Mechanical and tribological properties of thin films under changes of temperature conditions

Abstract

Direct measurements of tribological and mechanical properties of thin films are important to predict the life-time of micro/nano-devices using thin films as a protective layer in order to reduce the stiction, adhesion and wear. This paper presents the analysis of mechanical and tribological properties of thin films at different temperatures using atomic force microscope (AFM) and nanoindentation. A thermal stage is used to control the temperature of investigated samples in the range of 20°C to 100°C. Thin films as SiO2, polysilicon and dielectric films as Si3N4 are deposited on different substrates (silicon and silicon dioxide) and analyzed.Nanoindentation is performed using a Berkovich indenter with diamond tip in order to analyze the variation of modulus of elasticity and hardness for different temperatures. Under the same indentation load, the indentation depth increases as temperature increases and the hardness and modulus of elasticity decrease, respectively. The thickness influence of these thin films on hardness and modulus of elasticity is also observed.The aim of tribological investigations is to estimate the variation of the friction force for different temperatures using the AFM lateral mode. The adhesion force between the AFM tip and investigated thin films is measured using the spectroscopy in point of AFM. Decreasing of the adhesion force as temperature increases is experimentally observed.Measuring mechanical properties like hardness and modulus of elasticity to evaluate their behavior at different temperatures can help designers to improve the reliability of the materials and components and to understand the strengthening and deformation mechanisms at small scales. The visco-elastic effect makes friction rate and temperature dependent. The friction forces increase as a function of temperature based on the change of the material strength. As the temperature increases, the material properties such as modulus of elasticity and hardness slowly decreased based on the material thermal relaxation.