C. Serre

Ion‐beam synthesis of amorphous SiC films: Structural analysis and recrystallization

The analysis of SiC films obtained by carbon ion implantation into amorphous Si (preamorphized by Ge ion implantation) has been performed by infrared and Raman scattering spectroscopies, transmission electron microscopy, Rutherford backscattering, and x‐ray photoelectron spectroscopy (XPS). The data obtained show the formation of an amorphous Si1−xCx layer on top of the amorphous Si one by successive Ge and C implantations. The fitting of the XPS spectra indicates the presence of about 70% of Si–C bonds in addition to the Si–Si and C–C ones in the implanted region, with a composition in the range 0.35<x<0.6. This points out the existence of a partial chemical order in the layer, in between the cases of perfect mixing and complete chemical order. Recrystallization of the layers has been achieved by ion‐beam induced epitaxial crystallization (IBIEC), which gives rise to a nanocrystalline SiC layer. However, recrystallization is not complete, observing still the presence of Si–Si and C–C bonds in an amorphou...

Determination of micromechanical properties of thin films by beam bending measurements with an atomic force microscope

Micromechanical measurements have been performed with a beam bending based technique using an atomic force microscope (AFM). This technique combines a very high load resolution with a nanometric precision in the measurement of the cantilever deflection. It has been applied to the determination of the Youngs modulus of different micromachined structures as polysilicon and β-SiC cantilever beams. This has required the previous calibration of the technique. The different characteristics of the analysed structures determined the need to use different AFM probes, being the optimum measuring condition achieved when both the probe and the beam have similar force constants. The results obtained show the ability of the proposed technique for the micromechanical assessment of miniaturised structures, which is required for development and optimisation of advanced micromachining technologies.

Analysis of ion beam induced damage and amorphization of 6H-SiC by Raman scattering

Raman scattering analysis of damaged SiC layers obtained by 200 keV Ge+ ion implantation into 6H-SiC has been performed as a function of the implanted dose (up to 1015 cm−2) and annealing temperature (up to 1500°C). The results obtained show the presence of three different damage levels: low damage level (doses ≤3 × 1012 cm−2), medium to high damage level (doses between 1013 and 1014 cm-2), and formation of a continuous amorphous layer for doses higher than the amorphization threshold of 2–3 × 1014 cm−2.Moreover, at doses of about 1014 cm−2 (below the amorphization threshold) amorphous domains are already observed. The Raman spectra indicate the existence of structural differences between the amorphous phase at doses below and above the threshold. After annealing, there is a residual damage which cannot be removed even at the highest annealing temperature of 1500°C. Differences in residual damage between the samples implanted at doses of 1014 and 1015 cm-2 and annealed at the highest temperatures are observed from the peaks in the 1000–1850 cm-1 spectral region. Finally, annealing at the highest temperature is required to observe the complete disappearance of the amorphous bands.

Spectroscopic characterization of phases formed by high-dose carbon ion implantation in silicon

High‐dose carbon‐ion‐implanted Si samples have been analyzed by infrared spectroscopy, Raman scattering, and x‐ray photoelectron spectroscopy (XPS) correlated with transmission electron microscopy. Samples were implanted at room temperature and 500 °C with doses between 1017 and 1018 C+/cm2. Some of the samples were implanted at room temperature with the surface covered by a capping oxide layer. Implanting at room temperature leads to the formation of a surface carbon‐rich amorphous layer, in addition to the buried implanted layer. The dependence of this layer on the capping oxide suggests this layer to be determined by carbon migration toward the surface, rather than surface contamination. Implanting at 500 °C, no carbon‐rich surface layer is observed and the SiC buried layer is formed by crystalline β‐SiC precipitates aligned with the Si matrix. The concentration of SiC in this region as measured by XPS is higher than for the room‐temperature implantation.

Synthesis of SiC Microstructures in Si Technology by High Dose Carbon Implantation: Etch‐Stop Properties

The use of high dose carbon ion implantation in Si for the production of membranes and microstructures is investigated. Si wafers were implanted with carbon doses of 10{sup 17} and 5 {times} 10{sup 17} cm{sup {minus}2}, at an energy of 300 keV and a temperature of 500 C. The structural analysis of these samples revealed the formation of a highly stable buried layer of crystalline {beta}-SiC precipitates aligned with the Si matrix. The etch-stop properties of this layer have been investigated using tetramethyl-ammonium hydroxide as etchant solution. Secondary ion mass spectrometry measurements performed on the etched samples have allowed an estimate of the minimum dose needed for obtaining an etch-stop layer to a value in the range 2 to 3 {times} 10{sup 17} ions/cm{sup 2}. This behavior has been explained assuming the existence of a percolation process in a SiC/Si binary system. Finally, very thin crystalline membranes and self-standing structures with average surface roughness in the range 6 to 7 nm have been obtained.

Growth of GaN layers on SiC/Si(111) substrate by molecular beam epitaxy

High quality GaN layers were grown by molecular beam epitaxy (MBE), with and without AlN buffer, on SiC/Si(111) substrates obtained by C implantation into Si(111) at 500 °C to avoid amorphization. Thermal annealing at 1150 °C for 6 h produced crystalline SiC layers embedded into the Si(111). The SiC top stoichiometry is controlled by reactive ion etching (RIE), after what, all SiC layers show a fairly flat (4 nm) and specular surface. Photoluminscence spectra reveal that all GaN layers are under tensile biaxial strain of thermal origin. GaN layers grown on stoichiometric SiC have lower mosaicity, but also less photoluminescence efficiency and tensile strain, as compared to GaN on bare non-stoichiometric SiC. This, most likely, relates to changes in microcrystals size and grain boundaries density, that depend strongly on the GaN nucleation process. Despite the partial polycrystalline nature of the SiC/Si(111), the grown GaN quality is as high or even better than that from GaN grown on Si(111).

Test microstructures for measurement of SiC thin film mechanical properties

In this work, test microstructures for SiC film mechanical property measurements by beam bending using an atomic force microscope are presented. Crystalline 300 nm thick -SiC layers obtained by high temperature multiple C implantation into Si have been used. The low residual stress level in the layers along with the high stiffness and excellent etch-stop properties of SiC allowed the fabrication of free standing microstructures using standard Si bulk micromachining techniques. This demonstrates the potential of SiC as an alternative to Si for MEMS applications.

Detailed analysis of β-SiC formation by high dose carbon ion implantation in silicon

The detailed characterization of β-SiC formation in silicon by high dose carbon ion implantation is reported. A buried layer containing β-SiC precipitates of 7–10 nm in size is directly formed by implanting at 500 °C. The precipitates formed are almost perfectly aligned with the silicon substrate, but they present incoherent interfaces to it, and are nearly free of defects. After implantation, the crystallinity of β-SiC precipitates is improved by an annealing step, although their size remains unchanged.

β-SiC on SiO2 Formed by ION Implantation and Bonding for Micromechanics Applications

β-SiC on SiO2 multilayer structures have been fabricated by ion implantation into Si substrates and thermal bonding. This process involves three steps: i) multiple energy C+ implants into Si, to obtain a broad buried β-SiC layer, ii) selective oxidation of the top Si layer, and iii) bonding and etch-back of Si. These are processes compatible with Si processing technology, and permit high crystalline quality β-SiC films on SiO2 to be formed without using expensive bulk SiC or Silicon-On-Insulator wafers. The structures have been characterised after the different process steps mainly by Fourier Transform Infrared Spectroscopy, X-Ray Photoelectron Spectroscopy, Secondary Ion Mass Spectroscopy and Atomic Force Microscopy. The analysis of samples processed after the different steps has allowed the key parameters for fabricating high quality structures for electronic devices and sensors applications to be defined.

Microinductive Signal Conditioning With Resonant Differential Filters: High-Sensitivity Biodetection Applications

Inductive-based devices integrated with Si technology for biodetection applications are characterized, using simple resonant differential filter configurations. This has allowed the corroboration of the viability of the proposed circuits, which are characterized by their very high simplicity, for microinductive signal conditioning in high-sensitivity sensor devices. The simulation of these simple circuits predicts sensitivities of the differential output voltage which can achieve values in the range of 0.1-1 V/nH, depending on the coil parameters. These very high-sensitivity values open the possibility for the experimental detection of extremely small inductance changes in the devices. For real microinductive devices, both series resistance and parasitic capacitive components contribute to the decrease of the differential circuit sensitivity. Nevertheless, measurements performed using micro-coils fabricated with relatively high series resistance and coupling parasitic effects have allowed detection of changes in the range of 2 nH. which are compatible with biodetection applications with estimated detection limits below the picomolarity range.