Objective: To evaluate modifications occurring in cognitive functions and behavioural aspects in a group of 72 consecutive patients with Parkinson’s disease (PD) 15 months after bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN). Methods: 72 consecutive PD patients bilaterally implanted for DBS of the STN were evaluated before and after surgery with a mean follow-up of 15 months. A neuropsychological assessment was performed to evaluate reasoning (Raven Colour Matrices), memory (Bisyllabic Word Repetition Test, Corsi’s Block-Tapping Test, Paired-Associate Learning) and frontal executive functions (Trail Making Test Part B, Nelson Modified Card Sorting Test, phonemic and category verbal fluency tasks). Mood and suicidal ideation were evaluated using the Beck Depression Inventory (BDI). Anxiety was measured by means of the State-Trait Anxiety Inventory and personality traits were evaluated with the Structured Clinical Interview for the DSM-III-R Axis II Disorders (SCID-II). Assessment of thought disorders and apathy was based on subitems of the Unified Parkinson’s Disease Rating Scale. Results: The comparisons between pre- and postoperative neuropsychological test scores showed a significant worsening only in phonemic and semantic verbal fluency tasks, while fewer errors were found in the Nelson Modified Card Sorting Test. Globally, behavioural assessment evidenced a small improvement in mood, as assessed by the BDI, in obsessive-compulsive and paranoid personality traits (SCID-II). Thought disorders worsened while suicidal ideation, anxiety and apathy showed no postoperative modifications. The analysis of individual outcomes (±1 SD criterion) evidenced a relevant postoperative cognitive decline in 3 patients out of 65 (4.5%). Moreover, following implantation, 1 patients exhibited psychosis (1.5%), 2 patients experienced a clinically relevant worsening of depressive symptoms (3%), 7 patients showed an increase in anxiety (12%) and 3 patients a worsening in depression and anxiety symptoms (3%). On the contrary, 12 patients (20%) showed a relevant improvement in mood and 14 patients (23%) a relevant reduction of anxiety symptoms after the surgery. Conclusions: The present study confirms that STN DBS is cognitively safe since the only relevant change observed was a mild decrease in verbal fluency tasks. Globally, a small postoperative improvement was found in the BDI, and in two SCID-II subscales concerning obsessive-compulsive and paranoid personality traits, even though postoperative behavioural disturbances can occur in individual patients.

X-ray fluorescence (XRF) techniques have been used to study, on different pretreated substrates, deposition kinetics of HfO2 and Al2O3, two of the possible high-K materials under evaluation for future integration in microelectronic devices. X-ray fluorescence (XRF) and total X-ray fluorescence (TXRF) measurements demonstrate their capability to give useful information on the very initial growing cycles of deposition and on carbon and chlorine inclusion in the film. Moreover, XRF signal shows a good linear correlation with layer thickness for thick samples of both materials. (C) 2004 Elsevier B.V. All rights reserved.

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 Al 2 O 3 mol%. Post-deposition annealings were carried out in single or sequential mode using purified N 2 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 Al 2 O 3 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 Al 2 O 3 mol% aluminate, change in k form 19 to 40-45 was observed together with limited degradation in conduction and breakdown characteristics.

In this paper, it is reported a Spectroscopic Ellipsometry (SE) study of several high K materials, such as HfO2, ZrO2, Zr-aluminates and Hf-aluminates deposited by Atomic layer chemical deposition. UV extended SE represents a fast measurement and non-destructive technique that in many cases provides not only optical indices but also interesting information about cristallinity, interface states and surface roughness. Results obtained by SE have been correlated with other techniques, such as X Ray Fluorescence, Atomic Force Microscopy, and electrical measurements.

An important aspect for the device manufacturing is the integration of high K materials into the current process flows. One important part is the possibility to use the cleaning chemistry and equipments used in present semiconductor device manufacturing.This paper presents a study about the compatibility with the HF and RCA based cleanings of several high K materials, deposited by ALCVD(TM) and MOCVD.The etching behavior of high K materials was studied by repeated cleanings in SC1 and HF, while particle removal efficiency in SCI, with and without megasonics was evaluated contaminating the samples by Si3N4 powders dispersed in a DIW tank.

To realise gate dielectrics in the present ULSI technology ultra thin oxynitrides are used. Nitrogen quantitative depth profiles are mandatory to characterise this material.

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.

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.

This paper presents a systematic investigation of thermal stability of high-k materials deposited on RCA cleaned wafers by ALCVDTM in an ASM PulsarTM 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, ALCVDTM 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.

Thin oxides deposited by low‐pressure chemical vapour deposition (LPCVD) at high temperature are being widely investigated in VLSI technology to be used as possible substitutes for the usual thermal oxides. High‐temperature oxide deposition involves reactions between N2O and dichlorosilane or silane. Considering possible active dielectric applications, the effect of further nitridation and annealing of deposited films has to be considered. Evaluation of the nitrogen content and the distribution profile of these dielectrics then becomes a relevant analytical issue. Moreover, it is also crucial to monitor the amount of possible contaminant species, such as chlorine, introduced by the precursor gases during the deposition. In this work we present the development of an analytical methodology for quantitative depth profiling of chlorine in thin oxides using SIMS and XPS. In addition, the evolution of chlorine distribution in an appropriate set of high‐temperature oxide films submitted to nitridation and further thermal processes will be shown. Copyright © 2002 John Wiley & Sons, Ltd.

A newly developed technique for the simultaneous measurement of the oxide–silicon interface properties and of minority carrier lifetime in the silicon volume was used for a systematic study of the nitridation process of oxide films.This technique is based on the surface recombination velocity measurements, and does not require the formation of a capacitor structure, so it is suitable for the measurement of as-grown interface properties. Oxides grown both in dry and in wet environments were prepared, and nitridation processes in N2O and in NO were compared to N2 annealing processes. The effect of nitridation temperature and duration were also studied, and processes of rapid thermal oxidation (RTO) and nitridation (RTN) were compared to conventional furnace nitridation processes. Surface recombination velocity was correlated with nitrogen concentration at the oxide–silicon interface obtained by secondary ion mass spectroscopy (SIMS) measurements. Surface recombination velocity (hence surface state density) decreases with increasing nitrogen pile-up at the oxide–silicon interface, indicating that in nitrided interfaces surface state density is limited by nitridation. NO treatments are much more effective than N2O treatments in the formation of a nitrogen–rich interface layer and, as a consequence, in interface state reduction. X-ray photoelectron spectrometry (XPS) analyses were used to extend our correlation to very thin oxides (3 nm).

A significant increase of HF etching rate and mean surface roughness (monitored by atomic force microscopy) was observed after P ion implantation on thin thermal SiO2 films (150 Å). The dependence upon the ion fluence (in the range 3×1012–5×1013 ions/cm2) and energy (in the range 270–500 keV) was analyzed, together with the recovery effect of a postimplantation annealing in N2 atmosphere. Moreover, the impact of P implants on oxides grown by different sequences, considering postoxidation annealing in N2O or N2 atmospheres, was also studied. The effect of ion irradiation was investigated by thermally stimulated luminescence (TSL) above room temperature in order to obtain information on point defects present in the layers. The results showed that postoxidation annealing treatments in N2 atmosphere carried out not only after, but also before ion implantation, were particularly useful in order to lower the concentration of TSL active defects. This can be interpreted as a role of N2 annealing in favoring a structural rearrangement of the SiO2 layers.

Thin wet oxides have been grown by in situ steam generation technique and nitrided by NO or N2O in a RTP Centura by applied material system after the oxidation. Nitrogen distributions are obtained by SIMS measurements and correlated with the charge trapping characteristics, showing relevant differences with respect to the oxide grown in furnace.The oxide quality is found to be strongly affected by a too high N concentration within the dielectric. On the other hand, the nitrogen concentration effectively stops B diffusion from the poly-Si gate.The very high temperature treatment has a great impact on substrate dopant redistribution influencing the reliability evaluation from constant voltage stress. When properly normalized similar results are obtained for current and voltage stresses. A significantly improved oxide quality is observed for ISSG oxide grown after the nitridation of the native oxide and associated with a more distributed N peak within the oxide, It is then possible to obtain a trade off between B barrier diffusion and high dielectric quality. (C) 2001 Elsevier Science Ltd. All rights reserved.