Paper PS-MoM9
Mechanisms of Residue Formation on TiN Hard Mask after Patterning of Porous SiOCH Films in Fluorocarbon-Based Plasma

Monday, October 20, 2008, 11:00 am, Room 304

For the 45 nm interconnect technology node, the introduction of porous SiOCH materials (p-SiOCH) brings major concerns such as the sidewall modifications induced by ashing plasmas used to strip the photoresist. Metallic hard mask (MHM) integration avoids exposure of the porous SiOCH films to resist stripping plasmas but generates its own set of issues such as metal contamination of the patterned structures. In particular, the growth of metallic residues on the MHM is often observed after p-SiOCH etching in fluorocarbon (FC) plasmas. Since, these defects are not removed after wet cleans, they directly impact the electrical performance measured on via chains. This work focuses on the mechanisms of residue formation on metallic hard mask (titanium nitride, TiN deposited by Physical Vapor Deposition) when exposed to FC based plasma etching. In situ post-etch plasma treatments have also been investigated as potential solution to remove these defects. The mechanisms of residue formation have been investigated using different analyses techniques such as ex-situ x-ray photoelectron spectroscopy (XPS), scanning electron microscopy cross section and energy dispersive x-ray (EDX). These experiments have been performed on TiN blanket wafers deposited on 200 nm thick SiO₂ layers and on patterned wafers etched in a dual frequency capacitive etcher. The growth of residues on metallic hard mask is observed when the wafer is etched in FC plasmas and exposed to air. EDX and XPS analyses both show that these residues are TiF_x like residues. We have also observed that the kinetic of residue formation after air exposure on metal hard mask is correlated with the etching chemistry (SF₆, C_xF_y, ...), the plasma operating conditions (w or w/o ion bombardment), the chemical composition of the etched materials (SiO₂, p-SiOCH, SiCN) and moisture content. Based on these results, the mechanisms of the residues formation will be presented and discussed.