Atomic layer deposition of tungsten and tungsten-based compounds using WCl5 and various reactants selected by density functional theory

Highlights: • DFT calculation for ALD reactions between WCl₅ and different reducing agents. • ALD processes using WCl₅ and H₂ plasma, DEAB, TEA, TBH, and NH₃. • The formations of ALD-W, WN_x, WN_xC_y, and WC_x with reducing agents. • High quality ALD-W films using WCl₅ and H₂ plasma. Atomic layer deposition (ALD) of metals and metal nitrides consist a major portion of the advanced thin film deposition technology owing to their wide applications in the field of the semiconductor industry. In this regard, the ALD of tungsten (W) is one of the vital processes which is mostly studied using WF₆ precursor. However, the presence of corrosive fluorine in WF₆ restricts its applications due to severe disadvantages like F-contamination and etching of the deposited films and/or the underlying substrate. Therefore, developing F-free W (FFW) precursor to deposit W (and other W-based compounds like WN_x) is of significant importance. The current article investigates several possible routes that can give rise to the successful growth of ALD-W or W-based thin films using WCl₅ as an FFW precursor. Density functional theory (DFT) simulation was carried out to check the feasibility of the reactions between a reactant and tungsten chloride as well as to predict the composition of the deposited film. The exothermic reactions for ALD of W metal were realized with H, diethylamine borane (DEAB), and dimethylamine borane (DMAB), whereas it was endothermic for H₂, triethylaluminum (TEA), trimethylaluminum (TMA), tert-butyl hydrazine (TBH), and NH₃. The detailed reaction mechanisms for predicting the growth of tungsten or tungsten compounds were simulated and are helpful to explain the growth of WN_xC_y by TBH and WC_x by TEA. On the other hand, the experimental findings also confirm the W film deposition with H₂ plasma and DEAB, between 200 and 300 °C. However, the best quality as-grown W-films (polycrystalline with a resistivity of ~395 µΩ-cm) were obtained only with H₂ plasma as a reactant, which shows the largest negative reaction energy (ΔE) in DFT calculation. Further, the Cl content of much below 1 atomic% in the as-grown films deposited with H₂ plasma was evident. Additionally, the experimental findings also confirmed the deposition of crystalline-W₂N when NH₃ was used as a reactant.