Schottky Barrier Height Measurements Research Articles

Effects of Rapid Thermal Annealing on W/Si1−xGex Contacts

ABSTRACTThermal reaction of W with Si1−xGex films epitaxially grown by Rapid Thermal Chemical Vapor Deposition was investigated in the temperature range 500°C - 1000°C. The samples were annealed either in a Rapid Thermal Annealing (RTA) system or in a conventional furnace, both in flowing nitrogen. The reaction products were investigated by Rutherford Backscattering Spectroscopy (RBS), Energy Dispersive Spectrometry (EDS) and X-ray diffraction (XRD). Sheet resistance measurements were also performed to follow the progress of the reaction. The reaction of W with Si0.67Ge0.33 is similar to that of W with silicon. W reacts with silicon to form tetragonal WSi2. The Ge-content in the silicide is lower than that of the asdeposited alloy. It is shown that an oxygen contamination occurs during conventional annealing and leads to the formation of non homogeneous Si1−x Gex unreacted alloy below the silicide film. Rapid thermal annealing prevents this parasitic effect and the unreacted film remains homogeneous although a slight decrease in the Ge-content is observed. These results are correlated with Schottky barrier height measurements on p-Si0.83Ge0.17 partially strained films. We observed an increase of the barrier height with increasing the temperature for annealing from 500°C to 1000°C. This trend may be explained either by strain relaxation or (and) Ge-content decrease in the unreacted alloy.

Interfacial reactions and Schottky barriers of Pt and Pd on epitaxial Si1−xGex alloys

The evolution of interfacial reactions during the deposition of Pt and Pd on epitaxial Si1−xGex alloys was studied using x-ray photoelectron spectroscopy (XPS) for metal coverage up to 10 Å. Auger electron depth profiling was performed on a thicker metal overlayer before and after in vacuo annealing to study the redistribution of composition in the reactions. We have found that Pt and Pd react mainly with Si to form silicides at 350 °C, leaving some Ge to segregate at the surface. These results were correlated with Schottky barrier height measurements. We found that the Schottky barrier heights of Pt/n-Si0.8Ge0.2 and Pd/n-Si0.8Ge0.2 are about the same, pinned at 0.68 eV, which is much smaller than those of n-Si. These barrier heights are quite stable up to 550 °C.

Quaternary Alloys InxAlyGa1−x-yAs Grown on GaAs with A Compositionally-Step-Graded Buffer

ABSTRACTFundamental bandgaps and Schottky barrier heights of strain-relaxed quaternary InxAlyGa1−x-yAs alloys with 0 < x < 0.35 and 0 < y < 0.30 were studied. The alloys were grown on GaAs substrates by molecular beam epitaxy. The lattice mismatch (up to 2.5%) and mismatch strain were accommodated by a compositionally-step-graded buffer. A residual compressive strain of less than 0.5% was determined by x-ray diffraction. Measured Schottky barrier heights v.s. bandgap deviate from the values predicted by the “commonanion” rule. This behavior is attributed to the compositional inhomogeneities and chemical reactivity of the air-exposed InAlGaAs surfaces.

Novel GaAs/AlGaAs multiquantum-well Schottky-junction device and its photovoltaic LWIR detection

The authors have demonstrated photovoltaic detection for a multiple-quantum-well (MQW) long-wavelength infrared (LWIR) detector. With a blocking layer, the MQW detector exhibits Schottky I-V characteristics with extremely low dark current and excellent ideality factor. The dark current is 5*10/sup -14/ A for a 100*100 mu m/sup 2/ detector (designed for 10- mu m response) at 40 K, nearly nine orders of magnitude lower than that of a similar MQW LWIR detector without the blocking layer. The ideality factor is approximately 1.01-1.05 at T=40-80 K. The measured Schottky-barrier height is consistent with the energy difference between first excited states and ground states, or the peak of spectral response. The authors also report a measured effective Richardson constant (A**) for a GaAs/AlGaAs heterojunction using this blocking layer structure. The A** is approximately 2.3 A/cm/sup 2//K/sup 2/. >

Interaction of Pd with Strained Layers of Si1-xGex Epitaxially Grown on Si(100)

This work describes the interaction of Pd with MBE grown strained epitxial layers of Si1-xGex on Si(100), at low and at high temperatures (250°C and 550°C). Pd was deposited to a thickness of 1700 Å, on the Si1-xGex/Si(100) layers with thicknesses of 3300 Å and 2300 Å, and with a Ge contents of x=0.09 and 0.18, respectively. Samples were annealed at temperatures ranging from 250 to 550°C. The reaction products were investigated by Transmission Electron Microscopy, Energy Dispersive Spectroscopy, X-ray dlffraction and Auger Electron Spectroscopy. Strain in the Si1-xGex layers was measured by Double Crystal X-ray Diffractometry. Diodes were prepared on n-type substrates, and were characterized by current-voltage techniques. The low temperature interaction is characterized by uniform incorporation of Si and Ge in the Pd2Si1-yGey compound (textured on the Si1-xGex substrate), and at high temperatures a Ge rich double layer strcucture formed, accompanied by strain relaxation of the Si1-xGex layer. The measured Schottky barrier heights were φb=0.67 and 0.65 for x=0.09 and x=0.18, respectively.

Characterization of interface states at III-V compound semiconductor-metal interfaces

Surface photovoltage spectroscopy (SPS) has been used for direct measurements of the extrinsic surface states within the band gaps of p-InP (110) and (100) and n-GaAs(110) before and after Al and Au deposition. The observed metal-induced surface states are found to pin the Fermi level at monolayer coverages at Ev+0.83 eV for Au/p-InP(110), Ev+1.10 eV for Al/p-InP(110), Ec−0.94 eV for Au/n-GaAs(110), and Ec−0.80 eV for Al/n-GaAs(110). The Au/Al/p-InP(110) structure, studied for the first time using SPS provides evidence of strong Al clustering upon the InP surface. Chemically etched and UHV-cleaved p-InP surfaces and Au interfaces are also compared. The correlation between the observed energy state positions and electrically measured Schottky barrier heights is discussed.

Surface photovoltage spectroscopy of gap states at GaAs and InP metal interfaces

Surface photovoltage spectroscopy has been used in order to investigate surface states at Al/n-GaAs (110), Au/n-GaAs (110) and Al/p-InP (110), Au/p-InP (110),(100) interfaces. Our results show formation of metal-induced surface states, which can be correlated with Fermi level pinning positions. The observed energy positions are found to be in good agreement with electrically measured Schottky barrier heights. The results obtained for these metals and the different surface types are discussed and compared to published data.

Plasma etching of III–V semiconductors in CH4/H2/Ar electron cyclotron resonance discharges

We have investigated the etch rates, residual lattice damage, surface morphologies, and chemistries of InP, InGaAs, AlInAs, and GaAs plasma etched in electron cyclotron resonance (ECR) CH4/H2/Ar discharges. The etch rates of InP and InGaAs increase linearly with additional rf biasing of the substrate, and are approximately a factor of 2 faster than for GaAs. Under our conditions the etch rate of Al0.52Ga0.48As is very low (∼25 Å min−1) even for the addition of 100 V rf bias. In all of these materials the residual damage layer remaining after dry etching is very shallow (∼20 Å) as evidenced from Schottky barrier height and photoluminescence measurements combined with wet chemical etching. InP shows significant P depletion with the addition of rf biasing during the ECR etching while GaAs retains a near-stoichiometric surface. Hydrogen passivation of shallow donors in n-type GaAs occurs to a depth of ∼3000 Å during exposure to the CH4/H2/Ar discharge for long periods (60 min). The surface morphologies in the In-based materials become roughened for etching with the addition of rf biasing while GaAs displays smooth, residue-free surfaces under these conditions.

Growth of CoSi2 on Si(001): Structure, defects, and resistivity

Epitaxial films of CoSi2 on Si(001) have been grown by molecular-beam epitaxy, and their electrical and structural properties studied by resistivity and Schottky barrier height measurements, by Rutherford backscattering spectroscopy (RBS), and by transmission electron microscopy (TEM). Most growth conditions successful on Si (111) have been found to result in misoriented grains when applied to Si(001). However, single-orientation (001) CoSi2 films, with low resistivities (16 μΩ cm) and low ion channeling minimum yields (χmin=5%) have been obtained by direct codeposition of Co and Si at ∼500 °C at Co-rich stoichiometries. Single orientation (001) CoSi2 films have also been obtained by using a template method on epitaxially grown Si buffer layers, but the resistivities of these films have not been as good. A Schottky barrier height of 0.71 eV has been measured for single-orientation CoSi2(001)/Si(001). This is significantly higher than the barrier height of 0.64 eV for CoSi2(111)/Si(111).

Damage in silicon caused by magnetron ion etching and its recovery effect

Damage in silicon exposed to an MIE (magnetron ion etching) plasma has been investigated. The damage was characterized by Schottky barrier height measurements using Al/n-Si diodes. The depths of the damaged layer are determined as a function of RF power. It is found that the damaged layer at an RF power of 2 kW (self-bias: 270 V) is about 12 nm, and that the damage depths correlate with the self-bias voltage, that is, the energy of ions impinging on the Si surface during plasma exposure. Several methods for removal of the damaged layer were examined. It was found that the damaged layer can be removed by a wet Si etching. >

Ballistic-electron-emission microscopy of subsurface defects at the Au-GaAs(100) interface

Semiconductor interface electronic properties are strongly influenced by the presence of defects. Throughout the long history of interface investigation, the study of interface defect electronic properties has been seriously hindered by the fundamental experimental difficulty of probing subsurface structures. A new method, ballistic-electron-emission microscopy (BEEM), has been developed which not only enables probing of subsurface interface properties, but also provides nanometer-resolution imaging capabilities. BEEM employs scanning tunneling microscopy (STM) and a unique spatially localized ballistic electron spectroscopy method. The imaging of subsurface interface structure and spectroscopic measurement of local Schottky barrier height have been demonstrated by BEEM. Recent BEEM results include the first direct observation of a multiphase defect structure at the important Au-GaAs(100) Schottky barrier interface. This paper describes the application of BEEM to a study of the influence of GaAs(100) substrate conditions on the formation of this defect structure at the Au-GaAs(100) interface.

Plasma Etching of InP and Related Materials in Electron Cyclotron Resonance CH4/H2/Ar Discharges

We have investigated the etch rates, residual lattice damage, surface morphologies and chemistries of InP, InGaAs, AlInAs and GaAs plasma etched in electron cyclotron resonance (ECR) CH4/H2/Ar discharges. The etch rates of InP and InGaAs increase linearly with additional RF biasing of the substrate, and are approximately a factor of two faster than for GaAs. Under our conditions the etch rate of Al0.52Ga0.48As is very low (≈25γ · min−1) even for the addition of 100 V RF bias. In all of these materials the residual damage layer remaining after dry etching is very shallow (≈20γ) as evidenced from Schottky barrier height and photoluminescence measurements combined with wet chemical etching. InP shows significant P depletion with the addition of RF biasing during the ECR etching while GaAs retains a near-stoichiometric surface. Hydrogen passivation of shallow donors in n-type GaAs occurs to a depth of ≈3000γ during exposure to the CH4/H2/Ar discharge for long periods (60 mins). The surface morphologies of the In-based materials become roughened for etching with the addition of RF biasing while GaAs displays smooth, residue-free surfaces under these conditions.

TiW AND Al CONTACTS TO SHALLOW p+ JUNCTIONS - A COMPARISON BETWEEN FURNACE AND RAPID THERMAL ANNEALING (RTA)

The use of sputter deposited TiW (15/85 w.t.%) as a direct contact material to p+ silicon is evaluated. The effect on the contact resistance of different post-implant activation conditions, e.g. rapid thermal processing and conventional furnace annealing in dry or wet ambients, has been studied. For comparison parallell measurements were done on identically processed wafers metallized with aluminium. The resulting dopant profiLes were determined by spreading resistance profiling (SRP). Schottky barrier height measurements were performed on n-type wafers metallized with TiW or Al. The respective values were ? Bn = 0.55 eV and ? Bn = 0.8 eV. The results from contact resistance and SRP measurements show that a high surface carrier concentration is necessary in order to achieve a low contact resistance. This effect was more pronounced for the material with the higher barrier height to p+ silicon i.e. TiW was found to be sore sensitive to a small variation in the boron surface carrier concentration. Despite of this it was observed that given a high surface carrier concentration, after RTP the performance of TiW contacts to p+ silicon surpassed that of Al. in case of a direct Al-Si contact, silicon precipitation occurs in the contact hole thereby reducing the effective contact area. This will cause an increase in the resistance of contacts which becomes more pronounced for small dimensions. With TiW, silicon precipitation is avoided.

Initial stages of reaction and barrier heights in nickel silicide interface growth.

A time-resolved study of the initial stages of the formation of Ni-silicide growth using a pulsed-light annealing technique is described. The changes at the interface were measured as a function of the number of the annealing pulses. We used Auger electron spectroscopy to measure elemental composition and shapes of Si LVV and Ni LMM lines. Electrical changes at the interface were observed by Schottky barrier-height measurements. Ni diffuses into the Si, creating an amorphous interface layer at the silicon surface. A silicide phase emerges in this region by an amorphous-to-crystalline phase transition.

A comparison of different methods for removal of damage caused by reactive sputter etching of silicon

The influence of etch time and power density on damage introduced in silicon by reactive sputter etching has been investigated. The induced damage was characterized by Schottky barrier height measurements, backscattering–channeling technique, and transmission electron microscopy. The study also comprises three methods for removal of the damage. It was found that the surface could be fully restored by means of thermal oxidation or plasma oxidation followed by a HF dip. These results were verified both by electrical measurements and by backscattering–channeling technique. The rapid thermal annealing treatment seems to fully restore the surface etched at a power density of 0.5 W/cm2 or lower. For higher power densities, the surface is not fully restored, but a considerable improvement is found.

The Electronic Properties of Silicon-Silicide Epitaxial Interfaces

ABSTRACTThe selfconsistent electronic properties of the epitaxial Si(111)-NiSi2 interface are computed for the experimentally observed type-A and type-B growth orientations. The densities of states projected on the various sites provide a detailed analysis of the siliconsilicide interface electronic states. The measured Schottky barrier heights may be interpreted by assuming that deviations from epitaxy must be taken into account.

Au/Ni bilayers on n-type silicon: Metallurgical and electrical behaviour

Diffusion effects during the formation of silicides in the Ni-Au-Si system were investigated by means of 4He + MeV Rutherford backscattering spectrometry, Auger electron spectroscopy coupled with Ar + ion sputtering and X-ray diffraction as a function of the heat treatment temperature (280–350°C) and time (10–1000 min). Schottky barrier heights were used to identify the type of metal present at the silicon surface. Au/Ni/Si and Ni/Au/Si structures were prepared by electron gun deposition of thin gold and nickel films onto n-type Si〈111〉 single crystals. After thermal treatment only Ni 2Si and NiSi compounds were observed and their formation follows the phase order confirmed by previous investigations on the Ni/Si system, with a growth controlled by a lattice diffusion process. In the Ni/Au/Si〈111〉 structure the diffusion of the silicon through the gold film was detected during the formation of nickel silicide and the kinetics of growth of Ni 2Si and NiSi were similar to those studied in the Ni/Si〈100〉 system. A diffusion of gold towards the Si-NiSi interface was observed during the growth of NiSi in the Au/Ni/Si〈111〉 structure. The Schottky barrier height measurements confirm these findings.

Schottky barrier height measurements of type-A and type-B NiSi2 epilayers on Si

Schottky barrier heights of single-crystal type-A and type-B NiSi2 epilayers on nondegenerate n-(111) Si have been measured by photoresponse and forward I–V methods. High-quality molecular beam epitaxy grown NiSi2 layers of thicknesses ranging from 70 to 600 Å on sputter-cleaned, P-doped Si subtrates (∼1.5×1015 cm−3) were studied. The type-A and type-B orientations consistently yield photoresponse barrier heights which differ by greater than 0.1 eV. We observe the value φBn=0.62±0.01 eV for all type-A structures from both photoresponse and I–V measurements. However, we obtain a discrepancy between barrier heights measured by I–V (φBn=0.69±0.01 eV) and photoresponse (φBn=0.77±0.05 eV) methods, and in addition consistently observe an unusual bowing of the type-B photoresponse curves at low photon energies. We show that both the detailed shape of the type-B photoresponse curves and the discrepancy between I–V and photoresponse-measured barrier heights can be accounted for by modeling the type-B barrier as a mixture of high and low barrier regions. Quantitative agreement with experiment is obtained for the values φhi =0.81±0.01 eV and φlo 0.64±0.01 eV, with effective fractional area coverages of 91% and 9% for high- and low-barrier regions, respectively.

Summary Abstract: Schottky barrier height measurements of type A and type B NiSi2 on Si

We have made photoresponse measurements of the Schottky barrier heights of epitaxial NiSi2 on non-degenerate n-(111) Si substrates, for the cases of type A and type B epitaxy, on several samples with NiSi2 layer thicknesses ranging from 70 to 600 A. Nominal doping in all Si substrates was about 1.5 x 10^15 cm^-3. The photoresponse measurements were performed on broad-area-coverage regions of NiSi2 on Si. No processing subsequent to growth took place on these silicide layers.

Electrical Properties, Structure, and Phase Morphology of Au‐Ga Alloy Films Codeposited on GaAs Substrates

Electrical properties, structure, and phase morphology of gold‐gallium alloy films codeposited on {100} substrates of gallium arsenide have been investigated by measurement of Schottky barrier height φ and breakdown voltage as a function of film composition and annealing conditions and comparison with corresponding structure and phase morphology, as determined by x‐ray diffraction and transmission electron microscopy. Both φ and decrease with increasing composition of gallium in the codeposited films and with increasing severity of annealing conditions. These decreases are attributed to formation of gold‐gallium phases, either directly through codeposition of alloy films or through annealing of pure gold films on substrates of gallium arsenide, and localized current or field concentrations due to nonplanar phase morphologies. General behavior of electrical properties is reported and interpreted in terms of the existing structure and phase morphology near the original alloy film/gallium arsenide interface.