Back-side De-processing using CMP for bulk silicon 40-nm graphics processors
A back-side de-processing process by chemical mechanical polishing (CMP) is developed. The process has been optimized to produce repeatable results. The process is capable of exposing the circuitry of the die uniformly and is able to target more than one area for units with multiple defect locations; front-side de-processing process has difficulty achieving the same results due to the unevenness of the die
Effects of Mechanical Parameters on CMP Characteristics Analyzed by Two-Dimensional Frictional-Force Measurement
The effects of mechanical parameters on the characteristics of chemical mechanical polishing ~CMP! were evaluated by directly measuring frictional force acting on a wafer in terms of two components, i.e., the tangential and axial components of the platen’s rotation. It was found that, when the platen and the wafer were rotated at the same speed, the tangential component of the frictional force was dominant. Also, frictional force was in linear proportion with removal rate. Though frictional force increased in linear proportion to down force when mechanical-effect-dominant CMP for silicon ~Si! or silicon dioxide (SiO2) was carried out, it decreased gradually as platen rotational speed was increased. Copper ~Cu! polishing using abrasive-free polishing solutions, a typical example of chemical-effect-dominant CMP, showed much more complex behavior. Namely, dependence of frictional force on down force and on platen rotational speed showed nonlinear characteristics. Even when a nonlinear characteristic slurry was used, it was found that removal rate and frictional force were almost linearly correlated. It can thus be considered that frictional force is a basic parameter to determine CMP characteristics. From these results, an experimental equation was proposed to describe CMP characteristics by modifying Preston’s empirical equation.
Complete-abrasive-free process for copper damascene interconnection
Complete-abrasive-free process for copper (Cu) damascene interconnection has been developed. The process is a combination of a newly developed abrasive-free chemical polishing (AFP) of Cu and dry etching of a barrier metal layer. Complete stop-on-barrier characteristics of Cu polishing are attained by using the new polishing agent and a polyurethane polishing pad. This combination produces a very clean, scratch-free, anticorrosive polished surface, and the total depth of erosion and dishing is reduced to less than one fifth of that produced by conventional slurries even after 100% over polishing. And it is shown that the developed AFP significantly reduces both Cu line resistance and its deviation.