Yong-Da Chiu

Microvia Filling by Cu Electroplating Over a Au Seed Layer Modified by a Disulfide

A plating process for microvia filling by Cu electroplating, carried out in a plating bath without an accelerator but with a suppressor only, is proposed in this work. The seed layer of microvia used for subsequent Cu-filling plating is Au formed by electroless plating. The surface of the Au seed layer is modified in a solution containing bis(3-sulfopropyl)-disulfide (SPS) and various supporting electrolytes. This pretreatment is similar to the self-assembly monolayer (SAM) of a thiol molecule on a Au substrate. The coverage density of the adsorbed thiolate strongly depends on the presence or the absence of a supporting electrolyte and it crucially determines the filling performance of the plating process. The plating results demonstrate that the thiolate adlayer which is initially formed on the Au seed layer is transferable onto the surface of the plated Cu and then interacts with chloride ions to further facilitate Cu nucleation and growth. According to the results of the filling plating and the electrochemical analysis, an accelerating mechanism of SPS-SAM for copper electrodeposition and its transferring mechanism are proposed in this work.

Sensitivity Enhancement for Quantitative Electrochemical Determination of a Trace Amount of Accelerator in Copper Plating Solutions

An accelerator is an indispensable organic additive for the bottom-up filling of copper electroplating in nano- or micro-scale features. However, its effective concentration is too low to be easily determined and controlled. Herein, a new electrochemical analysis method based on self-assembly monolayers of thiol molecules on a gold electrode was developed to accurately determine a trace amount of accelerator. The accelerator employed in copper plating solutions is bis-(3-sulfopropyl) disulfide (SPS), which is the most common accelerator for the filling of vias and trenches of interconnects. The SPS concentration in copper plating solutions ranged from 0.3 to 9.0 ppm. Following selective chemisorption of SPS onto the gold electrode, the SPS-modified gold electrode was transferred into a specific electrolyte composed of CuSO 4 , H 2 SO 4 , polyethylene glycol and chloride ions to run cyclic voltammetry (CV) for copper deposition and stripping. A specific peak current of copper reduction formed in the CV, and its peak area depended on the SPS concentration in the copper plating solution. A good linear calibration line was obtained by using this electrochemical analysis method, which can determine a trace amount of SPS in a concentration range of 0.3-1.0 ppm, which is a significant challenge for traditional instruments.