The effect of nitrogen doping on the elastic modulus and hardness of 3C-SiC thin films deposited using methyltrichlorosilane

Abstract

For thin-film sensor applications, the mechanical properties, such as the hardness and elastic modulus, of the sensing material are important in addition to its electrical properties. The mechanical properties of the material need to be known at the design stage of the sensor because these properties are influenced by doping. The effect of in situ nitrogen doping on the mechanical properties of 3C-SiC (111) thin films are presented in this paper. These films are deposited at a pressure of 2.5 mbar and a temperature of 1040 °C on thermally oxidized Si (100) substrates from methyltrichlorosilane and ammonia using a resistively heated vertical hot-wall low-pressure chemical vapour deposition reactor. The effect of in situ nitrogen (0, 9 and 17 atomic per cent of nitrogen) doping on the mechanical properties of the material is investigated using nanoindentation. The x-ray diffraction patterns of 3C-SiC thin films show a decrease in the crystallanity and the intensity of the peak (111), with an increase in the dopant concentration from 0 to 17 atomic percent (%). AFM investigations show a decrease in the roughness and an increase in grain size of the 3C-SiC thin films with an increase in the nitrogen concentration. Nanoindentation measurements revealed that the elastic modulus and hardness of nitrogen doped 3C-SiC thin films decreased from 353 ± 5 to 178 ± 3 GPa and from 35 ± 1.4 to 22 ± 0.6 GPa, respectively, with an increase in the nitrogen doping concentration. This study shows that the mechanical properties of films strongly depend on the grain size, which is influenced by the effects of nitrogen doping. The elastic modulus and hardness are found to be 178 GPa and 22 GPa, respectively, for 3C-SiC thin films doped with 17 atomic % of nitrogen concentration, making it suitable as a sensing material for sensor applications.