Metallization-Induced Oxygen Deficiency of γ-Al₂O₃ Layers

Abstract

γ-Al 2 O 3 layers fabricated by annealing-induced crystallization of ALDgrown amorphous (a-) Al 2 O 3 films were studied using near-edge-X-ray absorption fine structure, soft X-ray reflection spectroscopy, photoelectron spectroscopy, internal photoemission spectroscopy, and X-ray diffraction method. Despite the crystallization at high (1100 °C) temperature expected to deliver a thermodynamically stable Al 2 O 3 phase, the development of oxygen deficiency upon roomtemperature deposition of TiN and TaN electrodes was established. We ascribe this effect to oxygen scavenging by chemically active metals such as Ti and Ta during electrode sputtering. As a result, a high density of gap states is generated in the insulating oxide near the metal surface, which may impair insulating properties of γ-Al 2 O 3 .

Re-distribution of oxygen at the interface between γ-Al2O3 and TiN

“…However, retention properties of the Al 2 O 3 -insulated memory cells appear to critically depend on the oxygen deficiency developed during post-deposition anneal mandating application of an oxygen-containing ambient 25 . As we have established earlier 8 , γ-Al 2 O 3 layers obtained by high-temperature crystallization anneal may develop oxygen deficiency upon the later processing steps carried out at significantly lower temperature. The near-edge X-ray absorption fine structure (NEXAFS) experiments reveal that even in the initially stoichiometric γ-Al 2 O 3 the room-temperature plasma-enhanced deposition of metal electrodes (TiN or TaN) leads to formation of O deficient region in the oxide 8 and gap states, which may cause electron leakage current.…”

“…5b). As follows from refs 8, 50, 51. this feature β is associated with oxygen deficiency of the γ-Al 2 O 3 layer, promoted by oxygen scavenging by active metal such as Ti during electrode sputtering.…”

“…2, a complex multiphase composition of the 10 nm TiN electrode related to its oxidation can be clarified. While the oxidation of TiN in air is well known 29, 31 to result in few nm thick oxide and oxynitride layers, a possible oxygen scavenging from underlying oxide layer (γ-Al 2 O 3 ) was first revealed in our previous work 8 . To evaluate the actual depth distribution of chemical states of titanium atoms and to determine the thicknesses of individual layers, which constitute the “real” TiN electrode, we used the approach described in details in our previous reports 40, 42 .…”

“…Furthermore, in the case high-κ oxide insulators used in modern ICc such as HfO 2 , generation of oxygen imbalance at the interface by introducing metal scavenging layer is shown to result in nearly 1 eV metal/oxide barrier variations 6, 7 . The O loss from the thermodynamically-stable γ-Al 2 O 3 phase has recently been reported to be induced by a simple metallization (TiN) process 8 . While the mentioned observations leave no doubt that oxygen re-distribution at the metal/oxide interface represents the major driving force of interface barrier and EWF variation, atomic picture of this crucial process remains incomplete: most of the attention has been devoted so far to the electron states inside the near-interface insulating layer leading to the break of electro-neutrality while the “fate” of oxygen leaving the insulating film as well as its influence on the EWF remains unknown.…”

Chemical and Morphological Inhomogeneity of Aluminum Metal and Oxides from Soft X-ray Spectromicroscopy

“…Hence, unraveling the rates and mechanisms of Al metal reactivity with O2 in fine powders, nanoparticles, thin films, and molecular clusters has been the subject of considerable experimental [2][3][4][5][6][7] and theoretical effort. [8][9][10][11][12][13] Understanding how changes in the phase of Al2O3 can impact reactivity has important consequences for scientific and technological applications for aluminum in ceramics, catalysis, coatings, separations, [14][15][16][17][18][19][20] and energetic materials. [21][22][23][24][25] To optimize the synthesis of well-defined nanoparticles and control their reactivities, characterization tools are needed that can probe the structure of heterogenous materials over multiple length scales and under real-world conditions.…”