We demonstrate a superpolishing electrolyte, which consists of acid additives in conventional Cu polishing electrolytes (H 3 PO 4 ), for efficiently planarizing Cu damascene features. The significant additive concentration gradient in features, resulting in a selective Cu dissolution rate within features, is explored as a major mechanism that yields such electrolytes with high planarization efficiency. Moreover, another additive, polyethylene glycol as a suppressor, is also employed to reduce oxygen bubbling on polished films. Consequently, a smooth surface with a complete step height elimination is obtained in a 70 m trench after electropolishing.Chemical mechanical polishing ͑CMP͒ of Cu and barrier metals is widely recognized as the most promising technology for planarizing Cu damascene interconnects. 1-4 However, conventional Cu-CMP slurries contain mechanically hard abrasives that scratch and damage polished Cu surfaces. Recently, Cu electropolishing has been explored as a replacement of Cu-CMP due to its higher polishing rate, lower waste stream, no scratching, and no mechanical stress on substrates. TSMC company announced CMP-free and CMP-less approaches by integrating Cu electropolishing. 5 Sony company announced a 25 m wide line formed by soft polishing technology. 6 They used a complexing agent to block Cu surface and introduced a soft pad to remove Cu complex outside of pattern, thereby producing selective electrochemical dissolution.Cu electroplating generally produces a step on/between damascene features after deposition. Moreover, planarization efficiency ͑PE͒ of Cu electropolishing is a strong function of the feature size ͑also for Cu CMP͒. 7,8 Those issues necessitate additional modifications to conventional polishing techniques. Because Cu dissolution rate depends on the pH value of polishing electrolytes and increases with solution conductivity, an addition of acid additives into polishing electrolytes can enhance Cu removal rate. Based on this mechanism and additive distributions controlled in diffusion limit, a presence of concentration gradient of additives in damascene features forms a selective electrochemical dissolution, thus enhancing step height reduction and improving PE of Cu electropolishing. In this article, we demonstrate a superpolishing electrolyte with high PE by adding acid additives into the polishing electrolyte (H 3 PO 4 ). Additionally, oxygen formation during Cu electropolishing often causes severe etched pits on polished surfaces. With polyethylene glycol ͑PEG͒ as a suppressor in the electrolyte, the overpotential of oxygen formation is significantly elevated, thus leading to less damage on polished surfaces. A polishing electrolyte with those additives can planarize damascene interconnects even with feature sizes in several tens of micrometers. ExperimentalThe patterned wafer used in PE measurements was composed of a 30 nm thick ionized metal plasma ͑IMP͒-TaN layer as the diffusion barrier, a 200 nm thick IMP-Cu film as the seed layer, and a 1.7 m electroplated Cu as the ...

In this study, the effect of plating current densities on self-annealing behaviors of electroplated Cu films was found to be relevant to the polarization resistance of electroplating systems. Porous films with defects occurred at low plating current density or at low polarization resistance. In contrast, dense films with small grains occurred at higher plating current density or at higher polarization resistance. However, when more current was further supplied, Cu aggregation occurred and deposited films became spongy or dendritic. We suggest that both the defects within porous films and the underlying energy of fine-grained deposits accelerated self-annealing. These two characteristics competed with each other to determine the resistivity drop by self-annealing. On the other hand, the ͑111͒ texture evolutions of deposited Cu films with an increase of plating current densities were consistent with the evolutions of resistivity and surface morphology.

Understanding the adsorption and organization of nanocelluloses at oil/water interfaces is crucial to develop a promising route to fabricate functional materials from the bottom-up. Here, we prepare acetylated cellulose nanofibrils (CNFs) with 2 degrees of substitution and investigate their assembly behavior at the oil/water interface. We study the adsorption process by tracking the dynamic interfacial tension using pendant drop tensiometry and further characterize the viscoelasticity of the CNF interfacial films as a function of ionic strength. The results show that the adsorption of the CNFs at the interface is dominated by energy barriers associated with electrostatic repulsion. With the addition of NaCl, the fibrils are rapidly accumulated at the oil/water interface and jammed into a solidlike film. The overall accumulation of the fibrils is related to the competition between van der Waals attractive forces and electrostatic repulsive forces according to the Derjaguin-Landau-Verwey-Overbeek theory. By screening on the fibril-fibril and fibril-interface electrostatic repulsive forces, the salt addition facilitates the formation of packed fibril clusters and the development of the clusters into a solidlike film. Moreover, the salt addition is assumed to trigger an abrupt density fluctuation in the vicinity of the interface (the formation of locally dense clusters and voids), leading to an increase in brittleness of the film.

The optimization of Cu electropolishing processes was explored to be in the mass-transfer-limited plateau with a stable limiting current density and in concentrated phosphoric acid by elucidating surface morphologies and potentiodynamic polarization. After electropolishing, the average roughness of polished surfaces achieved to 1.1 nm. Both the x-ray photoelectron spectroscopy and the electrochemical impedance spectroscopy suggest that the existence of a passivation film on the polished surface contributed to the microleveling effect of Cu electropolishing. Moreover, this passivation layer also induces an application of end point in electropolishing.

Through elucidating the effects of current density, cupric ion concentration, bath temperature, and air agitation on plating uniformity and filling capability of copper electroplating, the deposition of copper in an acid copper electrolyte will be illustrated to scale down to the sub-0.13 m features with uniform plating, which is required by chemical mechanical polishing in current damascene techniques. In order to achieve the defect-free filling in sub-0.13 m vias and trenches, the electrolyte must be composed of proper amounts of cupric ions, sulfuric acid, chloride ions, wetting agent, and filling promoter. The supplied current controlled at a lower current density, agitation acceded to the electroplating process were found as further keys. In the electrolyte, the filling promoter was consisted essentially of thiazole derivatives with benzyl groups and amino-group (ϪNH 2 ͒ offering sufficient inhibition on copper depositing and selective inhibition gradient. Moreover, a lower resistivity film and higher filling capability could be obtained by using periodic pulse current plating as compared with direct current plating.