In SituReaction Mechanism Studies on the New^tBuN=M(NEt₂)₃-Water and^tBuN=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 D 2 O and ozone processes at 250°C for t BuN=Nb(NEt 2 ) 3 and t BuN=Ta(NEt 2 ) 3 . In the D 2 O processes, the ligand exchange reaction is demonstrated by the formation of D 2 N t Bu and DNEt 2 as byproduct. For t BuN=Nb(NEt 2 ) 3 , one out of three -NEt 2 ligands is exchanged during the precursor pulse, whereas for t BuN=Ta(NEt 2 ) 3 , it is 1.7 -NEt 2 ligands and 0.3 =N t Bu ligand that are exchanged during the t BuN=Ta(NEt 2 ) 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 t BuN=Nb(NEt 2 ) 3 and an exchange of at least two ligands for t BuN=Ta(NEt 2 ) 3 . QMS indicates a typical ozone combustion byproduct, such as CO 2 (m/z = 44), CO (m/z = 28), H 2 O (m/ z = 18), and NO (m/z = 30) or N 2 O (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. KEYWORDS: atomic layer deposition (ALD), mass spectrometry, quartz crystal microbalance (QCM), niobium oxide, tantalum oxide ■ INTRODUCTIONAtomic layer deposition (ALD) is a unique chemical gas phase method for depositing thin films. 1−3 In ALD the precursors are alternately pulsed into the reactor and separated by inert carrier gas purging. The precursors saturate the surface one at a time, forming at most monolayers that induce a self-limiting growth mechanism. Consequently, the thickness of the growing film is accurately controlled, and the films exhibit excellent uniformity and conformality. Understanding the mechanisms of reactions occurring at each step of an ALD deposition can help to control and optimize the growth processes and accelerate the development of new ALD processes and precursors. Most commonly, ex situ analyses are performed: the films are first grown and their characteristics are examined separately. However, the development of in situ measurements has become an important approach for mechanistic studies in the past decade. Several techniques such as FT-IR, ellipsometry, and in our case quartz crystal microbalance (QCM) and quadrupole mass spectrometry (QMS) 4−8 are used for in situ investigations. The QCM indicates the mass changes of the growing film, while the QMS follows the composition of the gas phase inside the reaction chamber. The identification of gaseous byproduct and the recorded mass changes during the pulses of the different precursors provide direct information on the reaction mechanism.Nb 2 O 5 and Ta 2 O 5 are high-permittivity materials with potential thin film applications in DRAM devices, 9,10 ca...

Ozone‐Based Atomic Layer Deposition of Gd2O3 from Tris(isopropyl‐cyclopentadienyl)gadolinium: Growth Characteristics and Surface Chemistry

“…However, such a combustion reaction mechanism has been reported for a number of O 3 ‐based ALD processes . Many of these ALD processes have been reported to lead to hydroxyl‐terminated surfaces, in agreement with the above observations. Moreover, it has been shown that the hygroscopicity of Gd 2 O 3 will lead to an additional parasitic non‐uniform CVD component for the H 2 O‐based Gd 2 O 3 process due to sorbed H 2 O .…”

“…The absence of the parasitic CVD reaction (and the much improved WiWNU) also suggests the suppression of non‐uniform sorption reactions with H 2 O generated during combustion. While the impact of the presence of NO x as an admixture in O 3 in the gas phase on the surface chemistry of metal oxides has not been studied in detail before, it is instructive to compare the above results to reports on O 3 ‐based ALD using N‐containing precursors, such as amides or amidinates . In such processes, NO x is formed as a reaction product of the precursor combustion during the O 3 exposure .…”

“…The surface chemistry of O 3 ‐based processes has been studied in less detail than for H 2 O–based processes . Exposure to O 3 has typically been found to lead to combustion reactions rather than to ligand release.…”

Comparison of thermal and plasma-enhanced atomic layer deposition of niobium oxide thin films

“…al work was reported by Tomczak et. al 24 on the reaction mechanism using in-situ analysis techniques for the same precursor t BuN=Nb(NEt2)3 with D2O and O3 as co-reactants. In case of the D2O process, it was observed that -NEt2 ligands reacted with the surface -OH reactive sites during the first half cycle, while the remaining ligands were exchanged during the second half cycle.…”

“…10,11 Nb2O5 has been synthesized adopting various techniques, such as sol-gel, 12 sputtering, 13 e-beam evaporation, 14 pyrolysis, [15][16][17] chemical vapour deposition (CVD), 18 pulsed laser deposition (PLD), 6 and atomic layer deposition (ALD). 3,[19][20][21][22][23][24][25][26][27][28][29] Of aforesaid techniques, ALD has the advantage of achieving precise thickness control, conformality, and uniformity over a large area, which are valuable assets for most of the abovementioned applications. 30 ALD is a cyclic process where in the first half-cycle the precursor is dosed into the reaction chamber and followed by a purge step, and in the second half-cycle the co-reactant is dosed which is followed by a second purging step.…”