Chemical interaction of B4C diffusion barriers with Mo/Si layered nanostructures

B4C barrier layers are added to Mo/Si multilayer structures for EUV optics to enhance thermal stability. However, detailed knowledge about the chemical interaction between B4C and Mo or Si is lacking. The chemical processes during annealing up to 600 °C of a Mo/B4C/Si layered structure were investigated with in-situ hard X-ray XPS and ex-situ depth profiling soft X-ray XPS. A two-stage chemically steered diffusion process was identified. If the diffusion barrier consists of C or B4C, relatively stable intermediate compounds form at the initial stage. The results show that the diffusion barrier functionality of the B4C interlayers is caused by the stability of these compounds.