Nanoindentation Investigation of HfO[sub 2] and Al[sub 2]O[sub 3] Films Grown by Atomic Layer Deposition

Abstract

The challenges of reducing gate leakage current and dielectric breakdown beyond the 45 nm technology node have shifted engineers' attention from the traditional and proven dielectric SiO 2 to materials of higher dielectric constant also known as high-k materials such as hafnium oxide ͑HfO 2 ͒ and aluminum oxide ͑Al 2 O 3 ͒. These high-k materials are projected to replace silicon oxide ͑SiO 2 ͒. In order to address the complex process integration and reliability issues, it is important to investigate the mechanical properties of these dielectric materials in addition to their electrical properties. In this study, HfO 2 and Al 2 O 3 have been fabricated using atomic layer deposition ͑ALD͒ on ͑100͒ p-type Si wafers. Using nanoindentation and the continuous stiffness method, we report the elastomechanical properties of HfO 2 and Al 2 O 3 on Si. ALD HfO 2 thin films were measured to have a hardness of 9.5 Ϯ 2 GPa and a modulus of 220 Ϯ 40 GPa, whereas the ALD Al 2 O 3 thin films have a hardness of 10.5 Ϯ 2 GPa and a modulus of 220 Ϯ 40 GPa. The two materials are also distinguished by very different interface properties. HfO 2 forms a hafnium silicate interlayer, which influences its nanoindentation properties close to the interface with the Si substrate, while Al 2 O 3 does not exhibit any interlayer.For the past 40 years the microelectronics industry has relied on the scaling down of device size in order to improve the performance, functionality, and bit density of chips, as described by Moore's law. As microelectronics is transitioning into deep nanotechnology, the drawback of the increasing miniaturization of devices is the increase of gate leakage current and oxide breakdown. 1 To reduce the gate leakage current and breakdown field across the gate insulator, researchers are looking into high-k dielectric materials. High-k materials such as HfO 2 and Al 2 O 3 will increase the transistor drive current and the transistor switching speed. 2 HfO 2 is predicted to replace SiO 2 , SiO x N y , and Si 3 N 4 as the gate dielectric of complementary metal oxide semiconductor ͑CMOS͒ devices at the 45 nm technology node and beyond. HfO 2 and Al 2 O 3 have dielectric constants of approximately k = 25 and 8, respectively, 3 which compare favorably with k = 3.9 for SiO 2 . Various deposition techniques have been used to deposit high-k materials. Among these growth techniques are metallorganic chemical vapor deposition ͑MOCVD͒, 4-6 pulsed laser deposition ͑PLD͒, 7 and atomic layer deposition ͑ALD͒. 4-6,8 MOCVD and PLD require a high temperature during processing and film fabrication. 9 For example, a minimum temperature of 600°C is required to deposit HfO 2 with MOCVD, whereas HfO 2 crystallizes once the temperature reaches 600°C. 10 ALD is a chemical reactionbased deposition technique that requires only relatively low temperatures. ALD provides absolute film deposition uniformity ͑atomic layer by atomic layer͒, precise composition control, high conformality, and completely self-limiting surface reactions, which makes ALD the most...

Review—Investigation and Review of the Thermal, Mechanical, Electrical, Optical, and Structural Properties of Atomic Layer Deposited High-kDielectrics: Beryllium Oxide, Aluminum Oxide, Hafnium Oxide, and Aluminum Nitride

“…This is consistent with the observations of Ritala where crystallites with a preferential orientation in the [100] direction was observed for ALD HfO 2 films. 181 However, we note that a more random orientation has been reported by others for thinner films 56,60 and a [111] orientation has been reported by Berdova for ALD HfO 2 films annealed at 700−900…”

“…60,180,181 For the latter, we note that in some cases the degree of crystallinity in ALD HfO 2 has been observed to increase with thickness/number of growth cycles, 18,30,56 and that other tetragonal and orthorhombic crystalline phases have been reported. 180,181 Post-deposition annealing at 500-900…”

“…We again note the extremely low value of 74 ± 1 GPa reported by Ilic for a 21 nm ALD HfO 2 film 61 indicated a mass density of 6.1 ± 0.1 g/cm 3 , substantially reduced relative to the values of 9.7-9.8 g/cm 3 reported for the other ALD HfO 2 films with considerably higher Young's modulus values. 60,251,252 This may be related to the extremely small thickness for the Ilic HfO 2 film relative to the other studies (60-200 nm). Even so, Zizka 253 determined a substantially higher density (9.8 g/cm 3 ) and modulus (166 ± 10 GPa) for an ALD HfO 2 film of similar thickness.…”

“…44,45 For such devices, knowledge of properties such as Young's modulus and film stress are critical for predicting the flexure and resonance frequencies of bridged and cantilevered switches and sensors, [46][47][48][49] stretched transistor device performance, 50,51 buckling failures in nanopatterned structures, 52,53 and macroscale buckling and nanoscale wrinkling effects for stiff high-k films deposited on compliant polymeric substrates. 54,55 Unfortunately, only a limited number of studies have reported on the thermal [56][57][58][59] and mechanical 42,[60][61][62][63][64][65][66] properties of ALD highk dielectric materials, and the numerous reviews [2][3][4][5][6][7][8] of high-k dielectrics have focused primarily on the electronic structure and interfacial properties of high-k dielectrics from a CMOS device perspective. To the authors' knowledge, a clear correspondence between thermal/mechanical and electrical/optical properties for ALD high-k dielectrics has yet to be established.…”

A Review of Atomic Layer Deposition for Nanoscale Devices

“…It has been applied in the numerous advanced technologies for the fabrication of nanoscale thin films such as microelectronics, Complementary Metal oxide Semiconductor (CMOS) transistors, DRAM memory, MEMS/NEMS, energy conversion, photovoltaics, and display devices [8][9][10][11][12] that require precise control of film properties in thickness, uniformity, and conformability.…”