Papers by Keyword: Passivation

Abstract: One challenge for the realization of electrically drive nano-photonic devices is the formation of metal contacts and passivation. In this paper, we report a novel self-aligned method suitable for the formation of the metal contact and passivation for submicron photonic devices. Two different dielectric materials with high selectivity in wet chemical etching and a wet etching of semiconductor to create an undercut are involved. The whole process is completely compatible with existing compound semiconductor process. As a demonstration of this method, the fabrication and characterization of an InGaAsP/InP submicron-ridge waveguide lasers is presented. The method is extendable to high aspect ratio-submicron ridge waveguide and other device fabrication.

Abstract: In order to identify an appropriate low-temperature surface passivation that could be used for bulk lifetime estimation of high resistivity (HR) (> 1 k
·cm) silicon for radiation detectors, different passivating layers were evaluated on n-type and p-type standard Czochralski (CZ), HR magnetic CZ and HR float zone (FZ) substrates. Minority carrier lifetime measurements were performed by means of a μW-PCD set-up. The results show that SiNx PECVD layers deposited at low temperatures (≤ 250°C) may be used to evaluate the impact of different processing steps and treatments on the substrate characteristics for radiation detectors. First results are obtained about a preliminary thermal treatment experiment to evaluate the thermal stability of the passivating layers, as well as the potential impact of the generation of thermal donors on minority carrier lifetime.

Abstract: Interstitial iron and iron-acceptor pairs are well studied but undesirable defects in Si as they are strong recombination centers which resist hydrogen passivation. Thermal anneals often result in the precipitation of Fe. Relatively little information is available about the interactions between Fe and native defects or common impurities in Si. We present the results of first-principles calculations of Fe interactions with native defects (vacancy, self-interstitial) and common impurities such as C, O, H, or Fe. The goal is to understand the fundamental chemistry of Fe in Si, identify and characterize the type of complexes that occur. We predict the configurations, charge and spin states, binding and activation energies, and estimate the position of gap levels. The possibility of passivation is discussed.

Abstract: Characterizations of Al/Polyimide/Al capacitors in a temperature range extended up to 400°C are presented. The aim is to determine the retained BPDA/PPD polyimide (PI) intrinsic dielectric and conduction properties, as a first stage in the evaluation of its ability to be applied as a passivation material for high temperature operating silicon carbide power devices. The dielectric constant, dielectric loss factor, and the static leakage current of the “as-prepared” Al/PI/Al structures are strongly affected above 175°C, reaching critical values at 400°C with regard to the aimed application. However, an evolution of these characteristics after the sample exposure at high temperature is observed, resulting in a very good and stabilized electrical behavior even at 400°C.

Abstract: This study examines how the increased density of passivated metallic conductor lines caused by large circuit integration in semiconductor devices influence their reliability during a thermal-cycling test. It was found that a decrease in the size of the trench-shaped space formed between two passivated conductor lines reduces the thermal cycling reliability of the passivation layer (i.e. in this case, consisting of Si3N4). The increased depth of the trenches results in more severe deformation in the surrounding area and brittle fractures in the passivation layer. In particular, the present work indicates that as the ratio of trench depth to trench width increases from 1:1 to 5:1, the number of failures caused by thermal cycling increases up to 2-fold. Numerical calculation also shows that the region of maximum stress is found at the corner of the interface between the flat passivation layer (i.e., the surface without any trenches) and its underlying metallic conductor. In cases where trenches exist, however, the region of maximum stress shifts from the interface corner to the trench corner. Furthermore, the level of the maximum stress was calculated to be lower at the interface corner than the trench corner, by 11%.

Abstract: In this paper, we have investigated the near-infrared luminescence emitting from NiSi2 passivated silicon nanocrystals (NCs) embedded in SiOx films. For comparison, we also prepared the regular specimen without NiSi2 passivation. In the both systems, the intensity of photoluminescence emission from NC-Si increased with the increase of annealing temperature, which was explained by the crystallization of amorphous silicon in SiOx films. The maximum intensity of near-infrared emission from NiSi2-passivated NC-Si was stronger by factor 5 than that of regular specimen without NiSi2 passivation. The model of NiSi2 passivation was employed to explain this phenomenon.

Abstract: Metal alloys containing chromium (Cr), primarily stainless steels and CoCr alloys, are used in a wide variety of implantable medical devices. These alloys are exposed to chloride containing environments with varying oxidizing potential and complexing agents. These corrosion assisted environmental effects may result in metal ions going into solution. The toxicity of Cr is dependent on valence state. Hexavalent Cr ions are recognized to be more toxic than trivalent Cr. This paper discusses the state of knowledge regarding Cr release, the chemical and mechanical factors that most significantly affect Cr release, and the potential toxicity of Cr as it applies to longterm implantable medical devices.

Abstract: Post-oxidation anneals that introduce nitrogen at the SiO2/4H-SiC interface have been most effective in reducing the large interface trap density near the 4H-SiC conduction band-edge for (0001) Si face 4H-SiC. Herein, we report the effect of nitridation on interfaces created on the (11 20) a-face and the (0001) C-face of 4H-SiC. Significant reductions in trap density (from >1013 cm-2 eV-1 to ~ 1012 cm-2 eV-1 at EC-E ~0.1 eV) were observed for these different interfaces, indicating the presence of substantial nitrogen susceptible defects for all crystal faces. Annealing nitridated interfaces in hydrogen results in a further reduction of trap density (from ~1012 cm-2 eV-1 to ~5 x 1011 cm-2 eV-1 at EC-E ~0.1 eV). Using sequential anneals in NO and H2, maximum field effect mobilities of ~55 cm-2 V-1s-1 and ~100 cm-2 V-1s-1 have been obtained for lateral MOSFETs fabricated on the (0001) and (11 20) faces, respectively. These electronic measurements have been correlated to the interface chemical composition.

Abstract: Silicon has been the semiconductor of choice for microelectronics largely because of the unique properties of its native oxide (SiO2) and the Si/SiO2 interface. For high-temperature and/or high-power applications, however, one needs a semiconductor with a wider energy gap and higher thermal conductivity. Silicon carbide has the right properties and the same native oxide as Si. However, in the late 1990’s it was found that the SiC/SiO2 interface had high interface trap densities, resulting in poor electron mobilities. Annealing in hydrogen, which is key to the quality of Si/SiO2 interfaces, proved ineffective. This paper presents a synthesis of theoretical and experimental work by the authors in the last six years and parallel work in the literature. High-quality SiC/SiO2 interfaces were achieved by annealing in NO gas and monatomic H. The key elements that lead to highquality Si/SiO2 interfaces and low-quality SiC/SiO2 interfaces are identified and the role of N and H treatments is described. More specifically, optimal Si and SiC surfaces for oxidation are identified and the atomic-scale processes of oxidation and resulting interface defects are described. In the case of SiC, we conclude that excess carbon at the SiC/SiO2 interface leads to a bonded Si-C-O interlayer with a mix of fourfold- and threefold-coordinated C and Si atoms. The threefold coordinated atoms are responsible for the high interface trap density and can be eliminated either by H-passivation or replacement by N. Residual Si-Si bonds, which are partially passivated by H and N remain the main limitation. Perspectives for the future for both Si- and SiC-based MOSFETs are discussed.