High Energy Ion Implantation Research Articles

High concentration nitrogen ion doping into GaAs for the fabrication of GaAsN

Nitrogen atoms were introduced into liquid encapsulated Czochralski (LEC) grown GaAs substrates for the nitrogen concentration ([N]) range of 1 × 10 18 cm −3 to 1 × 10 22 cm −3 by high-energy (400 keV) ion implantation. For heat treatment, both furnace annealing (FA) and rapid thermal annealing (RTA) were adopted. Novel emissions denoted by N i ( i = 1–5), were observed in the 2 K photoluminescence (PL) spectra of FA samples with [N] higher than 2 × 10 21 cm −3. An emission at around 1.30 eV denoted by N 5 or N′ 5, were suggested to be related with the band gap energies of GaAs 1− x N x alloys, which was predicted by a theory on the band gap bowing of this alloy system. Based on this empirical model, we estimated the amount of nitrogen x to be around 0.018.

The application of high energy ion implantation for silicon radiation detectors

High energy ion implantation of phosphorous and boron in the MeV-range has been applied to modify the vertical electric field distribution of silicon pn-junction radiation detectors. Low dose phosphorous implantation (10 MeV, 10 11–10 12 cm −2) was used to realize detectors with local high field regions characterized by an internal electric field strength up to 150 kV/cm. A field related decrease of the effective window down to 35 nm and a corresponding reduction of the pulse height defect (PHD) for the spectroscopy of low energy heavy ions have been obtained. Additional subjects for the application of the MeV-ion implantation technique are briefly summarized.

Radiation damage in nuclear fuel materials: the “rim” effect in UO 2 and damage in inert matrices for transmutation of actinides

Polygonization or grain subdivision at high damage levels (often referred to as “rim effect”) is gaining increasing importance for UO 2 which is the fuel of nuclear electricity producing power stations. Also, recently, the concept of replacing U-238, and hence replacing natural UO 2, by “inert matrices” for fissile U-235 or Pu-239, or also for transmutation of higher actinides (Np, Am, Cm) is being studied. High energy ion implantation was used to simulate fission damage in both UO 2 and in such matrices (e.g. Al 2O 3, MgAl 2O 4 etc.). The energy of implanted ions was varied between 40 keV and 2.6 GeV. Emphasis is given to the search for possible dose rate effects. Results on damage formation in UO 2 exist now for dose rate variations by more than a factor of 10 10. The implications for the technological application of inert matrix materials are briefly discussed.

Polarization insensitive InGaAs/InGaAsP/InP amplifiers using quantum well intermixing

A polarization insensitive optical amplifier based on a lattice matched InGaAs/InGaAsP/InP multiple quantum well (MQW) laser structure operating at 1.5 μm has been fabricated through vacancy enhanced quantum well intermixing using broad area, high energy (1 MeV P+) ion implantation. A simple model shows that if the interdiffusion rate of the anions is larger than that of the cations, the blue shift in the ground state heavy hole transition energy after implantation and annealing is greater than the light hole state blue shift, bringing the two bands together. Current–voltage measurements indicate that junction characteristics are well maintained after implantation. This simple technique for fabricating polarization insensitive optical amplifiers is readily extended to the monolithical integration of such devices along with other passive and active optoelectronic devices and opens the door to practical photonic integrated circuits.

Spectroscopic ellipsometry applied to the determination of an ion implantation depth profile

Spectroscopic ellipsometry (SE) has been used to characterise damage depth profiles in silicon. The damage was produced by implantation of high energy ions of various atomic number with variable charge state and using various energies. The effect of substrate temperature was also investigated. In all cases a first characterisation was made using Rutherford backscattering experiments. Attempts were then made to extract accurate data from SE measurements. If the damage depth profile is thin ( < 200 nm), a simulation of SE in the range 0.25–0.82 μm using mixed materials and a simple or complex depth profile can give very accurate information. When the damage profile is thick enough (> 200 nm), an extended measurement in the near infrared (0.25–1.5 μm) gives direct information on the thickness of the damaged layer. In this latter case, data reduction is performed using Forouhi-Bloomer dispersion relations for the amorphized silicon layer.

Exact energy values of ‘‘low-energy ion beams’’

Ion beams with energies of several tens of electron volts are used for forming special films with excellent physical and chemical properties by ion-beam deposition. Although the ion energy values are considered very important for controlling physical and chemical characteristics of the deposited films, most reported values for such film formation have been considerably inaccurate since they have been given simply by multiplying the power supply voltages to the discharge chambers with electron charge e. In practice, the plasma potential at which ions are generated is several to several tens of volts higher than the discharge chamber, so that the real beam energy is that much higher. Although the excess energy originating from the plasma floating potential has been negligible for usual high-energy ion implantation, it cannot be neglected for ion-beam deposition where low-energy ion beams below 100 eV are used. In this article it is indicated that knowing electron temperatures of plasmas is necessary to get the exact energy values of low-energy ion beams. Thus, it is also clarified that ion energy spreads of usual ion beams may be caused by possible fluctuation of the electron temperatures as well as by thermal motion of ions in the plasma.

Amorphization in Al induced by high-energy Ni ion implantation

High-energy nickel ion implantation into pure aluminum targets induces local phase transformations. Samples implanted in a TANDEM accelerator at room temperature were studied by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The TEM observations revealed the presence of spherical amorphous zones. In order to understand this not yet fully explained amorphous phase formation, the mean diameter of the amorphous zones, their numerical density and their amorphous fraction have been determined for samples implanted with different doses. Electron dispersive spectroscopy (EDS) measurements performed on the sample implanted with a dose corresponding to 3.05 at.% Ni have shown that the Ni concentration inside the amorphous zones is about 25 at.%, whereas it is 2.1 at.% in the matrix. Mechanisms explaining the relatively high Ni concentration inside the amorphous zones are discussed.

Substrate Engineering for Reduction of Alpha-Particle-Induced Charge Collection Efficiency

Measurements of alpha-particle-induced charge collection efficiency (CCE) together with simulation analysis have been carried out for several types of substrates: a double well, a p-well in a p- epitaxial layer grown on p+ substrate (epi-substrate) and a p-well with a buried defect layer. As a result, the following have been clarified. CCE for the double well is low because the bottom n-layer acts as an effective electron absorber. CCE for the p-well in the epi-substrate increases with increase in the thickness of the epilayer because the potential difference between the heavily doped substrate and the lightly doped epilayer forms a barrier which prevents electrons from traveling into the substrate. Even for the p-well in a thin epilayer, CCE is comparable to that for the p-well in the conventional p- substrate. CCE for the p-well with a buried defect layer formed by high-energy and high-dosage ion implantation is as low as CCE for the double well because the carrier lifetime is short in the buried layer due to lattice defects.

Demonstration of an ion-implanted, wavelength-shifted quantum-well laser

A technique for fabricating many different wavelength lasers on the same wafer has been developed. High energy ion implantation was used to selectively blue shift the emission wavelength of an InP-based quantum well laser structure. This structure was then processed into fully functional broad-area lasers whose current threshold was unaffected by the implantation process, indicating extremely high material quality after bandgap-shifting. This process has the potential for the integration of not only different wavelength lasers, but also other devices, such as waveguides, detectors, modulators, etc., on a single wafer.

Device characteristics of MOSFETs with self‐aligned punch‐through stopper structure

AbstractSelf‐aligned punch‐through stopper (SPS) MOSFETs are made using high energy ion implantation; punch‐through stopper (PTS) layers are formed after gate electrode delineation. The SPS structure features: 1) a retrograded PTS layer with a gradually increasing impurity profile; and 2) a relatively lower impurity concentration around the source and drain region. These characteristics of the PTS structure permit both junction capacitance reduction and adjustment of threshold voltage (Vth) (specifically, a reduced Vth and suppressed reverse short‐channel effect) and improved current drivability, short‐channel characteristics, and hot‐carrier immunity. The proposed structure is also effective in reducing process steps because only one implantation is needed to adjust the profile.

Effects of Latent Tracks Formed by High-Energy Ion Implantation in Crystals

The influence of various effects inherent to the high-energy ion bombardment of crystals on the latent track formation is treated. The nature of tracks is dependent on a type of solids. The relaxation of strong electron excitation which occurs under irradiation of materials by energetic ions is the main parameter which defines the nature of track regions. The track migration of implanted atoms as well as track channeling of incident ions is discussed for ion implantation in semiconductors.

Surface generation lifetime of MeV implanted Si

The use of high-energy (≳0.5 MeV) ion implantation potentially has distinct advantages for deep-submicron, ultralarge-scale integrated devices. Most reports on this technique focus on the formation and characterization of bulk properties at a depth of 1 μm or greater. In contrast, studies of the surface properties of MeV implanted wafers are few. Those that exist depend on C–V or C–t structures and do not provide in situ, on-wafer measurements of surface properties such as surface charge and generation lifetime of minority carriers on the processed material. This is important since it is important to observe the relationship between dose, formation of buried layers, use of hydrogen denuding cycles, and defect gettering on the surface carrier properties at a common energy level. For this study we report on the application of optical surface/interface charge analysis by time resolved surface photovoltage to both quantify and qualify surface charge and the interface generation lifetime characteristics on MeV implanted surfaces.

Production of buried waveguides in PMMA by high energy ion implantation

Optical waveguiding structures in PMMA were produced by irradiation with ions in the dose range of 10 12–10 14 ions/cm 2. Waveguides buried in various depths of the bulk material were generated using ions with different energies between 100 keV and 180 MeV. Optical devices such as Y-branches, couplers and Mach-Zehnder interferometers were produced using ion irradiation through a mask. The refractive index and profile as well as the attenuation of the waveguides were measured at different wavelengths. These properties of the waveguiding structures at different depths of the bulk material will be discussed.

Novel optical features in Cd + ion-implanted LEC-grown GaAs

High-energy Cd + ions were implanted into undoped GaAs grown by the liquid encapsulated Czochralski (LEC) method for a wide Cd concentration, [Cd] between 1 × 10 16 and 3 × 10 21 cm −3. Raman scattering spectra indicate that for [Cd] lower than 1.7 × 10 18 cm −3, the damage induced by high-energy ion-implantation can be eliminated by high-temperature annealing. For [Cd] higher than 3 × 10 18 cm −3, the intensity of the LO-phonon mode gradually reduces and its width significantly broadens with increasing [Cd]. For [Cd] = 1 × 10 21 and 3 × 10 21cm −3, a forbidden mode appears on the lower-frequency side of the LO-phonon mode. The results of Rutherford backscattering spectrometry (RBS), and Hall-effect measurements suggest that a solid solution of Cd in GaAs is formed in this high-concentration region. 2 K photoluminescence (PL) spectra indicate that four emissions related with acceptor-acceptor pairs, [g-g], [g-g] 2, [g-g] 3, and [g-g] β are formed in the near band-edge region even by using LEC-GaAs as a substrate. In the energy region far below the band-edge, many emissions associated with vacancies and complexes with doped Cd atoms are produced specifically for high [Cd].

Novel beam effect: mass transport due to the lateral component of the ion momentum

A new effect in ion beam-solid interaction is described, namely mass transport in the bombarded solid due to lateral momentum transfer from the ions. It manifests itself, after high energy (several MeV) ion implantation at low temperature through a contact mask, as a surface depression at one end, and an elevated surface at the other end of the masked region. It is only evident for off-normal implantations, and then the depressed surface is always on the windward side of the mask and the elevated surface region is always on the downwind side, and it increases superlinearly with ion energy. Electronic stopping effects play a major role not only for the momentum transfer but also for the plastic deformation of the solid.

Band-gap tuning of InGaAs/InGaAsP/InP laser using high energy ion implantation

The technique of ion-induced quantum well intermixing using broad area, high energy (1 MeV P+) ion implantation has been used to tune the emission wavelength of an InGaAs/InGaAsP/InP multiple quantum well (MQW) laser operating at 1.5 μm. The optical quality of the band-gap shifted material is assessed using low-temperature photoluminescence (PL). The band-gap tuned lasers are characterized in terms of threshold current density and external quantum efficiency and exhibit blue shifts in the lasing spectra of up to 63 nm. This approach offers the prospect of a powerful and relatively simple fabrication technique for integrating active as well as passive optoelectronic devices.

Density of amorphous Si xGe 1− x alloys prepared by high-energy ion implantation

The atomic density of amorphous Si x Ge 1− x alloys (0 ⩽ x ⩽ 1), has been measured. The amorphous alloys were made by high-ion-energy implantation into monocrystalline Si x Ge 1− x layers, deposited epitaxially on silicon substrates. During the bombardments, a steel contact mask was used to create alternating lines of amorphous and crystalline material. The ratio between the densities of crystalline and amorphous alloys was measured with 0.1–0.2% accuracy using surface profilometry and Rutherford backscattering spectrometry in conjunction with channelling. Amorphous pure elements and alloys are less dense by 1.5–2.1% than the crystalline pure elements and alloys. By comparing both the amorphous and crystalline densities with Vegard's law, it is found that this law underestimates the a-Si x Ge 1− x densities by the same amount as those of c-Si x Ge 1− x .

Silver colloidal waveguides for non-linear optics: a new methodology

High energy ion implantation on ion-exchanged glass is explored as a new suitable method to obtain waveguiding structures that contain small silver clusters. Optical and compositional measurements on these systems are presented.

Quantum-well intermixing for optoelectronic integration using high energy ion implantation

The technique of ion-induced quantum-well (QW) intermixing using broad area, high energy (2–8 MeV As4+) ion implantation has been studied in a graded-index separate confinement heterostructure InGaAs/GaAs QW laser. This approach offers the prospect of a powerful and relatively simple fabrication technique for integrating optoelectronic devices. Parameters controlling the ion-induced QW intermixing, such as ion doses, fluxes, and energies, post-implantation annealing time, and temperature are investigated and optimized using optical characterization techniques such as photoluminescence, photoluminescence excitation, and absorption spectroscopy.

Optimization of buried implanted layer in dynamic random access memories by soft error mapping and ion beam-induced current

Soft error testing using scanning nuclear microprobes, i.e., soft error mapping combined with ion beam-induced current (IBIC) measurements, can reveal device immune against soft errors, and, hence, optimal design and process parameters can be determined from the data obtained using nuclear microprobes. Well structures or buried barrier layers to suppress charge carriers, generated by incident energetic particles in DRAMs, have been fabricated by high-energy ion implantation and the suppression efficiency by the well structure was clarified using probe ion-induced current measurement.