Damascene copper electroplating for on-chip interconnections, a process that we conceived and developed in the early 1990s, makes it possible to fill submicron trenches and vias with copper without creating a void or a seam and has thus proven superior to other technologies of copper deposition. We discuss here the relationship of additives in the plating bath to superfilling, the phenomenon that results in superconformal coverage, and we present a numerical model which accounts for the experimentally observed profile evolution of the plated metal.

Damascene copper electroplating for chip interconnections

Copper plating baths used for forming integrated circuit interconnects typically contain three or four component additive mixtures which facilitate the superfilling of via holes and trench lines during damascene plating. Extensive study over the last two decades has provided researchers with an understanding of the underlying mechanisms. The role of cuprous intermediates in the copper deposition reaction has long been acknowledged, but it is not yet fully understood. In this paper we describe the results of an electrochemical study of the interaction of the organic additives used with copper and copper ions in solution. It is shown that cuprous intermediates near the copper surface affect the overpotential and the kinetics of plating. The additives regulate the presence of cuprous species on the surface; levelers and suppressors inhibit Cu+ formation, whereas accelerating additives enhance Cu+ formation. Acceleration by the bis(sodiumsulfopropyl) disulfide (SPS) additive results from accumulation of cuprous complexes near the surface. Adsorbed cuprous thiolate [Cu(I)(S(CH2)3 SO3H)ad] is formed through interaction of Cu+ ions and SPS rather than Cu2+ and mercaptopropane sulfonic acid (MPS).

https://www.webpages.uidaho.edu/nanomaterials/research/Papers/IBM%20papers/Vol%2049,%20No%201,%202005,%20p.%203%20Vereecken-Chemistry%20of%20additives.pdf

The chemistry of additives in damascene copper plating

The synergic effect of poly(ethylene glycol) together with chloride ion for inhibiting copper deposition in copper electroplating has been of particular interest for some time. In this study, the potential-dependent behavior of poly(ethylene glycol), with or without chloride ion in a copper electroplating bath is investigated using the surface-enhanced Raman spectroscopy technique. The presence of chloride proves to play a significant role in enhancing PEG adsorption to the Cu electrode surface. More importantly, spectroscopic evidence strongly suggests the formation of a PEG−Cu−Cl complex. By comparing experiment with vibrational modes calculated by using the Hartree−Fock method with a 3-21G* basis set, the structure of this complex is proposed to be a three-coordinated Cu center with two oxygen atoms from PEG and one chloride ligand.

Inhibition due to the interaction of polyethylene glycol, chloride, and copper in plating baths: A surface-enhanced Raman study

Extreme Bottom-Up Superfilling of Through-Silicon-Vias by Damascene Processing: Suppressor Disruption, Positive Feedback and Turing Patterns

Microvias with various diameters formed by laser ablation on a printed circuit board (PCB) were used to investigate the filling mechanism of the microvia in copper electroplating. The plating solution consisted of acid copper sulfate, polyethylene glycol (PEG), 3-mercapto-1-propanesulfonate (MPS), and chloride ions. Superfill was obtained using a specific concentration ratio of MPS to chloride ions. According to the examinations of the vias by an optical microscope (OM) for cross-sectional views, a scanning electron microscope (SEM) for top views, and by an energy dispersive spectrometer (EDS) for surface element analyses, chloride ions were verified to be a key factor in determining the superfilling behavior. They play three roles, namely, the electron bridge of Cu 2 + reduction, the anchor of suppressor (i.e., PEG + Cl - ), and the promoter of accelerator (MPS + Cl - ) in copper electroplating. The distribution of the surface coverage of the suppressor and the accelerator adsorbed along the via profile was revealed by tracing the distribution of CuCl crystals generated by synergistic interactions among MPS, Cl - , metallic copper, and Cu 2 + . Plating results indicate that the adsorptive abilities of the suppressor and the accelerator, and whether a suppressor can displace the accelerator adsorbed on the cathode are convection-dependent.

Roles of Chloride Ion in Microvia Filling by Copper Electrodeposition I. Studies Using SEM and Optical Microscope

Copper bottom-up deposition in 200 nm trenches by an acid-copper sulfate with only two additives [poly(ethylene glycol) (PEG) and Cl ] is achieved. The inhibiting effect of electrodeposition by PEG is strongly related to Cl - concentration. Secondary-ion mass spectroscopy measurements show that Cl - is consumed in the electroplating process. The explanation of bottom-up deposition realized in copper superfilling, in which the decrease of Cl - concentration causes rapid electrodeposition on trench bottoms, is verified experimentally.

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Copper Bottom-up Deposition by Breakdown of PEG-Cl Inhibition

A new structure for display devices is proposed and fabricated by the microelectromechanical systems process. The device is based on physical contact and evanescent coupling between a sheet waveguide and electrostatically driven multicantilevers. When incident light is propagated into the waveguide and the cantilevers contact the waveguide by applying a dc voltage, the switched light is emitted from the side edges of the contacted multicantilevers, resulting in a display device. The device contributes to the expansion of the switching area, the removal of unnecessary scattered light, and high contrast due to the simple fabrication and structure with corner spacers for the optical separation between the cantilevers and the waveguide. Based on the experimental results with the device, a contrast of 0.9 is obtained at 170 V, and a stable drive is realized up to 1 kHz. Therefore, the device can be expected to be used for display devices by the fabrication of an array structure.

Micromachined display device using sheet waveguide and multicantilevers driven by electrostatic force

Electric field analysis in a dilute solution for the vibrating electrode technique

A novel linear actuator has been developed using the vibration of angled thin short fibers—cilia vibration (CV). The actuator consists of two ciliary fiber arrays together with vibrators. The cilia array is made of carbon fibers bounded with a plastic resin and angled to the object so that it has directional flexure and anisotropic friction. When the two cilia arrays are vibrated, a standing-up and falling-down motion of the cilia linearly squeezes objects out of two plates, realizing a linear movement. A macro model of the CV actuator was developed using a carbon fiber-reinforced plastic (CFRP) cilia array and bolted-Langevin vibrators. A maximum drive speed of 99 mm/s, and a maximum shearing drive pressure of 400 Pa were obtained for a vibration frequency of 28 kHz. Also, a miniature model of the CV actuator was developed using stacked piezo vibrators. In this case, a maximum drive speed of 6.1 mm/s and a maximum shearing drive pressure of 38 Pa were obtained for a vibration frequency of 400 Hz.

A linear actuator based on cilia vibration

Two types of electrostatically driven optical switching devices have been developed in this paper. An interferometric optical switching device realizes selective wavelength filtering by the interference of lightwaves between two half mirrors. Also, an evanescent coupling surface-output optical switching device realizes on-off switching by evanescent coupling and physical contact. Their basic characteristics are experimentally evaluated. By integrating these devices on a substrate, switching devices with wavelength filtering and on-off switching are proposed.

Masanori Hayase

Papers

Copper Bottom-up Deposition by Breakdown of PEG-Cl Inhibition

Micromachined display device using sheet waveguide and multicantilevers driven by electrostatic force

Electric field analysis in a dilute solution for the vibrating electrode technique

A linear actuator based on cilia vibration

Electrostatically driven micro-optical switching device based on interference of light and evanescent coupling