Development and application of instrumental methods for strain analysis ofsemiconductor layers and devices

Strain effects on semiconductor layers were studied by means of optical spe ctroscopic techniques with a device developed especially for the study of l ayered structures and microstructures. Raman, modulated photoreflectance an d reflectance anisotropy spectroscopy (RAS) were applied. Measurements were performed on elemental semiconductors (Si), semiconductor alloys (Si-Ge) a nd III-V semiconductor compounds (GaAs). By application of RAS, strains low er than 10(-4) could be resolved, which is at least one order of magnitude lower than those observable with Raman and modulated reflectance techniques . The RAS spectra of layers strained along either the [010] or [011] direct ion showed a derivative-like structure at El-gap energies, which increased linearly and very quickly with increasing strain. The dependence of this sp ectral feature on applied strain was used to evaluate strain-dependent effe cts. This behaviour strongly suggests that RAS can be applied for the optic al characterisation of strain in semiconductor microstructures and devices, with a higher efficiency and accuracy than that achieved by previously est ablished optical methods such as Raman and modulation spectroscopy. In addi tion, the compactness and ease of operation of the instrumentation of RAS p rovides considerable potential for in situ monitoring/control of semiconduc tor fabrication conditions.