Superconformal Growth of Thin Films by Two-Component CVD

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Non-Technical Description: Integrated circuits require multi-level microscopic wiring of transistors, i.e., ten or more layers of vertical columns and horizontal rows of copper are needed to interconnect all the transistors into a functional chip. For each layer, advanced patterning and etching methods are required to create cylindrical and trench-shaped openings with dimensions well below one micrometer. Fabricating this exquisite structure on ever-smaller size scales, without any trapped void space or "seam" of low-density material along the centerline, is a significant challenge. This project explores a new method to accomplish the filling step: a material is deposited from the gas phase using two chemical species under special conditions that cause the growth rate to be faster at the bottom of the opening than at the top, termed as superconformal growth. During the filling process, the deposited material forms a V-shaped profile and the apex moves up from the bottom to afford a perfectly filled structure. The research project is integrated with various educational activities: involving graduate students in every aspect of the research, supervising undergraduate students on senior projects, and disseminating the research findings to the scientific and technical communities. Technical Description: This research project develops an innovative approach to deposit thin film materials in a superconformal fashion inside of high aspect ratio (depth : width) openings such as trenches and vias in a substrate, leading to complete and void-free filling. Such superconformal growth is needed for a wide variety of nanoscale fabrication processes. In this project, growth proceeds by chemical vapor deposition using two reactants at a relatively low temperature, generally below 300 degrees C. A kinetic regime exists where the competitions in species transport and surface reaction rates lead to the superconformal growth. The project tasks include (1) to demonstrate and evaluate the superconformal filling method for a variety of materials and in various openings; (2) to create a mathematical model of the effect that can predict superconformal growth conditions in general; and (3) to determine what distribution of chemical species within the structure is needed to eliminate the growth of low-density material. These experiments generate detailed kinetic data that are tested against a diffusion-based model. The atomic-scale mechanisms of the process are determined using in-situ analyses of the film surface, detailed calculations of particle transport and filling profiles, and a critical examination of the role of reaction byproducts.