MRI: Development of an in-situ controlled Atomic Layer Deposition Tool (iCALD) for the Preparation of 3D Photonic Materials with Ultrahigh Aspect Ratios

Optical materials composed of three-dimensional structures with ultra-high aspect ratios and coated with ultra-thin conformal layers enable a vast array of active and passive devices and components operating in the infrared and terahertz spectral range. Applications for these materials include environmental sensors with unprecedented sensitivity and multifunctional coatings to enhance three-dimensional micro-optical structures. The proposed in-situ controlled, atomic layer deposition (iCALD) instrument which will be developed at the University of North Carolina (UNC) at Charlotte and integrated in the cleanroom facility of the Center for Optoelectronics and Optical Communications will enable the fabrication of these optical materials. The ability to conformally coat structures with virtually arbitrary geometries enabled by the iCALD instrument will transform the use and scope of materials, structures, and optical devices, synthesized and fabricated using the existing cleanroom facilities. The iCALD instrument will enable research by over 40 faculty members from five departments across the UNC Charlotte campus, their students, and national and international collaborators. In addition, this unique instrument will be accessible for research organized in two NSF-funded Industry/University Cooperative Research Centers (I/UCRCs), the Center for Metamaterials and the Center for Freeform Optics. Through these Centers the iCALD development will lead to new opportunities for industry funded research projects and directly benefit more than 30 industry partners nationwide. The Optics Center together with the two I/UCRCs create an environment where the developed iCALD instrument will have a very significant impact due to its potential for commercialization of research results, along with enabling advanced training of MS and PhD students. The project aims to develop this unique iCALD instrument for the synthesis of three-dimensional photonic materials. This new class of materials is composed of three-dimensional structures with ultra-high aspect ratios, coated with ultra-thin conformal layers. The preparation of conformal coatings for such structures and surfaces using atomic layer deposition (ALD) techniques requires the precise control of numerous crucial ALD process parameters to ensure quality, thickness, and conformity of the ultra-thin films. It is therefore imperative to control the ALD process parameters using layer thickness and conformity information obtained from non-contact, in-situ, measurement techniques. The iCALD instrument will allow in-situ monitoring and control of the layer-by-layer deposition process by using an innovative in-situ Mueller matrix ellipsometer operating at infrared wavelengths. The iCALD instrument will enable the accurate control of ultra-thin coatings, with sub-nanometer accuracy, deposited onto structures with feature sizes on the order of several hundred nanometers. The iCALD instrument thereby will allow the fabrication of novel infrared and terahertz photonic materials with unprecedented accuracy. Based on these novel three-dimensional photonic materials, a vast array of active and passive devices and components operating in the infrared and terahertz spectral range can be made. In addition, the iCALD instrument will provide valuable insights about layer-by-layer deposition onto structures with arbitrary geometries, which have not been demonstrated experimentally yet. The controlled deposition and in-situ monitoring capabilities developed by this project will further expand crucial understanding of the atomic layer deposition process required for the fabrication of structures with ultra-high aspect ratios. Significant improvement of the optical material properties of three-dimensional photonic materials enabled by this instrument is anticipated. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.