Paper PS1-TuA9
Ash Plasma Exposure of Hybrid Material (SiOCH and Porogen): Comparison with Porous SiOCH

Tuesday, October 16, 2007, 4:20 pm, Room 606

In CMOS technology, the dominant strategy to achieve future generation of ultra low-k interlayer dielectric materials with a dielectric constant close to 2.2 is to introduce porosity into a SiOCH matrix. However, porous materials are very sensitive to etch and ash plasma exposure and one of the major integration challenges is to reduce the impact of plasma processes on the ultra low-k degradation. To solve this issue, one of the emerging solutions is the late porogen removal process. In this approach, the porosity is generated by a sacrificial carbon based porogen which is desorbed after patterning or copper filling. Such hybrid materials (SiOCH matrix and porogen) are expected to behave like dense materials and therefore to be less sensitive to plasma processes (etching and ashing). In this work, the hybrid material and the porous material are compared in terms of sensitivity to ash plasmas. The ash plasmas are performed in an industrial MERIE (Magnetically Enhanced Reactive Ion Etcher) and in an ICP (Inductively Coupled Plasma) reactor using oxygen-, ammoniac- or methane-based plasmas. X-ray photoelectron spectroscopy studies shows that the surface composition of the porous SiOCH is modified after the ash plasma treatments (SiO, SiON, and SiOC after O₂, NH₃ and CH₄ treatments, respectively) and X-ray reflectometry measurements indicate an increase of the surface density. Hybrid materials and porous SiOCH after ash plasma treatments present similar surface composition but no surface densification is evidenced. After the pore release process of the treated hybrid material, the surface composition remains close to the treated porous SiOCH and the top surface is denser than as deposited porous SiOCH. Infrared spectroscopy (FTIR) shows an important bulk modification of the porous SiOCH after ash plasma exposure (carbon depletion and new absorption bonds depending on ashing plasmas), whereas the hybrid material volume is hardly modified. After the pore release process of the treated hybrid materials, FTIR spectra are identical to an untreated porous SiOCH indicating an almost unmodified porous SiOCH. The porogen of the hybrid material prevents the bulk modification potentially induced by the different ash plasmas. Consequently, after the pore release process the material is similar to an unmodified porous SiOCH with only a slight modification of the top surface.