The Adsorption Structure of Polyethylene Imine on Copper Surfaces for Electrodeposition

Abstract

Electrodeposition of copper constitutes a key process for fabrication of modern microelectronic devices. [1][2][3][4] Commonly, the deposition process is required to fill recessed structures with metal. The size scales of such recessed structures range from nanometer-sized dual damascene structures for production of microprocessors, [5,6] to micrometer-sized through-silicon vias (TSVs) for 3D integration of different components within a package. [7,8] Despite the huge differences with regard to the dimensions, the various filling applications share the requirement of different local deposition rates to fill the recessed structures with copper. In order for filling to occur, the deposition needs to be accelerated at the bottom of the features, whereas it should be suppressed at the top. [9][10][11][12][13] These differential deposition rates may be obtained by the addition of suitable organic additives to the electrolyte. [1,6,[9][10][11][12][13][14][15] Electrolytes for electrolytic copper deposition typically consist of a cupric ion source, sulfuric acid, and halides such as chloride. Deposition of metallic copper from cupric ions is generally accepted to take place via cuprous ion intermediates. [6,[16][17][18] Industrially relevant plating electrolytes further contain a set of typically three organic additives, which provide the differential deposition rates to allow feature filling. [1,6,[9][10][11][12][13][14][15] Local acceleration of copper electrodeposition at the feature bottom is achieved by the accelerator and inhibition at the feature top by the suppressor. [10,11,13,14,19,20] The leveler further supports filling by local inhibition at exposed areas and may, thereby, prevent mounding over the recessed features. [14,21] Leveler additives typically consist of (poly) cationic alkylamines, e.g., PEI, which are supposed to interact with the surface by hydrophobic and interfacial anion/cation pairing effects. [15,21,22] Previous and recent spectroelectrochemistry investigations further supported interaction of this class of molecules to surface-confined halides. [23,24] An additional contribution to the adsorption by the formation of insoluble complexes with cuprous ions was proposed. [22] However, no direct evidence for interaction of the hydrophobic alkyl moieties with the bare or halide-covered copper surface, electrostatic interactions between halide anions and cationic ammonium ions, or complex formation with cuprous ions is available. Furthermore, the exact mechanism of the inhibition of the deposition is unclear and has been ascribed to the formation of a physical barrier for cupric ions by either adsorption or precipitation. [15,21,22] Recently, computational modeling and comparison of the results with electrochemical and spectroelectrochemical data was shown to be a suitable approach to reveal the detailed mechanism of the adsorption and inhibition of polyethylene glycol (PEG)-based suppressors. [25] Here, we use this approach to address PEI, which serves as reference compound for leveler additives...

Properties and microstructure regulation of electrodeposited ultra-thin copper foil in a simple additive system

“…Additives are usually classified as wetting agents, leveller, brightener, and chloride ions (Cl − ) according to their effects. Brighteners are mainly sulfur-containing organics [13,14], levellers are mainly quaternary ammonium-containing polymer [15][16][17][18] or small molecule dyes [19], and wetting agents are mainly polyether compounds [20,21]. Wetting agents contribute to the enhancement of plating solution wettability, reducing interfacial tension.…”