L. Nyns

Silicate formation and thermal stability of ternary rare earth oxides as high-k dielectrics

Hf-based dielectrics are currently being introduced into complementary metal oxide semiconductor transistors as replacement for SiON to limit gate leakage current densities. Alternative materials such as rare earth based dielectrics are of interest to obtain proper threshold voltages as well as to engineer a material with a high thermal stability. The authors have studied rare earth based dielectrics such as Dy2O3, DyHfOx, DyScOx, La2O3, HfLaOx, and LaAlOx by means of ellipsometry, time of flight secondary ion mass spectroscopy x-ray diffraction, and x-ray photoelectron spectroscopy. The authors show that ellipsometry is an easy and powerful tool to study silicate formation. For ternary rare earth oxides, this behavior is heavily dependent on the composition of the deposited layer and demonstrates a nonlinear dependence. The system evolves to a stable composition that is controlled by the thermal budget and the rare earth content of the layer. It is shown that silicate formation can lead to a severe overe...

The VO2 interface, the metal-insulator transition tunnel junction, and the metal-insulator transition switch On-Off resistance

Transition metal compounds showing a metal-insulator transition (MIT) show complex behavior due to strongly correlated electron effects and offer attractive properties for nano-electronics applications, which cannot be obtained with regular semiconductors. MIT based nano-electronics, however, remains unproven, and MIT devices are poorly understood. We point out and single out one of the major hurdles preventing MIT-electronics: obtaining a high Off resistance and high On-Off resistance ratio in an MIT switch. We show a path toward an MIT switch fulfilling strict Off and On resistance criteria by: (1) Obtaining understanding of the VO2-interface, a protoypical MIT material interface. (2) Introducing a MIT tunnel junction concept to tune switch resistances. In this junction, the metal or insulating phase of the MIT material controls how much current flows through. Adapting the junctions parameters allows tuning the MIT switchs Off and On resistance. (3) Providing proof of principle of the junction and its...

ALD and Parasitic Growth Characteristics of the Tetrakisethylmethylamino Hafnium ( TEMAH ) / H2O Process

The continuous downscaling of complementary metal oxide semiconductor devices has required the integration of Hf-based high-k materials as gate dielectrics deposited by atomic layer deposition (ALD). When tetrakisethylmethylamino hafnium (TEMAH) is used as the metallic precursor to deposit such Hf-based materials, its limited thermal stability can result in precursor decomposition. This paper shows to what extent precursor decomposition affects the growth behavior of the TEMAH/H 2 O ALD in the temperature range 285-365 °C as well as the properties of the deposited HfO 2 layer. In this temperature range, the TEMAH pulse does not saturate up to pulse lengths of 10 s due to parasitic growth. Parasitic growth occurs when chemisorbed TEMAH ligands decompose and newly introduced precursor molecules react with these decomposed surface sites. The existence of such uncontrolled growth was proven by the repetition of TEMAH/N 2 reaction cycles, resulting in the deposition of a poor-quality Hf-based layer, while its contribution depends on both the reaction temperature and the TEMAH pulse length. Finally, also the H 2 0 pulse needs to be strictly controlled because too long pulses result in temperature-induced dehydroxylation of the surface, lowering the GPC of the TEMAH/H 2 O process with up to ~ 12% at 285°C.

Direct observation of both contact and remote oxygen scavenging of GeO2 in a metal-oxide-semiconductor stack

In the path to incorporating Ge based metal-oxide-semiconductor into modern nano-electronics, one of the main issues is the oxide-semiconductor interface quality. Here, the reactivity of Ti on Ge stacks and the scavenging effect of Ti were studied using synchrotron X-ray photoelectron spectroscopy measurements, with an in-situ metal deposition and high resolution transmission electron microscopy imaging. Oxygen removal from the Ge surface was observed both in direct contact as well as remotely through an Al2O3 layer. The scavenging effect was studied in situ at room temperature and after annealing. We find that the reactivity of Ti can be utilized for improved scaling of Ge based devices.

Passivation Challenges with Ge and III/V Devices

Ge and III/V materials are being investigated as high mobility channel materials for devices beyond the 14 nm technology node. These materials bring new issues to the forefront and device engineering can help solve these problems: an Implant Free Quantum Well design (IFQW) is introduced in order to enhance the channel control. An additional benefit of this design is that the passivation problem of the interface between the channel material and the high-κ oxide is reduced to half of the band gap: upper or lower part depending on the type of device addressed (nor p-FET). Nevertheless, the goal is to reduce these defect states to the minimum to get the maximum device performance. Besides the passivation of the interface between III/V and the high-κ oxide, the low conduction band density of states is raising the probability of charge trapping action at accumulation between the oxide border traps and conduction band electrons due to the fact that the surface Fermi level can be biased well into the conduction band [1,2]. Any defects in the oxide will therefore also play a role in the final device performance.

Electrical Properties of Low- Metal-Gated n-MOSFETs Using as Interfacial Layer Between HfLaO High- Dielectrics and Si Channel

In this letter, we report that by employing the La₂O₃/SiO_x interfacial layer between HfLaO (La = 10%) high- and Si channel, the Ta₂C metal-gated n-MOSFETs V_T can be significantly reduced by ~350 mV to 0.2 V, satisfying the low-Vy device requirement. The resultant n-MOSFETs also exhibit an ultrathin equivalent oxide thickness (~1.18 nm) with a low gate leakage (J_G = 10 mA/cm² at 1.1 V), good drive performance (I_on = 900 muA/mum at I_soff = 70 nA/mum), and acceptable positive-bias-temperature-instability reliability.

Effect of Remote Oxygen Scavenging on Electrical Properties of Ge-Based Metal–Oxide–Semiconductor Capacitors

Remote oxygen scavenging has been studied in a metal/high-k dielectric/GeO2/Ge stack, where a thin Ti layer inserted into the metal/high-k dielectric interface serves as the scavenger. First, we established that remote oxygen scavenging indeed occurs specifically in the studied HfO2/Al2O3/GeO2/Ge stack. It was also established that the source for oxygen is decomposition of the GeO2 layer. Then, the effect of remote oxygen scavenging of the GeO2 layer on the electrical characteristics of the metal/oxide/Ge capacitors was investigated. The electrical properties were studied in comparison with identical gate stacks with a Pt electrode, before and after annealing. Although a decrease in effective oxide thickness was demonstrated as a result of this process, clear degradation of the interface electrical quality was observed after scavenging. Initiation of the scavenging process was witnessed upon deposition of Ti at room temperature, emphasizing that this process could not be controlled.

Electrical Properties of Low-

In this letter, we report that by employing the La₂O₃/SiO_x interfacial layer between HfLaO (La = 10%) high- and Si channel, the Ta₂C metal-gated n-MOSFETs V_T can be significantly reduced by ~350 mV to 0.2 V, satisfying the low-Vy device requirement. The resultant n-MOSFETs also exhibit an ultrathin equivalent oxide thickness (~1.18 nm) with a low gate leakage (J_G = 10 mA/cm² at 1.1 V), good drive performance (I_on = 900 muA/mum at I_soff = 70 nA/mum), and acceptable positive-bias-temperature-instability reliability.