Damage In GaAs Research Articles

Lateral damage extension during masked ion implantation into GaAs

We have studied both experimentally and theoretically the generation of damage in GaAs due to ion implantation through mask openings of small dimensions. We show that it is possible to master the generation of damage, i.e., the amorphization phenomenon in the direction perpendicular to the ion beam and close to the mask edges. A theoretical model is used to simulate the ion implantation process and damage accumulation through Ti–Au masks. After comparing the shape of the crystalline/amorphous interfaces as revealed by cross-sectional electron microscopy with our simulations, this model is used to predict the evolution of the two-dimensional damage distributions beneath the mask edges as functions of ion beam and implantation mask parameters. Undamaged regions of nanometer dimensions can be preserved even when using masks of reasonable dimensions (100–200 nm). This can be done only by adjusting the ion beam parameters through the accurate simulation of the two-dimensional damage generation.

C+-energy-dependent residual ion damage in GaAs:C grown by the low-energy ion-beam doping method

The effects of residual ion damage in low-energy (30 eV–30 keV) C+-doped GaAs were investigated with regard to the electrical and optical activation of C as a function of C+ ion acceleration energy EC+. Systematic variation of EC+ demonstrated that, in the energy range of EC+<170 eV, the net hole concentration (|NA−ND|) slightly increases as EC+ increases and the highest |NA−ND| was obtained at EC+=170 eV under the constant C+ ion-beam current density. For EC+≳170 eV, an increase in EC+ gave rise to an abrupt decrease of |NA−ND| down to two orders of magnitude smaller than that obtained at EC+=170 eV. In low-temperature (2 K) photoluminescence spectra for as-grown samples with EC+=240 and 350 eV, a novel emission ascribable to residual ion damage was observed instead of an essential acceptor–acceptor emission of [g−g]β. However, subsequent annealing at 850 °C made this novel emission disappear and the proper [g−g]β emission was merely observed. An activation process observed for EC+=5, 10, and 30 keV samples was very similar to that by high-energy ion implantation, indicating low activation rate of 10%–15%. Minority-carrier lifetime measurements using scanning tunneling microscope stimulated time-resolved luminescence demonstrated the presence of residual ion damage in as-grown samples at EC+=240 and 350 eV and annealed ones at EC+=5, 10, and 30 keV while no ion damage was observed in as-grown sample at EC+=30 eV. The incorporation and activation behaviors of C atoms that take the form of low-energy ions were found to be considerably affected by changes in ion–surface interaction with increasing EC+ and by the presence of residual ion damage in the layer.

Reactive-ion etching of WSix in CF4+O2 and the associated damage in GaAs

Assessments of WSix reactive-ion etching in terms of the different CF4 to O2 flow rate ratio were characterized. Based upon the evaluations from etching rates, side-wall profiles, surface roughness, and damages, we observed that the optimum etching condition was at a ratio of 10:1. The recovery of reactive-ion-etching-treated GaAs damaged layers through the thermal treatment was also investigated as a function of the annealing temperatures and duration times. These parameter evaluations were for the purpose of achieving a high performance GaAs metal–semiconductor field-effect transistor.

Investigation by ellipsometry of the damage in GaAs bombarded with low-energy Ar ions

The crystalline-amorphous transition in GaAs induced by Ar ions (energy 1–3 keV) has been investigated using single-wavelength ellipsometry. The experiments have been performed in-situ at room temperature. Ion damage straggling, amorphization threshold and critical energy density have been derived by means of a simple analytical model for the growth of the amorphous layer. This model is discussed and the corresponding calculations are found to be in satisfactory agreement with experimental data.

Laser induced damage in GaAs at 1.06 μm wavelength: surface effects

An experimental study of single shot damage to monocrystal GaAs by a free running laser pulse of 1.06 μm wavelength is described. In order to see the role of surface effects on laser induced damage, samples of different surface finish were prepared. The laser induced damage threshold (LIDT) of lapped GaAs samples is considerably lower than that of the mirror polished samples (ratio 1 2 ). Damage threshold results are analysed in terms of a thermal model incorporating the temperature dependent thermal and optical parameters of GaAs. The combined effect of the enhanced surface absorption and high surface recombination velocity of photo-excited carriers significantly enhances the surface temperature rise and reduces the damage threshold value of GaAs. The evolution of damage morphology is governed by the mechanical damage caused due to the polishing process.

Investigation by ellipsometry of the damage in GaAs bombarded with low-energy Ar ions

Investigation by ellipsometry of the damage in GaAs bombarded with low-energy Ar ions

Raman study of damage processes in Si+-implanted GaAs

Ion-induced damage in GaAs as a function of ion dose following 100 keV Si+ implants has been investigated by Raman spectroscopy. A new approach for decomposition of Raman scattering intensity on to the crystalline and amorphous phase components has been used in analysis of Raman spectra. With increasing ion dose the following was observed: a) the widths of vibrational bands of a-phase significantly increase, while the width of the LO(γ) phonon band of c-phase remains unchanged; b) the longitudinal optical phonon band of c-phase completely dissappears, while the transverse optical phonon mode evolves in to a new band of a-phase; c) the wavenumbers of all vibrational bands of a- and c-phase shift to lower values by ∼ 10–15 cm−1. A number of mechanisms possibly accountable for these shifts were analysed and evaluated.

Schottky barrier study of ion implantation damage in GaAs

Ion bombardment damage on GaAs surface has been studied with Ar ion implantation, followed by controlled removal of the damaged GaAs surface layer by anodic oxidation/stripping prior to Schottky metallization. The electrical characteristics of subsequently fabricated Au/n-GaAs Schottky barriers display progressive recovery towards those of undamaged control samples as a function of implanted Ar dose. The recovery depth for different material/device parameters are well in excess of the projected range for 10-keV Ar ions (10.5 nm) in GaAs. Deep level transient spectroscopy measurements of the Ar-implanted samples show both suppression and enhancement of deep levels in the GaAs surface region. A Ga-rich surface region introduced by low-energy Ar implantation appears to be responsible for the modification of deep level traps. The recovery in Schottky barrier height with a postimplantation rapid thermal anneal process is very poor at temperatures below 600 °C and significant degradation occurs at a higher temperature of 700 °C. Carrier compensation and suppression of donorlike antisite defects AsGa have been found in a Ga-rich region resulting from either ion bombardment or high-temperature annealing.

Ion-induced annealing of damage in GaAs implanted with argon ions

Abstract The process of the structure restoration of GaAs implanted with Ar+ ions at the ion current densities of 10 and 25 μA/cm2 and in the fluence interval of 6 × 1013–1 × 1016 cm−2 has been analysed on the basis of Raman scattering (RS) and Rutherford backscattering (RBS) data taken into account the target heating during the irradiation. The current dependence of threshold fluences which the recrystallization begin at is explained in assumption that the structure restoration is caused of by the mobile monovacancies interaction with the stable vacancy cluster. The existence of the critical ion fluence corresponded to the most perfect GaAs structure has been shown.

Measurement of ion induced damage-profiles in GaAs

In this study, with the use of a sensitive optical technique, we demonstrate the possibility of measuring the depth distribution of damage in GaAs that is generated by various ion-assisted processes such as ion implantation and ion assisted plasma etching. We have used this technique to measure the depth distribution of damage in both He and Ar implanted GaAs and in inert gas and reactive ion etched GaAs. The sensitivity of the technique allowed us to measure damage profiles over a large range of ion energies and ion doses. We have also confirmed previously published results indicating that damage created by sputter etching is inversely proportional to the mass of the ions used in the etching process.

Plasma-Induced Damage Behavior in GaAs by Photoreflectance Spectroscopy

Photoreflectance spectroscopy (PR) is applied to in situ, noninvasive determination of plasma-induced damage in GaAs for the first time. PR can evaluate damage such as nonradiative recombination centers and compensation centers in a near-surface layer. A new source of damage is revealed: short-term introduction followed by reduction of nonradiative recombination centers. This phenomenon cannot be detected by photoluminescence spectroscopy, a conventional noninvasive method. Comparing PR to the C-V method, we show that PR can be used as a highly sensitive probe for damage confined within the near-surface layer. This discovery will be helpful in developing methods that can be used for real-time, noninvasive detection of process-induced damage occurring during device processing.

Dry-Etch-induced damage in GaAs investigated via TEM

Plasma-assisted etching is an important III-V semiconductor fabrication technique for patterning device structures on the nanometer scale with high accuracy. The quality of the processed surface is of primary importance for most electronic applications. It is well documented that reactive ion etching (RIE), with its high self-biases, usually incurs material damage via ion bombardment which ultimately limits device performance. Magnetron ion etching (MIE) is an attractive alternative to RIE. Specifically, MIE has a lower sheath voltage than RIE and the discharge contains low to moderate energy ions, both of which allow wafer processing with less ion-induced damage. This study investigated the nature and extent of near surface disorder resultant from MIE with freon-12 (CCl2F2) via cross-sectional transmission electron microscopy (TEM). The effect of residual damage on device performance was evaluated via Schottky diode measurements. The GaAs wafers were etched under the following conditions:

Measurement of damage profile in semiconductors: A sensitive optical technique

We have used differential reflectance spectroscopy in combination with chemical-etch removal of surface layers to measure the depth profile of damage in GaAs. Damage was created by one of several ion-assisted processes, including sputter etching, reactive-ion etching, hydrogenation, and ion implantation. The sensitivity of this optical technique is shown to be comparable or greater than that obtained by other previous methods. From our measurements we estimate the lowest detectable damage level to be equivalent to damage created by 50 keV He+ ions at an ion dose of 1×108 ions/cm2. The depth resolution of this method is approximately 60 Å. Two examples of measured damage profiles are shown in this communication.

New technique for dry etch damage assessment of semiconductors

Surface conductance measurements, using the transmission line model (TLM) technique, have been used to assess surface electrical damage in GaAs resulting from dry etching. Reactive ion etching (RIE) in CH4/H2 and SiCl4, ion beam etching in Ne and Ar and electron cyclotron resonance etching (ECR-RIE) in CCl2F2/He have been investigated. A phenomenological model is proposed for determining the extent of the surface etching damage. It is found that the use of slow etch rates, high bias/accelerating voltage and light ions in etching increases the electrical damage in GaAs. Possible causes for the creation of deep damage are discussed, and the criteria for low damage etching are suggested. The TLM method is a powerful technique for assessing etching processes used for semiconductors.

Characterization of Reactive Ion Etch Damage in GaAs by Triple Crystal X-Ray Diffraction

AbstractTriple crystal x-ray diffraction (TCXD) is a non-destructive structural characterization tool capable of the separation and direct observation of the dynamic (perfect crystal) and the kinematic (imperfect crystal) components of the total intensity diffracted by a crystal. Specifically, TCXD can be used to measure the magnitude of the diffuse scattering arising from defects in the crystal structure in the immediate vicinity of a reciprocal lattice point. In this study, the effects of BC13 reactive ion etching (RIE) on the near-surface region of GaAs were investigated by analyzing the changes in the diffuse scattering using both the symmetric 004 reflection as well as the highly asymmetric and more surface sensitive 113 reflection. While the results from the 004 reflections revealed little difference between the unetched and the BC13-etched samples, maps of the diffracted intensity around the 113 reflections showed an unexpected and reproducible decrease in the extent of the diffuse scattering in the transverse direction (perpendicular to the < 113 > direction) as the RIE bias voltage was increased. This decrease suggests that the degree of etch damage induced in the GaAs near-surface region is reduced with increasing bias voltage and ion energy. Additionally, the symmetry and orientation of the kinematic scattering was altered. Possible mechanisms for these results willbe discussed.

Photoreflectance Characterization of Etch-Induced Damage in Dry Etched GaAs

AbstractPhotoreflectance has been used to characterize the etch-induced damage in GaAs processed in an Ar/Cl2 plasma generated by an electron-cyclotron resonance (ECR) source. We show that the damage is localized to the surface and that it is most influenced by the RF power, with little effect from the microwave power. The Fermi-level is observed to be unchanged in n-GaAs and remains near midgap, while for p-GaAs, the Fermi level shifts from near the valence band to midgap. Etch-induced anisite defects are proposed as a possible source of the damage.

Lattice Damage in Ion-Implanted Compound Semiconductors and Its Effect on Electrical Activation

ABSTRACTIn recent years, a number of experimental observations have indicated that interactions between mobile point defects generated during ion implantation play an important role in the damage production in Ill-V compound semiconductors, and particularly GaAs. This paper reviews a set of such observations based on ion channeling measurements of the lattice damage in GaAs implanted with Si ions. Selected independent observations are also surveyed to illustrate the importance of point-defect interactions. Taken together, these show that at least two contributions to the lattice damage must often be considered: a “prompt” contribution attributed to direct-impact amorphization, and a “delayed” contribution attributed to point-defect clustering. New measurements are then described which show the different effects that these two damage components have on the electrical activation in annealed, Siimplanted GaAs. The aim is to indicate the potential to exploit the balance between these two damage contributions in order to improve the electrical performance and reproducibility of ion-implanted and annealed layers. Finally, the applicability of these concepts to other ion species and other compound semiconductors (GaP and InP) is briefly discussed.

Differential Reflectance Studies of Structural Changes in GaAs Caused by Ar+ Ion Bombardment

ABSTRACTDifferential reflection (DR) spectrometry has been used to investigate and characterize the effect of sputter damage of GaAs by Ar+ ions. The DR technique provides the photon-induced critical point interband transition energies which are sensitive to the electron and the crystal structure. The spectral dependence of the normalized difference in reflectivity is obtained by periodically scanning monochromatic light across a pair of GaAs samples. In the present case one part has been damaged by Ar+ ions with energies ranging from 500 to 5000 eV. The other half is the undamaged reference. The DR structure caused by interband transitions and designated as E1 and E1 + δ1 were found to shift in energy with increasing ion beam energy or with sputter damage. Two annealing stages were observed, one at 200°C and the other between 400°C and 450°C. They were attributed to different recovering mechanisms of As Frenkel pairs.

Variable angle spectroscopic ellipsometric characterization of surface damage in chemical-mechanical polished GaAs

Variable angle spectroscopic ellipsometry (VASE) was applied to the quantitative characterization of surface and subsurface damage in GaAs, induced by conventional chemical-mechanical (CM) polishing. We show that the optimum selection of angle of incidence (75°) and spectral range (greater than or equal to 430 nm) is of crucial importance for detecting and evaluating surface and subsurface quality. The measured VASE data from 249 to 789 nm were analyzed with several fitting models. A two-layer model, with a GaAs oxide overlayer on a subsurface layer on a GaAs substrate, was found consistently to yield the best fits, suggesting the presence of subsurface damage in CM polished GaAs. In the model calculations, each composite layer was assumed, in the Bruggeman effective medium approximation, to be a simple physical mixture of the chosen constituents. The fitting results indicated that, typically, the thickness values were 2–3 nm of oxide overlayer and 15–40 nm of subsurface damage beneath it, consisting of about 1%–2% reduction in density. Independent atomic force microscopy (for surface characterization) and X-ray diffraction (for subsurface characterization) measurements were also made, for comparison with the VASE results. Consistent agreement was found.

Reactive ion etching induced damage in GaAs and Al0.3Ga0.7As using SiCl4

The authors have investigated the etching characteristics of GaAs and Al0.3Ga0.7As using SiCl4 as the etching gas. The effect of damage caused on the etched surface has been characterized by employing Schottky diode performance, low-temperature integrated band-gap photoluminescence, Raman scattering and high-resolution X-ray photoelectron spectroscopy, and, for the first time, the usefulness of employing glancing X-ray reflectivity for the identification of surface damage is explored. Using high-resolution fabrication techniques, a novel procedure for constructing a sidewall Schottky diode has been developed to allow the amount of induced sidewall damage to be quantified. In addition, the deteriorative effect of the surface damage layer is observed to remain unchanged with etch time.