Giuseppe Arena

Fabrication of miniaturised Si-based electrocatalytic membranes

The increasing interest for light and movable electronic systems, cell phones and small digital devices, drives the technological research toward integrated regenerating power sources with small dimensions and great autonomy. Conventional batteries are already unable to deliver power in more and more shrunk volumes maintaining the requirements of long duration and light weight. A possible solution to overcome these limits is the use of miniaturised fuel cell. The fuel cell offers a greater gravimetric energy density compared to conventional batteries. The micromachining technology of silicon is an important tool to reduce the fuel cell structure to micrometer sizes. The use of silicon also gives the opportunity to integrate the power source and the electronic circuits controlling the fuel cell on the same structure. This paper reports preliminary results concerning the micromachining procedure for fabricating a Si-based electrocatalytic membrane for miniaturised Si-based proton exchange membrane fuel cells (PEMFC).

Fabrication of miniaturized Si-based electrocatalytic membranes

Abstract The increasing interest for lightweight and portable electronic systems, cellphones and small digital devices is driving technological research towards integrated regenerating power sources with small dimensions and great autonomy. Conventional batteries are already unable to deliver power in ever smaller volumes while maintaining the requirements of long duration and light weight. A possible solution to overcome these limits is the use of miniaturized fuel cells. The fuel cell offers a greater gravimetric energy density compared to conventional batteries. The micromachining technology of silicon is an important tool to reduce the fuel cell structure to micron sizes. The use of silicon also gives the opportunity to integrate the power source and the electronic circuits controlling the fuel cell on the same structure. This article reports preliminary results concerning the micromachining process for fabricating a silicon-based electrocatalytic membrane for miniaturized Si-based proton-exchange membrane (PEM) fuel cells.

The effect of reactive plasma etching on the transient enhanced diffusion of boron in silicon

Silicon wafers oxidized and stripped by reactive plasma etching were implanted with 5 keV B, 1×1013/cm2. The transient enhanced diffusion of B, usually observed in samples which receive such implants over characteristic time scales, is strongly retarded in these plasma etched samples upon annealing at 800, 900, or 1000 °C, as measured by secondary ions mass spectrometry. These results suggest that the defects generated by the plasma etching procedure in the near surface region, represent an efficient sink against the flow of interstitials which cause the transient enhanced diffusion. A slow release of interstitials from this trapping immobile background occurs with characteristic time scales which are, however, a factor of 30–60 times higher than the usual lifetimes of transient diffusion. This release is characterized by an activation energy of 2.4 eV. These data are reported and their implication on shallow junction formation are discussed.

Hydrogen Flux Influence on Homo-Epitaxial 4H-SiC Doping Concentration Profile for High Power Application

Doping incorporation and good uniformity along the wafer it is a mandatory for application in high voltage electronic devices. In this work the effect of the Hydrogen (H) flux position inside the reaction chamber on homo-epitaxial 4H-SiC growth process has been studied. Capacitance-Voltage and FT-IR analyses show as the different position of the gas injector affect the doping and thickness uniformity and profile. On the other hand, By Candela and AFM analyses no morphological or surface influence by Hydrogen flux position has been observed.

Voids-Free 3C-SiC/Si Interface for High Quality Epitaxial Layer

A study of the carbonization process and of a low temperature buffer layer on the Cubic Silicon Carbide (3C-SiC) epitaxial growth has been reported in this work. From this study it has been evidenced the importance of the C/H2 ratio and of the buffer layer process on the voids formation at the 3C-SiC/Si interface. From our study, the influence of the voids the wafer curvature is highlighted. It has been observed that decreasing the density of these voids, decreases the stress of the 3C-SiC film; consequently, the wafer curvature is reduced.

Plasma processing of the silicon surface: A novel method to reduce transient enhanced diffusion of boron

We investigate in detail the effect of plasma processing on the transient enhanced diffusion of implanted boron in silicon. Thermally oxidized silicon wafers were first processed with CHF3/CF4 plasma and subsequently implanted with boron, with energies ranging from 3 to 20 keV and a dose of 1×1013/cm2. Chemical profiles were measured by secondary ion mass spectrometry while lattice extended defects induced in silicon by plasma processing were characterized by transmission electron microscopy. Secondary ion mass spectrometry measurements reveal that the transient enhanced diffusion of boron after rapid thermal annealing is strongly reduced in plasma processed samples with respect to unprocessed samples. Defects induced by plasma processing are responsible for the reduction by acting as very efficient traps for the interstitial atoms generated during the implant. We note that the trapping efficiency is critically dependent on the projected range of the boron implant, being extremely evident at low energies ...

Incoming and Inline Defectivity Control Solutions for Silicon Carbide Manufacturing

Si l icon car b ide (Si C ) man u f act u ring is transitioning from 4 inch wafers to 6 inch wafers for production line devices. The main obstacle for SiC manufacturing high yield is defect control. Defectiveness inline control is well established for silicon power device. However, there are two main challenges related to SiC technology. The first challenge is incoming 4H-SiC substrates defectivity and epi layer crystallographic defects. The second challenge is inline defect detection at process steps such as implantation and annealing activation [,]. Defect detection and classification are difficult with current defect inspection tools because of substrate transparency at visible light, color variation, roughness, and wafers’ high warpage. In addition, SiC device integration has been requesting specific optimization. In this paper, collaboration studies have been done to develop solutions to these challenges. Yield correlation analyses have validated the process control flow set to address these two major challenges and to enable the fast ramp of the 6” production line of SiC devices.

Stress Relaxation Mechanism after Thinning Process on 4H-SiC Substrate

In this work a comparison between different 6 inches 4H-SiC commercial substrates after post processing has been shown. The main comparison was done between two different suppliers after a thinning process that leaves the sample with a final thickness of 150 microns. After the processing the two substrates show different behavior with different curvature and residual stress. X-Ray diffraction show different crystal quality and curvature values of the substrates. Micro-Raman show different residual stress of the substrates before and after the thinning process. Moreover, molten KOH etching for dislocation detection also show different value of dislocation density for both substrates.

Hydrogen etching influence on 4H-SiC homo-epitaxial layer for high power device

The surface preparation of 4H-SiC substrate plays a crucial role for the epitaxial growth. In the present work, the Hydrogen etching influence on 4H-SiC surface of substrate before the growth process was studied. The epi-layer was grown .with a commercial low-pressure, hot-wall Chemical Vapor Deposition (CVD) reactor by Tokyo Electron Limited. The etching time of the surface was increased until three time (x3) respect with the normal value usually adopted for the growth. Photoluminescence and optical inspection analyses show a clear relationship between the etching time and the defectivity. Atomic Force Microscope (AFM) measurements also show an increase of step bunching with the etching time.