Abstract
We compare the performance of conventional DC magnetron sputter-deposited (DCMS) TiN diffusion barriers between Cu overlayers and Si(001) substrates with Ti0.84Ta0.16N barriers grown by hybrid DCMS/high-power impulse magnetron sputtering (HiPIMS) with substrate bias synchronized to the metal-rich portion of each pulse. DCMS power is applied to a Ti target, and HiPIMS applied to Ta. No external substrate heating is used in either the DCMS or hybrid DCMS/HiPIMS process in order to meet future industrial thermal-budget requirements. Barrier efficiency in inhibiting Cu diffusion into Si(001) while annealing for 1 hour at temperatures between 700 and 900 °C is investigated using scanning electron microscopy, X-ray diffraction, four-point-probe sheet resistance measurements, transmission electron microscopy, and energy-dispersive X-ray spectroscopy profiling. Ti0.84Ta0.16N barriers are shown to prevent large-scale Cu diffusion at temperatures up to 900 °C, while conventional TiN barriers fail at ≤700 °C. The improved performance of the Ti0.84Ta0.16N barrier is due to film densification resulting from HiPIMS pulsed irradiation of the growing film with synchronized Ta ions. The heavy ion bombardment dynamically enhances near-surface atomic mixing during barrier-layer deposition.
Highlights
Diffusion barriers are vital components in integrated circuits (ICs), designed to impede interdiffusion between Cu metallization and doped Si layers[1,2]
We present the results of a comparative investigation of the diffusion barrier performance of DCMS TiN films and hybrid DCMS/high-power impulse magnetron sputtering (HiPIMS) Ti0.84Ta0.16N layers, both deposited without external substrate heating on Si(001) substrates with a native oxide layer
The results are consistent with previous measurements showing that DCMS/HiPIMS TiTaN layers grown without substrate heating provide a smoother surface for Cu film growth than comparable DCMS TiN films[16]
Summary
Diffusion barriers are vital components in integrated circuits (ICs), designed to impede interdiffusion between Cu metallization and doped Si layers[1,2]. A recent innovation in low-temperature thin film synthesis by Greczynski et al is hybrid DC/high-power impulse magnetron sputtering (DCMS/HiPIMS), which has been shown to be capable of producing dense transition-metal nitride films without external substrate heating[16,17,18]. A certain degree of film densification can already be achieved by pulsed Ti+/Ti2+ metal-ion irradiation during Ti-DCMS/Ti-HiPIMS film deposition[19] This is not nearly as effective as higher-mass Ta+/Ta2+ bombardment in densifying the growing film[16]. We evaluate whether this new hybrid deposition process can provide the missing link between the low-temperature processing needs of integrated circuit manufacturers and the requirement of a dense diffusion barrier microstructure. Cu diffusion in barrier layers is investigated using cross-sectional transmission electron microscopy (XTEM) combined with energy-dispersive X-ray spectroscopy (EDX)
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