In this paper, we explore the loading effect during reactions of TiC14(g) with Si(s) to form selective TiSi2 in a tungsten halogen lamp heated, cold wall rapid thermal chemical vapor deposition reactor. The process is intended as a replacement for the conventional sellaligned silicide process with the capability of reducing the process steps from four to one. In the absence of a Si source gas for this process, the Si is supplied from the substrate forming TiSi2 via consumption. The chemistry is highly selective to both Si02 and Si3N4. However, it has been previously shown by our group and others that TiSi2 formation can be accompanied by Si substrate etching which can be suppressed by adding H2 to the chemistry. In this study, we have considered cxposed Si area percentages ranging from 18% to 88% on 4” Si substrates. Two simplified gas systems are used to closely examine substrate etching and consumption: TiCI4 - Si(s) and TiCI4 - Si(s) - H2 The Si etch and consumption rates are evaluated for these varying exposure percentages. We have found that the substrate etch rate increases as the exposed area to be etched is decreased as does the substrate consumption rate.

CVD WSix, films have found widespread use as ultra thin gate, wordline and bitline interconnects due to the lower resistance that polycide offers. For submicron technologies, WSix films based on the monosilane chemistry shows limitations due to the incorporation of high concentrations of Fluorine ions and poor step coverage. Recent work has shown that, WSix films based on the dichlorosilane (DCS) chemistry minimizes these problems. One of the major issues in DCS WSix films is the in-depth compositional non uniformity, especially those deposited on poly-Si substrates. The formation of a W-rich region at the WSix/poly-Si interface can cause localized stresses which can result in cracking and adhesion problems. In this paper, we report the composition and structure of DCS WSix, films deposited on undoped, doped and in situ doped poly-Si and oxide substrates. We have investigated the effect of different processing conditions on Si/W uniformity and the formation of W-rich and Si-rich interfaces, and the role of the nucleation step in modulating the Si/W ratio at the WSix/poly-Si interface. The impact of a Si-rich region at the WSix/poly-Si interface on silicide film properties has also been explored. RBS measurements were used to determine the composition profile through the depth of the film and Si/W uniformity in terms of Si-rich and W-rich interfaces. SIMS measurements were used to determine the impurity content in the silicide film and at the film/substrate interface.

The structural, electronic, optical, and electrical properties of semiconducting silicides with transition metals from the VIth to the Vlllth Group of the Periodic Table are reviewed. Main emphasis is put on ß-FeSi2. The review includes recent results on optical measurements from the infrared up to 24 eV. Typical similarities in the phonon and interband spectra are outlined. Gap energy determinations are critically discussed. Doping impurities are characterized by EPR. Electrical investigations revealed characteristic features of transport parameters depending on temperature and magnetic field. Possible fields of application are analyzed.

The kinetics of the phase transformations of the Fe-Si system and the Si/Fe and Fe/Si interfaces have been investigated by 57Fe conversion electron Mössbauer spectroscopy (CEMS). Single crystalline Fe films grown on Si(111) by molecular beam epitaxy (MBE) and polycrystalline Fe films grown by pulsed laser ablation deposition (PLD) have been thermally treated in vacuum and the formation of the different silicide phases has been monitored as function of temperature and time by CEMS.

Amorphous irondisilicide thin films were deposited on silicon substrates in a RF sputtering process, followed by rapid thermal crystallization by means of moving the thin film beneath a line-shaped electron beam to form β-FeSi2. Depending on the deposition process parameters, films of a different stoichiometry can be produced. The deviations from the 1:2 stoichiometry, which have been determined by Rutherford Backscattering (RBS), are related to changes in the microstructure (studied by microscopic methods like TEM and AFM), the infrared phonon spectra (measured by FTIR spectroscopy) and the electrical properties of the crystallized films. The microstructure of the iron disilicide thin films is improved when the composition significantly deviates from 2.0, probably due to silicon interstitials in the silicide thin film. Films of different stoichiometry result in p- or n-type thin films with carrier densities below 5×1018cm−3 and hall mobilities up to 180cm 2/Vs. First results show that not only β-FeSi2-siliconheterojunctions as reported before but also pn-β-FeSi2-homojunctions show rectifying behavior. Rapid thermal processing with the line electron beam leads to a further improvement of the film quality when the scan velocity is increased up to the order of several cm/s.

We report on the synthesis of β-FeSi2 bulk materials using Horizontal Gradient Freeze (HGF) method. Chunk and powder FeSi2 or high-purity Fe (4N) and Si (9N) were used as starting materials. Three values (1:2, 2:5 and 1:3) of the Fe:Si ratio were selected in the very narrow α and β ranges of the equilibrium phase diagram. Samples were melted between 1300°C and 1500°C in high purity graphite crucibles covered with boron nitride. After cooling, the samples were kept at 800°C and 900°C during 66 to 100 hours, leading to transformation from α to β phase. Cooling rate and annealing time were taken as the two main parameters to optimize the growth conditions. Principal structural characterization was made by X-ray diffraction (XRD). Correlation with stoichiometry was achieved using the results of Rutherford Backscattering Spectroscopy (RBS) and Electron Probe X-Ray Micro Analysis (EPXMA). The samples obtained from 1:2 ratio exhibited mainly β phase while the 2:5 ratio specimens revealed almost α phase structure. The samples prepared with 1:3 ratio was found as a mixture of α and β phases under Si-rich conditions.

The solid phase reaction of Fe thin films with (111) Si substrate was investigated at constant annealing temperature and time (700°C, 7 minutes) as a function of the initial iron film thickness (from 5 nm to 27.5 um in 2.5 nm steps). The formed phases were analysed by X-ray diffraction, Rutherford backscattering and transmission electron microscopy and optical microscopy.

After annealing FeSi phase was detected in the thinner samples. Samples with Fe layers thicker than 12.5 nm contained a β-FeSi2 phase. This special phase sequence was explained with the help of a nucleation controlled phase formation model, taking into consideration the critical radius of nuclei of the new phase. The advantages of using the film thickness as a variable during investigation of solid phase thin film reactions and the probable substrate effects are also discussed.

We have measured the Hall coefficient and the resistivity of single crystals of CrSi2. This compound crystallises in the hexagonal C40 structure and is generally reported as a semiconductor with a gap of around 0.35 eV. The resistivity is large, several hundreds of μΩ.cm and exhibits a metallic behaviour. RH leads to a hole concentration of 8.5×1026 m−3 at 300K.

The specific heat at low temperature (0.7 K < T < 8 K ) can be describe as the sum of an electronic (γΓ) and a phonon (βT3) contribution. The analysis of the data leads to θD = 556 K and to an electronic density of states which is only two times smaller than those obtained for the metallic parent compounds VSi2, NbSi2 and TaSi2. This result questions the semiconducting nature of the chromium disilicide.

Ellipsometric and reflectance spectroscopy in the range 1.4-5.0 eV as well as reflectance measurements in the infrared (10–80 meV) were performed on small single crystals of β FeSi2. The results show a clear anisotropy in the optical response which has been compared with theoretical calculations and data obtained on thin epitaxial films. Such a comparison gives evidence of the dependence of the optical response on the crystalline orientation of the film with respect to the surface.

Polycrystalline ß-FeSi2 layers prepared by codeposition of Si and Fe on cold and hot Si substrates and ß-FeSi2, crystals grown by chemical vapor transport were investigated. Resistivity and Hall effect measurements revealed the p-type conductivity of undoped material and the influence of some dopants of the iron group. The activation energy of a Cr-related acceptor was determined to about 85 meV. The mobility data were found to depend significantly on the purity of the preparation process.

A study of the electrical resisitivity of (Fex.Mn1−x)Si with 0 < x < 1 indicates a crossover from an almost semiconducting state in FeSi to a metallic one in MnSi. Optical measurements show that the electronic structure and the vibrational behaviour appears to be essentially uneffected by the Fe/Mn substitution. Instead, a change of the free carrier density occurs, yielding a temperature and stoichiometry dependent plasma frequency.

We report the vibrational spectra of β-FeSi2 calculated by molecular dynamics simulations with a tight binding potential and provide a quantitative confirmation of the anisotropic behaviour found by new Infrared (IR) measurements for small monocrystals This analysis allows for the interpretation of more complex IR results previously found for epitaxial samples.

This paper reports on the formation of FeSi and β-FeSi2by rapid thermal anneal (RTA). Sputtered Fe layers with a thickness of 25 nm and 40 nm on (100) Si wafers were subjected to RTA-treatment at temperatures ranging between 500 and 700 °C. This leads to three different types of growth. Two types of lateral growth and a hillock like growth. All the growth modes were nucleation controlled. The lateral growth rates of β-FeSi2 were measured at temperatures ranging from 625 to 700 °C, this provided a value for the activation energy of this process of about 1.35 eV. Positron annihilation analysis and scanning electron microscopy were used to study the onset of the transformation.

It is suggested that the lateral growth appears when the Fe layer is completely transformed to FeSi before FeSi2 nucleates and that the hillock-like growth emerges when FeSi2 nucleates before the complete transformation of the Fe layer to FeSi.The RTA formed P3-FeSi2 layers have a roughness of the order of the thickness of the layer and a high defect density as observed by cross-section transmission electron microscopy. In order to decrease the surface roughening a-Si and Si3N4 capping layers were deposited with plasma enhanced vapour deposition before RTA.

The phase-breaking time τφ'. in thin α-FeSi2 films was obtained from the analyses of the lowtemperature magnetoresistance (MR). The films were grown by molecular beam epitaxy (MBE) on Si(111) and capped with epitaxial Si. The MR behavior is interpreted in terms of two-dimensional (2D) weak localization with strong spin-orbit interaction and electron-electron interaction (EEI). By fitting the MR data we obtained the temperature dependence of τφ. The results indicate the phase-breaking time to vary as T− over a large temperature range from 1.7 to 15 K, in agreement with the dependence predicted by the EET in 2D systems.

We have investigated the electrical and structural properties of zirconium germanosilicide (Zr-Si-Ge) films formed during the Zr-Sil−xGex solid state reaction. Thin films of C49 Zr(Si1−xGex)2 were formed from the solid phase reaction of Zr and Si1−xGex bilayer structures. It was observed that Zr reacts uniformly with the Sil−xGex alloy and that C49 Zr(Si1−x Gex)2 is the final phase of the Zr-Si1−xGex, solid phase reaction (such tht y = x) for all compositions examined (x = 0.20, 0.33, and 0.50). The sheet resistance of the Zr(Si1−xGex)2 thin films were higher than the sheet resistance measured for ZrSi2 films. The stability of Zr(Sil−x Gex)2 in contact with Si1−Gex was investigated and no germanium segregation was detected in the Zr(Si1−xGex)2/Si1−Gex structures.

The thermal reaction of Ir/SiGe structures following ion implantation induced Ir grain boundary mixing has been studied. The morphology of the final interface has been investigated by Cross-sectional Transmission Electron Microscopy (XTEM) and Rutherford Backscattering Spectrometry (RBS) has been used to detect the redistribution of constituent atoms in the reacted layers. A 20 nm iridium film was deposited in vacuum by electron beam evaporation onto p-Si1-xGex (x = 0.25, 0.33) fully relaxed MBE grown layers. Implantation conditions used were effective in amorphizing the interface-close region of the Ir film and the SiGe substrate. After regrowth, XTEM results show that the interface quality is improved with respect to the material that had not been implanted. RBS results on the other hand show Ge incorporation in the reacted layer to occur in contrast to the non implated case where the Ge piles up at the silicide/SiGe interface. The effect of a second anneal step at higher temperatures (in the range 800°C – 900°C) is also investigated.

The phase development sequences for Pt layers on Si, Ge, and Si-Ge at 327°C were studied by X-ray diffraction, energy dispersive spectroscopy, and transmission electron microscopy. The reactions on pure Si and pure Ge followed the sequences reported previously. The reactions on the alloy layers differed slightly from the simple binary reactions. A ternary Pt(Si,Ge) reacted layer was formed on the alloy samples as the final phase on the Si-Ge alloy layer. This is discussed in terms of enthalpies of formation and the relative diffusion rates of Pt, Si, and Ge.

The effect of Si1−xGex alloy composition on the titanium germanosilicide phase formation sequence during the Ti-Si1−xGex solid phase reaction was examined. For the Ti-Si reaction the initial formation of C49 TiSi2 is followed, at higher temperatures, by the formation of C54 TiSi2. For the Ti-Ge reaction the initial formation of Ti6Ge5 is followed, at higher temperatures, by the formation of C54 TiGe2. It was determined that the Ti-Si1−xGex reaction follows three different reaction paths depending on the composition of the initial Si1−xGex alloy. For Si rich Si1−xGex alloys the Ti-Si1−xGex reaction follows a “Ti-Si like” reaction path (Ti+M ↠ C49 TiM2 ↠ C54 TiM2, where M = Si1−xGex). For Ge rich Si1−xGex alloys the reaction follows a “Ti-Ge like” reaction path (Ti+M ↠ Ti6M5 ↠ C54 TiM2). Both Ti6M5 and C49 TiM2 form during the reaction of titanium with Si1−xGex alloys in an intermediate composition range. Properties of the final C54 phase were observed to be strongly dependent on the phase formation sequence. Smooth continuous C54 titanium germanosilicide forms during the “Ti-Si like” reaction and discontinuous islanded C54 titanium germanosilicide forms during the “Ti-Ge like” reaction. An optimum Si1−xGex alloy composition range of 0.00 ≤ x ≤ 0.36 was determined for the formation of continuous- low-resistivity- C54 titanium germanosilicide films from the solid phase reaction of Ti and Si1−xGex alloy.

In this work iridium silicidation of high dose Ge+ implanted Si layers has been studied. Compositional graded SiGe layers with a Ge peak concentration between 6 at.% and 12 at.% have been fabricated using 200 keV Ge+ ion implantation into (100) Si. A 20 nm thick Ir film was then deposited by e-beam evaporation with thermal reaction being performed to both regrow the implantation damage and form the silicide. The crystal quality of the SiGe layer and its interaction with the Ir film have been studied by cross-sectional Transmission Electron Microscopy (XTEM) and Rutherford Backscattering Spectrometry (RBS).

Solid Phase Epitaxial Growth (SPEG) in the low dose case has produced a defect free SiGe layer with the formation of the IrSi phase. The annealing ambient was found to be critical for the silicidation. For the high dose case, as expected, strain relaxation related defects were observed to nucleate at a depth close to the projected range of the Ge+ implant and to extend up to the surface. A second rapid thermal annealing at higher temperatures, performed in forming gas, consumed most of the defective layer moving the silicide interface closer to the peak of the Ge distribution. A second low dose Ge+ implant following the metal deposition has been found to have a beneficial effect on the quality of the final interface. An amorphizing 500 keV Si+ implant followed by SPEG has finally been used to move the end of range defects far from the interface.

The theory of recently-reported cut-off wavelength-tunable silicide/SiGe/Si detectors is presented. The SiGe layer provides voltage-tunable barrier heights by tailoring the shape of the Schottky barrier. The increased tunability provided by the SiGe layer is now understood as being due to two related effects: first, keeping the barrier peak position fixed with bias, and second, moving the barrier peak further away from the interface. The second effect decreases quantum efficiency, which depends on the peak-to-interface distance. However, maximizing the first effect allows us to obtain desired levels of tunability without potential decreases in quantum efficiency. For voltage-switched, dual-window imaging, a tunable range of 5-12 μm is required over moderate voltages (10-15 volts), for which calculated detector parameters are total SiGe thicknesses (uniform plus graded) of ∼ 60-100 Å and boron doping levels of ∼ 4-8 × 1016 cm−3 throughout the depletion layer width (∼ 4000 Å, in the SiGe and in the underlying Si).