Abstract
In this contribution highly sensitive and quantitative analytical methodologies based on femtosecond Laser Ablation Ionization Mass Spectrometry (fs-LIMS) for the analysis of model systems and state-of-the-art Cu interconnects are reviewed and discussed. The method development introduces in a first stage a 1D chemical depth profiling approach on electrodeposited Cu films containing periodically confined organic layers. Optimization of measurement conditions on these test platforms enabled depth profiling investigations with vertical resolution at the nm level. In a second stage, a matrix-free laser desorption methodology was developed that allowed for preliminary molecular identification of the embedded organic contaminants beyond elementary composition. These studies provided specific fragmentation markers in the lower mass range, which support a previously proposed reaction mechanism responsible for successful leveling employing a new class of plating additives for Damascene processes. Further combined LIMS and Scanning Auger Microscopy (SAM) studies on through-silicon-vias (TSV) interconnects confirmed the embedment upon plating of the organic additives at the upper side-walls of the TSV channel in the boundary between the Cu seed layer and the electrodeposited Cu.
Highlights
imidazole and epichlorohydrin (IMEP) belongs to a new type of leveler additives, which exhibits a convoluted behavior of traditional type I and type II suppressors in Damascene electroplating processes.[12,13,14]
While the working principle of classical type-II suppressors relies on specific mass transport limitations and consumptive inclusion in the deposited material,[54,55,56,57] these hybrid-type additives exhibit a more selective activation that is not based on the transport and inclusion model
Linear sweep voltammetry (LSV) experiments of Cu electrodeposition in the presence of IMEP and SPS have demonstrated the occurrence of a partially hidden N-shaped negative differential resistance (N-NDR)[58] which is indicative for a delayed suppressor activation process superimposed on the primary Cu deposition.[20,59]
Summary
10 μm 10 μm 10 μm 10 μm to 15.4 μm potentiostat/galvanostat (PGSTAT 128). The cell consisted of a double junction Ag/AgCl3M reference electrode (Metrohm, Switzerland) and a Pt-wire counter electrode, which was placed inside a glass compartment holding a ceramic frit at the bottom. Once a measurement is finished, the recorded time spectra are converted to mass spectra using the relation m/z(t) = a(t-t0)[2], with a and t0 as instrument specific calibration factors that depend on the applied ion optical system.[43] In-house designed software packages, written in Java/C++/Matlab/Phyton are used for the sample positioning, laser system operation, data acquisition and analysis and processing of the acquired spectra.[51]. Measurements.—For each ablation experiment the optimal measurement conditions, e.g. laser irradiance (pulse energy / (pulse width ∗ crater area)) [TWcm−2], total number of applied laser shots, laser pulse burst (sequences of laser pulses at a specific repetition rate), repetition rate and number of accumulated single mass spectra are defined according to the specific analyte. The repetition rate was kept constant at 1 kHz during all experiments
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