Efficiency of reducing and oxidizing ash plasmas in preventing metallic barrier diffusion into porous SiOCH

This work focuses on the efficiency of reducing and oxidizing plasma chemistries in preventing metallic barrier diffusion into porous dielectric materials (SiOCH with a k value close to 2.2, porosity content around 40%). The ash processes have been performed on SiOCH coated blanket and patterned wafers in either reactive ion etching (RIE) or downstream (DS) reactors. The Rutherford backscattering spectroscopy technique (RBS) has shown that titanium based compounds diffuse into the blanket porous SiOCH without treatment during a typical TiN barrier deposition process by chemical vapor deposition (CVD). The metallic barrier diffusion is strongly limited on blanket wafers when the porous SiOCH has been previously modified (partially or fully) by ash plasmas (RIE-O"2, RIE-NH"3, DS-H"2/N"2 and DS-O"2/N"2) while the metallic barrier diffusion occurs with no modifying ash plasmas (DS-H"2/He). We have shown that ellipsometric porosimetry (EP) measurements clearly point out that no complete pore sealing is achieved with all the investigated ash plasmas. Energy-filtering transmission electron microscopy experiments (EFTEM) performed on single damascene structures have revealed significant titanium diffusion into the porous dielectric lines for DS-H"2/He and RIE-O"2 and sidewalls modification of the porous SiOCH lines (lower C/O ratio) for all the ash plasmas. The RC product (resistancexcapacitance) have been extracted from the single damascene structures and the evolution of RC product will be discussed in terms of lines modification (titanium diffusion and porous SiOCH modification).