Residue growth on metallic hard mask after dielectric etching in fluorocarbon based plasmas. II. Solutions

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Metallic hard mask architecture becomes an integration of choice for an advanced back end of the line interconnect technology node. However, one of the main integration issues is the growth of residue (titanium based compounds) after dielectric etching. In this article, the authors study the efficiency of different in situ postetch plasma treatments such as hydrogen, oxygen, and methane based plasmas, which are investigated in order to prevent the residue formation. The efficiency of those plasma treatments is demonstrated for a C045 dual-damascene level technology using a trench first hard mask integration with a porous SiOCH dielectric (porosity of 25%, k=2.5, deposited by plasma enhanced chemical vapor deposition). The authors show that they strongly improve the yield after a 1 day air exposure. Complementary x-ray photoelectron spectroscopy analyses performed on blanket titanium nitride wafers revealed that oxygen or hydrogen based plasmas act on the kinetics of residue formation by removing the fluorine species concentration on top of the titanium nitride layer. On the other hand, with methane based chemistry, the formation of a carbon and nitrogen based passivation layer on top of the titanium nitride layer prevents a reaction with air moisture and thus leads to a residue free surface. The authors also show that the methane based in situ postetch treatment presents superior efficiency than any other investigated chemistries since its efficiency to limit residue growth is independent of fluorocarbon etching process conditions.