This study systematically investigates the effect of B4C barrier layers insertion in Ti/Cr multilayer structures − specifically how the order of their deposition affects thermal stability of the system. The analysis, carried out using X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR), and X-ray diffraction (XRD), compares samples before and after annealing at various temperatures. Intermixing of the Cr and Ti layers results in the formation of titanium chromide. The insertion of a thin B4C layer at any interface only partially prevents the formation of a titanium chromide. Annealing of the system already at 200 °C leads to further layer intermixing and promotes diffusion of oxygen from natural surface oxides deeper into the structure. The introduction of B4C enhances thermal stability, effectively preventing oxygen diffusion into the multilayer during annealing up to 500 °C. However, annealing at 700 °C causes complete structural degradation, characterized by intermixing of all layers with each other and with the Si substrate, resulting in the formation of silicides. The layers in the structure were found to be X-ray amorphous up to 500 °C regardless of the barrier layer deposition sequence. All the fundings are crucial for subsequent interface engineering of this system aimed at increasing its reflectivity.