Gundu M. Sabde

Effects of CMP Process Conditions on Defect Generation in Low-k Materials An Atomic Force Microscopy Study

The effects of chemical mechanical planarization (CMP) process parameters and consumables on the polish rate and defects generated in various low-k materials with k values ranging from 2.2 to 3.0 were studied in detail. The process consumables and conditions evaluated include slurry material (alumina and silica), pad type (soft and hard), polish pressure, and polish time. Atomic force microscopy (AFM) images and roughness numbers were used to evaluate the post-CMP defect generation under various process conditions and revealed nano/microscratches, pits, voids, and film delamination. For a given material, the removal rate increased with increasing pressure. The dependence of defects on pressure appeared highly driven by the slurry material, pad type, and low-k material properties. Defects increased with increasing pad hardness and decreasing k values. The increasing defects with decreasing k value can be attributed to the lower elastic modulus observed with low-k materials. Removal rates exhibited both a decrease and an increase in conjunction with polish time, depending on the type of low-k material used. AFM analysis showed an improvement in global surface roughness with increasing polish time; however, an increase in localized defects such as pits was also observed. Fourier transform infrared and X-ray photoelectron spectroscopy analyses showed no change in film chemistry under the conditions studied here.

Effect of Ceria Particle-Size Distribution and Pressure Interactions in Chemo-Mechanical Polishing (CMP) of Dielectric Materials

Effect of ceria particle-size distribution and pressure interactions in CMP of dielectric materials and the subsequent surface generation mechanisms is investigated in detail. The removal rate is observed to correlate primarily with the slurry mean particle-size distribution (D50) and reach early rate saturation with decreasing particle size. Slurries with tighter particlesize distribution exhibit a logarithmic relationship with pressure, while a linear relationship is observed for wider distribution slurries. In contrast to the removal rate, surface roughness and degree of microscratches depend primarily on the tail distribution (D99) and increase with increasing particle size. The addition of a selective component to the slurry increases the rate differential between the slurries.