Copper Deep Via Filling with Selective Accelerator Deactivation by a Reverse Pulse

Accelerator dominant bottom-up copper superfilling of through silicon vias (TSVs) was demonstrated. Because of the 100 times large dimensions compared to on-chip interconnections, strong inhibition on the top surface is needed and the superfilling of TSVs are generally achieved by addition of levelers in the plating bath. Without leveler, abundant accelerator adsorption diminishes acceleration difference between via opening and bottom and the superfilling is usually failed in. Recently, we reported that accelerator can be deactivated by reverse pulses and the deactivation needs solution agitation. Due to viscosity, fluid movement is suppressed inside small vias and agitation hardly penetrates into deep area of TSVs. Using this behavior, it is expected that reverse pulses deactivate the acceleration selectively on the top surface and the acceleration around via bottoms is preserved. Therefore, bottom-up deposition might be achieved without leveler. In order to verify the strategy, three step plating with two plating baths was proposed and obvious bottom-up superfilling was demonstrated. Furthermore, accelerator distribution along via depth was controlled in some extent by reverse pulse tuning.