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Ammonia production is a capital-intensive industry as it requires high temperature (400-500oC) and also high pressure (150-300 bar) for its daily operations. An earnest effort was made to synthese ammonia gas using an in-house designed microreactor. The production of ammonia was carried out in a magnetic field reaction zone, with the reaction temperature of 30°C - 280°C and ambient operation pressure. Mn0.8Zn0.2Fe2O4 nanoparticles, synthesized using the sol gel method, were used as the catalyst for the ammonia synthesis. XRD confirmed the single phase ferrites and FESEM images revealed nanofibre-like morphology when sintered at 700oC in argon gas. Electron diffraction was performed using HRTEM and obtained diffraction patterns confirmed the crystal structure of the catalyst. By using the Kjeldahl method it was found that the reaction carried out in 1 Tesla magnetic field gave approximately 46% ammonia yield. The proposed new method could be appealing for ammonia manufacturers due to highly economical implication which may offer urea producers a potential contender in the competitive market place.

In this paper we address the problem of revealing copper contamination induced in the device region by the final part of the process. A method to reveal the effects of copper contamination is identified based on the recovery of MOS capacitors from deep depletion. In the presence of copper contamination carrier generation is dominated by surface generation, which is not surprising because copper is known to be prone to surface segregation. Copper segregation at the wafer surface was also confirmed by TOF-SIMS measurements. The measurements of surface generation velocity are non-destructive and the required structures can be easily integrated in device wafers. However, a recovery of the copper-related surface generation velocity with the time spent after the thermal treatment was observed. For this reason, it is important that the measurements are carried out in a short time after the thermal treatment responsible for copper segregation at the wafer surface.

The uncontrolled formation of an interfacial layer between high-κ oxides and semiconductors is a major concern in advanced microelectronics not only for Si-based devices but also for those exploiting the higher mobility of Ge and GaAs. Using transmission electron microscopy, the authors investigate the interfacial layer formed between as-grown thin Al2O3 films, deposited using atomic layer deposition, and oxide free Si(100), Ge(100), and GaAs(100). In particular, they compare the effects of two different oxygen sources (H2O and O3) on interfacial layer formation during the growth process. They show that no interfacial layer can be distinguished unambiguously between the Al2O3 films, grown using TMA and H2O or O3, and all the semiconductor substrates.

In this article the phenomenology related to the mechanisms of defect generation in Shallow Trench Isolation (STI) processes is discussed, and the role of the structure pattern is investigated. Defect formation is studied by plan and cross TEM analyses of wafers with different boron doses and after annealing at various temperatures. In addition, to obtain a wider statistics our analysis was extended by electrical measurements of defect-sensitive structures. It is shown that a modification of the STI flow suppresses the main mechanism of mechanical stress accumulation, hence stress-induced defects are eliminated. However, this approach is found to be critical from the point of view of the implantation damage recovery, specifically for what concerns the implantations carried out before the trench etch. This result can be explained by the role of the silicon surface in reducing the point defect excess generated in the implantation. As a consequence, in this example the presence of the STI structure is beneficial, in that it assists in annealing implantation-related defects. An attempt is also presented to model the evolution of implantation-induced defects by a Kinetic Monte Carlo code. The calculation results are promising, though the capabilities of the model are limited by the computation time.

Due to the continuous scaling down of equivalent oxide thickness requested for inter-poly dielectric material in the next technology nodes, the Oxide-Nitride-Oxide structure is not able anymore to guarantee charge retention because of high leakage current. An alternative stack with higher dielectric constant is needed in order to have lower EOT together with higher physical thickness which fulfils retention requirements. With this purpose we have studied nitrided Hf-silicates (k=15÷20) grown by Atomic Layer Deposition at 350ºC starting from HfCl4, SiCl4 and H2O. The attention has been focused on how the thermal stability of these materials is improved when nitrogen is inserted in the film by NH3 annealing. Their chemical properties have been studied by Time of Flight-Secondary Ion Mass Spectrometry and X-ray Photoemission Spectroscopy, while their morphological evolution has been followed by means of X-Ray Reflectivity, X-Ray Diffraction and Transmission Electron Microscopy.

Thin TiSiN flat films deposited by MOCVD have been analysed in order to evaluate their microstructure and physical properties. TEM, XRR and RBS techniques have been utilised as complementary analyses to evaluate thickness, density and composition. The main composition is Ti : N : Si = 0.9 : 1.1 : 0.14 with carbon and oxygen up to 5% as a result of organic residuals and oxidation. The analysis shows a layered structure which well correlates with deposition steps. TiN nanocrystals embedded in a SiN x -rich amorphous matrix result confined into each TiSiN deposited layer. The silane soak produces a low concentration silicon inclusion, mainly stabilising the grain boundaries and not affecting the TiN crystalline morphology. AES profiles show that the TiSiN film consists of Ti–N rich layers, separated by C and Si rich “interface” layers which are the result of the process sequence. Densification and crystallisation of the film were observed after high temperature annealing in vacuum, resulting in an electrical resistivity decrease. PECVD deposition of an oxide layer on TiSiN causes a strong oxidation and resistivity increase of the film.

The scaling down of Flash memories can be pursued using the conventional stacked gate architecture only with major changes of the active dielectrics, mainly the inter-poly dielectric (IPD).The required 4-6 nm EOT thickness for the IPD cannot be achieved by the conventional ONO (Oxide-Nitride-Oxide) technology which starts failing in the 10-12 nm range in terms of charge retention properties. Therefore high-k materials are currently investigated for IPD formation in future Flash memories. It is worth noticing that the requirements for IPD are very different from those of the gate dielectrics used in logics. Alumina and alumina based materials (like hafnium aluminates) are among the possible candidates. Promising and tunable electrical and structural properties are achieved for these materials by varying the high-k stack chemical compositions and post- deposition thermal treatments. Different material combinations have been selected as potential solutions for the replacement of the conventional ONO (Oxide-Nitride-Oxide) stack.

a c Abstract Metal oxides of high dielectric constant are candidates to substitute SiO as gate dielectric in complementary metal-oxide- 2 semiconductor technology. In this contribution we present the application of X-ray techniques to the study of thermal stability of 5-, 10- and 20-nm-thick HfO deposited by atomic layer deposition. Grazing incidence X-ray diffraction spectra are refined by 2 Rietveld analysis. X-Ray reflectivity (XRR) data are fitted in order to evaluate the thickness, the surface roughness and the interface stability upon thermal processing between 300 and 1050 8C. The electronic density values obtained from the scattering coefficients of the crystallographic phase are compared to the values related to the critical angle of the XRR spectra. The thickness and the electronic density of the as grown layer are slightly affected by the thermal treatment. The surface and interfacial roughness are also very stable. The crystallographic ordering evolves starting from the amorphous structure of the as-deposited film towards the polycrystalline monoclinic HfO films obtained by annealing at high temperatures. The results are discussed and 2

Cobalt silicide films have been prepared by rapid thermal annealing of cobalt layers sputter deposited on silicon substrates. We report on the evolution of silicide phases, surface and interface roughness as a function of the annealing temperature and silicon surface preparation. The characterizations are carried out by atomic force microscopy, X-ray diffraction, X-ray reflectivity, Raman spectroscopy, and transmission electron microscopy. The cleaning procedure of the silicon substrate affects the interface roughness and the silicide thickness, whereas little effects are found on the surface. On the other hand, surface roughness increases with annealing temperature. © 2003 Elsevier B.V. All rights reserved.

In this paper, the correlation between dislocation density and transistor leakage current is demonstrated. The stress evolution and the generation of defects are studied as a function of the process step, and experimental evidence is given of the role of structure geometry in determining the stress level and hence defect formation. Finally, the role of high-dose implantations and the related silicon amorphization and recrystallization is investigated.

Solid-state transformations occurring in thin films can be studied by directing a laser beam on to the sample surface and measuring the reflected intensity by means of a photodiode. The technique, called Time-Resolved Reflectivity, is an in-situ technique very fast and simple. Under proper conditions, it allows the entire evolution of a transformation to be followed while it occurs during a thermal treatment, allowing the kinetics of the process to be studied. In this work we present a method and some criteria to extract physical information on layered samples interesting for the microelectronic industry. The surface reflectivity depends on the refractive indices (wavelength dependent) of the materials employed and on the thicknesses of the layers. The results extracted from the raw reflectivity data (obtained with a conventional He–Ne 632.8 nm laser) by means of few simple assumptions, are discussed and compared to those obtained with more conventional, but in most cases, destructive and ex-situ techniques.

The use of TiSi 2 layers as ohmic contacts in complementary MOS (CMOS) devices is expected to introduce large distortions in the underlying silicon which may degrade the device performances. In this work, the TEM technique known as convergent beam electron diffraction (CBED) has been employed to map the strain distributions across 〈1 1 0〉 cross-sectional specimens of sub-quarter-micron CMOS structures. Different experimental set-ups in terms of energy filtering, liquid nitrogen cooling and zone axis have been explored and compared to each other by using three differently equipped microscopes. The strain induced on silicon by TiSi 2 layers has then been investigated, quantified and compared with that due to the presence of an oxide isolation trench. Also, the effects of depositing a TiN capping layer on TiSi 2 have been analysed. Our results show that its presence results in a more tensile strain without altering the strain distribution trend.

In titanium silicide, the transition from the high (C49) to the low resistivity phase (C54) is difficult in small areas. This has been attributed in the literature to the lack of the nucleation sites for phase transition in small areas [1] . The mean grain size is directly related to the nucleation point density and its evaluation is important in obtaining data on nucleation mechanism of a new crystalline phase. TEM and SEM cross sections show that a silicon ridge is formed on the silicon substrate at the silicide grain boundaries, due to the equilibrium between the forces related to the grain–grain and to the grain–silicon interface energies [2] , [3] . AFM measurements have been performed on the interface between silicon and silicide after the removal of the silicide film. The grain boundaries of the silicide were imaged using the silicon ridges, allowing us to obtain unambiguous and statistically relevant data on the grain size.

In this paper we propose a new model to describe the quantum effects at the SiO2/Si interface of metal-oxide–semiconductor (MOS) devices. Using this model we developed a method to extract the thickness of thin oxides (in the range of 3–20 nm) from capacitance (C) as a function of voltage (V) measurements, C(V). The results of our extraction are in good agreement with transmission electron microscopy (TEM) measurements, within the accuracy of both techniques, while classical electrical methods are inadequate for a precise evaluation of the oxide thickness. Moreover this new method is suitable for in-line monitoring of oxide thickness in advanced MOS processes.

Rare-earth oxides are among the materials which are presently studied as possible replacements of amorphous silicon dioxide as gate insulators in nanometric Si devices; in fact, they generally exhibit high values of the dielectric constant ('high kappa'), a necessary requirement to obtain a high capacitance with layer thickness greater than the value below which tunneling currents become unacceptably high. Lu2O3 is one of the rare-earth oxides which may have the required properties in view of its quite high values of kappa and forbidden band gap. Since the envisaged dielectric layers are only a few nanometers thick, a description and a physical understanding of the atomic and electronic structure of the interface are of great importance. In this paper, we report a study by synchrotron radiation photoemission and transmission electron microscopy of the growth of Lu2O3 on Si(001). Thanks to the high spectral and spatial resolution, we provide clear evidence of a rather complex structure in which all silicon suboxides and SiO2 are present at the same time, along with a silicatelike phase and Lu2O3 itself; moreover, some grains and both crystalline and amorphous portions are present. In the photoemission experiment, the contribution of the Si surface to the core level line shapes has been taken into account; in the electron microscopy measurements, we present line scans on the nanometer scale of O, Si, and Lu concentrations and a Fourier transform discussion of the structure of the crystalline portions of the overlayer. The valence band discontinuity, which is measured in situ and is relative to the structurally well characterized interface, is found to be 3.16 +/- 0.16 eV. These findings are discussed in relation to the suitability of Lu2O3 as a high-kappa dielectric and in the context of available theoretical predictions of thermodynamic stability versus the formation of silicon oxide, silicates, and silicides and of the band discontinuity problem. (c) 2007 American Institute of Physics.

The evolution of the morphology and of the crystallographic ordering of hafnium aluminates deposited by atomic layer deposition has been investigated. Annealing at temperatures as high as 900 °C in N2 or O2 atmosphere is found to promote crystallization of the high-κ layer, together with the growth of an interfacial low-κ oxide. The crystallographic phase has been identified by indexation of transmission electron microscopy selected area diffraction patterns and by Rietveld refinement of grazing incidence x-ray diffractograms. The high κ is found to crystallize in an orthorhombic ternary Hf1−xAlxO2 phase even for an Al content as high as x=0.74. The temperature of crystallization is higher for the Al-richer alloy. The thickness and the electronic density of the interfacial layer are evaluated by combining cross-sectional transmission electron microscopy and x-ray reflectivity analysis.

We investigate the formation, crystallinity, size, and depth distribution of Sb nanoclusters in thin SiO2 matrix by grazing incidence x-ray diffraction (GIXRD) and reflectivity (GIXRR). The complementarity of these two techniques reveals the formation of Sb nanocrystals after a rapid thermal treatment at 1000 °C and their depth distribution. The implantation profile is found to have its maximum centered in the middle of the SiO2 layer. After thermal treatment, the Sb atom redistribution, monitored by the variation in the electron density profile obtained by GIXRR, corresponds to the formation of metallic Sb nanoclusters, as confirmed by transmission electron microscopy (TEM) and GIXRD. The cluster distribution within the SiO2 layer presents a maximum at the center of the layer and their average diameter is 67±3 A. The results are in agreement with TEM analyses.

NiO films were grown on Si(100) by atomic layer deposition using Ni(Cp)(2) (Cp=cyclopentadienyl, C5H5) or Ni(EtCp)(2) [EtCp=ethylcyclopentadienyl, (C2H5)C5H4)] and ozone in the 150-300 degrees C temperature range. The growth temperature dependence of structure, electronic density, and impurity levels for the prepared NiO films was studied using X-ray reflectivity, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, time of flight-secondary ion mass spectroscopy (ToF-SIMS), and transmission electron microscopy. The behavior of films deposited using Ni(Cp)(2) and Ni(EtCp)(2) is compared and discussed. NiO films with good stoichiometry and low amounts of contaminants are obtained at a growth temperature (T-g) of 250 degrees C or above. At a fixed T-g, the growth rate for NiO films deposited using Ni(Cp)(2) is higher than the one of films deposited using Ni(EtCp)(2). Furthermore, the growth rate for NiO deposited using Ni(Cp)(2) at T-g = 150 degrees C is 0.32 nm/cycle and decreases substantially in films deposited at higher temperatures. The electronic density of NiO films deposited at 300 degrees C is close to the one of bulk NiO (1.83 e(-)/A(3)). According to XRD and FTIR results, films deposited at T-g >= 200 degrees C have a simple cubic polycrystalline structure. Impurities in NiO films decrease with increasing T-g, as detected by ToF-SIMS.

In this paper, we describe an inline method to reveal crystal defects in the device fabrication process by voltage contrast detection with an electron beam inspection tool. Suitably designed monitor structures are used to this purpose. The correspondence between bright voltage contrast defects and dislocations connecting the transistor source and drain is demonstrated by selective etching followed by SEM review and by TEM inspection. In addition, it is shown that the voltage contrast defects correlate with the leakage current of the dislocation monitor structures, though some electrically active defects are missed by the electron beam inspection. Possible approaches to improve the capture rate of dislocations and correlation to leakage current are discussed. Finally, the correlation between e beam inspection of dislocation monitor structures and parametric test on a 65nm DR wafer is demonstrated

In this paper we discuss the physical mechanism and the critical factors for the dislocation generation in device processing. The mechanisms of the stress development are identified. Elastic stress is estimated from the convergent beam electron diffraction (CBED) measurements using transmission electron microscopy (TEM), and the defect generation is monitored by electrical measurements of a specific monitor structure. The implantation conditions and the implantation damage recovery is shown to be another key factor in the defect generation. Thermal oxidations of the STI structure are shown to be a major responsible of the stress increase. In addition to the process the pattern geometry strongly affects the mechanical stress. Minimum geometry structures with a complex layout are prone to defect generation.

A method of obtaining quantitative two-dimensional (2D) maps of strain by the convergent beam electron diffraction technique in a transmission electron microscope is described. It is based on the automatic acquisition of a series of diffraction patterns generated from digital rastering the electron spot in a matrix of points within a selected area of the sample. These patterns are stored in a database and the corresponding strain tensor at each point is calculated, thus yielding a 2D strain map. An example of application of this method to cross-sectioned cells fabricated for the 0.15 μm technology of flash memories is reported.

This paper presents a systematic investigation of thermal stability of high-k materials deposited on RCA cleaned wafers by ALCVD™ in an ASM Pulsar™ 2000 reactor. Physical-chemical evolution of Al2O3, HfO2 and Al/Hf composite materials (nanolaminate and aluminates) was studied considering two types of thermal treatments: quenched vacuum anneals from 300°C to 900°C and furnace atmospheric processes in N2 or O2 at 850°C and 900°C. Material crystallization and changes in film structure were studied by means of TEM, XRD, XRR, XRF, RBS and TOF-SIMS. Non-contact electrical measurements were used to detect modification in EOT and fixed charge. Al2O3 was found still amorphous at 900°C. Not so for HfO2 that crystallized in monoclinic phase at a temperature between 300–400°C. Crystallization temperature and possible phase separation of Al/Hf composite materials were found to be a function of Al2O3 content and film type. In most of these samples, however, a chemical evolution was detected in addition to the above reported crystallization phenomena. All the achieved results demonstrate that depending on thermal treatment conditions, ALCVD™ high-k stability does not only concern phase transition effects but also a transformation of the “SiO2/high-k” system into “doped-SiO2/silicate” stack.

The convergent beam electron diffraction (CBED) technique of transmission electron microscopy (TEM) has been applied to 〈1 1 0〉 cross-sections of shallow trench isolation structures in silicon, in order to evaluate the strain field distribution in 0.22 μm wide active areas. Different spot sizes (1 and 10 nm) and sample temperatures (room temperature with energy filtering, liquid nitrogen cooling without filtering) have been employed. It has been found that the regions of the active area closer than about 100 nm to the padoxide/substrate interface can be analysed only by using a 1 nm spot size. Moreover, the use of an energy filter to reduce the inelastic scattering improves the contrast of the diffraction lines in the CBED pattern, thus allowing the analysis to be performed at room temperature.

The convergent beam electron diffraction technique (CBED) of the transmission electron microscopy (TEM) has been employed to determine the strain distribution along a cutline parallel to the padoxide/Si interface in a 0.80 micron wide recessed-LOCOS structure. The values of the components of the strain tensor so obtained have been compared with those computed by two simulator codes. It has been found that both the LOCOS morphology and the strain distribution deduced from TEM images and TEM/CBED patterns, respectively, were in agreement with the simulation results, if some oxidation-related parameters were modified.

In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (fluences of 0.1-1 × 1016 cm−2) Sn implantation in 85 nm thick SiO2, followed by annealing (800-1000°C for 30-300 sec under Ar or N 2 dry ambient) in a rapid thermal processing (RTP) system, leads to the formation of two cluster bands, near the middle of the SiO2 layer and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed between the two bands. Cluster-size distribution and cluster-crystallinity are related to implantation fluence and annealing time. Low energy (10-12 keV) Sb and Sn implantation (fluences 2-5 × 1015 cm−2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed.

In this letter, we show that the polymorphic C49 form of TiSi2 has much smaller elastic constants than those of the C54 bulk-stable structure and that its melting temperature is about 300 degrees C lower. These issues supply intriguing hints in explaining the kinetic advantage of the C49 over the C54 phase and in understanding the role of the elastic energy in the phase transformation from C49 to C54. (c) 1999 American Institute of Physics. [S0003-6951(99)03023-5].

A method for measuring denuded zone depth from lifetime measurements is proposed and compared to observations by microscopy techniques and to Electron Beam Induced Current (EBIC) analyses. The surface photovoltage (SPV) method is chosen for measuring lifetime, as it is found to be extremely sensitive to oxygen precipitation. Samples prepared according to three typical thermal hystories are used as test vehicles.Correlating the results given by the different techniques, this study points out a few relevant features from the point of view of wafer processing. For instance, processes starting with a low temperature treatment are poorly reproducible for what concerns oxygen precipitation and denuding, as shown by SPV data, and do not guarantee a defect-free denuded zone, as seen in EBIC images. Additional high temperature treatments during the process increase the denuded zone depth and improve uniformity.Techniques which rely on a selective etching for defect detection, such as the Secondary Electron method of Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), are limited by etching sensitivy. On the other hand, the Transmission Electron Microscopy (TEM) statistics is too poor for this sort of observations. Instead, as a technique based on the recombination activity of defects, EBIC has roughly the same sensitivity as SPV. Both these techniques detect the formation of a denuded zone even when other methods fail, and can be considered as complementary tools.

It is now widely accepted that one of the major issues for the future deep sub-micron integrated circuit (IC) technologies regarding yield, device performance and stability and device and product reliability, is the mechanical stress built up in the layers and substrate. It is therefore important to give a quantitative account of these stresses and this can only be achieved by disposing of reliable, performant (as to spatial resolution) and quantitative techniques for the local stress determination in the substrate, of adequate and dedicated process simulation tools and of sensitive methods to analyse the stress effects on device performance.The only experimental technique presently available which allows the strain field distribution in sub-micron CMOS devices is the convergent beam electron diffraction technique of the transmission electron microscopy. Its sensitivity is of the order of 10-4 and its spatial resolution is of 1 nm if a TEM/FEG is employed.

The authors present novel results on the interface between silicon and the high-κ oxides Al2O3 and HfO2 grown by atomic layer deposition. The determination of the thickness of the interfacial layer between oxide and Si(100) is crucial to the evaluation of the performances of devices based on high-κ dielectrics. They find through hard x-ray photoemission spectroscopy (HaXPES) that no interfacial layer forms between Al2O3 and Si(100) whereas almost one monolayer forms between HfO2 and Si(100). HaXPES does not involve any destructive procedure nor any sample preparation. High-energy photoemission could therefore be widely employed for the characterization of real devices.

One of the candidates for the Oxyde-Nitride-Oxyde replacement in next generations Flash Non Volatile Memories is aluminum oxide deposited by Atomic Layer Deposition, which guarantees excellent film conformality, a feasible dielectric constant and low leakage current (1). Al2O3 films are grown in an ALD reactor at 300{degree sign}C using Trimethylaluminium and H2O as precursors. The impact of NH3 and O2 post deposition treatments on Al2O3 thermal stability up to N2 Rapid Thermal Process (RTP) at 1030{degree sign}C has been investigated. After RTP, while the O2 treatment prevents N incorporation and does not induce any crystallographic modification of the Al2O3 layer, the NH3 treatment causes an increase of the N content in the film and induces a reduction of the preferential orientation of the crystallized Al2O3 grains. Actually, the crystallization on set temperature is shifted to higher temperatures when Al2O3 is exposed to NH3 treatment before RTP.

Rare-earth silicates are promising materials for future microelectronic devices based on high dielectric constant dielectrics. In this work, we report the investigation of Lu silicate films deposited using atomic layer deposition on Si(100). The films were grown from tris[bis(trimethylsilyl)amido]lutetium-[(Me 3 Si) 2 N] 3 Lu (where Me = CH 3 ), which can supply both Lu and Si. Water or ozone were used as oxygen sources. The films deposited using the latter are shown to be richer in Si. The films are amorphous as grown, have a low physical roughness, an electronic density lower than expected for both crystalline and amorphous stoichiometric Lu silicates, and promote a SiO 2 -rich interfacial layer on Si(100). Crystallization, observed only in films deposited using O 3 , has an onset temperature above 900°C. Annealing at 950°C induces film densification. Signs of crystallization are observed only in the electron diffraction patterns of the annealed film deposited using O 3 as oxygen source, but the resulting crystallographic phases cannot be unequivocally identified. The K values of the dielectric stacks are between 5 and 7. The conduction band offset between the Lu silicate laver and Si(100) measured for the film deposited using O 3 is 2.2 eV.

In this work the use of lifetime techniques in the presence of a non-uniform profile of recombination centers is discussed. It is shown that measurements with different probing depths can be used in order to obtain information about the in-depth distribution of recombination centers. Molibdenum was chosen for this study, because it is probably the most common slowly diffusing contaminant. In this study, it is also shown that molibdenum inactivation does take place by segregation at the wafer surface. The evidence from lifetime techniques is confirmed by TEM analyses, revealing tiny molibdenum clusters at the wafer surface.

This study presents an investigation on physical-chemical stability of (HfO2)x(Al2O3 )1-x alloys upon prolonged post-deposition annealings. Two different Hf-aluminates were deposited by ALCVDTM, containing 34% and 74% Al2O3 mol% respectively. Post-deposition annealings (PDA) were carried out in O2 or N2 atmosphere, at 850°C and 900°C for 30 minutes. Interfacial layer (IL) increase after PDA was detected on all the samples, but with small differences between N2 and O2 treatments. Stack composition was characterized by means of XRR, XRF, RBS and TOF-SIMS. Growth of interface layer was justified by limited oxygen incorporation from external ambient. Silicon diffusion from the substrate into high-k material and aluminum/hafnium redistribution were observed and associated to annealing temperature. XRD and planar TEM analysis evidenced first grain formation and then, in the case of Hf-rich samples, almost complete crystallization. Overall, Hf-aluminates were found to remain XRD amorphous during high temperature prolonged treatments up to 900°C for 74% and 850°C for 34% alloys respectively. Differently from HfO2, (HfO2)0.66(Al2O3 )0.34 alloy was observed to crystallized in orthorhombic phase. Hf-aluminates were also electrically characterized by means of C(V) and I(V) measurements on basic capacitors. Variations in material electrical properties were found consistent with change in physical-chemical film structure. Increase in k value up to 30 was observed on Hf-rich samples crystallized in orthorhombic phase.

In this study, the investigation of crystallization behaviour of Hf-rich aluminate is presented. Different alloys were deposited by ALCVD™ with composition ranging between 16 and 47 Al2O3 mol%. Post-deposition annealings were carried out in single or sequential mode using purified N2 at atmospheric pressure. Process temperature and time were varied from 700°C to 900°C and from 1' to 30' respectively. Upon these conditions, film thermal evolution was observed without any relevant increasing of in interface layer and any change in material composition. Measurements on 20 Al2O3 mol% films evidenced that thermal treatments up to 800°C promoted initial shrinking in thickness and material densification. Above 900°C, all considered aluminates were found to crystallize in orthorhombic phase maintaining original alloy composition. The higher the alumina content, the lower the grain size, the higher the crystallites density. Stability of orthorhombic crystalline structure was demonstrated upon single prolonged annealing up to 30' and upon sequential processes. In correspondence with film crystallization, enhancement of dielectric constant was detected with an increasing trend upon hafnia content. For 20 Al2O3 mol% aluminate, change in k form 19 to 40-45 was observed together with limited degradation in conduction and breakdown characteristics.

In this paper we show that dopant decoration of process-induced defects is responsible for a failure mechanism of memory devices. From the electrical point-of-view, the defect-related failure consists in a source-to-drain resistive path formed by junction piping. This mechanism is made active by the very close spacing which is typical of present device structures. A device-like test structure is used for defect detection. This structure proves to be a very effective tool for studying the impact of various process steps on defect generation, in that it allowes statistical data about the formation of these defects to be collected. TEM analyses are extensively used for studying the evolution of end-of-range defects during subsequent thermal treatments and for measuring the amorphous layer width under various implantation conditions.The role of high dose implantations in the generation of this sort of defects is discussed. Even if the amorphous layer is completely recovered by a suitable recristallization annealing, residual defects grow and become dopant-decorated during post-implantation thermal treatments. Defect density is increased by oxidizing treatments. In this case point defect injection is active both in enhancing dopant diffusion and in growing defects.Defect formation is suppressed if the amorphous layer is made very shallow (≤ 50 nm) by suitable choices of the screen oxide and of the implantation energy. A binary collision code is used in order to estimate the dependence on energy of the self-interstitial excess outside the amorphous region. The results of these calculations indicate that defect suppression can be tentatively explained by point defect annihilation at the silicon surface.

A method for measuring denuded zone depth from lifetime measurements is proposed and compared to observations by microscopy techniques. The surface photovoltage (SPV) method is chosen for measuring lifetime, as it is found to be extremely sensitive to oxygen precipitation. SPV estimates of denuded zone depth are compared to observations by microscopy techniques, such as selective etching and inspections by a scanning electron microscope or an atomic force microscope, and analysis by transmission electron microscopy. SPV estimates agree with microscopy inspection, provided defect density is high enough to allow a denuded zone to be identified.