Plasma-induced damage to dielectric materials

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

1066231 Shohet Plasma exposure, although often required for processing materials, has the potential to damage these materials so significantly that microfabricated devices will fail. This, project, conducted jointly between the University of Wisconsin-Madison and Stanford University, investigates the nature of charging and defect formation in dielectrics during plasma exposure and explores several methods to cure these potentially damaging effects. The goal of this project is to optimize the plasma conditions and processing methodologies in order to minimize the damaging effects. The plasma creates damage from the bombardment of photons, charged particles and free-radicals. In the past, it has not been possible to separate the plasma-induced damage effects from charged particle and photon bombardment during plasma processing. Furthermore, it has not been possible to measure the magnitude and distribution of charge outward from a dielectric-substrate and/or a dielectric-dielectric boundary, using conventional techniques such as surface-potential measurements. To measure the spatial charge distribution, a measurement technique using pulsed electroacoustic excitation of mechanical vibrations in dielectrics is implemented. This has the potential of fundamentally transforming how charge accumulation is measured in nanoscale dielectric films. Based on the optimization of the plasma conditions to minimize damage of the dielectrics, damage-curing methods will be directly linked into the processing steps. A controllable and functional processing/curing plasma reactor will be developed. Conventional post-processing curing will be replaced by an in-situ curing methodology that makes the processing more efficient and cost less. Unpatterned dielectric-semiconductor layers are evaluated for charge accumulation with surface potential and capacitance-voltage (C-V) characteristics, defect-state formation with vacuum ultraviolet (VUV) spectroscopy and electron-spin resonance (ESR), observe modifications of bonding structures with Fourier Transform Infra-Red (FTIR) spectroscopy, surface morphology with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), and physical changes with ellipsometry and nanoindentation. The proposal investigates the nature of the defects produced during processing and their effect on dielectric charging. Methods such as VUV/UV curing for low dielectric constant materials and annealing for high dielectric constant materials will be implemented during processing to minimize processing-induced damage. Intellectual Merit: The ability to combine, in a single cross-disciplinary project, the required expertise in plasma processing and damage diagnostics, optimization of the processing conditions, separation of the processing-induced damage effects, accurate measurements of charge distributions stored in electronic materials, and the development of a predictive model will result in a determination of the conditions that will permit design and fabrication of new dielectric materials that are damage-free and highly-resistant to processing damage. Broader Impacts: This project, being cross-disciplinary and multi-institutional, will result in a number of unique aspects. A connection between materials science, plasma science, chemistry and electrical engineering is a key feature. This impacts courses at the undergraduate and graduate levels, and allows key roles to be played in the project by undergrad and grad students from a variety of disciplines. Providing presentations to multiple student groups, the direct involvement of a local community college, along with high school science teachers and their students will extend the project well beyond its specific goals.