Investigation into the mechanism and performance of 4-aminopyrazolo[3,4-d]pyrimidine as a novel leveler for copper electroplating

Abstract

4-aminopyrazolo[3,4-d]pyrimidine (PPA) was explored, for the first time, as a novel and high-performance leveler for acid copper (Cu) electroplating. Electrochemical characterization revealed that PPA possesses appropriate adsorption characteristics and mass transport regulation capabilities, which are crucial for achieving effective leveling performance. Chronopotentiometry and electrochemical impedance spectroscopy (EIS) under different convection intensities were used to study the leveling ability of PPA. Under strong convective conditions, the negative shift of the cathodic potential by 7mv and the increase of the charge transfer impedance with the convective intensity (90.24 Ω at 1200 rpm vs. 72.32 Ω at 200 rpm) both indicate that PPA follows a diffusion-controlled adsorption mechanism and has the ability of superconformal filling. The coordination interaction between PPA and Cu²⁺ions was systematically investigated by in-situ Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopy, and the results inferred the adsorption configuration of PPA which was anchored to the copper surface through the N-terminal of the C = N bond. The use of PPA as a leveler has been proven to yield a denser copper coating with a higher proportion of Cu (111) planes, and has achieved practical application in void-free and compact filling of PCB blind vias (150 µm × 150 µm) within 150 min.