Adsorption behavior of redox-active suppressor additives: Combined electrochemical and STM studies

The redox chemistry and the related surface phase behavior of Safranine (SAF) and Janus Green B (JGB) have been studied by means of cyclic voltammetry in combination with in situ Scanning Tunneling Microscopy using HOPG (Highly Oriented Pyrolytic Graphite) and single crystalline Cu(1 0 0) as model substrates, both revealing different widths of the accessible potential windows. JGB and SAF serve as prototypical heterocyclic suppressor/leveler additives that are used for the metallization of 3D-TSVs (3D Through Silicon Vias) following a classical "leveling" concept. SAF can be considered as the reductive decomposition product of JGB that is formed at the copper/electrolyte interface upon electroplating. Both additives reveal a pronounced pH-dependent redox-chemistry with redox-transitions lying close to or even beyond the anodic limit of the copper potential window. Affected by these redox-processes are in particular the aromatic cores of those heterocycles that can be (quasi)reversibly reduced by a two electron transfer process within the potential window of copper. Therefore we identify the reduced form of those dyes as the active components for the suppressing/leveling effect in copper plating. STM data clearly shows a dye surface phase behavior that is crucially determined by its potential-dependent redox-chemistry. This will be exemplarily discussed for the SAF dye. On chloride-modified Cu(1 0 0) mono-reduced SAF forms a structurally well-defined monolayer of cationic stacking polymers. However, this coupled anion/cation layer reveals only minor suppressing capabilities with respect to the copper dissolution and deposition processes. Complete reduction of the aromatic heterocycle finally leads to the 3D precipitation of hydrophobic reaction products. 3D clusters of this SAF precipitate are discussed as the active structural motif for the suppressing effect of these dyes. (C) 2011 Elsevier Ltd. All rights reserved.

High-Resolution Chemical Depth Profiling of Solid Material Using a Miniature Laser Ablation/Ionization Mass Spectrometer

High-resolution chemical depth profiling measurements of copper films are presented. The 10 μm thick copper test samples were electrodeposited on a Si-supported Cu seed under galvanostatic conditions in the presence of particular plating additives (SPS, Imep, PEI, and PAG) used in the semiconductor industry for the on-chip metallization of interconnects. To probe the trend of these plating additives toward inclusion into the deposit upon growth, quantitative elemental mass spectrometric measurements at trace level concentration were conducted by using a sensitive miniature laser ablation ionization mass spectrometer (LIMS), originally designed and developed for in situ space exploration. An ultrashort pulsed laser system (τ ∼ 190 fs, λ = 775 nm) was used for ablation and ionization of sample material. We show that with our LIMS system, quantitative chemical mass spectrometric analysis with an ablation rate at the subnanometer level per single laser shot can be conducted. The measurement capabilities of our instrument, including the high vertical depth resolution coupled with high detection sensitivity of ∼10 ppb, high dynamic range ≥10(8), measurement accuracy and precision, is of considerable interest in various fields of application, where investigations with high lateral and vertical resolution of the chemical composition of solid materials are required, these include, e.g., wafers from semiconductor industry or studies on space weathered samples in space research.