On The Effects Of Interface Roughness Upon The Characteristics And Uniformity Of Thin Dielectric Films For Advanced Nano-device Applications

With the rapid development of modern CMOS integrated circuits in to decanometer range,the conventional dielectrics such as SiO2 can no longer meet the critical requirements.The conventional dielectrics has now been replaced by a physically thicker layer of a higher dielectric constant(high-k)materials.However,high-k/Siusually has a poor interface.When the feature size of the film and device continues to reduce,the effects of surface roughness on the characteristics of the film,including the capacitance,barrier height,leakage mechanism and breakdown voltage,have become more significant.In this paper,we took Al2O3 thin film,which are important to analog and RF circuit applications also,fabricated using atomic layer deposition(ALD)technology as an example,to investigate the effects of bottom electrode surface roughness on the device characteristic uniformities.This work reveals some important theoretical grounds and technological issues on the the non-ideal surface effects of high dielectric constant materials and then the variabilities of nanoelectronic devices.This work focus on the effects of surface morphology of both high-k dielctrics and and metal electrodes on the electrical characteristics of metal-insulator-metal(MIM)capacitors.The bottom TiN electrodes were deposited by using DC magnetron sputtering in a vacuum chamber,and their structure were studied by XRD and AFM.Then Al2O3dielectric film was synthesized utilizing ALD process.The cross-section and morphologies of the films were further characterized with STEM and AFM.We found that this film has good coverage and also has a "surface smoothing effect" on the rough TiN bottom electrode.Top TiN layer wasdeposited with the same process as the bottom ones.MIM capacitors were prepared by patterning these films stacks.Asymmetric current-voltage characterisctics under different temperatureswere measuredand the current conduction mechanisms and then the barrier height variation due to the surface roughness were studied in detail.In particular,results showed that the rougher the bottom electrode surface,the greater the leakage current and the worse the homogeneity.For the Al2O3dielectric film deposition,we found that the film deposited at 200? has smaller surface roughness in general.We also analysed the effects of thermal annealing on high-k dielectric filmsand then the MIM capacitors.We found that the annealing the leakage current can be reduced significantly with proper thermal annealing.Amongst the investigated temperature range,the best annealing temperature is around 400? which is mainly due to the change of the surface morphorlogies of the both interfaces.