Diffusion barrier property of sputtered molybdenum nitride films for DRAM copper metallization was investigated as a function of annealing temperature. Molybdenum nitride thin films on silicon remained stable upon annealing 650°C-30min, but h-MoSi2 and t-MoSi2 were formed after the heat treatment at 700°C and Mo5Si3 phase was formed at 850°C. Increasing the annealing temperature decreased the stress of the γ-Mo2N/Si film down to about 0.8×1010dyne/cm2 at 800°C due to the reduction of the intrinsic stress component. Copper films on silicon substrates separated by thin layers of molybdenum nitride remained stable during the heat treatment at 600°C, but they began to fail as a diffusion barrier after the heat treatment at 650°C, when molybdenum silicides and copper silicide were thought to be formed. On heating, Cu/γ-Mo2N/Si films were affected by thermal stress as due to the thermal expansion coefficient between copper and molybdenum nitride thin films. Furthermore, interlayer interactions between copper and silicon increased with increasing the annealing temperature. The interlayer reactions were investigated by Rutherford backscattering spectrometry, X-ray photoelectron spectrscopy and Nomarski microscopy.
The effect of laser thermal annealing ͑LTA͒ on ␦-doped B has been investigated for the applications of super-steep-retrograde ͑SSR͒ 70 nm n-type metal-oxide-semiconductor field-effect transistors using undoped selective silicon epitaxy. Shallow (р50 Å) melting by LTA was found to suppress the B loss, causing an anomalous lowering and fluctuation of threshold voltage (V t ), upon epitaxial channel growth and rapid thermal annealing ͑RTA͒. Under the laser fluence of 0.42 J/cm 2 , the B profile was also observed to freeze without further diffusion upon RTA at 900°C for 20 s.Significant B loss observed in conventional ␦-doped SSR devices stemmed from the hydrogen ambient at 800°C required for selective silicon epitaxy as well as the rapid B outdiffusion behavior. The laser-induced surface melting decreased the outdiffusion rate by increasing the portion of substitutional B, and also led to a surface roughening which made the B loss from the silicon surface difficult. As a result of LTA, much lower V t fluctuation with reasonable V t was obtained along with improved short channel characteristics.
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Thermal stability, microstructure and electrical property of molybdenum nitride film were studied for application of ULSI's DRAM capacitor electrode and copper diffusion barrier. Phase transformation from Mo to Y-Mo, 2 N was observed at 20% Nz/(Ar+N 2 ) flow ratio and Y-Mo 2 N and 8-MoN phases coexisted at 50% N 2 flow ratio. f-Mo 2 N film was found to crystallize at 4001C. Amorphous -t-Mo 2 N deposited at 3001C remained stable upon 7501C heat treatment. Breakdown strengths of f -Mo 2 N/Ta 2 O5/Si MOS capacitor before and after 8501C annealing were 2.4 MV/cm and 1.85 MV/cm at 1x10 6 A/cm 2 , respectively. After 8501C annealing, dielectric constant of Ta 2 O5 film decreased to 19.
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