Borderless via Clean Study for Minimizing Al-Cu Loss in 58nm Flash Devices

Abstract

The borderless (BDL) vias landing on the metal lines were demanded in high-density flash memory devices due to the reduced die size, compared with non-borderless (NBDL) vias. IMD material recess in un-landed via dry etching and the Al-Cu metal line undercut caused by post-etch cleaning may lead to via resistance Rv high and EM reliability issue. In this work, the Al-Cu loss mechanism in BDL-via cleaning by using amine- and fluoride-based chemicals were studied in 58nm flash devices. We found that the Al-Cu undercut can be minimized in HDA containing solvent by controlling the formation of Al2O3/Al/HDA gel-like material to the less amounts; the shorter HDA processing time with sufficient IPA rinse generated the thinner gel-like layer leading to the less Al-Cu undercut in DIW rinse step. For TMAH/H2O2-containing semi-aqueous solution, the metal contained etched-residues can be removed by reaction of OH- with Al to form dissolved Al(OH)4-; addition of H2O2 will form a oxidized passivation layer on the metal surface to prevent from metal corrosion. On the other hand, the Al/Al2O3 contained polymer was removed by fluoride-based solvent or DSP+ through the reaction with [F-] to form the DIW-dissolved AlFx by-products; while the dilute H2SO4 and H2O2 in DSP+ will oxidize Al to form Al2O3 that will be further etched by HF, the severe Al-Cu undercut was found in DSP+.