Effect of Ti buffer layer on stress and time evolution characteristics of boron carbide thin films

This work investigates the effects of a titanium (Ti) buffer layer on the residual stress of boron carbide (B4C) thin films with different structures (monolayer, bilayer, and multilayer). Film thickness, microstructure, and residual stress of the samples are characterized by x-ray reflectivity, x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy (XPS), and a wafer curvature measurement system. The results show that the B4C monolayer film is amorphous and exhibited relatively high intrinsic compressive stress. An optimized Ti/B4C multilayer structure effectively reduces residual stress by more than 46% compared to the monolayer and bilayer structures. Time-dependent stress evolution analysis suggests that the residual stress of B4C-based thin films gradually decreases after deposition and stabilized after 168 h. XPS results indicate negligible changes in chemical bonding, suggesting that the stress variation is primarily related to structural factors rather than chemical effects. This work provides a reliable experimental basis for the stress control of B4C-based thin films, supporting their implementation in extreme ultraviolet and x-ray optical systems.