Wetting process of copper filling in through silicon vias

Abstract

In this paper, wetting process of copper filling in through silicon vias was investigated by agitation and vacuum pretreatment. Copper filling followed the pretreatment was fabricated in electrolyte with optimal additives concentration. By agitation pretreatment, a large void was observed at the bottom of the vias where the copper seed layer was clearly seen, which was attributed to the insufficient wetting of vias. In the blind vias with higher aspect ratio, the ambient gas phase was difficult to be completely removed from the vias by agitation. This resulted in electrolyte having better wettability does not reach all the places of the vias by capillarity. The vacuum pretreatment results suggested that the air inside the vias was almost completely evacuated. Hence, the deionized water used as wetting solution easily permeated the blind vias relying on atmospheric pressure. Consequently, the uniform, complete and void-free copper filling was achieved due to better wettability of 273K deionized water. Nevertheless, deionized water with temperature higher than the critical vaporization temperature yielded a void formation at the bottom of the vias, which resulted from the insufficient wetting caused by the vaporization of deionized water. The conclusions drawn by the experimental results were employed in the through silicon vias, and void-free copper filling in the vias having aspect ratio as high as 16 was fabricated.