Colorado State University

Fisher group research centers on using analytical and materials chemistry methods to understand underlying mechanisms of chemical vapor deposition (CVD) and plasma-enhanced CVD (PECVD) processes. Plasmas (partially ionized gases comprising ions, electrons, and neutral species) are used extensively for etching and depositing many materials, including silicon, III-V semiconductors, metal oxides, nitrides, and polymers and for surface modification to improve adhesion and biocompatability. Our research bridges the gap between chemistry and technology by measuring surface reactivities of radicals during plasma processing; creating dynamic photochemical experiments to provide energetics on plasma species; and studying plasma systems and plasma-produced materials of industrial and scientific importance. Current areas of emphasis include plasma etching and deposition of silicon-based materials, plasma polymerization and processing of polymers, and synthesis of nanostructured materials. In all areas, we combine studies of “macroscopic” materials properties with molecular-level experiments at the gas-surface interface. IRIS. To study plasma species on a molecular level, we have developed a novel laser-based technique, Imaging of Radicals Interacting at Surfaces (IRIS), designed to explore the gas-surface interface. IRIS combines spatially resolved laser-induced fluorescence (LIF) with plasma molecular beam techniques to measure the steady-state surface reactivity of radicals during plasma processing. Spatially resolved signals are collected with a chargecoupled device (CCD) camera, which is also used for velocity distribution experiments. Virtually all plasma systems can be studied with IRIS. Examples of recent studies include CF and CF₂ radicals in fluorocarbon plasmas for Si etching and fluorocarbon polymer deposition; SiH radicals in SiH₄ and Si₂H₆ plasmas for deposition of solar cell materials; NH₂ radicals in NH₃ plasmas; and OH radicals in alkoxysilane/O₂ plasmas for SiO₂ deposition. The versatility of IRIS is increased by mass spectrometric capabilities and additional optical diagnostics, providing information on plasma species and molecules scattering off surfaces. We also have a new resonantly enhanced multiphoton ionization (REMPI)-based IRIS apparatus. Plasma Etching and Deposition. We are fundamentally interested in new plasma technologies for synthesizing novel materials. Our work here focuses on pulsed plasma polymerization to create films with particular chemical functionalities; plasma modification of membranes for improved wettability; deposition/ etching of Si-based films for semiconductor devices; and materials synthesis of nanostructured materials for secondary batteries and thermoelectric devices. Analytical techniques employed include optical emission spectroscopy (OES), mass spectrometry, Raman spectroscopy, FTIR, X-ray photoelectron spectroscopy (XPS), contact angle, X-ray powder diffractometry (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and spectroscopic ellipsometry.