-free solder bumps, which are relevant to the interconnect technology 20 and typically have dimensions in the micrometre range.…”