Periodic reverse electrodeposition of (111)-oriented nanotwinned Cu in small damascene SiO2 vias

It is quite challenging to electrodeposit (111)-oriented nanotwinned Cu in small damascene SiO2 vias because of the existence of the sidewalls of the vias. However, by tailoring electroplating waveforms and temperatures, one can overcome this difficulty. Fine pitch nanotwinned Cu (NT-Cu) with high ratio of (111) surface grains were fabricated using periodic reverse (PR) electrodeposition in damascene SiO2 vias. The PR electroplating parameters for via-filling were adjusted by tuning duty cycle and electrolyte temperatures. The PR current may remove randomly oriented nuclei caused by the sidewall-growing front. Thus, the bottom-up filling of the highly (111)-oriented NT-Cu was achieved. (111) surface ratios greater than 85% and 50% were obtained in 10-mu m and 2-mu m vias in diameter, respectively. Besides, a mathematical model was proposed to predict the (1 1 1) surface ratio of the ultra-fine pitch vias fabricated by PR electrodeposition. This investigation offers a new route to the development of NT-Cu interconnects for ultra-fine pitch packaging.