One of the earliest examples of the use of CrossCourt and HR EBSD (High Resolution Electron Backscatter Diffraction) was measuring strain in semiconductor samples. In these cases the devices were strained over a very small range, about 1 micron across.
Crosscourt uses cross-correlation techniques to compare crystallographic zone axes and Kikuchi-band positions of neighboring EBSD patterns emanating from the specimen surface. If the crystal becomes distorted because of residual strain then the EBSD pattern will become distorted: one can be directly related to the other. To measure this CrossCourt compares two patterns. The first is collected from a unstrained region of the specimen -in this case around 3 microns from the strained area, the second from the strained region. The software then selects small regions of the pattern (ROI’s). Each region is compared, one pattern to the next and the movement of the pattern measured. These movements are used to determine all of the components of the strain tensor.
A micro hardness indent in silicon was made and the raw data collected using an EDAX-TSL OIM system equipped with a DigiView III EBSD detector. The data was exported to CrossCourt for analysis. The results for strain about the indent are shown below and can with confidence be stated as absolute values within 2 parts in 10000.
Normal strains, shear strains shear stress and rotations as examples of absolute strain measurement together with one stress map, that for E12.
The figures above show maps of the normal strain components, shear strains and rotations as measured using the Cross Correlation (XC) EBSD procedure described for CrossCourt. The x and y axes define the lateral dimensions scanned during the collection of EBSD patterns and the vertical (right) axis shows the strain or rotation values. Strain is a dimensionless parameter. The rotations are in radians. The vertical axis in the stress map is in Giga Pascals.
Raw data courtesy of Ben Britton and Angus Wilkinson of Oxford University