M. Östling

Enhanced formation of the C54 phase of TiSi2 by an interposed layer of molybdenum

The phase formation during rapid thermal annealing of a Ti/Mo bilayer sequentially deposited on Si substrates has been studied. The Mo layer varied from 0.5 to 2 nm and the Ti layer was always 60 nm thick. The presence of the Mo interposing layer enhances the formation of the C54 of TiSi2 by first forming a Mo‐bearing silicide phase of hexagonal structure. The desired C54 phase then nucleates and grows on top of this Mo‐bearing silicide phase at a temperature as low as 650 °C via Si diffusion through the growing silicide layers. This is about 100 °C lower than what is usually needed for the C49–C54 transformation. The significance of this finding is that the usual route for the formation of TiSi2, i.e., the C49 phase forms as a result of the Ti–Si interaction and the C54 phase forms as the product of phase transformation, is altered by the interposition of a thin refractory metal (here Mo) layer between Ti and Si.

Thermally stable low ohmic contacts to p-type 6HSiC using cobalt silicides

Abstract Cobalt silicide (CoSi 2 ) ohmic contacts possessing low specific contact resistivity ( p c −6 μ cm 2 ) to p -type 6HSiC are reported. The contacts were fabricated through sequential electron-beam evaporation of Co and Si layers forming a Si/Co/SiC structure, followed by a two-step vacuum annealing process at 500 and 900°C, respectively. Specific contact resistivities were extracted from transmission line model (TLM) structures at temperatures ranging from 22 to 200°C. p c is investigated as a function of current density, temperature and ageing in a vacuum furnace at 1100°C. Furthermore, comparison with a Co SiC contact structure subjected to an identical annealing process revealed higher p c and a modified sheet resistance requiring a different method of contact parameter extraction.

Morphological instabilities of nickel and cobalt silicides on silicon

Abstract The morphological instability of bilayers of NiSi, or CoSi 2 , on polysilicon has been investigated as a function of the thickness of the silicide, the presence of alloying additions and the initial oxidation of the silicide layer. The effect of Ir additions in enhancing the stability of the bilayers and the formation of NiSi 2 confirms the expectation that the morphological instabilities and the nucleation of NiSi 2 are dictated by surface energy effects (capillarity). Stresses may play a role in the initial step of the process which ultimately leads to a nearly complete inversion of the positions of the silicide and polysilicon layers. However, it is quite certain that the main driving force is the change in grain boundary energy of the polysilicon which starts with very small grains to begin with and ends up, at a different location, with much bigger grains.

Lateral encroachment of Ni-silicides in the source/drain regions on ultrathin silicon-on-insulator

Lateral growth of Ni silicide towards the channel region of metal-oxide-semiconductor transistors (MOSFETs) fabricated on ultrathin silicon-on-insulator (SOI) is characterized using SOI wafers with a 20-nm-thick surface Si layer. With a 10-nm-thick Ni film for silicide formation, p-channel MOSFETs displaying ordinary device characteristics with silicided p+ source/drain regions were demonstrated. No lateral growth of NiSix under gate isolation spacers was found according to electron microscopy. When the Ni film was 20 nm thick, Schottky contact source/drain MOSFETs showing typical ambipolar characteristics were obtained. A severe lateral encroachment of NiSix into the channel region leading to an increased gate leakage was revealed, while no detectable voiding at the silicide front towards the Si channel was observed.

1/f noise in Si and Si/sub 0.7/Ge/sub 0.3/ pMOSFETs

Strained layer Si/sub 0.7/Ge/sub 0.3/ pMOSFETs were fabricated and shown to exhibit enhanced hole mobility, up to 35% higher for a SiGe device with 3-nm-thick Si-cap, and lower 1/f noise compared to Si surface channel pMOSFETs. The 1/f noise in the investigated devices was dominated by mobility fluctuation noise and found to be lower in the SiGe devices. The source of the mobility fluctuations was determined by investigating the electric field dependence of the 1/f noise. It was found that the SiO/sub 2//Si interface roughness scattering plays an important role for the mobility fluctuation noise, although not dominating the effective mobility. The physical separation of the carriers from the SiO/sub 2//Si interface in the buried SiGe channel pMOSFETs resulted in lower SiO/sub 2//Si interface roughness scattering, which explains the reduction of 1/f noise in these devices. The 1/f noise mechanism was experimentally verified by studying 1/f noise in SiGe devices with various thicknesses of the Si-cap. A too large Si-cap thickness led to a deteriorated carrier confinement in the SiGe channel resulting in that considerable 1/f noise was generated in the parasitic current in the Si-cap. In our experiments, the SiGe devices with a Si-cap thickness in the middle of the interval 3-7 nm exhibited the lowest 1/f noise.

CoSi2 ohmic contacts to n-type 6HSiC

Cobalt disilicide (CoSi2) ohmic contacts possessing low specific contact resistivity (ϱc < 3.0 ± 0.4 × 10−5 ωcm2) to n-type 6HSiC are reported. The contacts were fabricated via sequential electron-beam evaporation of Co and Si layers followed by a two-step vacuum anealing process at 500 and 900°C. Stochiometry of the contact so formed was confirmed by Rutherford backscattering spectrometry and X-ray diffraction. Specific contact resistivities were obtained via current-voltage (I-V) analysis at temperatures ranging from 25 to 500°C. ϱc is compared as a function of carrier concentration, current density, temperature and time at elevated temperature.

Formation of iron disilicide on amorphous silicon

Abstract Thin films of iron disilicide, β-FeSi 2 were formed on both amorphous silicon and on crystalline silicon. The β-phase is reported to be semiconducting with a direct band-gap of about 0.85–0.89 eV. This phase is known to form via a nucleation-controlled growth process on crystalline silicon and as a consequence a rather rough silicon/silicide interface is usually formed. In order to improve the interface a bilayer structure of amorphous silicon and iron was sequentially deposited on Czochralski 〈111〉 silicon in an e-gun evaporation system. Secondary ion mass spectrometry profiling (SIMS) and scanning electron micrographs revealed an improvement of the interface sharpness. Rutherford backscattering spectrometry (RBS) and X-ray diffractiometry showed β-FeSi 2 formation already at 525°C. It was also observed that the silicide growth was diffusion-controlled, similar to what has been reported for example in the formation of NiSi 2 for the reaction of nickel on amorphous silicon. The kinetics of the FeSi 2 formation in the temperature range 525–625°C was studied by RBS and the activation energy was found to be 1.5 ± 0.1 eV.

Silicon nitride films deposited from SiH2Cl2NH3 by low pressure chemical vapor deposition: kinetics, thermodynamics, composition and structure

Abstract The growth of stoichiometric and non-stoichiometric silicon nitride films was studied experimentally on 100 mm silicon wafers by batch depositions from the dichlorosilane (SiH2Cl2)-ammonia (NH3) system in a hot-wall horizontal low pressure chemical vapor deposition (LPCVD) reactor. The growth kinetics were discussed in terms of the Langmuir adsorption isotherm. The kinetic parameters were determined by comparing the experimental data with a one-dimensional simulation model. The decomposition of NH3 at high temperatures was included in the simulation procedure. When the SiH2Cl2:NH3 ratios were greater than 1.5, a quantity higher than the thermodynamic critical values above which Si-rich nitride films begin to deposit, various SiNx films with x 4 3 were obtained. The composition of the SiNx films was found to vary along the LPCVD reactor. The film stoichiometry was examined by Rutherford backscattering and ellipsometry measurements. According to kinetic and thermodynamic studies, the pyrolysis of dichlorosilane at elevated temperatures (> 700 °C) is the cause for the deposition of Si-rich nitride films. Furthermore, two types of deposited SiNx films were observed; one type showed a typical film density around 3.70 g cm−3 while the other type exhibited a remarkably lower film density below 3.50 g cm−3.

A low-complexity 62-GHz fT SiGe heterojunction bipolar transistor process using differential epitaxy and in situ phosphorus-doped poly-Si emitter at very low thermal budget

A low-complexity SiGe heterojunction bipolar transistor process based on differential epitaxy and in situ phosphorus doped polysilicon emitter technology is described. Silane-based chemical vapor d ...

Strain balance approach for optimized signal-to-noise ratio in SiGe quantum well bolometers

This work presents thermal and electrical characterization of SiGe/Si multi-quantum wells (MQWs) with different layer profiles in complete bolometer structures. The thermal property of the bolometers was studied by measuring thermal coefficient of resistivity (TCR) through I–V curves for five temperatures (25, 40, 55, 80 and 100°C) and for four different pixel areas. The results show a strong dependency of TCR on the Si/SiGe layer thickness and the presence of dopant impurity in the MQW. The noise measurements of MQWs were performed carefully by eliminating all external contributions and the noise spectroscopy provided the noise characteristic parameters. The results demonstrate that the noise depends on the geometric size of the MQW and it increases with decreasing of the pixel area. The investigations show the noise level in the bolometer structures is sensitive to any dopant segregation from the contact layers.