Abstract
Ultra-thin tungsten films were prepared using hotwire assisted atomic layer deposition. The film thickness ranged from 2.5 to 10 nm, as determined by spectroscopic ellipsometry and verified by scanning electron microscopy. The films were implemented in conventional Van der Pauw and circular transmission line method (CTLM) test structures, to explore the effect of film thickness on the sheet and contact resistance, temperature coefficient of resistance (TCR), and external electric field applied. All films exhibited linear current-voltage characteristics. The sheet resistance was shown to considerably vary across the wafer, due to the film thickness non-uniformity. The TCR values changed from positive to negative with decreasing the film thickness. A field-induced modulation of the sheet resistance up to $\sim 4.6\cdot 10^{-4}\,\,\text{V}^{-1}$ was obtained for a 2.5 nm thick film, larger than that generally observed for metals.
Highlights
The continuous downscaling of electronic devices poses an increasing demand for the use of ultra-thin films in a variety of applications such as microprocessors, image sensors, memories, and physical unclonable-function devices [1,2]
The accuracy of the model is determined by the mean square error (MSE), which mathematically quantifies the difference between the experimental and model-generated data
The magnitude of the temperature coefficient of resistance (TCR) is determined by TCR = 1/Rsh,T =0 ◦C × (∆Rsh/∆T ), where ∆Rsh is the change in Rsh due to a change in temperature ∆T and Rsh,T =0 ◦C is the Rsh measured at T = 0 ◦C
Summary
The continuous downscaling of electronic devices poses an increasing demand for the use of ultra-thin films in a variety of applications such as microprocessors, image sensors, memories, and physical unclonable-function devices [1,2] Both isolating and metallic layers are widely requested. ALD is known to provide high layer uniformity and conformality, together with excellent step-coverage and precise layerthickness control, due to its attribute of sequential, selflimiting surface reactions [11]. This makes ALD the method of choice for many applications. X-ray diffraction (XRD) analysis of the crystal structures of HWALD W films is provided
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