Effect of nitrogen and oxygen annealing on the morphology and hardness behavior of copper thin films

The morphology and hardness behavior of the 0.25-μm thick, chemical vapor-deposited (CVD) copper on SiO2 on top of Si substrates annealed under oxygen and nitrogen atmosphere were evaluated by atomic force microscopy (AFM) and ultra micro-indentation technique. The surface morphology and roughness of post-annealing copper films were likewise examined by AFM. Results showed that the copper film surface was rougher after oxygen treatment compared to the one after nitrogen treatment. The roughness (standard deviation) values of oxygen- and nitrogen-annealed copper films were 10.4±1.9 and 4.1±0.2 nm, respectively. Surface oxidation of copper film after oxygen annealing was also observed and identified through an elemental analysis technique. Indentation depth was continuously and automatically measured along with the pre-set increase in load on the surfaces. Dynamic hardness (DH) of copper films after annealing was calculated and compared using dynamic ultra micro-hardness tester. It was observed that copper films annealed under oxygen had relatively lower DH vs. those that were nitrogen-annealed, and DH continuously decreased with increasing load. Furthermore, the oxygen-annealed copper film, after being kept in dessicator for 2 days, exhibited a slightly higher degree of plastic deformation compared to that of nitrogen-annealed film.