ALD Precursors Research Articles

Luminescent thin films of Eu-bearing UiO-66 metal organic framework prepared by ALD/MLD

Crystalline Eu3+-2-aminoterephthalic acid thin (ca. 22 µm) films have been prepared by Atomic/Molecular Layer Deposition (ALD/MLD) on Si/SiO2 substrates. The β-diketonate complex precursor europium(III)-tris-(2,2,6,6-tetramethyl-3,5-heptanedionate, Eu(thd)3, was reacted with 2-aminoterephthalic acid, NH2TA. X-ray diffraction indicates the films deposited at 180 °C exhibit the structure of UiO-66, a Zr-bearing metal organic framework. Scanning electron microscopy and atomic force microscopy show that the prepared films are very smooth and uniform, essentially defect-free, with a surface topography comprising evenly distributed hills without sharp edges, well adherent to the substrate. Attenuated total reflectance fourier transform infrared witnesses the presence of the organic ligand in the film and its coordination to the metal. X-ray photoelectron spectroscopy confirms the trivalent Eu oxidation state. Due to their thermal stability, fair volatility and facile synthesis, β-diketonate complexes have been shown to be suitable ALD precursors for preparing high-quality lanthanide organic framework thin films, enabling a single-step gas phase method for the synthesis of luminescent films.

Growth without Postannealing of Monoclinic VO2 Thin Film by Atomic Layer Deposition Using VCl4 as Precursor

Vanadium dioxide (VO2) is a multifunctional material with semiconductor-to-metal transition (SMT) property. Organic vanadium compounds are usually employed as ALD precursors to grow VO2 films. However, the as-deposited films are reported to have amorphous structure with no significant SMT property, therefore a postannealing process is necessary for converting the amorphous VO2 to crystalline VO2. In this study, an inorganic vanadium tetrachloride (VCl4) is used as an ALD precursor for the first time to grow VO2 films. The VO2 film is directly crystallized and grown on the substrate without any postannealing process. The VO2 film displays significant SMT behavior, which is verified by temperature-dependent Raman spectrometer and four-point-probing system. The results demonstrate that the VCl4 is suitably employed as a new ALD precursor to grow crystallized VO2 films. It can be reasonably imagined that the VCl4 can also be used to grow various directly crystallized vanadium oxides by controlling the ALD-process parameters.

Room-Temperature Atomic-Layer-Deposited Al2 O3 Improves the Efficiency of Perovskite Solar Cells over Time.

Electrical characterisation of perovskite solar cells consisting of room-temperature atomic-layer-deposited aluminium oxide (RT-ALD-Al2 O3 ) film on top of a methyl ammonium lead triiodide (CH3 NH3 PbI3 ) absorber showed excellent stability of the power conversion efficiency (PCE) over a long time. Under the same environmental conditions (for 355 d), the average PCE of solar cells without the ALD layer decreased from 13.6 to 9.6 %, whereas that of solar cells containing 9 ALD cycles of depositing RT-ALD-Al2 O3 on top of CH3 NH3 PbI3 increased from 9.4 to 10.8 %. Spectromicroscopic investigations of the ALD/perovskite interface revealed that the maximum PCE with the ALD layer is obtained when the so-called perovskite cleaning process induced by ALD precursors is complete. The PCE enhancement over time is probably related to a self-healing process induced by the RT-ALD-Al2 O3 film. This work may provide a new direction for further improving the long-term stability and performance of perovskite solar cells.

Inherently area-selective hot-wire assisted atomic layer deposition of tungsten films

This work demonstrates area-selective growth of tungsten (W) films by hot-wire assisted atomic layer deposition (HWALD). With this recently developed technique, low-resistivity alpha-phase W films can be deposited by using sequential pulses of atomic hydrogen (at-H) and WF6 at a substrate temperature of 275 °C. As reported in this article, the deposition is highly selective. HWALD tungsten grows with little to no incubation time on W, Co and Si surfaces. On the other hand, no growth is observed on TiN, Al2O3 and SiO2 surfaces. The interfaces of W and various substrates are examined by transmission electron microscopy. The absence of oxygen in the interfaces indicates that the atomic-hydrogen not only serves as a suitable ALD precursor for W, but is here shown to effectively reduce the native oxides of W and Co at the ALD process conditions, enabling in situ surface preparation before starting the deposition sequence.

Synthesis, characterisation and thermal properties of Sn(ii) pyrrolide complexes.

SnO is a rare example of a stable p-type semiconductor material. Here, we describe the synthesis and characterisation of a family of Sn(ii) pyrrolide complexes for future application in the MOCVD and ALD of tin containing thin films. Reaction of the Sn(ii) amide complex, [{(Me3Si)2N}2Sn], with the N,N-bidentate pyrrole pro-ligand, L1H, forms the hetero- and homoleptic complexes [{L1}Sn{N(SiMe3)2}] (1) and [{L1}2Sn] (2), respectively, bearing the 2-dimethylaminomethyl-pyrrolide ligand (L1). Reaction of [{(Me3Si)2N)}2Sn] with the pyrrole-aldimine pro-ligands, L2H-L7H, results in the exclusive formation of the homoleptic bis-pyrrolide complexes [{L2-7}2Sn] (3-8). All complexes have been characterised by elemental analysis and NMR spectroscopy, and the molecular structures of complexes 1-5 and 8 are determined by single crystal X-ray diffraction. TG analysis and isothermal TG analysis have been used to evaluate the potential utility of these systems as MOCVD and ALD precursors.

Determination of Trap Density in Hafnium Oxide Films Produced by Different Atomic Layer Deposition Techniques

Hafnia-based high-κ dielectrics are used in MOS devises as gate dielectrics [J.Robertson Rep.Prog.Phys.69,327(2006)]. The electronic properties of HfO2, including leakage currents, are defined by traps and defects [V.A.Gritsenko Phys.Rep.613,1(2016)]. Traps play different roles in different HfO2-based devices. When hafnia is used as a gate dielectric, traps increase its conductance. Electron or hole localization on traps shifts the threshold voltage and leads to the MOSFET degradation. In active layers of RRAM, traps act as precursors of the filament during the switch from a high-resistance state to a low-resistance state. In this case, the traps are used for device switching and information storing. The trap density in RRAM ranges as N~1019-1022cm-3. On the one hand, this is a huge defect concentration, which corresponds to the degeneration in semiconductors. On the other hand, such density is very low for modern analytical methods of analysis. Recently, it was reported that the charge transport in HfO2 is limited by the phonon-assisted tunneling between traps [D.R.Islamov Appl.Phys.Lett.105,222901(2014)]. The theory of phonon-assisted tunneling between traps allows defining the traps density from the slope of log J-V dependences. [K.A.Nasyrov J.Appl.Phys.109,097705(2011)]. In the study, we demonstrate the described approach and define the trap density in HfO2films after annealing in the inert atmosphere for two different ALD synthesis technologies. The HfO2 films with the thickness of 40nm were deposited on Si(100) substrates in a hot-wall Picosun Sunale R-200 ALD reactor (Finland) at an evacuation to ~1mbar. Pure nitrogen was used as a carrier gas and for purging the reactor after each reagent pulse. The well-known TEMAH+H2O precursor system was used. TEMAH was delivered into the reactor from the heated source at 100°C. The substrate temperature was 250°C. To compare the film quality of the TEMAH+H2O system, we studied a novel ALD precursor system Hf(thd)4+O2. Hf(thd)4 was delivered into the reactor from a heated source at 240°С. The substrate temperature was 440°C. The samples were annealed in the N2 flow for 1 hour at different temperatures. Annealing was performed directly in the reaction chamber at T ann=440, 550 and 700°C for TEMAH+H2O samples and T ann=550, and 700°C for the samples deposited from the Hf(thd)4+O2 system. The samples were taken out from the reactor after cooling to room temperature. For transport measurements, top Al electrode with the area of 0.5mm2, was deposited. The current-voltage characteristics were measured at room temperature. A set of the experimental current-voltage characteristics (log J-F) of n-Si/HfO2/Al structures from TEMAH+H2O series is shown by characters in Fig.1. The slope of log J-F curves depends on the temperature annealing. The experimental data are described by phonon-assisted tunneling between traps with the thermal (W t=1.25eV) and optical (W opt=2.5eV) trap energies (lines in Fig.1). These values are equal to that obtained from the literature [D.R.Islamov (2014)]. Annealing leads to a trap density decrease. After annealing at 700°C, the trap density value is N=1.2×1020cm-3. A set of experimental log J-F of n-Si/HfO2/Al structures from Hf(thd)4+O2 series is shown by characters in Fig.2. These curves can be described by the phonon-assisted tunneling theory with the same values of trap parameters as that obtained for TEMAH+H2O series. The trap density rises with the annealing temperature increase to 1.2×1020cm-3. The trap density dependences on the annealing temperature are shown in Fig.3. The HfO2 films from TEMAH+H2O series have more defects (and traps) than those from Hf(thd)4+O2series. After high-temperature annealing, the amount of the defects is the same for both series. We explain the obtained traps density values by the presence of hydrogen in HfO2 precursor. The presence of OH-groups in such films was also confirmed by infrared spectroscopy, wherein the sharp reduction in their concentration during annealing in the nitrogen atmosphere at 700°C was recorded. Since the hydroxyl groups are a fixture of the H2O-based ALD process, then a certain amount of hydroxyl groups unreacted with TEMAH will be integrated into the film structure. High temperatures in an inert atmosphere can lead to the destruction of OH-groups. The scheme could look like (≡Hf–OH–Hf≡)+→≡Hf–O–Hf≡+H+, with the subsequent hydrogen removal from HfO2 bulk due to low pressure annealing. Thus, we assume that reverse process has been observed in comparison with [S.Kim Nanotechnology23,325702(2012)] where high-pressure H2-annealing was performed for oxygen vacancies generation and the great influence of mobile OH-groups on the film conductivity was noted. The OH-groups are missing in the precursors of Hf(thd)4+O2 system, and their formation is unlikely during ALD. Therefore, annealing leads to the generation of a small number of additional oxygen vacancies in the HfO2film. The work was supported by the Russian Science Foundation, grant #16-19-00002. Figure 1

Reversible Low-Temperature Metal Node Distortion during Atomic Layer Deposition of Al2O3 and TiO2 on UiO-66-NH2 Metal-Organic Framework Crystal Surfaces.

Metal-organic frameworks (MOFs) are chemically functionalized micro- and mesoporous materials with high surface areas and are attractive for multiple applications including filtration, gas storage, and catalysis. Postsynthetic modification (PSM), via solution or vapor-based techniques, is a way to impart additional complexity and functionality into these materials. There is a desire to shift toward vapor-phase methods in order to ensure more controlled modification and more efficient reagent and solvent removal from the modified MOF material. In this work we explore how the metal precursors titanium tetrachloride (TiCl4) and trimethylaluminum (TMA), commonly used in atomic layer deposition, react with UiO-66-NH2 MOF. Using in situ quartz crystal microbalance (QCM) and Fourier transform infrared spectroscopy (FTIR) at 150 and 250 °C, we find that the ALD precursors react with μ3-OH hydroxyl and μ3-O bridging oxygen groups on Zr6 nodes, as well as oxygen from carboxylate linker groups. The reactions occur predominantly at the crystal surface at μ3-OH hydroxyl sites, with TiCl4 exhibiting greater diffusion into the MOF subsurface. FTIR analysis suggests that, at 150 °C, both TiCl4 and TMA reversibly dehydroxylate the hydroxylated UiO-66-NH2, which is accompanied by distortion of the zirconium metal clusters. Finally, we show that TiCl4 is able to react with the dehydroxylated UiO-66-NH2 structure, suggesting that TiCl4 is also able to react directly with the bridging oxygens in the metal clusters or carboxylate groups on the organic ligand. A better understanding of chemical and thermally driven MOF dehydroxylation reactions can be important for improved postsynthetic modification of MOFs.

Bismuth amides as promising ALD precursors for Bi2Te3 films

The thermal properties of five homoleptic bismuth amides of the general type (R1R2N)3Bi (R1, R2=Me 1, R1, R2=Et 2, R1, R2=n-Pr 3, R1=Me, R2=Et 4, R1=n-Bu, R2=Et 5) and the cyclo-dibismadiazane [(Me3Si)2NBi-μ-NSiMe3]26 were studied by DSC and TGA/DTA (1, 6) and their reactions with (Et3Si)2Te were investigated by in situ NMR spectroscopy. Based on these results, the potential application of 1, 4 and 6 to serve as ALD precursors for the deposition of Bi2Te3 films in reactions with (Et3Si)2Te were investigated. The resulting films were characterized by XRD, EDX, AFM and SEM and the crucial role of the substrate material and substrate temperature on the film growth rate and the morphology and chemical composition of the Bi2Te3 films was determined.

Second-generation hexavalent molybdenum oxo-amidinate precursors for atomic layer deposition.

The synthesis of molybdenum oxo-amidinate complexes MoO2(R2AMD)2 [AMD = N,N'-di-R-acetamidinate; R = Cy (2; cyclohexyl) and iPr (3)], and their characterization by 1H, 13C NMR, X-ray diffraction, and thermogravimetric analysis is reported. Quartz-crystal microbalance and X-ray photoelectron spectroscopic studies confirm that 3 is an improved ALD precursor versus the R = t-butyl derivative for MoO3 film growth. Complex 3 is accessible in higher yields (80%+), is easier to handle without mass loss, and in conjunction with O3 as the second ALD reagent, yields nitride-free MoO3 films.

(Invited) Using Inherent Substrate-Dependent Nucleation to Promote Metal and Metal Oxide Selective-Area Atomic Layer Deposition

Substrate-dependent nucleation during CVD has been heavily studied, and several strategies for selective growth are known. Compared to CVD, atomic layer deposition generally allows more precise control over surface reactions, but to date, the most successful selective-area deposition processes are based on CVD and not ALD mechanisms. Most ALD processes have an inherent substrate bias during nucleation, leading to problems in process development. Better understanding of this native substrate bias can be used to promote and enhance selective-area ALD. We have studied nucleation of ALD metals and dielectrics to promote native substrate bias and improve selectivity. Tungsten ALD using WF6/SiH4 onto SiO2 proceeds when surface Si-H (from SiH4) begins to form, allowing WF6 reduction to W and elimination of SiF4. We hypothesized that the introduction of a H2 or H-plasma exposure into the ALD sequence may help remove Si from the SiO2, which could extend the nucleation delay on SiO2, while not affecting W growth on Si. Using ellipsometry, XPS, high resolution SEM and in-situ quadrupole mass spectrometry we find that a H2 exposure during W ALD on ex-situ prepared SiO2 decreased the rate of W nucleation compared to growth without the H2 step, effectively increasing the selectivity window. Also, using XPS in-situ FTIR, we explored how various oxide ALD precursors react with different surfaces. For example, doing TiO2 ALD using TiCl4 with titanium isopropoxide as the oxygen source (instead of water), we find that eliminating water slows the substrate oxidation in areas where TiO2 deposition is not desired, thereby promoting the nucleation delay to as much as 200 ALD cycles at 170°C, resulting in a maximum selectivity thickness, ts,max ≈ 2–3 nm. We will discuss other details of initial reactions obtained from in–situ infrared spectroscopy, quartz crystal microbalance, TEM, SEM, ellipsometry and other tools to better understand and improve “inherent” substrate selective ALD of metals and metal oxides.

Thermoelectric Properties of Highly Ordered Metal-Organic Framework Films

Surface Anchored Metal-organic-framework (SURMOF) films are designed quasi-crystalline compounds that consists of metal ions connected by organic ligands, forming highly ordered porous structures. The SURMOF films initially were considered to have limited applications in electronic devices because of their insulating character. Recently, several approaches were found to tune the electrical conductivity of MOFs [1]. One of the effective methods found is to infiltrate guest molecules inside the porous framework to transport ions, and hence to modulate the electrical properties of the host framework. MOF Cu3(BTC)2 (BTC: benzene tricarboxylate) is a typical MOF film known as HKUST-1 (Hong Kong University of Science and Technology 1). Its electrical conductivity could increase up to 7 orders of magnitude by introducing tetracyano-quinodimethane (TCNQ) guest molecules. Recently MOFs films received more attention in the fields of switching nanodevices [2], sensors, and thermoelectrics. reported MOF films loaded with TCNQ@Cu3(BTC)2 exhibiting high Seebeck coefficients and low thermal conductivity [3]. However, the low electrical conductivity reduces the figure of merit ZT of MOFs. In this work we present alternating MOF/PbTe and MOF/PbSe nanolaminate structure synthesized by alternately depositing SURMOF films and lead chalcogenide films. The SURMOFs were fabricated by liquid phase epitaxy (LPE) technique. Ethanoic solution of copper acetate hydrate (1mM) and organic linker solution (1, 3, 5-benzenetricarboxylic acid) (0.2mM) were used as precursors for HKUST-1 MOFs. TCNQ was loaded to modulate electrical conductivity of MOFs. PbTe and PbSe were synthesized on the top of MOFs by thermal ALD technology. Lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2), (trimethylsilyl) telluride ((Me3Si)2Te) and (trimethylsilyl) selenide ((Me3Si)2Se) were employed as the chemical ALD precursors for lead, telluride and selenide, respectively. 20 sccm N2 was used as a carrier gas to transport the chemical precursors into the ALD reaction chamber. The ALD growth temperature was 150 ˚C. The solid lead precursor was volatilized at a temperature of 170 ˚C, the liquid Te precursor required heating to 40 ˚C, and the liquid Se precursor was kept at room temperature. The chamber base pressure was kept at 30 mTorr. Composite nanolaminate structure of MOF/PbTe and MOF/PbSe with film thickness of 10 nm/ 10 nm, 20 nm/ 20 nm, and 60 nm/ 60 nm were fabricated and investigated. Several physical characterization techniques have been employed to determine the surface characters of the sample. The samples were characterizated by X-ray diffraction (XRD) for film crystal structure, and by field emission scanning electron microscopy (FE-SEM) for film morphology and structure. For thermoelectrical properties of the sample, Seebeck coefficient both in vertical and horizontal directions were measured. Electrical conductivity and thermal conductivity of the films were investigated as well to envaluate ZT value of the samples. Figure 1 shows the IV characteristics of MOF films loaded with TCNQ. The linear IV curve indicates Ohmic conduction in TCNQ loaded MOFs. Figure 2 displays the Seebeck coefficient of TCNQ loaded MOF films over a temperature range of 290 K ~330 K. The maximum Seebeck coefficient of the film occurs at 290 K and the positive Seebeck coefficient reveals positive charge carriers in the MOF film.

Synthesis of Calcium(II) Amidinate Precursors for Atomic Layer Deposition through a Redox Reaction between Calcium and Amidines

AbstractWe have prepared two new CaII amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N′‐diisopropylformamidinato)calcium(II) (1) and bis(N,N′‐diisopropylacetamidinato)calcium(II) (2) adopt dimeric structures in solution and in the solid state. X‐ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η2‐L)Ca(μ‐η2:η2‐L)(μ‐η2:η1‐L)Ca(η2‐L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available CaII precursor, [Ca3(tmhd)6]. In CaS ALD with 1 and H2S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca3(tmhd)6] and H2S. Complexes 1 and 2, with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic CaII amidinates suitable for use as ALD precursors.

Synthesis of Calcium(II) Amidinate Precursors for Atomic Layer Deposition through a Redox Reaction between Calcium and Amidines.

We have prepared two new CaII amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N′‐diisopropylformamidinato)calcium(II) (1) and bis(N,N′‐diisopropylacetamidinato)calcium(II) (2) adopt dimeric structures in solution and in the solid state. X‐ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η2‐L)Ca(μ‐η2:η2‐L)(μ‐η2:η1‐L)Ca(η2‐L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available CaII precursor, [Ca3(tmhd)6]. In CaS ALD with 1 and H2S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca3(tmhd)6] and H2S. Complexes 1 and 2, with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic CaII amidinates suitable for use as ALD precursors.

Seebeck Coefficient Enhancement of ALD PbTe/PbSe Nanolaminate Structures Deposited inside Porous Silicon Templates

In this paper, lead chalcogenide based thermoelectric nanolaminate structures were fabricated by alternately depositing PbTe and PbSe ALD layers on regular planar silicon wafers and on microporous silicon templates. Lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2), plus (trimethylsilyl) telluride ((Me3Si)2Te) and (trimethylsilyl) selenide ((Me3Si)2Se) were used as the chemical ALD precursors for lead, tellurium and selenium, respectively. The Seebeck coefficient in horizontal direction (parallel direction to the surface) to the multiple layered PbTe/PbSe nanolaminate structures was measured by an MMR Seebeck system, and benchmarked against the Seebeck coefficient in the vertical direction to the sample surface. The results of the Seebeck measurements clearly indicate that the multiple layered PbTe/PbSe nanolaminate structures synthesized by ALD on microporous silicon templates exhibit significantly increased Seebeck coefficients in both horizontal and vertical directions, in stark contrast to the case when the same ALD thermoelectric nanolaminates are grown on regular planar bulk Si substrates.

Catalyst synthesis and evaluation using an integrated atomic layer deposition synthesis-catalysis testing tool.

An integrated atomic layer deposition synthesis-catalysis (I-ALD-CAT) tool was developed. It combines an ALD manifold in-line with a plug-flow reactor system for the synthesis of supported catalytic materials by ALD and immediate evaluation of catalyst reactivity using gas-phase probe reactions. The I-ALD-CAT delivery system consists of 12 different metal ALD precursor channels, 4 oxidizing or reducing agents, and 4 catalytic reaction feeds to either of the two plug-flow reactors. The system can employ reactor pressures and temperatures in the range of 10(-3) to 1 bar and 300-1000 K, respectively. The instrument is also equipped with a gas chromatograph and a mass spectrometer unit for the detection and quantification of volatile species from ALD and catalytic reactions. In this report, we demonstrate the use of the I-ALD-CAT tool for the synthesis of platinum active sites and Al2O3 overcoats, and evaluation of catalyst propylene hydrogenation activity.

Harnessing ALD to directly map the morphology of organic photovoltaic bulk heterojunctions

The selective diffusion of small molecules into the amorphous domains of semi-crystalline polymer films is used here to probe the complex morphology of all-organic photovoltaic films. In this case, the ALD precursors of ZnO diffuse into poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) BHJs and spatially map the distribution of P3HT amorphous and crystalline domain, and probe the distribution and miscibility of PCBM and P3HT.

Design and Operation of an Optically-Accessible Modular Reactor for Diagnostics of Thermal Thin Film Deposition Processes.

The design and operation of a simple, optically-accessible modular reactor for probing thermal thin film deposition processes, such as atomic layer deposition processes (ALD) and chemical vapor deposition (CVD), is described. This reactor has a nominal footprint of 225 cm2 and a mass of approximately 6.6 kg, making it small enough to conveniently function as a modular component of an optical train. The design is simple, making fabrication straightforward and relatively inexpensive. Reactor operation is characterized using two infrared absorption measurements to determine exhaust times for tetrakis(dimethylamino)titanium and water, proto-typical ALD precursors, in a pressure and flow regime commonly used for ALD.

Engineering the III-V Gate Stack Properties by Optimization of the ALD Process

The passivation of the interface between the IIIV substrate and the high-k is key in order to bring these materials into the 7nm technology node. A high amount of interface states (Dit>1E13 /cm2eV) will trap the electrons resulting in a reduced mobility and degraded subtreshold slope[1]. Additional defects present in the oxide near the IIIV interface will generate device instabilities[2]. The goal should be to reduce the amount of oxide traps below 1.5E10/cm2at an operating field of 3.5E6 V/cm in order to meet the 10 years reliability target. In this paper, it will be shown that careful engineering of the ALD process can yield a high quality interface at low CET values (<1.5nm). However, the bulk oxide trapping behavior is not changed accordingly with the ALD process and further improvement is required.TMA prepulsing, H2S exposure as well as the incorporation of a thin ALD rare earth (RE) oxide layer have been studied as a way to reduce the Dit level at the In0.53Ga0.47As/high-k interface. In addition, we present the oxide trap behavior for these different pretreatment/high-k combinations.TMA prepulsing has been reported to improve the interface quality of the In0.53Ga0.47As/ high-k interface[3]. We have studied the influence of the TMA pulse length in combination with ALD Al2O3 (TMA/H2O), HfO2 (HfCl4/H2O) and AlSiOx (TMA based and C-free process). For a 4nm Al2O3 layer, an optimal Dit is obtained when the TMA pulse length is increased from the standard 0.1 s up to 5 s during the first 5 ALD cycles (Figure 1). For a higher number of cycles with long TMA pulses, the Dit level increases again. This could be attributed to the increase of unreacted –CH3 groups as the H2O pulses were kept the same as compared to the standard TMA pulse length. Similar behavior can be found with a 4nm HfO2 stack: pretreatment of the interface with 5 cycles (TMA/H2O purge) with a 5s TMA pulse lowers the Dit by a factor ~2 compared to no pretreatment.The idea of using AlSiOx is to slow down the oxide trap response because of a possible higher Ec offset to the InGaAs channel. The incorporation of Si into the Al2O3 stack is accompanied with a Dit reduction, but at the expense of a CET increase. Again, prepulsing with TMA lowers the Dit level as seen with the Al2O3 process down to a midgap Dit of ~8E11 /cm2eV (see Figure 2). However, in the case of a C-free AlSiOx process, a Dit increase is accompanied when prepulsing with TMA. For this process, a S-terminated InGaAs surface lowers the Dit of the formed gate stack and a similar level of ~8E11 /cm2eV can be reached.Finally, the incorporation of RE-oxides as an interfacial passivation layer was studied for both Al2O3 (4nm) and HfO2 (4nm). Both Sc2O3 ((MeCp)3Sc/H2O) and Gd2O3 (i(PrCp)3Gd)/H2O) were studied and in each case, the insertion of 4 ALD cycles reduces the Dit. The lowest Dit level was observed for Gd2O3 (~2E12/cm2eV independent of the cap layer).The oxide trap behavior for several of these gate stacks was also studied. An H2S treatment improves the oxide trap behavior slightly (~2% reduction of oxide traps). Shifting from a TMA based AlSiOx process to a C-free AlSiOx process yields a reduction of a factor ~1.5. However, the range of oxide traps for all these stacks is higher than 5e11/cm2 at the target field, which is still 1 order of magnitude too high.We demonstrate that the final gate stack passivation is dependent on the interaction between the In0.53Ga0.47As surface termination and the ALD precursors. A long TMA prepulse seems to be beneficial for most of the gate stacks but the improvement cannot be generalized. We demonstrate that the pretreatments used for Dit optimization of the Al2O3 stack, can also be applied in combination with HfO2. This means that we can reach similar Dit levels with a HfO2 based stack using the right pretreatment with large reduction in CET. Despite this improvement on interface traps, the improvement on oxide traps is not substantial. A further reduction of interface traps, will not yield a proportional device improvement 1. However, a further reduction of oxide traps is a prerequisite in order to introduce the IIIV channel materials into the 7nm technology node.[1] G. Hellings et al, IEEE Transactions on Electron Devices, 58(4), (2011), 938-944.[2] D. Lin et al., IEDM, (2012), p645-648.[3] J.B. Clemens et al., J. Chem. Phys., 133, (2010), 154702.

Growth of Nanolaminates of Thermoelectric Bi2Te3/Sb2Te3 by Atomic Layer Deposition

The fabrication of thermoelectric nanolaminate structures of alternating Bi2Te3 and Sb2Te3 ALD layers for thermoelectric application is reported. Trimethylsilyl telluride ((Me3Si)2Te), bismuth trichloride (BiCl3) and antimony trichloride (SbCl3) were utilized as chemical ALD precursors for telluride, bismuth and antimony, respectively. The results of field emission scanning electron microscopy (FE-SEM) indicate both metal tellurides exhibit the prevalent Volmer-Weber island growth mechanism with characteristic hexagonal crystallites. High resolution TEM X-section analysis reveals localized epitaxial growth of alternating ALD Bi2Te3 and Sb2Te3 layers within the large islands.

Microstructure Analysis of ALD Bi2Te3/Sb2Te3 Thermoelectric Nanolaminates

The fabrication of thermoelectric nanolaminate structures of alternating Bi2Te3 and Sb2Te3 ALD layers for thermoelectric application is reported. Trimethylsilyl telluride ((Me3Si)2Te), bismuth trichloride (BiCl3) and antimony trichloride (SbCl3) were utilized as chemical ALD precursors for tellurium, bismuth and antimony, respectively. The results of field emission scanning electron microscopy (FE-SEM) indicate that both metal tellurides exhibit the prevalent Volmer-Weber island growth mechanism with characteristic hexagonal crystallites. High resolution TEM X-section analysis reveals localized epitaxial growth of alternating ALD Bi2Te3 and Sb2Te3 layers within the large islands.