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

Abstract

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 WNx) 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 WNxCy by TBH and WCx by TEA. On the other hand, the experimental findings also confirm the W film deposition with H2 plasma and DEAB, between 200 and 300 degrees C. However, the best quality as-grown W-films (polycrystalline with a resistivity of -395 mu S2-cm) were obtained only with H2 plasma as a reactant, which shows the largest negative reaction energy (Delta E) 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.