Modifications of dielectric films induced by plasma ashing processes: Hybrid versus porous SiOCH materials

This work focuses on the impact of oxidizing (O₂) and reducing plasma ashing chemistries (NH₃, CH₄) on the modifications of dielectric materials in a porous or an hybrid state (SiOCH matrix+porogen). The plasma ashing processes have been performed on blanket wafers using O₂, NH₃, and CH₄ based plasmas. The modifications of the remaining film after plasma exposures have been investigated using different analysis techniques such as x-ray photoelectron spectroscopy, infrared spectroscopy, x-ray reflectometry, and porosimetric ellipsometry. For the porous material the authors have shown that NH₃ and O₂ plasmas induce carbon depletion and moisture uptake while the CH₄ plasma only leads to important carbon depletion without moisture uptake and to the formation of a thin carbon layer on the surface. For the hybrid material, no significant material modification is evidenced with the O₂ plasma while an important methyl depletion and porogen degradation are observed with reducing chemistries such as CH₄ and NH₃ plasmas. The impact of the porogen on the film modification and the value of the dielectric constant will be presented and discussed.