Five-membered heterocyclic small molecule compounds as novel levelling agents for blind-hole copper plating

A defect free copper interconnect is crucial for ensuring the electrical connection and transmission of high-density interconnect printed circuit boards. Leveling agent is a key regulatory factor for achieving dense copper super filling from bottom to top in blind holes during the electroplating process of high-density interconnect boards. Here, two small molecule five-membered heterocyclic compounds with different side chains, namely 3-amino-5-mercapto-1,2,4-triazole (AMT) and 2–5-methyl-1,3,4-thiadiazole (MMT), were selected to be as levelling agents to study their effect on the copper filling behavior on blind holes. Electrochemical tests including cyclic voltammetry solvation (CV) and linear sweep voltammetry (LSV) were firstly used to analyze the inhibitory effect of two leveling agents on copper deposition and it was indicated that the MMT has a more significant inhibitory effect on the copper deposition than the AMT. Subsequently, the influence of different concentrations of MMT on the inhibition of copper deposition and the blind hole filling performance were also further analyzed by LSV, CV, and constant current measurement (GM), where an optimal concentration of 7 ppm was obtained for the maximum inhibitory ability on the copper deposition accompanied by the best blind hole filling ability. The characterization analysis from the field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) also illuminates that the MMT leveling agent can effectively reduce the surface roughness of copper filled with micropores and promote the selective growth of copper coatings along the (1 1 1) crystallographic plane. The adsorption behavior of the levelling agent on the cathode surface during electrodeposition was further also studied by the quantum chemical calculations and molecular dynamics simulations combined with the in situ electrochemical surface enhanced Raman spectroscopy (EC-SERS) experiments. It has been suggested that the thiol, sulfur, and alkyl groups in the leveling agent MMT molecule are nucleophilic groups, providing preferred active sites for adsorption reactions and thus generating effective inhibition ability on copper deposition formation. Thermal shock experiments based on tin immersion showed the copper layer obtained under the addition of the levelling agent MMT has excellent reliability. The comprehensive results indicated that 2-mercapto-5-methyl-1,3,4-thiadiazole (MMT) was an effective levelling agent for the blind hole supperfilling.