Combined Ion Beam Research Articles

Strain Measurements of Sigec Heteroepitaxial Layers On Si(100) Using Ion Beam Analysis

AbstractThe strain in SiGeC heteroepitaxial films grown on Si(100) substrates has been quantified using ion channeling. The films were grown both by combined ion beam and molecular beam epitaxy (CIMD) and chemical vapor deposition (CVD). Rutherford backscattering spectrometry (RBS) was used to quantify the Ge concentration as well as the film thickness, nuclear resonance elastic ion scattering was used to quantify the carbon concentration, and ion channeling was utilized to measure film quality. Channeling angular scans across an off normal major axis were used to quantify the strain. Part of the film was removed by using a solution of HF, HN03 and CH3COOH in order to obtain a reliable scan in the substrate. The results indicate that C may be compensating for the strain introduced by Ge.

Low energy (100 eV) C+ ion doping into GaAs using combined ion beam and molecular beam epitaxial technology

Low-energy (100 eV) carbon ion (C+) irradiation during molecular beam epitaxy of GaAs was carried out using combined ion beam and molecular beam epitaxy (CIBMBE) technology for the growth temperature (Tg) range between 500 and 590 °C. Carbon incorporation was identified by both low-temperature (2 K) photoluminescence and Hall effect measurements. In the PL spectra, two well-established specific emissions, ‘‘g’’ and [g-g], which are closely related to acceptor impurities, were observed for the above Tg range. The results indicate that carbon was both optically and electrically well activated as an acceptor even at Tg as low as 500 °C. Maximum net hole concentration, ‖NA-ND‖, as high as 3×1018 cm−3 was obtained with no appreciable radiation damages and undesired impurity contamination.

Optical Characterization of 100 eV C+ Ion Doped GaAs

ABSTRACTLow energy (100 eV) impinging of carbon (C+) ions was made during molecular beam epitaxy (MBE) of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) technologies for the growth temperature ( Tg ) between 500 °C and 590 °C. 2 K photoluminescence (PL), Raman scattering and Hall effect measurements were made for the samples. In the PL spectra two specific emissions, “g” and [g-g], were observed which are closely associated with acceptor impurities. PL and Hall effect measurements indicate that C atoms were very efficiently introduced during MBE growth by CIBMBE and were both optically and electrically well activated as acceptors even at Tg=500 °C. The results reveal that defect-free impurity doping without subsequent annealing can be achieved by CIBMBE method.

Low temperature photoluminescence from GaAs impinged by mass-separated low-energy C+ ion beams during molecular beam epitaxy

ABSTRACTC-doped GaAs films were prepared by novely a developed, combined ion beam and molecular beam method (CIBMBE) as a function of hyperthermal (30–500 eV) energies (EC+) of carbon ion (C+) beam. Ion beams of a fixed beam current density were impinged during molecular beam epitaxy growth of GaAs at substrate temperature of 550 °C. Low temperature (2 K) photoluminescence (PL) has been used to characterize the samples together with Hall effects measurements at room temperature. Through the spectral evolution of an emission denoted by [g-g]β which is a specific emission relevant to acceptor-acceptor pairs, the activation rate was confirmed to increase with increasing EC+ for EC+ lower than 170 eV. It was explicitly demonstrated that the most effective Ec+ to establish highest activation rate is located at ~170 eV. This growing activation rate was suggested to be attributed to the enhanced migration of both impinged C and host constituent atoms with increasing EC+. This surmise was supported also by Hall effect measurements which revealed the maximum net hole concentration ( |NA-ND| ) for EC+=170 eV. For EC+ higher than ~170 eV, increasing EC+ was found to induce the reduction of activation rate. It was suggested that this observation is ascribed not to the formation of C donors but to the enhanced sputtering effect of impinged C+ ions with increasing EC+.

Structure and Mechanical Properties of Coatings Produced by Dynamic Ion Mixing

Ion implantation is now applied on a wide scale for Si doping in the semiconductor industry but its application to other materials is more recent. The ion beam mixing of predeposited surface layers with substrate materials has expanded the potential uses of ion beams to modify material properties. However, the shallow implanted or mixed layers (about 0·1 μm) are often insufficient for many technological applications and a new method combining ion beam mixing with simultaneous deposition, dynamic ion mixing (DIM), removes the thickness limitation imposed by finite ion ranges and allows for the buildup of thicker coatings on engineering components. The characteristic of the DIM technique is the use of a high energy (100-400 keV) heavy ion beam (Ar + or Xe +) to produce localised energetic deposition of the target atoms. One of the most important features of this surface alloying process is to produce atomic mixing at the film/substrate interface which is important in the first stage of coating. This deposition results in an intermixed layer of graded composition which improves markedly the adhesion performance of the film. Moreover, the high atomic displacement rate achieved during heavy ion bombardment can also be considered to be a modification of the process itself which is used to control the microstructural state of the film. For instance, crystallisation of amorphous coatings can be obtained by DIM at temperatures much lower than those required in conventional thermal treatment. Some recent examples of coatings produced by this method on stainless steel and tool steel are described, including intermetallics (CuNi, FeAl) and ceramics (TiC, SiC, TiB2). The microstructural characteristics of the coatings were studied by TEM observations on crosssectional samples and composition-depth profiles were carried out by secondary ion mass spectroscopy. In all cases it was demonstrated that thick and adherent coatings with homogeneous and controlled structures could be produced. The adhesion performance of the coatings has been studied by means of scratch tests and the friction and wear behaviour assessed on a standard ball on disc tribometer. The hardness of the coatings was determined from nanoindentation experiments.

Damage-Free Ion Beam Doping of Carbon During Molecular Beam Epitaxy of GaAs

ABSTRACTRecently, we introduced various acceptor impurities into MBE-grown ultra-pure GaAs by conventional high-energy ion implantation and found many novel shallow emissions associated with acceptor-acceptor pairs. Most of these emissions were easily quenched by extremely small amount of residual donor atoms which were unintentionally introduced during doping processes. For the interpretation of impurity effects, the usage of mass-separated atom as dopant source was strongly suggested. Along this consideration, we developed combined ion beam and molecular beam epitaxy (CIBMBE) technology, in which damage-free doping with high mass purity (M/ΔM=100) is expected to be possible. We here present the results of low-energy (100 eV) carbon ion doping using CIBMBE method. Samples were prepared asa function of growth temperature (Tg=400-700°C) and ion beam current. Net hole concentration, |NA-ND| as high as ~1×1020 cm-3 was obtained in as-grown samples. In 2K photoluminescence spectra, emissions due to acceptor-acceptor pairs exhibit specific energy shift with growing |NA-ND|. Results indicate that carbon doping can be made efficiently even at Tg as low as 500°C without any post heat treatment. These results also tell that by CIBMBE method no serious radiation damages are produced and the undesired impurity contamination can be considerably suppressed.

Excimer Laser Melting of MBE-ZnSe

ABSTRACTIt has. generally been concluded that good doping in wide-gap semiconductors is best accomplished by non-equilibrium means. Excimer lasers, because of their high intensity and short pulses, are ideal for this. Our earlier laser annealing work on bulk ZnSe resulted in complications due to increased twinning of the sample. Our present work shows that twinning can be eliminated by the use of originally untwinned MBE material. The MBE samples had the additional advantage, over bulk, of a far smoother surface, which simplified the investigation of melting and evaporation. Use of power levels of 10, 20, and 35 MW/cm2 showed no melting at 10 MW/cm2, melting and no detectable evaporation at 20 MW/cm2, and evaporation at 35 MW/cm2. Combined ion beam cratering and SEM examination showed a depth of the melted layer, at 20 MW/cm2, of - 0.5 μm. Moreover, AES analysis showed minimal decomposition of the 20 MW/cm2 sample.

Combination of ion beam techniques, AES and SIMS for the analysis of samples exposed in the plasma boundary of the JET tokamak

AbstractA system combining ion beam and surface‐specific techniques for the analysis of probes exposed in the edge region of the plasma produced by the Joint European Torus (JET) is described. Among examples of the use of the system are the demonstration that 10–40% of the ionic charge flux in the boundary can be due to impurities, erosion and redeposition phenomena can be observed with small probes placed in the plasma boundary, and most of the oxygen observed on collector probes is an artefact resulting from exposure to air.

Radical beam/ion beam etching of GaAs

A novel combined radical beam and ion beam etching (RBIBE) technique that uses a microwave-excited radical beam combined with an Ar+ ion beam has been developed for smooth, low damage, and rapid etching of GaAs structures. Separate control of both argon ion (Ar+) energy and/or current and chlorine radical (Cl*) beam flux density has enabled us to realize highly chemically enhanced GaAs etching. This RBIBE technique differs qualitatively from and offers greater flexibility than reactive ion etching (RIE), ion beam assisted etching (IBAE), where the reactive etch gas is not plasma excited, or reactive ion beam etching (RIBE), where independent control of radical and ion beam flux is difficult. Our work examines etch rate as a function of flow rate, temperature, microwave power, and ion beam current. The etch rate and reactive sputter yield are typically eight times greater with the microwave plasma on (RBIBE) than with the plasma off (IBAE). With RBIBE, high etch rates (2.5 μm/min) have been realized at room temperature and for low ion energies (200 eV). Optical emission spectroscopy is used to correlate the etch rate with the concentration of chlorine radicals in the microwave cavity. The reactive sputter yield and degree of anisotropy can be varied over a wide range by varying the microwave power level and the ion beam current density. We demonstrate that this etching technique should be capable of producing smooth, low-damage structures for applications in optoelectronics.

6148. A combined electron and ion beam lithography system

6148. A combined electron and ion beam lithography system

Ag Layers on Cu(110): Bonding, Structure, and Stability

ABSTRACTThe atomic-level properties ( bonding, structure, composition ) and thermal stability of Ag overlayers on Cu(110) have been investigated using combined surface and high energy ion beam techniques. Analysis of the first Ag adatom layer with LEED shows that the Ag is initially confined to the [110] troughs and that further deposition results in a Ag(111) layer exhibiting c(2×4) symmetry. Rutherford backscattering analysis gives absolute coverages that are consistent with the surface science coverage determination. Thermal desorption of CO from the trough composite reveals a lower ( more Ag-like ) binding energy than that for clean Cu(110). Continuous films grown cold at thicknesses <115 Å are found to agglomerate above 500 K exposing a tenacious Ag-Cu interface like that formed by one monolayer deposition. Ion beam analysis has been employed to characterize the agglomerate coverage and depth distribution for these degraded films. Thin films grown 900Å thick exhibit much higher thermal stability, giving detectable interfacial degradation only after heating above 725 K.

A combined electron and ion beam lithography system

In scanning beam microfabrication processes, including resist exposure, direct maskless ion implantation, and micromachining, ions and electrons have complementary roles. It is advantageous to have, within a single scanning beam machine, finely focused and precisely coregistered beams of both ions and electrons. The requirement for the ion beam and the electron beam to have a common axis and to be focused at the target by a high resolution lens with short working distance can be met both by solely electrostatic and by combined magnetic and electrostatic lenses. Such lenses, and complete probe‐forming systems incorporating them, are considered.

Metal/Insulator/Si structures with low interface state density fabricated by combined ion beam sputtering and atomic hydrogen beam treatment

Ion beam techniques, combining insulator deposition and atomic hydrogen treatment, are used for the fabrication of metal–insulator–silicon (MIS) structures at low temperature (300 °C). SiNxOy and AlNxOy insulating layers are deposited by reactively sputtering either a silicon or an aluminium target with a nitrogen ion beam. The y/x ratio is controlled by introducing pure molecular oxygen in the vicinity of the substrate. The resistivity and dielectric strength of the films increase with the y/x ratio and exceed typically 1016 Ω cm and 2×106 V/cm, respectively. The electrical properties of the MIS devices were investigated by the capacitance/conductance method. The dramatic reduction of the interface state density (below 1011 cm−2 eV−1 with AlNxOy) consecutive to H treatment and annealing in nitrogen at 300 °C, is interpreted on the basis of the formation, weakening, and strengthening of Si–H bonds.

Epitaxial Growth of FeSi2 on (111)Si

ABSTRACTIsothermal annealing, two step annealing and ion beam mixing were performed to induce interfacial reactions between iron thin films and silicon substrate. Both orthorhombic and tetragonal FeSi2 were found to grow epitaxially on (lll)Si with orthorhombic FeSi2 being the predominant phase. No epitaxial growth of FeSi2 on (001)Si was detected. Epitaxial islands as large as 40 μm in size were formed by a scheme combining ion beam mixing and two step annealing.

Combined ion beam deposition and etching for thin film studies

A dual ion beam system is used to deposit thin films in the presence of ion bombardment. This technique provides a measurement of sputter yields of elements in alloy films. Material is deposited by ion beam sputtering using a high current focused beam, while a second ion beam bombards the growing film. The film composition is modified by preferential resputtering of the high sputter yield component, analogous to the effect of substrate bias in diode sputtering. The advantage of the ion-beam technique is that ion energies, currents and angles may be directly measured and controlled. We have studied the sputter yield ratio of Gd to Co in binary Gd–Co films deposited with simultaneous ion bombardment by an argon beam of typically 500 eV ion energy. Gd is preferentially resputtered with a yield ratio which increases from 2 to 6 with increasing Co concentration in the film. This dependence of yield ratio on film composition is consistent with a model in which surface binding energy dominates the sputter yields.

Analysis of boron predeposited silicon wafers by combined ion beam techniques and X-ray microanalysis

During the thermal predeposition of boron in silicon, which is a step of the planar technology, a boron-rich layer (BRL) is known to grow onto the surface of the silicon wafers and to control the doping profile inside the substrate. The composition and structure of these layers have not yet been accurately determined. In this paper, BRLs of different thicknesses, obtained by B-predepositing silicon wafers at 1000°C for 20 min with different gas flux compositions, have been analysed by combined X-ray microanalysis, Rutherford backscattering of He + ions and 10 B(α, p) 13 C, 16 O( d, p) 17 O and 10 B( d, p) 11 B nuclear reactions, in order to determine the composition and the boron chemical profile. The X-ray measurements have been carried out on BRLs which were removed from the silicon substrate and the compositions were calculated according to the thin film approximation. With all the techniques, the presence of boron, silicon and oxygen in the BRLs was ascertained. This confirms the hypothesis that these films consist not only of a SiB phase, but also of a B 6O phase, as previously suggested elsewhere 1−3). Moreover, the boron profile obtained in the thickest (2600 Å) specimen by the 10B( α, p) 13C reaction is constant and falls down below 10 21 at/cm 3 at the BRLSi interface, in agreement with the corresponding profile in the silicon substrate determined by electrical resistivity measurements.