Yuki Itakura, Shinji Tachibana, Hisamitsu Yamamoto and Shigeo Hashimoto
C.Uyemura & Co., Ltd.
Hirakata, Osaka, Japan
In developing high-speed electro “copper post” plating bath, 2 specific attributes were considered, namely the shape of the post (flat top) and the uniformity of the post height throughout the wafer.
It was considered important to make the post shape less susceptible to liquid agitation. Since the performance of the plating solution is greatly affected by organic additives, the influence of additives on agitation was investigated by electrochemical measurement based on the above idea. As a result, influence of agitation could be reduced by using leveler showing strong suppression effect particularly on strong agitation. When post was plated with using this leveler, the top shape became flat.
Regarding the uniformity of the post height, study of the composition conditions considered from Wagner number and supply of copper ions to the current density was important. It can be said that decrease the copper concentration and increase the sulfuric acid concentration is necessary in order to improve the uniformity from the Wagner number. This tendency can be seen when the supply of copper ions to the plating surface was sufficient. However, for high-speed plating, the supply of copper ions could not keep up with the consumption rate when the copper concentration was low. This could be confirmed from the formation of nodules, leading to a decrease in uniformity. From the above, it was effective to decrease the copper concentration and increase the sulfuric acid concentration within a range where nodule did not form in order to improve the uniformity. A plating bath was prepared with based on these results and plated on a 300 mm diameter whole wafer, and as a result, improved post-top flatness and post height uniformity were obtained at 20 A/dm2.
he post top shape was shown to be predictable from the influence of the agitation intensity on the polarization curve. The conditions for improving post height uniformity were mentioned from the consideration of Wagner number. Control of post shape and uniformity is a very important factor for plating technology which is required to increase speed. It was possible to develop a copper post plating bath with excellent performance for high current density by designing the bath based on these investigations.
Initially Published in the SMTA Proceedings