A model on pad surface roughness is proposed, in order to estimate the hydrodynamic pressure of slurry in CMP process. Measurements of the friction coefficient between wafers and pads show good agreement with the model at high viscosity and high speed conditions, wherein the hydrodynamic pressure is dominant. This model should be useful for the understanding of the contact mechanism between the wafers, the pads and the abrasives in CMP processes.

Chemical mechanical polishing is an essential process for achieving a high degree of planarization. The planarity after CMP sensitively depends on pattern scales, pattern densities and mechanical properties of polishing pads. In order to simulate the topography after CMP, a numerical model for the polishing pad is proposed. In this model, the surface roughness layer of the polishing pad is assumed as a flat soft layer. The distribution of the contact pressure between the patterned wafer and the polishing pad is calculated with finite element method, and the pattern topography is modified based on the pressure dependency of the polishing rate. The iterations of the contact pressure analyses and the topography modifications give the progress of the polishing process numerically. The model is applied to oxide CMP process with silica slurry and stacked pad of polyurethane and non-woven fabric. The compressive elastic moduli of polyurethane layer and non-woven fabric layer are measured dynamically. The elastic modulus of the soft layer is treated as a fitting parameter between the experimental results and the numerical model. The models with the elastic modulus of 10 MPa for the soft layer show good agreements with the experimental results in both of a short range, where the compressive deformation of the pad is dominant, and a long range, where the bending deformation is dominant. Static measurements for the surface elasticity of the polyurethane layer also give a good agreement with the model. The proposed pad model should be useful for the topography simulation, and it also guides the development of new polishing pads.

The focus margin of lithography becomes more critical as the LSI design rule decreases. Chemical Mechanical Polishing (CMP) is an essential process for achieving a high degree of planarization. The object of this paper is to clarify the polishing process. Using Atomic Force Microscope (AFM), micro-tribological experiments were performed in KOH solution and in pure water for the pH range of 7-12. The effect of slurry pH and the effect of applied load on removal rate in oxide CMP were investigated, and the wear phenomena were observed. The results show a significant difference between the two solutions.

Extendibility of CMP process to Cu / porous low-k interconnect fabrication will be discussed. In order to establish the damage free CMP process, not only the lowering of the down force, but also the control of the pad surface and the slurry design, is important. Based on the strength improvement of p-low-k materials, the increase of real contact area between wafer and pad with dressing optimization, the lowering friction with slurry additives, and the application of resin particles are expected to expand CMP process margin.