Tributyl(hexyl)phosphonium chloride as a new leveler for microvia copper superconformal electronic plating

A phosphorus-containing new compound of tributyl(hexyl)phosphonium chloride (TBHP), but not the commonly used nitrogen-containing heterocycles and quaternary ammonium salts, is successfully applied for the superconformal copper filling of microvia in acid sulfate electroplating bath for the application of electronic industry. The molecular interaction mechanisms of TBHP combined with suppressor (polyethylene glycol, PEG) and accelerator (bis-(sodium sulfopropyl)-disulfide, SPS) are investigated in detail. Galvanostatic measurements at platinum rotation disk electrode indicate that the leveler of TBHP among with the suppressor and accelerator behaves the key characters of inhibition and convection-dependent adsorption during copper ions electroreduction for the bottom-up filling of microvia. Cyclic voltammetry measurements and in-situ FTIR spectroscopy further reveal that TBHP synergistically interacts with the suppressor to inhibit copper ions electroreduction at the mouth of microvia; while TBHP competes for adsorption with the accelerator, behaving as TBHP gradually replaced by the accelerator at the bottom. Based on the sufficient theoretical supports, the practical copper electroplating is conducted for the verification of microvia void free filling. In the developed novel copper plating formula containing TBHP, PEG and SPS, the void free filling is successfully achieved and the filling percentage (FP) is high in 95.5%.