Development of a two-step electroplating process with a long-term stability for applying to Cu metallization of 0.1-μm generation logic ULSIs

Developed a two-step copper (Cu) electroplating (EP) process using a seed-enhancement step with an alkali-metal-free Cu-pyrophosphate solution. The solution for the seed-enhancement step has low solubility of Cu compared with conventional Cu-sulfate solution and high macrothrowing power. As a result, the two-step EP solution provided a superior seed-enhancement effect and filling properties compared to conventional Cu sulfate EP. The seed-enhancement solution has excellent long-term stability of each component´s concentration, and there is no change of process performance over a two-month period. The authors can easily control sheet resistance (Rs) of electroplated films which correlates with thickness and nonuniformity of seed-enhancement films with no maintenance other than the addition of de-ionized (DI) water to compensate for evaporated water. The two-step EP process achieved an excellent via-chain yield and a tight distribution of electromigration (EM) lifetime compared with the conventional EP process. Thus, the two-step EP process is a promising process for manufacturing technique of 0.1-μm generation and beyond logic LSIs.