Molecular analysis of additives and impurities accumulated on copper electrodeposited layer by time-of-flight secondary ion mass spectrometry

Abstract

The molecular analysis of additives and impurities accumulated on the copper electrodeposited layer from electroplating bath containing Cl−, polyethylene glycol (PEG), and (bis-(sodium sulfopropyl)-disulfide (SPS) was evaluated by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) under static conditions and atomic force microscopy (AFM). The hierarchical cluster analysis (HCA) was applied in order to classify the surface chemistry of copper electrodeposited layers to four different classes. The molecular structure of polymeric complexes of PEG-Cu(I)-Cl and Cu(II)-SO3(CH2)3-SO3 which existed on the copper surface were identified and confirmed. A coordinative dissolution of a complex layer of PEG-Cu(I)-Cl by MPS (sodium 3-mercapto-1-propanesulfonate) molecules incorporated into the copper deposit via a covalent bond was proven. The methodology of a proper identification of molecular species in mass spectrum without the use of reference was proposed. A semiquantitive analysis of CuCl and CuCl2 present on the copper layer was conducted by comparing relative intensities of CuCl2−/CuCl− ions. A higher ratio CuCl2−/CuCl− corresponds to a higher molecular ratio of CuCl2/CuCl compounds. Suppressing the role of PEG and the accelerated role of Cl− ions on a higher level of incorporation of thiolate molecules by Cu-S covalent bond in PEG/Cl/SPS system in comparison with SPS/Cl system was calculated. It was also discovered, for the first time, that phosphate ions accumulate in high concentrations on a copper surface without the presence of chloride adlayer. The presence of chloride adlayer in SPS/Cl system plays an antagonistic role towards phosphate and sulfate ions, effectively removing these ions from the copper surface. Our studies by TOF-SIMS under a static condition combined with atomic force microscopy measurements prove that PEG exerts a synergetic effect with chloride ions to reduce waviness of the copper electrodeposited surface in a micro scale without a significant role in reducing crystallite size in a nano scale, whereas the synergy effect of PEG-Cl-SPS reveals levelling abilities both in a micro scale (waviness) and a nano scale (roughness). It shows that TOF-SIMS under static conditions is a complementary technique for the investigation of a molecular and geometrical arrangement of adsorbed species on a copper electrodeposited layer.