A. Franquet

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...

Impact of Process Optimizations on the Electrical Performance of High-k Layers Deposited by Aqueous Chemical Solution Deposition

Alternative high-k materials are being researched for future dielectrics in various complementary metal oxide semiconductor applications. We report on the aqueous chemical solution deposition technique as an alternative material screening technique. We used ZrO2 as a reference material to explore the effect of different process parameters on the electrical performance of Pt-dot capacitors. We studied the effects of varying the molar ratio between citric acid and the Zr ions, as well as the conditions of the oxidizing postdeposition anneal. We found that proper optimization of these parameters can significantly reduce the amount of carbon in the layers and enhance the electrical performance of the films to similar levels as atomic layer deposition.

GeSn channel nMOSFETs: Material potential and technological outlook

Semiconducting germanium tin (GeSn) alloy has recently emerged as a candidate for optoelectronic and high performance CMOS devices because of its tunable direct gap and potential for high electron and hole mobilities. High hole mobility in GeSn channel pMOSFETs has already been demonstrated [1, 2]. However, GeSn as channel for nMOSFETs has not yet been explored. In this work we perform detailed theoretical analysis to gauge the benefits of GeSn channel over Ge for nMOSFETs. Our analysis predicts GeSn nMOSFETs to outperform Ge. GeSn n-channel devices have been successfully fabricated and factors limiting its performance.

Aqueous chemical solution deposition : Fast screening method for alternative high-k materials applied to Nd2O3

Material screening of gate dielectrics for complementary metal oxide semiconductor applications is often complicated by the inability to deposit test samples. We examine the aqueous chemical solution deposition (CSD) technique as a simple, inexpensive, and fast technique to deposit thin metal-oxide layers. We deposited Nd 2 O 3 layers on 1.2 nm SiO 2 . The thinnest stack (7.2 nm) yielded an equivalent oxide thickness (EOT) of 3.1 nm with a gate-leakage current of 1.4 X 10 -6 A/cm 2 at V FB - 3 V. EOT scales linearly with physical thickness, allowing a k-value extraction, approximately 14. Our results suggest that aqueous CSD is a viable method for fast gate-dielectrics screening.

Scalability of plasma enhanced atomic layer deposited ruthenium films for interconnect applications

Ru thin films were deposited by plasma enhanced atomic layer deposition using MethylCyclopentadienylPyrrolylRuthenium (MeCpPy)Ru and N2/NH3 plasma. The growth characteristics have been studied on titanium nitride or tantalum nitride substrates of various thicknesses. On SiO2, a large incubation period has been observed, which can be resolved by the use of a metal nitride layer of ∼ 0.8 nm. The growth characteristics of Ru layers deposited on ultra-thin metal nitride layers are similar to those on thick metal nitride substrates despite the fact that the metal nitride layers are not fully closed. Scaled Ru/metal nitride stacks were deposited in narrow lines down to 25 nm width. Thinning of the metal nitride does not impact the conformality of the Ru layer in the narrow lines. For the thinnest lines the Ru deposited on the side wall showed a more granular structure when compared to the bottom of the trench, which is attributed to the plasma directionality during the deposition process.

Alternative high-k dielectrics for semiconductor applications

Although the next generation high-k gate dielectrics has been defined for the 45nm complementary metal oxide semiconductor technology node, threshold voltage control and equivalent oxide thickness (EOT) scaling remain concerns for future devices. Therefore, the authors explored the effect of incorporating dysprosium in the gate stack. Results suggest that improved EOT-leakage scaling is possible by adding Dy to the interfacial SiO2 layer in a 1:1 ratio or by adding 10% Dy to bulk HfO2. The deposition of a 1nm Dy2O3 cap layer lowered the threshold voltage by ∼250mV. In addition, for future dynamic random access memory capacitor applications, dielectrics with e of 50–130 are projected by the International Technology Roadmap for Semiconductors, unachievable with standard high-k dielectrics. Theoretical modeling can help direct the experimental work needed for extensive screening of alternative dielectrics. Moreover, materials such as perovskites only exhibit a sufficiently high-k value when properly crystall...

High-k Dielectrics and Metal Gates for Future Generation Memory Devices

The requirements and development of high-k dielectric films for application in storage cells of future generation flash and Dynamic Random Access Memory (DRAM) devices are reviewed. Dielectrics with k-value in the 9-30 range are studied as insulators between charge storage layers and control gates in flash devices. For this application, large band gaps (> 6 eV) and band offsets are required, as well as low trap densities. Materials studied include aluminates and scandates. For DRAM metal-insulator-metal (MIM) capacitors, aggressive scaling of the equivalent oxide thickness (with targets down to 0.3 nm) drives the research towards dielectrics with k-values > 50. Due to the high aspect ratio of MIMCap structures, highly conformal deposition techniques are needed, triggering a substantial effort to develop Atomic Layer Deposition (ALD) processes for the deposition of metal gates and high-k dielectrics. Materials studied include Sr and Ba-based perovskites, with SrTiO3 as one of the most promising candidates, as well as tantalates, titanates and niobates.

Atomic layer deposition of high-k dielectric layers on Ge and III-V MOS channels

Ge and III-V semiconductors are potential high performance channel materials for future CMOS devices. In this work, we have studied At. Layer Deposition (ALD) of high-k dielec. layers on Ge and GaAs substrates. We focus at the effect of the oxidant (H2O, O3, O2, O2 plasma) during gate stack formation. GeO2, obtained by Ge oxidn. in O2 or O3, is a promising passivation layer. The germanium oxide thickness can be scaled down below 1 nm, but such thin layers contain Ge in oxidn. states lower than 4+. Still, elec. results indicate that small amts. of Ge in oxidn. states lower than 4+ are not detrimental for device performance. Partial intermixing was obsd. for high-k dielec. and GeO2 or GaAsOx, suggesting possible correlations in the ALD growth mechanisms on Ge and GaAs substrates. [on SciFinder (R)]

Properties of Ultrathin High Permittivity ( Nb1 − x Ta x ) 2O5 Films Prepared by Aqueous Chemical Solution Deposition

Ultrathin Nb1�xTax2O5 films, with thicknesses from 3t o 25 nm, were deposited by chemical solution deposition starting from aqueous precursor solutions. The film’s dielectric properties were characterized by capacitance–voltage and current–voltage measurements. Permittivities ranged from 20 to 31 after annealing at 600°C, with the highest value obtained for pure Nb2O5. With increasing Nb content, increasing leakage currents were observed. The crystallization temperature was determined by in situ X-ray diffraction measurement for films with 15 nm thickness: Nb2O5 was crystalline as deposited 600°C, while the crystallization temperature of solid solutions increased with increasing Ta content, up to 875°C for pure Ta2O5. NbTaO5 showed a marked increase in permittivity from 27 to 38 after crystallization anneal at 600 and 800°C, respectively. For Nb2O5, no significant difference in permittivity was observed between amorphous and crystalline layers.

Photoresist Characterization and Wet Strip after Low-k Dry Etch

[Claes, M.; Le, Q. T.; Kesters, E.; Lux, M.; Franquet, A.; Vereecke, G.; Mertens, P. W.] IMEC VZW, B-3001 Louvain, Belgium.