Properties of thermally annealed undoped and sulphur doped InP wafers

Abstract

Different thermal treatments on bulk undoped and S doped InP were carried out. The ambient atmosphere, temperature, heating, and cooling conditions were varied to study the influence of each individual parameter on sample characteristics. It is apparent that annealing in a P atmosphere is preferable for electrical and crystallographic homogeneity. The physical and structural properties of InP annealed under vacuum suggest that indiffusion of In takes place. The In at the surface is available because of the rapid P evaporation during the sample heating. Depending on the cooling conditions, the diffused In atoms can be gettered by dislocations and cause micro defects. A hypothesis of In_p antisite formation (and corresponding suppression of P vacancies) is also proposed to justify the Hall, photoluminescence, and positron lifetime data.

MST/3337     

Structural changes in phosphorus-ion-implanted silicon

The structural changes produced in the near-surface region of single-crystal Si upon fabrication of delta back-surface-field devices were studied by x-ray diffraction in an offset-asymmetric geometry. The results demonstrate that implantation of 180-keV P⁺ ions into Si with a dose on the order of 10¹⁵ cm^-2, followed by thermal annealing, allows buried amorphous Si layers to be produced. The structures thus prepared suffer a significant lattice strain perpendicular to the interface.     

Ion beam synthesis of aluminium nitride: characterisation of thin AIN layers formed in microelectronics aluminium

Abstract

Buried AlN thin layers have been formed by high dose N⁺ ion implantation into microelectronics grade Al films (containing 1 at.-%Si), which were deposited on Si wafers. The structures obtained have been characterised by spreading resistance measurements, transmission electron microscopy, secondary ion mass spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. The results show the formation of buried dielectric precipitates of crystalline AlN at implantation doses below the threshold and a continuous polycrystalline AlN layer at doses above the threshold. The AlN grains have the wurtzite structure, sizes of about 10–15 nm, and a preferred orientation in relation to the Al matrix, namely, <110>_AIN parallel to <110>_Al. The data also show that, under certain conditions, the main impurities (Si and O) are gettered in the buried layer. Moreover, for thin Al films, the formation of a Si rich surface layer is observed. This surface layer is formed by Si diffusion from the substrate, probably due to the penetration of N⁺ ions into the Si substrate. The distribution and evolution of these impurities and the different phases formed are studied as a function of the thickness and grain size of the Al film, as well as of the annealing processes.

MST/3304     

Some properties of metal/insulator/semiconductor structures with BN and carbon thin layers formed by the reactive pulse plasma method on silicon or SiO2 substrates and annealing effects

Thin layers (100–300 nm) of BN and diamond-like carbon were produced by the reactive pulse plasma method. On the basis of measurements and analysis of electrical properties of metal/insulator/semiconductor (MIS) capacitors, with a BN or carbon layer acting as the dielectric and silicon as the semiconductor, operating parameters were identified for the BN/Si and C/Si structures. A double layer of thermal SiO₂ and either BN or carbon was also used as a dielectric. The structures produced were subjected to annealing at temperatures from 100 to 500°C in N₂ and O₂ atmospheres.Using the spectral investigation method, BN and carbon layers produced on quartz and KBr substrates were examined for their probable composition (IR absorption analysis), absorption coefficient α and refractive index n. After annealing at temperatures of 300–400°C, a marked improvement in the electrical performance of MIS structures was found as well as storage of charge in the double-layer dielectric structures. Hydrogen and oxygen were also found to be present in the test layers. On the basis of the analysis of the electrical characteristics it is assumed that dehydrogenation of the layers during thermal treatment is one of the reasons why their electrical properties tend to vary with time.     

Heteroepitaxial growth of indium phosphide on silicon by MOCVD using adduct source

Abstract

The heteroepitaxial growth of InP on Si by low pressure metalor‐ganic chemical vapor deposition is reported. Trimethylindium‐trimethylphosphine adduct was used as In source in this study. From X‐ray and SEM examinations, good crystallinity InP epilayers with mirror‐like surfaces can be grown directly on (100) and (111) p‐type Si substrates. Carrier concentration profile shows that the carrier distribution in the InP epilayer is very uniform. The efficient photo‐luminescence compared with that of InP homoepitaxy shows the good quality of InP/Si epilayers.     

Properties of SiO2 films formed by oxygen implantation into silicon

Oxygen ions with energies of 5–60 keV were implanted into Si at doses of 10¹⁵–10¹⁸ ions cm^?2 to form SiO₂ layers. Annealing was carried out in nitrogen at 500–1000 °C and in hydrogen at 450 °C. By monitoring the IR transmission spectra, the refractive index, the etching behaviour and the electrical characteristics, it was established that stoichiometric SiO₂ layers can be produced with doses of 10¹⁸ ions cm^?2 on annealing at 700–1000 °C. A voltage-dependent capacitance was obtained only for samples implanted with a dose of 10¹⁸ ions cm^?2 and annealed at 1000 °C in nitrogen and at 450 °C in hydrogen. In the interface state spectrum of such samples, maxima at 0.55 eV and at 0.80 eV below the conduction band were found.     

Electronic properties of silicon nanocrystallites obtained by SiOx (x<2) annealing

Nanocrystal-based devices are possible candidates for future electronics. In this context, we have studied the electronic properties of Si nanocrystals (nc-Si) embedded in a SiO₂ matrix. This work is devoted to the characterization of nc-Si by means of morphological, optical and electrical techniques.SiO_x (x<2) layers are deposited by low-pressure chemical vapor deposition (LPCVD). Morphological measurements have shown that the as-deposited layers are homogeneous and that thermal annealing induces a precipitation of the excess silicon into nanocrystallites. Photoluminescence (PL) measurements show a large emission spectrum around 1.5 eV in agreement with the literature results for confined levels in 5-nm Si dots.Current–voltage (I–V) measurements recorded at different temperatures on metal-oxide-semiconductor (MOS) capacitors with nc-Si are analysed in terms of structural and electronic modifications induced by the annealing. The as-deposited SiO_x layers show a Poole–Frenkel conduction behavior. In annealed samples, it appears that the current follows a hopping transport mechanism. This is understood as a direct tunneling from dots to dots.Finally, it is shown that the annealed SiO_x is able to store carriers and is therefore a good candidate for non-volatile memory applications. Charging curves are presented and discussed with a model previously validated on MOS structures with silicon dots obtained by pure silane deposition.     

Growth condition dependence of structural and electrical properties of Mg2Si layers grown on silicon substrates

Mg₂Si layers were grown on Si substrates by thermal treatment of the substrates in a Mg vapor, and the growth condition dependence of the structural and electrical properties of the layers was investigated. The layers were grown by an interdiffusion process between the deposited Mg atoms and the substrates. The structural and electrical properties of the layers depend on the combinations of the Si substrate and Mg source temperatures during the heat treatment. Any deviation from the isothermal treatment conditions causes degradation of the structural and/or electrical properties of the Mg₂Si layers. It was confirmed that the layers with the optimum structural and electrical properties were obtained when the layers were grown under isothermal growth conditions.     

Formation and photoluminescence of Si nanocrystals in controlled multilayer structure comprising of Si-rich nitride and ultrathin silicon nitride barrier layers

The effect of ultrathin silicon nitride (Si₃N₄) barrier layers on the formation and photoluminescence (PL) of Si nanocrystals (NCs) in Si-rich nitride (SRN)/Si₃N₄ multilayer structure was investigated. The layered structures composed of alternating layers of SRN and Si₃N₄ were prepared using magnetron sputtering followed by a different high temperature annealing. The formation of uniformly sized Si NCs was confirmed by the transmission electron microscopy and X-ray diffraction measurements. In particular, the 1 nm thick Si₃N₄ barrier layers was found to be sufficient in restraining the growth of Si NCs within the SRN layers upon high annealing processes. Moreover, X-ray photoelectron spectroscopy spectra shown that films subjected to post-anneal processes were not oxidized during the annealing. X-ray reflection measurements revealed that high annealing process induced low variation in the multilayer structure where the 1 nm Si₃N₄ layers act as good diffusion barriers to inhibit inter-diffusion between SRN layers. The PL emission observed was shown to be originated from the quantum confinement of Si NCs in the SRN. Furthermore, the blue shift of PL peaks accompanied by improved PL intensity after annealing process could be attributed to the effect of improved crystallization as well as nitride passivation in the films. Such multilayer structure should be advantageous for photovoltaic applications as the ultrathin barrier layer allow better electrical conductivity while still able to confine the growth of desired Si NC size for bandgap engineering.     

Interfacial reaction of Mo-W alloys with silicon

Solid state contact reactions of thin films of Mo_xW_100−x (x =85, 57, 22) with silicon have been studied using Rutherford backscattering spectrometry, X-ray diffraction and scanning electron microscopy. Reactions and silicide formation were obtained by thermal annealing at temperatures between 450 and 900°C for all the alloys. No layer-by-layer phase separation was observed during silicide growth for the alloy-silicon reaction at these temperatures. The reaction temperature increased with increasing tungsten concentration in the alloys. Ion implantation of 4×10¹⁵ cm⁻² of silicon at 250 keV into Mo₅₇W₄₃/Si and Mo₂₂W₇₈/Si reduced their reaction temperatures and also made the reaction products more uniform.     

High-sensitive MIS structures with silicon nanocrystals grown via solid-state dewetting of silicon-on-insulator for solar cell and photodetector applications

This work reports an original method for the fabrication of metal–insulator–semiconductor (MIS) structures with silicon nanocrystals (Si NCs)-based active layers embedded in the insulating SiO₂ oxide, for high-performance solar cell and photodetector applications. The Si NCs are produced via the in situ solid-state dewetting of ultra-pure amorphous silicon-on-insulator (a-SOI) grown by solid source molecular beam epitaxy (SSMBE). The size and density of Si NCs are precisely tuned by varying the deposited thickness of silicon. The morphological characterization carried out by using atomic force microscopy (AFM) and scanning electron microscopy (SEM) shows that the Si NCs have homogeneous size with well-defined spherical shape and densities up to ~?10¹² /cm² (inversely proportional to the square of nominal a-Si thickness). The structural investigations by high-resolution transmission electron microscopy (HR-TEM) show that the ultra-small Si NCs (with mean diameter?~?7 nm) are monocrystalline and free of structural defects. The electrical measurements performed by current versus voltage (I–V) and photocurrent spectroscopies on the Si NCs-based MIS structures prove the efficiency of Si NCs to enhance the electrical conduction in MIS structures and to increase (×?10 times) the photocurrent (i.e., at bias voltage V = ??1 V) via the photo-generation of additional electron–hole pairs in the MIS structures. These results evidence that the Si NCs obtained by the combination of MBE growth and solid-state dewetting are perfectly suitable for the development of novel high-performance optoelectronic devices compatible with the CMOS technology.

     

Electrical properties of boron- and phosphorous-doped microcrystalline silicon thin films prepared by magnetron sputtering of heavily doped silicon targets

The boron(B)- and phosphorous(P)-doped microcrystalline silicon (Si) thin films were prepared by magnetron sputtering of heavily B- and P-doped Si targets followed by rapid thermal annealing (RTA), their electrical properties were characterized by temperature-dependent Hall and resistivity measurements. It was observed that the dark conductivity and carrier concentration of the 260 nm B-doped Si films annealed at 1,100 °C in Ar were 3.4 S cm^?1 and 1.6 × 10¹⁹ cm^?3, respectively, which were about one order of magnitude higher than that of P-doped Si films. The activation energy of the B- and P-doped Si films were determined to be 0.23 eV and 0.79 eV, respectively. The dark conductivity of B- and P-doped Si films increased with the increase of film thickness, RTA temperature, and the incorporation of H₂ in Ar during RTA. The present work provides an easy and non-toxic method for the preparation of doped microcrystalline Si thin films.     

Mixage ionique sur des structures Au/InP

The reactions induced by Zn⁺ implantations near the interface of Au/InP contacts have been studied by using scanning electron microscopy, X-ray diffraction, He⁺ Rutherford backscattering, secondary ion mass spectrometry and current-voltage measurements. A 5 × 10¹⁴ Zn ions cm^-2 dose does not induce compound formation but accelerates the growth of Au₃In and Au₂P₃ patches during post-annealing treatment. After a 5 × 10¹⁵ Zn ions cm^-2 implantation, many compounds, different from those obtained by a thermal anneal, are detected. These compounds, which depend on the implantation temperature (25 or 200°C), have a layered structure. In this case no Au₂P₃ is observed. However, for the range of doses (from 10¹⁴ to 5 × 10¹⁵ Zn ions cm^-2), the temperatures of implantation (25 and 200°C) and the range of annealing temperatures (from 320 to 450°C) that were studied, no contact with a low resistivity is formed. The electrical properties are in fact limited by an InP layer damaged by the ion implantation in which the zinc atoms are trapped in an electrically inactive form.     

Electrical characterization of deep levels existing in fully implanted and rapid thermal annealed p+n InP junctions

In this paper, the deep levels existing in fully implanted and rapid thermal annealed p⁺n junctions obtained by Mg/Si or Mg/P/Si implantations on nominally undoped n-type InP substrates were detected and characterized by the correlation of two electrical techniques: deep level transient spectroscopy (DLTS) and capacitance–voltage transient technique (CVTT). Two ion implantation-induced deep levels (at 0.25 and 0.27 eV below the conduction band) were detected by DLTS. Several characteristics of these traps were derived from CVTT measurements, paying special attention to their physical nature.     

The formation of SiO2 films on silicon by high dose oxygen ion implantation

High dose oxygen ion implantation into silicon at 30 keV was performed to produce SiO₂ surface layers.The oxygen profile, stoichiometry and volume swelling were studied by Rutherford backscattering at doses of up to 2 × 10¹⁸cm^?2 and for various current densities. The surface structure and lateral homogeneity of the inslation properties were investigated by scanning electron microscopy and the liquid crystal technique respectively. By means of current-voltage and capacitance-voltage measurements the electrical properties of the layers produced were determined.A qualitative model of the formation of SiO₂ during high dose oxygen implantation into silicon is proposed. Blistering caused by implantation at high current densities leads to oxygen losses and to conductive channels in the dielectric layer. Except for their interface properties the SiO₂ films produced are comparable with thermal oxides.     

Investigation of Sb diffusion in amorphous silicon

Amorphous silicon materials and its alloys became extensively used in some technical applications involving large area of the microelectronic and optoelectronic devices. However, the amorphous-crystalline transition, segregation and diffusion processes still have numerous unanswered questions. In this work we study the Sb diffusion into an amorphous Si film by means of Secondary Neutral Mass Spectrometry. Amorphous Si/Si_1−xSb_x/Si tri-layer samples with 5 at% antimony concentration were prepared by direct current magnetron sputtering onto Si substrate at room temperature. Annealing of the samples was performed at different temperatures in vacuum (p<10⁻⁷ mbar) and 100 bar high purity (99.999%) Ar pressure. During annealing a rather slow mixing between the Sb-alloyed and the amorphous Si layers was observed. Supposing concentration independent of diffusion, the evaluated diffusion coefficients are in the range of ∼10⁻²¹ m²s⁻¹ at 550 °C.     

Significance of the interface regarding magnetic properties of manganese nanosilicide in silicon

Magnetic properties of manganese (Mn) nanosilicide embedded in thin silicon-on-insulator (SOI) layers are investigated. Mn nanosilicide formed by Mn⁺ ion implantation into a thin SOI layer followed by a thermal annealing at 600-900 °C shows soft ferromagnetism or superparamagnetism at 5 K. A monotonic decrease of the saturation magnetization is observed with increasing temperature for post implantation annealing and consequently with increasing mean particle size of nanosilicide. In addition, the magnetization is found to be enhanced when the Si surrounding the Mn nanosilicide is selectively removed. These results indicate that the magnetic moment indeed arises from the nanosilicide and is sensitive to the interface conditions.     

Platinum gettering in silicon: precipitation of PtSi on diffusion induced dislocations and on SiP precipitates

Abstract

Transmission electron microscopy was used to study Si/SiO₂ interfaces in Pt doped fast rectifiers. Orthorhombic PtSi (monocrystalline) precipitates at the n⁺-Si/SiO₂ and p⁺-Si/SiO₂ interfaces were observed. This precipitation can be related to the presence of dislocations induced by the P or B doping (networks parallel to the surface) and to SiP precipitates. Two epitaxial relationships were observedfor the PtSi precipitation: (010) PtSi || {111} Si and (001) PtSi || {110} Si. Different Pt diffusion temperatures and cooling rates were used and it was shown that the reverse recovery time is influenced by the diffusion temperature, whereas the gettering efficiency and the occurrence of soft breakdown are reduced by slow cooling.     

Investigation of thermal properties of Al–Si matrix reinforced fine SiCp composites

Abstract

The characterisation of thermal expansion coefficient and thermal conductivity of Al–Si matrix alloy and Al–Si alloy reinforced with fine SiC_p (5 and 20 wt-%) composites fabricated by stir casting process are investigated. The results show that with increasing temperature up to 350°C, thermal expansion of composites increases and slowly reduces when the temperature reaches to 500°C. The values of both thermal expansion and conductivity of composites are less than those for Al–Si matrix. Microstructure and particles/matrix interface properties play an important role in the thermal properties of composites. Thermal properties of composites are strongly dependent on the weight percentage of SiC_p.     

Electron microscopy study of ion beam synthesized β-FeSi2

β-FeSi₂ embedded in a Si matrix was prepared by ion beam synthesis (IBS). Two step implantation, with energies 60 and 20 keV, of two different doses of the iron ions, 5 × 10¹⁵ and 5 × 10¹⁶ cm⁻¹, was performed. After the implantation, the samples were subjected to rapid thermal annealing (RTA) at 900 °C. The crystal structure of the resulting material was studied using cross-sectional transmission electron microscopy (XTEM), including high-resolution electron microscopy (HREM). The comparison of the XTEM images with the initial iron ions implantation profiles, simulated by SRIM (Stopping and Range of Ions in Matter) demonstrate that the process of IBS, followed by RTA, preserves the initial implantation profile, implying a negligible Fe atoms diffusion velocity in comparison with the one of the chemical reaction between Fe and Si. The XTEM images show that continuous β-FeSi₂ layers are fabricated when there is a stoichiometric region in the initial implantation profile. Fe concentration lower than the stoichiometric one in the whole implantation range results in formation of β-FeSi₂ nanocrystallites embedded in the Si matrix. The behavior of the absorption coefficient energy dependences, obtained from the optical transmittance and reflectance measurements, reflects the different crystal structures forming in the two types of samples.