Paper PS1-MoM11
Post Etch Treatments as Solution to Limit or Prevent Residue Growth on Metallic Hard Mask after Porous SiOCH Etching in Fluorocarbon Based Plasma

Monday, November 9, 2009, 11:40 am, Room A1

For 45 nm interconnect technology node, porous SiOCH (p-SiOCH) materials are being introduced, leading to complex integration issues due to their high sensitivity upon etching and ashing plasmas exposure . Metallic hard mask (MHM) integration avoids exposure of the porous film to plasma stripping processes but generate its own issues such as metal contamination on patterned structures ( leading to line and via opens, strongly impacting the yield performance).

In this work, we have investigated the efficiency of in situ post-etch plasma treatments (PET) such as NH₃, CH₄, O₂ and H₂ to limit or prevent residues formation.

First, the experiments have been performed on TiN blanket wafers deposited on 200 nm thick SiO₂ layers. The TiN layer has been exposed to conventional fluorocarbon (FC) based chemistry and PET in an industrial dual frequency capacitively coupled plasma etcher. Different analyses techniques such as scanning electron microscopy (SEM) and ex-situ x-ray photoelectron spectroscopy (XPS) have been used in order to analyze the presence of metal residues and have a better understanding of the residue formation mechanism .

After FC etching and atmosphere exposure, a huge density of residues is observed, correlated with the presence of significant fluorine concentration (33%) on the TiN surface. The mechanism of metallic residues formation on the metallic hard mask has been clearly identify as a reaction between fluorine and air moisture (forming HF acid) and the oxidized metal to form a metallic salt.

H₂, O₂, and NH₃ PET strongly reduce the density of residues by partially removing fluorine on the TiN surface (8-13%). With the CH₄ PET, no more residues are observed despite an important fluorine concentration (28%) remaining on the surface. The residue removal is explained by the formation of a thin carbon passivation layer on top of the TiN surface preventing reactions between fluorine and air moisture.

Furthermore, a complementary study has been performed on patterned wafers using trench first MHM integration with a PECVD p-SiOCH dielectric (porosity of 20%, k=2.5). The implementation of the post-etch plasma treatment show that the residues density on MHM strongly depends on the etching chemistry with H₂, O₂, NH₃ while with CH₄, the efficiency in preventing residues formation is not chemistry dependent. The implementation of such PETs using a MHM and a porous SiOCH has been successfully integrated with an improvement of the electrical performances.