Mixed Abrasive Slurries of Ceria and Silica Nanoparticles formed by Electrostatic Attraction for Shallow Trench Isolation Chemical Mechanical Polishing

• Author / Creator

  Dawkins, Korel V

• Device isolation is achieved using shallow trench isolation (STI) which requires chemical mechanical planarization (CMP) of the excess and unwanted oxide layer and stopping on the underlying silicon nitride layer. The increasing stringent requirement of the STI CMP performance is the driving force behind developing new slurries used in this process, which enhances oxide-to–nitride polish rate selectivity with little to no surface defects. In this study, mixed abrasive slurries (MAS) of colloidal ceria and silica abrasives are used to achieve high oxide-to-nitride polish rate selectivity through a systematic investigation of the electrostatic interactions between particle-particle and particle-wafer surface, the characteristics of the colloidal stability of the suspensions and their impact on polish rate along with the use of additives in suppressing nitride polish rate and the associated pH range in which high selectivity is observed. A model for the material removal mechanism using MAS is proposed, based on an adaptation of the surface area and indentation based mechanism. Within a range of ceria-to-silica weight ratios, known as the transition range, the mixed abrasive slurries were observed to be unstable which corresponded with high material removal rates of both oxide and nitride films. Polishing above this range, produced high oxide removal rates but low nitride removal rates giving relatively high selectivity. Frictional forces during polishing are investigated by using the table motor current; the results demonstrate that this has an impact on polish rates especially of nitride surfaces which polish mechanism appears to be predominately mechanical. The overall rate of material removal is maximized by polishing with such mixed abrasive slurries in a synergistic ratio compared to the slurries containing a single kind of abrasive under the same conditions and at high weight ratios of MAS (≥ 0.2), STI CMP selectivity is enhanced.

• Subjects / Keywords

  • Mixed Abrasive Slurries
  • Shallow Trench Isolation
  • Chemical Mechanical Polishing

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-g3c2-xe63

• License

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