Characteristics of Mixed Oxides and Nanolaminates of Atomic Layer Deposited HfO[sub 2]–TiO[sub 2] Gate Dielectrics

Abstract

Thin film characteristics of HfO 2 -TiO 2 mixed oxides and nanolaminates formed by atomic layer deposition were studied using transmission electron microscopy ͑TEM͒, atomic force microscopy, X-ray reflectometry, and metal oxide semiconductor capacitors. The role of HfO 2 underlayer and the impact of the location of TiO 2 in HfO 2 -TiO 2 gate dielectrics were also investigated. Some differences in grain-size distribution were observed between mixed oxides and nanolaminates. In mixed oxide films, the grains became smaller and clustered together to form elongated structures as TiO 2 is added. For nanolaminates, the grains became smaller than HfO 2 but they did not form elongated structures. Cross-sectional TEM showed that as-deposited HfO 2 -TiO 2 films were amorphous with a thinner interfacial layer than that of HfO 2 . After annealing, films became rougher, with an increase in interfacial layer thickness. A minimum of 20 cycles of HfO 2 ͑ϳ10 Å͒ was needed as an underlayer to obtain well-behaved electrical characteristics. Capacitance-voltage stressing performed on these films showed improved charge trapping behavior for mixed oxide and nanolaminate structures.

Influence of Material Composition on Structural and Optical Properties of HfO2-TiO2 Mixed Oxide Coatings

“…HfO 2 thin films consisted of small grains with dimensions of ca. 28 )O x , the coating of its surface consisted of grains with round shapes of mostly small sizes of ca. 15-25 nm, however also few grains with larger size of ca.…”

“…In the literature, the HfO 2 -TiO 2 pseudobinary systems have been investigated previously by others [17,[23][24][25], especially in view of their electrical properties [26][27][28]. As was shown by Li et al [26], mixed oxides of HfO 2 -TiO 2 had, for example, higher permittivity compared to undoped HfO 2 .…”

“…On the other hand, Deen et al [27] showed results that demonstrated enhanced electrical properties of high-k gate dielectrics based on a HfO 2 /TiO 2 multilayer stack. Sequentially deposited HfO 2 /TiO 2 thin layers lead to minimizing the gate oxide's physical thickness, while the gate leakage current suppression characteristics for the 2 + 5 nm thick films were shown to be equivalent to the 10 nm thick TiO 2 films [28]. Therefore, such mixtures can combine the advantages of HfO 2 and TiO 2 .…”

The influence of electron-beam irradiation on electrical characteristics of metal–insulator–semiconductor capacitors based on a high-k dielectric stack of HfTiSiO(N) and HfTiO(N) layers

“…The use of high dielectric constant (high-k) dielectrics as substitutes for SiO 2 in small feature complementary metal oxide semiconductor technology has been studied extensively in recent years [1][2][3][4][5][6][7]. Binary metal oxides [1][2][3]8] are usually used with HfO 2 being the material of choice for next generation 45 nm transistors [9].…”

“…Binary metal oxides [1][2][3]8] are usually used with HfO 2 being the material of choice for next generation 45 nm transistors [9]. More complex compound insulators such as HfTiO [4] or HfTiTaO [5] and nanolaminate stacks of HfO 2 -TiO 2 [6] and Al 2 O 3 -HfTiO [7] have also been demonstrated with superb electrical properties. Most of these materials, especially the most promising and widely studied HfO 2 films lack the ability to block oxygen diffusion and therefore the formation of low dielectric constant SiO 2 type interfacial layers.…”