TEM techniques for the development of ULSI technology

[eng] In the last decade transmission electron microscopy (TEM) has become one of the most powerful tools for the structural characterization of crystalline materials. Especially in the field of microelectronics development and production, the information obtained by this analytical tool has been of vital importance for the improvement of the different processing steps. With the reduction of the dimensions of the devices TEM is the only technique that can give information with enough spatial resolution. In this work applications of transmission electron microscopy for the study of processing steps of ULSI technology will be presented. In the first chapter special emphasize is given to the theoretical background of transmission e Some details about Secondary Ion Mass Spectrometry (SIMS) and Spreading Resistance Probe (SRP) are also given, as they will be used for cross-correlation in the following chapters. In semiconducting research and production the processes for the fabrication of devices are restricted to a small volume of the starting material. Only the areas close to the surface, about 5 μm deep, are used for the operation of the devices. Both for plan view and cross-section TEM investigation of integrated circuits special specimen preparation techniques had to be developed. These techniques are described in full detail in chapter two. Chapters 3 and 4 deal with the application of TEM for the characterization of two processing steps that are required for the fabrication of ULSI devices. Chapter 3 presents a structural study of the geometry and the defect generation in the substrate for one of the most important aspects of the process: the device isolation. In it modifications of the LOCOS process will be given, which try to solve the specific problems of LOCOS when applied to submicron devices. In chapter 4 the delineation of shallow junctions is treated. The dopant profiles have to be well characterized and analytical teehniques have to be used which have a high spatial resolution and a high sensitivity for dopant concentration. Especially the determination of two-dimensional dopant profiles poses severe problems. Special TEM techniques will be presented, which allow to determine the lateral dopant spread below implantation masks. Especially promising is the applieation of in-situ electron irradiation in a high voltage transmission electron microscope (HVEM) to this topic. It will be shown that the formation of extended defects in preferential areas of the specimens, induced by the high energy electrons, is dependent on the dopant concentration. Correlation with SIMS or SRP will allow to determine this doping level in a quite accurate way. Finally in chapter 5 the most relevant conclusions of this work will be presented. Further research on the treated topicswill be suggested

TEM techniques for the development of ULSI technology

In the last decade transmission electron microscopy (TEM) has become one of the most powerful tools for the structural characterization of crystalline materials. Especially in the field of microelectronics development and production, the information obtained by this analytical tool has been of vital importance for the improvement of the different processing steps. With the reduction of the dimensions of the devices TEM is the only technique that can give information with enough spatial resolution. In this work applications of transmission electron microscopy for the study of processing steps of ULSI technology will be presented. In the first chapter special emphasize is given to the theoretical background of transmission e Some details about Secondary Ion Mass Spectrometry (SIMS) and Spreading Resistance Probe (SRP) are also given, as they will be used for cross-correlation in the following chapters. In semiconducting research and production the processes for the fabrication of devices are restricted to a small volume of the starting material. Only the areas close to the surface, about 5 μm deep, are used for the operation of the devices. Both for plan view and cross-section TEM investigation of integrated circuits special specimen preparation techniques had to be developed. These techniques are described in full detail in chapter two. Chapters 3 and 4 deal with the application of TEM for the characterization of two processing steps that are required for the fabrication of ULSI devices. Chapter 3 presents a structural study of the geometry and the defect generation in the substrate for one of the most important aspects of the process: the device isolation. In it modifications of the LOCOS process will be given, which try to solve the specific problems of LOCOS when applied to submicron devices. In chapter 4 the delineation of shallow junctions is treated. The dopant profiles have to be well characterized and analytical teehniques have to be used which have a high spatial resolution and a high sensitivity for dopant concentration. Especially the determination of two-dimensional dopant profiles poses severe problems. Special TEM techniques will be presented, which allow to determine the lateral dopant spread below implantation masks. Especially promising is the applieation of in-situ electron irradiation in a high voltage transmission electron microscope (HVEM) to this topic. It will be shown that the formation of extended defects in preferential areas of the specimens, induced by the high energy electrons, is dependent on the dopant concentration. Correlation with SIMS or SRP will allow to determine this doping level in a quite accurate way. Finally in chapter 5 the most relevant conclusions of this work will be presented. Further research on the treated topicswill be suggested

Electrical properties of individual tin oxide nanowires contacted to platinum electrodes

A simple and useful experimental alternative to field-effect transistors for measuring electrical properties free electron concentration nd, electrical mobility , and conductivity in individual nanowires has been developed. A combined model involving thermionic emission and tunneling through interface states is proposed to describe the electrical conduction through the platinum-nanowire contacts, fabricated by focused ion beam techniques. Current-voltage I-V plots of single nanowires measured in both two- and four-probe configurations revealed high contact resistances and rectifying characteristics. The observed electrical behavior was modeled using an equivalent circuit constituted by a resistance placed between two back-to-back Schottky barriers, arising from the metal-semiconductor-metal M-S-M junctions. Temperature-dependent I-V measurements revealed effective Schottky barrier heights up to BE= 0.4 eV

Mesoporous Silica: A Suitable Adsorbent for Amines

Mesoporous silica with KIT-6 structure was investigated as a preconcentrating material in chromatographic systems for ammonia and trimethylamine. Its adsorption capacity was compared to that of existing commercial materials, showing its increased adsorption power. In addition, KIT-6 mesoporous silica efficiently adsorbs both gases, while none of the employed commercial adsorbents did. This means that KIT-6 Mesoporous silica may be a good choice for integrated chromatography/gas sensing micro-devices

Raman microprobe characterization of electrodeposited S-rich CuIn(S,Se)2 for photovoltaic applications: Microstructural analysis

This article reports a detailed Raman scattering and microstructural characterization of S-rich CuIn(S,Se)2 absorbers produced by electrodeposition of nanocrystalline CuInSe2 precursors and subsequent reactive annealing under sulfurizing conditions. Surface and in-depth resolved Raman microprobe measurements have been correlated with the analysis of the layers by optical and scanning electron microscopy, x-ray diffraction, and in-depth Auger electron spectroscopy. This has allowed corroboration of the high crystalline quality of the sulfurized layers. The sulfurizing conditions used also lead to the formation of a relatively thick MoS2 intermediate layer between the absorber and the Mo back contact. The analysis of the absorbers has also allowed identification of the presence of In-rich secondary phases, which are likely related to the coexistence in the electrodeposited precursors of ordered vacancy compound domains with the main chalcopyrite phase, in spite of the Cu-rich conditions used in the growth. This points out the higher complexity of the electrodeposition and sulfurization processes in relation to those based in vacuum deposition techniques

Fabrication, characterization and performance of low power gas sensors based on (GaxIn1-x)(2)O3 nanowires

Active research in nanostructured materials aims to explore new paths for improving electronic device characteristics. In the field of gas sensors, those based on metal oxide single nanowires exhibit excellent sensitivity and can operate at extremely low power consumption, making them a highly promising candidate for a novel generation of portable devices. The mix of two different metal oxides on the same nanowire can further broaden the response of this kind of gas sensor, thus widening the range of detectable gases, without compromising the properties related to the active region miniaturization. In this paper, a first study on the synthesis, characterization and gas sensing performance of (GaxIn1-x)2O3 nanowires (NWs) is reported. Carbothermal metal-assisted chemical vapor deposition was carried out with different mixtures of Ga2O3, In2O3 and graphite powders. Structural characterization of the NWs revealed that they have a crystalline structure close to that of In2O3 nanowires, with a small amount of Ga incorporation, which highly depends on the mass ratio between the two precursors. Dedicated gas nanosensors based on single NWs were fabricated and tested for both ethanol and nitrogen dioxide, demonstrating an improved performance compared to similar devices based on pure In2O3 or Ga2O3 NWs

Síntesis de capas de SiC en substrato de Si mediante implantación iónica

En este trabajo se investiga la síntesis de estructuras SiC/Si mediante implantación iónica de carbono en Si. Las implantaciones se han realizado a energías entre 25 y 300 keV y las dosis en el rango lO^^ylO^^ cm , manteniendo el substrato a temperatura ambiente o 500°C. Algunas estructuras han sido recocidas a 1150°C. Los resultados indican que implantando a temperatura ambiente se forma una capa de SiC amorfa y de composición gradual, que recristaliza formando precipitados de ß-SiC con orientaciones aleatorias después del recocido. Además se forma un capa superficial rica en carbono, debida a la difusión del carbono hacia la superficie durante la implantación, y que desaparece con el recocido. Implantando a 500°C se forma directamente una capa con una muy alta densidad de precipitados de ß-SiC orientados preferencialmente con la matriz de silicio. Dada la estabilidad térmica y química de dicha capa se han realizado membranas de SiC mediante técnicas fotolitográficas y ataque químico selectivo, cuya rugosidad superficial es inferior a 6 nm. Estas membranas muestran unos gradientes de tensiones residuales, que prácticamente desaparecen después del recocido. Los resultados confirman la potencialidad de la implantación iónica para la formación de estructuras microme-cánicas de SiC sobre Si

Colorimetric sensor for bad odor detection using automated color correction

Colorimetric sensors based on color-changing dyes offer a convenient approach for the quantitative measurement of gases. An integrated, mobile colorimetric sensor can be particularly helpful for occasional gas measurements, such as informal air quality checks for bad odors. In these situations, the main requirement is high availability, easy usage, and high specificity towards one single chemical compound, combined with cost-efficient production. In this contribution, we show how a well stablished colorimetric method can be adapted for easy operation and readout, making it suitable for the untrained end user. As an example, we present the use of pH indicators for the selective and reversible detection of NH3 in air (one relevant gas contributing to bad odors) using gas-sensitive layers dip coated on glass substrates. Our results show that the method can be adapted to detect NH3 concentrations lower than 1 ppm, with measure-to-result times in the range of a few minutes. We demonstrate that the color measurements can be carried out with the optical signals of RGB sensors, without losing quantitative performance

Site-selectively grown SnO2 NWs networks on micromembranes for efficient ammonia sensing in humid conditions

SnO2 NWs networks on heated micromembranes have been characterized as ammonia sensors. The approach allows achieving reproducible growth and stable and long-lasting ammonia sensors with site-specific grown SnO2 NWs. The devices have been tested both in dry and humid conditions showing response time down to two minutes. Sensors have been tested up to 1 month, only presenting variation of the base resistance with full retention of the response towards the gaseous analytes. Different concurrent sensing mechanisms have been identified relating the determined sensing kinetics with previous theoretical calculations. Specifically, oxygen dissociation seems to play a key role in the overall ammonia sensing sequence. In humid conditions, moisture reduces the response to ammonia but also lowers the activation energy of the reaction process

Formaldehyde sensing mechanism of SnO2 nanowires grown on-chip by sputtering techniques

Tin dioxide nanowires have been grown by thermal oxidation of sputtered thin films by means of a VLS method. A tin sputtered layer catalyzed by gold nanoparticles, acts as material seed for the localized growth of NWs directly on gas sensor devices, avoiding the manipulation and transport of the nanowires to the electrodes. XRD and HRTEM analysis show that the nanowires crystallize in a rutile structure with a [100] preferential growth direction and are single-crystalline with diameters lower than 50 nm. The response of nanowires to formaldehyde has been compared to thin film based sensors. A sensitivity of 0.10 ppm-1 is reported, twofold the sensitivity of the thin film and short response and recovery times are measured (6 times shorter than thin films). The sensing mechanism proposed for the SnO2 NWs under formaldehyde exposure is explained by means of conduction measurements and FT-IR analysis. Oxygen species chemisorbed on the surface of each SnO2 nanowire produce a band bending, which generates a potential barrier (of 0.74± 0.02 eV at 300 ºC) between the point contact of different nanowires. As evidenced by IR spectroscopy at 300 ºC, electrons in the conduction band and in mono-ionized oxygen vacancies (at 0.33 eV below the bottom of the conduction band) are responsible for gas detection