Spectroscopic Analysis
Non-destructive inspection techniques utilize the inelastic scattering of monochromatic light to measure localized stress variations in semiconductor structures at the sub-micrometer scale. Micro raman strain mapping provides a visual representation of the mechanical tension across a transistor or a micro-bridge. The technique relies on a laser beam focused through a microscope to excite the atomic vibrations of the material.
By analyzing the shift in the frequency of the scattered light, engineers can calculate the exact amount of lattice deformation. It is an essential tool for identifying points of potential failure in complex integrated circuits.
Phonon Shift
Changes in the distance between atoms alter the energy required to excite a crystal vibration. In micro raman strain mapping, these shifts in phonon energy are detected as a change in the wavenumber of the Raman peak. Tensile stress moves the peak to a lower frequency while compressive stress moves it higher.
Spatial Resolution
Precision in the horizontal plane is determined by the wavelength of the laser and the quality of the optics. Modern micro raman strain mapping systems can resolve features smaller than five hundred nanometers. This allows for the inspection of individual gates in a modern processor.
Laser Interference
Limits on the accuracy of the measurement are often caused by the heating effect of the probe beam itself. If the laser power is too high, micro raman strain mapping will induce thermal expansion that masks the original strain. Technicians must calibrate the power levels for every new material type.
