Characterization of Stress in GaN-on-Sapphire Microelectromechanical Systems (MEMS) Structures Using Micro-Raman Spectroscopy
Abstract
Micro-Raman (muRaman) spectroscopy is an efficient, non-destructive technique widely used to determine the quality of semiconductor materials and microelectromechanical systems. This work characterizes the stress distribution in wurtzite gallium nitride grown on c-plane sapphire substrates by molecular beam epitaxy. This wide bandgap semiconductor material is being considered by the Air Force Research Laboratory for the fabrication of shock-hardened MEMS accelerometers. muRaman spectroscopy is particularly useful for stress characterization because of its ability to measure the spectral shifts in Raman peaks in a material, and correlate those shifts to stress and strain. The spectral peak shift as a function of stress, known as the phonon deformation potential, is determined by applying strain to the material using a four-point strain fixture while simultaneously monitoring the applied strain and recording the Raman spectrum. The deformation potentials are then used to determine stress distribution; the spectral positions of the E2 Raman mode (nu = 569 cm-1) in GaN and A1g Raman mode (nu = 418 cm-1) in sapphire are recorded at each spatial position in a raster map. The muRaman spectroscopy is performed using a Renishaw InVia Raman spectrometer with argon ion (lamba = 514.5 nm, hnu = 2.41eV ) and helium-neon (lamba = 633 nm, hnu = 1.96 eV) excitation sources, and the data is collected across the samples with 5- to 10-micrometer spatial resolution. Inherent stress and evidence of significant damage in the GaN layer due to MEMS processing is discussed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2006
- Accession Number
- ADA450003
Entities
People
- Francisco E. Parada
Organizations
- Air Force Institute of Technology