In SituReaction Mechanism Studies on the NewtBuN=M(NEt2)3-Water andtBuN=M(NEt2)3- Ozone (M = Nb,Ta) Atomic Layer Deposition Processes

Abstract

In this work, quartz crystal microbalance (QCM) and quadrupole mass spectrometry (QMS) have been used for in situ investigations of the D2O and ozone processes at 250 °C for tBuN=Nb(NEt2)3 and tBuN=Ta(NEt2)3. In the D2O processes, the ligand exchange reaction is demonstrated by the formation of D2NtBu and DNEt2 as byproduct. For tBuN=Nb(NEt2)3, one out of three -NEt2 ligands is exchanged during the precursor pulse, whereas for tBuN=Ta(NEt2)3, it is 1.7 -NEt2 ligands and 0.3 =NtBu ligand that are exchanged during the tBuN=Ta(NEt2)3 pulse. This difference in the reaction mechanism of the two structurally similar precursors can be explained by the differences in their bond polarities as shown by our quantum chemical calculations. Regarding the ozone processes, QCM results point to a molecular adsorption of tBuN=Nb(NEt2)3 and an exchange of at least two ligands for tBuN=Ta(NEt2)3. QMS indicates a typical ozone combustion byproduct, such as CO2 (m/z = 44), CO (m/z = 28), H2O (m/z = 18), and NO (m/z = 30) or N2O (m/z = 44, 30). A major fragment of both types of ligands (m/z = 58) is also observed. Precise quantification of these byproduct is rendered impossible due to overlapping of different species with the same m/z value. However, careful examination of the data reveals general information on the different contributions to the signal.