The key issue, they found, was depth of penetration of the two techniques. Electron beams sample only the top 20 or 30 nanometers of the material, Cook explained, while the laser-generated photons used in CRM might penetrate as deep as a micrometer or more. The NIST researchers found that by varying the wavelength of the Raman photons and positioning the focus of the microscope they could select the depth of the features measured by the Raman techniqueand when the CRM was tuned for the topmost layers of the crystal, the results were in close agreement with EBSD measurements.
The NIST instruments also demonstrate the potential for using the two techniques in combination to make reliable, nanoscale measurements of stress in silicon, which enables device developers to optimize materials and processes. EBSD, although confined to near-surface stress, can make measurements with resolutions as small as 10 nanometers. CRM resolution is about 10 times coarser, but it can return depth profiles of stress.
|Contact: Michael Baum|
National Institute of Standards and Technology (NIST)