Growth and Characterization of Al2O3:HfO2 Nanolaminate Films Deposited by Atomic Layer Deposition (ALD)

As gate dielectrics in logic and memory continue to scale, higher dielectric
constant materials, such as Al2O3, HfO2, ZrO2 and others are under investigation to
replace silicon dioxide. Nanolaminates of these high-K films are easily grown by Atomic Layer Deposition (ALD) and may offer potential benefits by combining the best
properties of each metal oxide into one composite film. The physical and electrical
properties of Al2O3: HfO2 nanolaminate films, grown by ALD, were investigated for
compositional ranges from 4%-96% HfO2 in Al2O3. The ALD deposition technique
results in good within wafer electrical thickness uniformity (1-2%, 1 sigma). The
deposition kinetics of the nanolaminates shows good nucleation on SiO 2 surfaces and
deposition rates intermediary between Al2O3 and HfO2. The microstructure the as-deposited films, as determined by TEM cross-section, is observed to be amorphous
(depending on Hf content) with smooth interfaces to the bottom interfacial layer and top
polysilicon. Compositional analysis, as determined by Medium-energy ion scattering
(MEIS)and spectral ellipsometry, shows that the ratio of Al2O3 to HfO2 can be tuned
effectively by adjusting the pulse ratio of the two films in the nanolaminate growth
process. Poly- gate capacitor results show that the nanolaminates exhibit 4-7 orders of
magnitude lower leakage current than SiO 2 of the same electrical thickness, depending on the film composition. C-V measurements indicate that the flatband of these films can shift as much as 300-450 mV from thermal oxide. Hysterisis is present and charge trapping in the nanolaminates is more severe than in the individual metal oxide films.