GOALI: Shear thickening and defect formation in chemical mechanical polishing slurries

Colorado School Of Mines, Golden CO

Investigators

Abstract

0968042 - Liberatore The Chemical Mechanical Polishing (CMP) process is a critical piece of technology enabling the continued reduction in feature size in semiconductors, with the concomitant increase in feature density. CMP in turn is a major contributor to continuing increases in microprocessor speed and power with continuing reductions in cost to performance measures, often referred to as Moore's Law. Continued reduction of feature sizes on semiconductor chips has necessitated the recent introduction of low dielectric constant materials as the insulator between connectors. These low dielectric constant (low k) materials are generally fragile and much more prone to stress induced damage than the traditional silicon dioxide material. This stress induced damage can be severe enough to destroy the insulating capability in the vicinity of the damage event, leading to a short circuit and failure of the semiconductor device. Thus, a collaborative effort seeks to obtain detailed understanding of the high shear rheology of CMP slurries and both temporary and permanent changes to the particles in the polishing slurry, including both particle size distribution changes and the structure of any new particle agglomerates produced. Three objectives will test the hypothesis that shear thickening of concentrated slurries can cause solid like behavior during polishing, which can lead to defect formation when polishing dielectric wafer surfaces, particularly the newly introduced low dielectric constant insulating materials. The objectives are: 1. Integrate simultaneous structure and rheology studies using rheo-optic measurements on CMP slurries at process relevant shear rates in the presence and absence of shear thickening. 2. Quantify temporary and permanent changes to the particle sizes in the slurry using field flow fractionation (FFF) separation as the shear thickening of CMP slurries may be caused by a very small fraction of oversized particles. 3. Correlate shear response and particle size to polishing conditions causing surface defect formation on dielectric wafer surfaces. Intellectual Merit: Evaluate whether shear thickening is a reasonable hypothesis for defect formation in chemical mechanical polishing. Proving or disproving the hypothesis has immediate implications for slurry design, manufacture and use to enable future development of semiconductors with smaller feature sizes. Also, this work will extend the basic understanding of shear thickening in high solids colloidal dispersions to dispersions composed of particles with their own fractal structure. Broader Impact: The three pronged approach proposed here will provide important insights on the potential and limitations of the colloidal nature of CMP. This will enhance the ability of slurry producers and semiconductor manufacturers to optimize both the formulations and the processing parameters, thereby enabling rapid progress in future semiconductor production. The research will impact other industries that utilize large area silicon technology, e.g., flat panel displays and solar cells and tie into the Colorado School of Mines, NSF Materials Research Science and Engineering Center on renewable energy. In addition, this research will help educate graduate and undergraduate students in the fields of rheology and particle characterization as they apply to problems of real industrial interest. A senior industrial scientist will spend time teaching in the academic environment while students will spend months in residence in the industrial setting.