High energy N+ ion implantation in 4H–SiC

Depth profiles of Si nanocrystals formed in sapphire by ion implantation and the effect of charging during X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) measurements have been studied. Atomic concentration and the chemical environment of Si, Al, and O have been measured as a function of depth from the sample surface by SIMS and XPS. Both as-implanted and annealed samples have been analyzed to understand the effect of nanocrystal formation on the depth distribution, chemical structure, and the charging effect before and after the formation process. SIMS measurements have revealed that the peak position of the Si concentration shifts to deeper values with implantation dose. This is explained by the fact that the structure of the matrix undergoes a phase transformation from pure sapphire to a Si rich amorphous Al2O3 with heavy dose implantation. Formation of Si nanocrystals has been observed by XPS by an increase in the Si-Si signal and a decrease in Si-O bond concentrations after the annealing. Variation in binding energies of Si and O with Si concentration (i.e., with depth) has been studied in terms of chemical environments and charging effects. It is found that binding energy of these elements shifts to lower values with increasing Si content. This is a result of less charging due to the presence of easy discharge paths in the Si rich regions of the matrix. Nanocrystal formation leads to even less charging which is probably due to the further increase in conductivity with the formation.

The CdZnTe-based and GaAs-based HgCdTe epilayers were grown by liquid phase epitaxy and molecular beam epitaxy, respectively, and then coated by CdTe layers as barrier cap layers for ion implantation. Subsequently, arsenic ions were implanted into the samples at different implant energies, and the two-step high temperature annealing under Hg overpressure was operated on as-implanted samples to eliminate induced damages and activate arsenic ions. After thinning the as-implanted and annealed samples by ion milling, the microstructure of lattice defects in arsenic-implanted and annealed HgCdTe was characterized by high resolution transmission electron microscopy (HRTEM), while the arsenic profiles were measured by secondary ion mass spectroscopy (SIMS). By X-ray diffraction (XRD), the influences of pre-annealing, ion implantation and post-annealing on lattice structure were studied. The experimental results indicate that the implant induced defects underneath the amorphized layer contain dislocation clusters and dislocation lines. For the implant energy of 450keV, a residual point defect belt was observed around the previous amorphous/crystal (a/c) interface in the as-implanted sample after annealing, implying that the recrystallization occurs from surface towards a/c interface. The HRTEM observation of the point defect shows that the defect is a cluster of vacancies in fact. Also, the ion implantation not only broadens the XRD peak, but also makes the peak deviation and split. It indicates that the introduction of atomic stress changes the lattice constant, thereby leading to the peak deviation.

Photodissolution profile of silver in amorphous chalcogenide GeSe x thin films

This chapter describes the creation of an Intermediate Band (IB) on single crystal silicon substrates by means of high-dose Ti implantation and subsequent Pulsed Laser Melting (PLM). The Ti concentration over the Mott limit is confirmed by Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) measurements and the recovery of the crystallinity after annealing by means of Glancing Incidence X Ray Diffraction (GIXRD) and Transmission Electron Microscopy (TEM). Rutherford Backscattering Spectroscopy (RBS) measurements show that most of the atoms are located interstitially. Analysis of the sheet resistance and mobility measured using the van der Pauw geometry shows a temperature-dependent decoupling between the implanted layer and the substrate. This decoupling and the high laminated conductivity of the implanted layer could not be explained except if we assume that an IB has been formed in the semiconductor. A specific model for the bilayer electrical behaviour has been developed. The fitting of this model and also the simulation of the sheet resistance with the ATLAS code allow to determine that the IB energetic position is located around 0.36–0.38 eV below the conduction band. Carriers at the IB have a density very similar to the Ti concentration and behave as holes with mobilities as low as 0.4 cm2 Vs− 1.

200 nm thick SiO2 layers grown on Si substrates were implanted with 150 keV Ge ions at three different fluences. As-implanted samples were characterized with time-of-flight secondary ion mass spectrometry and Rutherford backscattering spectrometry to obtain depth profiles and concentration of Ge ions. As-implanted samples were annealed at 950 °C for 30 min. Crystalline quality of pristine, as-implanted, and annealed samples was investigated using Raman scattering measurements and the results were compared. Crystalline structure of as-implanted and annealed samples of embedded Ge into SiO2 matrix was studied using x-ray diffraction. No secondary phase or alloy formation of Ge was detected with x-ray diffraction or Raman measurements. Scanning transmission electron microscope measurements were done to get the nanocrystal size and localized information. The results confirmed that fluence dependent Ge nanocrystals of different sizes are formed in the annealed samples. It is also observed that Ge is slowly diffusing deeper into the substrate with annealing.

The structural and optical properties of carbon nanoclusters formed in thermally grown silicon dioxide film via the ion beam synthesis process have been investigated. A low-energy (70 keV) carbon ion beam (C−) at a fluence of 3 × 1017 atoms/cm2 was used for implantation into a thermally grown silicon dioxide layer (500 nm thick) on a Si (100) wafer. Several parts of the implanted samples were subsequently annealed in a gas mixture (4 % H2 + 96 % Ar) at 900 °C for different time periods. The as-implanted and annealed samples were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The carbon ion implantation depth profile was simulated using a widely used Monte Carlo-based simulation code SRIM-2012. Additionally, the elemental depth profile of the implanted carbon along with host elements of silicon and oxygen were simulated using a dynamic ion–solid interaction code T-DYN, which incorporates the effects of the surface sputtering and gradual change in the elemental composition in the implanted layers due to high-fluence ion implantation. The elemental depth profile obtained from the XPS measurements matches closely to the T-DYN predictions. Raman measurements indicate the formation of graphitic phases in the annealed samples. The graphitic peak (G-peak) was found to be increased with the annealing time duration. In the sample annealed for 10 min, the sizes of the carbon nanoclusters were found to be 1–4 nm in diameter using TEM. The PL measurements at room temperature using a 325-nm laser show broad-band emissions in the ultraviolet to visible range in the as-implanted sample. Intense narrow bands along with the broad bands were observed in the annealed samples. The defects present in the as-grown samples along with carbon ion-induced defect centers in the as-implanted samples are the main contributors to the observed broad-band luminescence centered around 2.4 and 2.9 eV. The intense narrow peaks observed in the PL spectra centered on ~2.67 and 2.8 eV with full width at half maxima ≤ 150 meV are believed to be mainly due to the quantum size effects of the carbon nanoclusters formed in the annealed samples. The relative intensities of the narrow peaks are seen to be changing with the annealing time interval. This may be due to the change in the size distribution of the carbon nanoclusters.

Erbium ion implantation into different crystallographic cuts of lithium niobate

In 4H-SiC electronic devices, Al+ ion implantation is often used to obtain selected regions of desired p-type conductivity in n-type epitaxial layers. A mandatory high temperature annealing is necessary after the implantation process for the electrical activation of the implanted Al. The temperature of the former and the density of the latter vary in the range 1600-1950°C and 1017-1020 cm-3, respectively. The switching properties of the so obtained bipolar junctions depend on carrier life-time in the n-type 4H-SiC epitaxial layers after processing. In the literature, it has been shown that carbon vacancy VC in n-type 4H-SiC epi-layers is a carrier life-time killer defect and that its concentration, after high temperature treatments in the range 1500-1950°C, saturates on values that are higher the higher are the applied temperature and cooling rate [1]. It has been also shown that, in the case the thermally treated 4H-SiC epi-layers were ion implanted, and whatever is the implanted ion species, VC annihilation took place from 1000°C till 1500°C, while at 1600°C the phenomena of VC annihilation and VC formation seem to compete [2], suggesting that up to 1500°C, a carbon interstitial IC’s injection from the implanted near-surface layer into the epi-layer can be sufficient to make dominant VCannihilation, but this is not the case at 1600°C. Our previous studies on carrier life-time in Al+ implanted p+-n-n+ diodes, with 6×1019 cm-3 and 2×1020 cm-3 Al+ implanted emitters after 1600 °C/20 min without carbon-cap (C-cap) and 1950 °C/5 min with C-cap post implantation annealing, respectively, have shown longer carrier life-time for diodes annealed at the lower temperature, about 700 ns against 170 ns [3], as measured by open circuit voltage decay (OCVD). The diodes annealed at the higher temperature have shown, by DLTS spectroscopy, a VC concentration lower by a factor ~ 3 relative to that in as-grown epi-layers subjected to almost the same thermal annealing (1950 °C /3 min) [1]. If the ion dose is sufficiently high, it is reasonable that injection of IC’s from the implanted layer into the epi-layer bulk takes place even at temperatures as high as 1950 °C but thermal generation of VCstill remains the prevailing process. Taking into account the above results, it sounds reasonable to deserve efforts to the investigation of an ion implantation technology for bipolar junction in 4H-SiC where the electrical activation of the implanted species is achieved by a high temperature treatment and the degradation of the carrier life-time in the device drift layer is rescued by a subsequent low temperature treatment. The first step towards such a technology is to verify that during the thermal treatment for carrier life-time rescue, none or negligible deactivation of the electrically activated dopant takes place. This is the purpose of this study. 4H-SiC materials, both high-purity-semi-insulating (HPSI) and low doped n-type, have been implanted with Al+ ions so to obtain a homogenous doped layer next of the wafer surface. Post implantation annealing has been performed at 1950°C for different times in the range 5-40 min. Some samples have been also thermally treated at 1500°C for 40 min or for 240 min. During every annealing, the sample were protected by a pyrolyzed resist film (C-cap), that was removed after the last thermal treatment. The implanted Al concentration was 1×1020 cm-3, that is lower than Al solubility in 4H-SiC at 1950°C, and higher than the expected, but never measured, Al solubility in 4H-SiC at 1500°C [4]. Van der Pauw devices were used for Hall effect and sheet resistance measurements in the temperature range 180-680 K. The temperature dependences of these data show that the 1500°C treatment has an effect ranging from “neutral” to “beneficial” on the electrical transport of the Al+implanted 4H-SiC layer submitted to a 1950°C annealing immediately after implantation. This result opens the way towards the fabrication of bipolar diodes with p-type emitters of almost identical hole density but different thermal treatments after implantation, thus with drift layers that might have very different current transport properties. [1] H. M. Ayedh, V. Bobal, R. Nipoti, A. Hallén, B. G. Svensson, J. Appl. Phys. 115, 012005 (2014) [2] H. M. Ayedh, A. Hallén, B. G. Svensson, J. Appl. Phys. 118, 175701 (2015). [3] H. M. Ayedh, M. Puzzanghera, B. G. Svensson, R. Nipoti, Mater. Sci. Forum 897, 279-282 (2017) [4] M. K. Linnarson, U. Zimmermann, J. Wong-Leung, A. Shoener, M.S. Janson, C. Jagadish, B. G. Svensson, Appl. Surf. Sci. 203-204, 427-432 (2003).

Correlations between the structural transformations and concentration quenching effect for RE-implanted ZnO systems

We report the first study of the effect of in situ ultrasound treatment during ion implantation on amorphization and transient enhanced diffusion (TED) in silicon. Rutherford backscattering spectroscopy, ion channeling, and Raman spectroscopy measurements show that amorphization of Si during Ar ion implantation is increased by ultrasound treatment, especially at ultrasound frequencies around 2 MHz. By secondary ion mass spectroscopy we investigate the influence of ultrasound treatment on TED of B atoms. Our data show that TED is reduced due to the influence of ultrasound treatment. The results are discussed in terms of the interaction of ultrasound waves with point defects and the ultrasound stimulated enhanced diffusion of interstitials.

Phosphorus doping of polycrystalline silicon by direct diffusion of PH3 at 685 and 785 °C followed by rapid thermal annealing (RTA) has been investigated. Unlike at 785 °C, the dopant profile is not uniform at 685 °C but becomes so after RTA at 1050 °C for 10 s, as revealed by secondary ion mass spectroscopy (SIMS). In the absence of any protection layer, RTA in N2 causes an out-diffusion of ∼50% of P from the sample diffused at 785 °C, although it activates ∼100% of the remaining P atoms as indicated by Hall and SIMS measurements. In contrast, RTA in O2 results in 95% activation of the incorporated P from the same sample, accompanying an oxidation of ∼7 nm polycrystalline Si. As regards the sample diffused at 685 °C, RTA in N2 does not cause any out-diffusion but activates less than 80% of the incorporated P atoms. This difference in behavior is attributed to the tendency to attain equilibrium concentrations of P in the crystallites and at the grain boundaries at the RTA temperature. The highest active P concentration achieved is 2.0×1020 cm−3 at 785 °C followed by RTA in O2 yielding a resistivity as low as 9×10−4 Ω cm. The simplicity of this relatively low temperature process is attractive for a single-wafer multisequence fabrication scheme.

The channeling effect of Al and N ion implantation in 4H–SiC during JFET integrated device processing

Diffusion of indium implanted in silicon: The effect of the pre-amorphisation treatment and of the presence of carbon

Quantitative dopant profile measurements are performed on a nanometer scale by scanning capacitance microscopy (SCM). An atomic force microscope is used to position a nanometer scale tip at a semiconductor surface, and local capacitance change is measured as a function of sample bias. A new feedback method has been demonstrated in which the magnitude of the ac bias voltage applied to the sample is adjusted to maintain a constant capacitance change as the tip is scanned across the sample surface. A quasi-1D model is used to extract dopant density profiles from the SCM measurements. The inverted SCM dopant profiles are compared with profiles obtained by process simulation and secondary ion mass spectroscopy measurement. Good agreement was found between the SCM measured profile and the lateral profile predicted by SUPREM 4 over the concentration range from 1017 to 1020 cm−3.

A study of high temperature oxidation of nickel after ion implantation