Low-Temperature CVD for Microelectronics: Utilizing Surface Reactions to Afford ALD-Like Conformality

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Technical: The proposed work will develop methods of low temperature chemical vapor deposition (CVD) to afford uniform, smooth, and pinhole free thin films on substrates that have high aspect-ratio openings such as deep trenches and vias. Such films are required for a wide variety of advanced technologies, e.g., diffusion barriers associated with copper metallization in integrated circuits. The CVD method can also completely fill these features at reasonable rates. Examples to date include the coating and filling of high aspect ratio (30:1) vias, 100 nm in diameter, with HfB2 or MgO films.Three experimental approaches are used to achieve excellent coating properties. (i) Unique CVD precursor molecules with high vapor pressure produce a site-blocking effect on the film growth surface, such that the surface reactivity is low but the growth rate is acceptable. (ii) Inhibitor species are added to the growth process to modify the surface reactivity: H atoms impinge on, and bind strongly to the most exposed (upper) surfaces and lead to bottom-up film growth; molecular species such as NH3 or dme uniformly lower the growth rate such that a ?non conformal? precursor will afford a highly conformal film. (iii) Inhibitor species are used to enhance the density of nuclei on a substrate by reducing the growth rate of the first-formed nuclei with respect to the rate at which new nuclei form. This has the effect of greatly smoothing films of few-nm thickness, and of eliminating pinholes. The approaches have transformative potential in the field of thin film growth.This research employs surface science techniques and kinetic modeling to obtain a mechanistic understanding of the surface reactions involved in highly conformal chemical vapor deposition of thin films. That intellectual synthesis across disciplines ? surface physics, surface chemistry, and thin film materials science provides enabling scientific knowledge to guide further development of conformal CVD. For example, it affords quantitative metrics for the necessary properties and behavior of precursor molecules and inhibitor species.Non-technical: The project addresses basic research issues in a topical area of materials science with technological relevance, and is expected to provide unique opportunities for graduate and undergraduate training in an interdisciplinary field. This research project is also expected to have broader impacts through the training of scientists in this research field and through the wide dissemination of the findings of this research through publications. The PI will mentor a REU student and one or two undergraduate senior theses in the group. Graduate students and undergraduates from under-represented groups are recruited via the University of Illinois programs SURGE (Support ofUnder-Represented Groups in Engineering) and WISE (Women in Science and Engineering). One woman Ph.D. student is associated with this project at the time of writing. Periodic news stories also report the developments and cite the crucial role of the National Science Foundation in the process of discovery.