Thermal and Plasma-Enhanced ALD of Ta and Ti Oxide Thin Films from Alkylamide Precursors

Abstract

We investigated the thermal and plasma-enhanced atomic layer deposition ͑PE-ALD͒ of tantalum and titanium oxides from representative alkylamide precursors, Ta͑NMe 2 ͒ 5 ͑pentakis͑dimethylamino͒Ta, PDMAT͒ and Ti͑NMe 2 ͒ 4 ͓tetrakis͑dimethylami-do͒Ti, TDMAT͔. ALD of Ta 2 O 5 by PDMAT with water or oxygen plasma produced pure Ta 2 O 5 films with good self-saturation growth characteristics. However, incomplete self-saturation was observed for TiO 2 ALD from TDMAT. The film properties including microstructure, chemical composition, and electrical properties are discussed focusing on the comparative studies between thermal and PE-ALD processes for both oxides. The results indicate that the PDMAT is a promising precursor for both thermal and PE-ALD of Ta 2 O 5 .Atomic layer deposition ͑ALD͒ is a gas-phase thin-film deposition method characterized by the alternate exposure of chemical species with self-limiting surface reactions, producing films with accurate thickness control, excellent conformality, and uniformity over large areas. 1 Due to these benefits, ALD is becoming one of the most promising thin-film deposition methods in the fabrication of nanoscale microelectronic devices, for which thickness controllability at atomic level and high conformality are required. 2 One of the critical issues for a successful ALD process is a proper selection of precursors and reactants. Among many metal precursors, alkylamide precursors have been widely used for ALD since they have suitable vapor pressure and Cl-and O-free ligands producing noncorrosive products and require relatively low growth temperatures.ALD of high-k dielectrics have been extensively studied using a variety of precursors and reactants. 3-6 As representative high k oxides, Ta 2 O 5 and TiO 2 have been studied for various applications including capacitor and gate dielectrics for the semiconductor industry and chemical sensors. 7,8 Although various precursors have been studied for ALD of Ta and Ti-based materials, 4,9-12 alkylamide precursors have been widely used for deposition of TaN 13 or TiN. 14 For example, plasma-enhanced ALD ͑PE-ALD͒ of TaN from ͑pentakis-͑dimethylamino͒Ta ͑PDMAT͒ and hydrogen plasma produced good quality TaN, showing very robust characteristics as a diffusion barrier for Cu interconnects. 13 However, the alkylamide precursors have rarely been used for deposition of Ta or Ti oxide, except in a couple of very recent reports. 15,16 This is quite contrary to other high-k materials such as ZrO 2 and HfO 2 , for which extensive studies have been reported by thermal and PE-ALD from various alkylamide precursors. 17-20 Especially, no comparative study between thermal and PE-ALD from alkylamide precursors for Ta and Ti oxides has been reported yet. In this study, we investigated the thermal and PE-ALD processes of both oxides using representative alkylamide precursors, Ta͑NMe 2 ͒ 5 ͓pentakis͑dimethylamino͒Ta, PDMAT͔ and Ti͑NMe 2 ͒ 4 ͓tetrakis͑dimethylamido͒Ti, TDMAT͔, which have the same dimethylamino ligands. The film properties including micros...

Low Temperature Plasma-Enhanced Atomic Layer Deposition of Metal Oxide Thin Films

“…Despite the similarity in the numbers of atoms being deposited per cycle between the ALD-I and FlexAL reactors, the film compo- 45,46 and our plasma-enhanced processes on ALD-I 27 and FlexAL. The TaCl 5 /H 2 O process is also shown for comparison.…”

Plasma-assisted atomic layer deposition of Ta2O5 from alkylamide precursor and remote O2 plasma

“…23 Moreover, it has a relatively high vapor pressure, and the absence of Cl-and O-containing ligands results in noncorrosive reaction products which are more compatible with processing of metals and organic materials and are considered more hardware friendly. The film growth of Ta 2 O 5 by plasma-assisted ALD using PDMAT and a remote O 2 plasma has recently been demonstrated by Maeng et al 24,25 A constant, relatively high growth rate of 1.2 Å / cycle was reported for deposition temperatures ranging from 150 to 250°C. The material properties obtained with plasma-assisted ALD were found to be better compared to thermal ALD grown Ta 2 O 5 from PDMAT by using H 2 O as oxidant.…”

Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

“…30,31,50,68,134,135,154,207,208,211,228,229,242,272,290,294,319 In most cases, these improved material properties are a result of the high reactivity provided by the plasma, which will be addressed in more detail below. However, more specifically, this improvement can often be attributed to kinetically driven, selective ALD surface reactions, for example, the abstraction of surface halogen atoms by H radicals and several ion-assisted surface reactions, as illustrated in Fig.…”

“…Consequently, this can lead to higher growth per cycle values. 31,32,40,58,60,134,154,187,207,208,229,233,254,259,261,274,294 Moreover, the plasma can be switched on and off very rapidly, which enables fast pulsing of the plasma reactant species 255,273,274,293,295 and reduced purge times (depending on the gas residence time in the reactor). 46,60 The latter is especially important for the ALD of metal oxides at low temperatures (room temperature up to 150 C), where purging of H 2 O, in the case of thermal ALD, requires excessively long purge times and, therefore, long cycle times.…”