Yoshikuni Tateyama

High Performance Photoresist Planarization Process by CMP with Resin Abrasive for Trench-First Cu/Low-k Dual Damascene Process

High performance photoresist planarization technology by chemical mechanical polishing (CMP) was developed for the trench-first Cu/low-k dual damascene (DD) process to reduce the focus error in the lithography process. To improve the planarity for the wide trench area, the planarization properties of alumina and resin-based slurries were investigated for different resist baking temperatures. Excellent planarity was obtained by high resist baking temperatures and using alumina slurry. However it became clear that the scratches caused by alumina particles were a critical issue for yield improvement. To improve the planarity and reduce the scratch density, the CMP process with a soft resin-based slurry at a low resist baking temperature was investigated. The addition of a nonionic water-soluble polymer to the resin particles was quite effective for planarity improvement, and the scratch level could be kept low by using soft resin abrasion. The resist planarization technology with a resin-based slurry was adapted to the trench-first DD process. The focus error was reduced and the process window in the lithography process was enhanced compared to the conventional process without a resist CMP, indicating that the resist planarization technology could be a strong tool for the 45 nm technology node and beyond.

Focus error reduction by photo-resist planarization in via-first dual damascene process

In order to reduce the focus error for the stacked mask process (SMAP) used in Cu/low-k dual damascene (DD) interconnect, a planarization technology of the under layer film by CMP was developed. Photo-resist was used for the under layer film. CMP slurry with resin abrasive was investigated for the photo-resist planarization. The slurry showed better planarity, lower risk to particle residue, and high selectivity to SiO/sub 2/ film. These advantages are attributable to the effects of the particle size and the material characteristics similar to photo-resist. Furthermore, it was found that it is effective for a higher CMP rate to turn the platen and head with lower rotational speed. Using the photo-resist planarization technology, application to via first DD process was investigated. It became clear that focus error reduction of 0.1 /spl mu/m is confirmed compared with conventional SMAP. The depth of focus (DOF) margin loss due to resist thickness variation caused by via density variation is completely canceled by photo-resist planarization.

Modeling on Mechanical Properties of Polishing Pads in CMP Process

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.