Steam laser cleaning of plasma-etch-induced polymers from via holes

Abstract

As the wafer industry enters into submicron processes and below, the demand for new cleaning technology after plasma etching increases. The cleanliness of via holes becomes very crucial for the success of low-resistance interconnecting high-density ultra-large-scale integrated devices. In this study, a relatively new approach in removing the sidewall and bottom polymers resulting from reactive ion etching of via holes, using dry and steam laser cleaning techniques is investigated. The presence of a layer of isopropanol (IPA) film on the wafer surface during excimer laser irradiation is found to improve the removal efficiency greatly even at fluences as low as 80-100 mJ cm-2-much lower than the damage threshold of the underlying Al-Cu metal film with titanium nitride anti-reflective coating of 250-280 mJ cm-2. The explosive evaporation of IPA and the creation of bubbles at the liquid-substrate interface were proposed to be the reason for the improvement. Experimental results show however that the presence of a layer of acetone film does not improve but even impedes the laser cleaning process. An explanation is offered for this phenomenon in terms of the difference in the absorbance of the two liquids at the laser wavelength. © 1998 Publication Board, Japanese Journal of Applied Physics.