Deep Ion Implantation Research Articles

A mathematical model for deep ion implantation depth profiling by synchrotron radiation grazing-incidence X-ray fluorescence spectrometry

Grazing-incidence X-ray fluorescence is applied to obtain shallow depth distributions using the X-ray standing wave (XSW). A new XSW-free mathematical model is proposed that allows the quantitative derivation of much deeper depth distributions.

Experimental Demonstration and Analysis of a 1.35-kV 0.92-m $\Omega \cdot \text {cm}^{2}$ SiC Superjunction Schottky Diode

This paper presents the fabrication, experimental analysis and electrical characterization of the first functional SiC superjunction (SJ) device. A trench-etching-and-sidewall-implant method has been developed to implement the SJ principle on a SiC Schottky diode. Several key process steps, including deep trench etching, ion implantation, and high-temperature annealing, are found to have noticeable influences on the device performances. The corresponding influences are studied by both simulation-aided theoretical analysis and experimental measurements. The highest measured cell blocking voltage was 1350 V, which achieves 95% of the simulated blocking voltage for the perfectly charge-balanced SJ structure. The measured device specific on-resistance was 0.92 $\text{m}\Omega \cdot \text {cm}^{2}$ . The SJ drift region specific on-resistance as low as 0.32 $\text{m}\Omega \cdot \text {cm}^{2}$ was obtained after subtracting the substrate resistance. This result successfully breaks the SiC 1-D unipolar limit.

High-intensity low energy titanium ion implantation into zirconium alloy

This research describes the possibility of ultra-high dose deep titanium ion implantation for surface modification of zirconium alloy Zr-1Nb. The developed method based on repetitively pulsed high intensity low energy titanium ion implantation was used to modify the surface layer. The DC vacuum arc source was used to produce metal plasma. Plasma immersion titanium ions extraction and their ballistic focusing in equipotential space of biased electrode were used to produce high intensity titanium ion beam with the amplitude of 0.5 A at the ion current density 120 and 170 mA/cm2. The solar eclipse effect was used to prevent vacuum arc titanium macroparticles from appearing in the implantation area of Zr sample. Titanium low energy (mean ion energy E = 3 keV) ions were implanted into zirconium alloy with the dose in the range of (5.4–9.56) × 1020 ion/cm2. The effect of ion current density, implantation dose on the phase composition, microstructure and distribution of elements was studied by X-ray diffraction, scanning electron microscopy and glow-discharge optical emission spectroscopy, respectively. The results show the appearance of Zr-Ti intermetallic phases of different stoichiometry after Ti implantation. The intermetallic phases are transformed from both Zr0.7Ti0.3 and Zr0.5Ti0.5 to single Zr0.6Ti0.4 phase with the increase in the implantation dose. The changes in phase composition are attributed to Ti dissolution in zirconium lattice accompanied by the lattice distortions and appearance of macrostrains in intermetallic phases. The depth of Ti penetration into the bulk of Zr increases from 6 to 13 μm with the implantation dose. The hardness and wear resistance of the Ti-implanted zirconium alloy were increased by 1.5 and 1.4 times, respectively. The higher current density (170 mA/cm2) leads to the increase in the grain size and surface roughness negatively affecting the tribological properties of the alloy.

Development of Self-Aligned Process to Decrease Gate Length in Recessed SiC SIT

Because of difficulty in deep ion implantation, the recessed gate structure has been favored in SiC SIT. In order to improve the frequency, it is a good method to decrease the gate length by eliminating the side wall ion implantation affection. We developed normally-on RF 4H-SiC SIT with high small signal gain. The effect of forming the side wall protection between the source mesa and the gate area was simulated

Removing the transients electron trapping in P-N junction diode by using soft X-ray annealing method

This paper describes a transient phenomenon in the reverse current of P-N junctions giving rise to a hump at a specific reverse bias. P-N diode as been fabricated by a deep boron ion implantation (120 keV) and a junction depth around 4 μm is expected. Ion implantation can cause defect in silicon substrate even if the device was cured by annealing process, the defect or its effect is still remained. I-V characteristic has been acquired from –10 V to 0 V in temperature variation of 30–80ºC. At the specific condition of –3 V, 80ºC humps occurred on the curve and when the device was exposed to X-ray at energy of 40, 55 and 70 keV. The humps were then shifted toward 0 V. Activation energy has been calculated in order to give an insight into the device characteristics. It revealed the presence of a non-uniform density of electron traps corresponding to a broad range of energy levels from about 0.65–0.67 eV above the intrinsic band. This report shows an interesting phenomenon of the deep P-N junction diode modified by X-ray irradiation.

Heavy ion beam factory for material science based on the KEK digital accelerator

The KEK digital accelerator (DA) is an alternative to high-voltage electrostatic accelerators and conventional cyclotrons and synchrotrons, which are commonly used as swift heavy ion beam drivers. Compared with conventional accelerators, KEK-DA is capable of delivering a wider variety of ion species with various energies, as a result of its intrinsic properties. It is expected to serve as a heavy ion beam factory for research in materials science. Plans for its utilization include unique application programs, such as laboratory-based space science using virtual cosmic rays, heavy-ion mutagenesis in microorganisms, deep ion implantation, and modification of materials, which may be categorized into systematic studies of the spatial and temporal evolution of the locally and highly excited states of materials.

Enhanced Performance and Reliability for Solid-Phase Crystallized Poly- Si TFTs with Argon Ion Implantation

High-performance solid-phase crystallized (SPC) polycrystalline silicon thin-film transistors (TFTs) with argon ion implantation (argon-implanted poly- TFTs) are proposed in this study. Compared to the control poly- TFT, the argon-implanted poly- TFT has superior electrical characteristics, including lower threshold voltage, higher field-effect mobility, steeper subthreshold swing, lower trap state density, etc. These electrical performance improvements could be attributed to the fine microstructure of the SPC poly- film improved by deep argon ion implantation beyond the interface of amorphous and underlying oxide. Therefore, a high-quality poly- channel accompanied with larger grain size and lower grain boundary trap states could be obtained. Moreover, the argon-implanted poly- TFT also exhibits an improved hot-carrier stress immunity owing to reduced weak or bonds from fewer grain boundaries in the poly- channel.

Compositional and structural changes in LiNbO3 following deep He+ ion implantation for film exfoliation

The physical mechanism of He-ion-based exfoliation in Z-cut LiNbO3 is investigated. Rutherford backscattering/channeling, nuclear-reaction analysis, and transmission electron microscopy are used to examine the compositional and structural changes caused by deep ion implantation followed by thermal annealing. Lattice disruption, He-bubble formation, and Li depletion are observed in the implantation region, as well as the onset of exfoliation. The implications of these observations for the crystal ion slicing method are discussed.

Surface roughness in sulfur ion-implanted InP with molecular beam epitaxy regrown double-heterojunction bipolar transistor layers

We report on deep ion-implantation of sulfur into InP substrates to replace the epitaxial subcollector layer of double-heterojunction bipolar transistors. Using optimized implantation conditions of 350keV energy and 1×1015cm−2 dose, we achieved a subcollector sheet resistance of 15Ω∕square. Under well-controlled regrowth conditions a root-mean-square roughness of 12Å is measured from DHBT epitaxial layers grown on implanted InP substrates, comparable to DHBT epitaxial layers grown on n+ epiready unimplanted substrates. We observe a pronounced increase in surface roughness of epitaxial layer beyond a threshold ion dose, depending on implantation energy. Large-area DHBT devices result with sulfur-ion implanted subcollector shows similar characteristics compared to devices fabricated on n+-doped InP substrates.

High-energy ion implantation: an alternative technology for micromachining three-dimensional GaAs structures

We present an alternative technology to micromachine gallium arsenide (GaAs) using deep ion implantation for MEMS applications. Energetic low dose nitrogen ions were used to implant deeply into n-type GaAs substrate. After annealing at 600 °C the nitrogen implanted n-GaAs top layer was converted to semi-insulating GaAs. A pulsed electrochemical etching process was used to selectively remove n-GaAs and leave the top patterned semi-insulating GaAs layer as mechanical membrane structures. Various GaAs microstructures, such as cross-bridge, coiled, and corrugated membranes have been successfully fabricated using this unique micromachining technology. By increasing the ion doses, the GaAs will be heavily damaged. The damaged GaAs shows much higher etch rate compared to the un-implanted GaAs using proper etch solutions and can be, therefore, used as sacrificial layer. A unique capacitive pressure sensor fabrication technology using AlGaAs/GaAs wafer is proposed, where the air gap between two electrodes is formed by releasing the locally damaged GaAs.

High-energy ion projection for deep ion implantation as a low cost high throughput alternative for subsequent epitaxy processes

Three-dimensional (3D) doping into depths up to 40 μm is of great interest for numerous device types. In particular, the production of high-power devices requires low cost vertically structured doping. State of the art epitaxial growth combined with diffusion and/or low-energy ion implantation is time consuming and cost intensive. We suggest 3D structured high-energy ion projection implantation as a simple cost effective and reliable alternative. This method allows controlled fast doping with high homogeneity and reproducibility. This article outlines some details of a feasibility study of the technique and discusses advantages and problems.

A JFET-CMOS Technology for Low-Noise Sensor Interface Circuits

In this paper, fabrication technology and device characteristics of junction field effect transistor (JFET) which can be integrated in CMOS sensor interface circuits are presented. The JFET is applicable to CMOS (operational) amplifiers to realize a very low-noise front-end amplifier in sensor interface circuits. It is formed with isolated p-well area in CMOS device. Extra processes to a standard CMOS technology are one photolithography process and two ion-implantation processes. N-type channel in JFET is formed by deep ion-implantation of phosphorous with energy of 150 keV to connect n+ source and drain regions. After that, p-type top gate region is formed by shallow ion-implantation of borron with energy of 30 keV. Fabricated JFET devices showed enough transconductance and low drain conductance, which are suitable to use them in analog amplifiers. Noise power-spectrum of the fabricated JFET was evaluated, and compared with n-MOSFET and p-MOSFET. As a result, noise-spectrum of JFET below 1 kHz was much lower than that of CMOS devices. Since many physical sensors have their signal bandwidth in low frequency band, this JFET device can be utilized in CMOS-based front-end amplifiers as the key device of low-noise sensor interface circuits.

Micromachining of three-dimensional GaAs membrane structures using high-energy nitrogen implantation

In this paper we present an alternative technology for micromachining gallium arsenide (GaAs) using deep ion implantation. Energetic nitrogen ions at 630 keV and 4 MeV have been used to implant deeply into an n-type GaAs substrate with doses of 2 × 1014 and 1 × 1015 cm−2. After annealing at 600 °C, the nitrogen implanted n-GaAs top layer was converted to semi-insulating GaAs with a thickness of 1 μm for 630 keV and 2.5 μm for 4 MeV nitrogen ions. A pulsed electrochemical etching process has been developed to selectively remove n-GaAs and to leave the top patterned semi-insulating GaAs layer as a mechanical membrane structure. Various GaAs microstructures, such as cross-bridge, coiled and corrugated membranes, have been successfully fabricated using this micromachining technology.

Deep nitrogen implantation for GaAs microstructuring using pulsed electrochemical etching

We present deep ion implantation technology to fabricate the GaAs microstructures for microelectromechanical systems applications. 630 keV and 4 MeV nitrogen ions were used to implant deeply into an n-type GaAs substrate with doses of 2×1014 and 1×1015 cm−2, respectively. The resistivity and I/V characteristics of implanted n-GaAs have been investigated as a function of the annealing temperature. The results demonstrate that the implanted n-GaAs surface layer annealed at 600 °C has the highest resistivity and maximum breakdown voltage. This layer is a semi-insulating layer and has a thickness of 1 and 2.5 μm for implantation with 630 keV and 4 MeV nitrogen ions, respectively. Deep-level transient spectroscopy measurement reveals that the EL2 trap contributes to the formation of semi-insulating GaAs layers. Rutherford backscattering measurements show that there is no significant crystalline damage in the nitrogen implanted GaAs layer. A pulsed electrochemical etching process has been developed to selectively remove n-GaAs, leaving the top patterned semi-insulating GaAs layer as mechanical microstructures. Using this technique, GaAs microstructures, such as cantilevers and cross bridges, have been successfully fabricated.

Stress tuning in crystal ion slicing to form single-crystal potassium tantalate films

We report on the implementation of crystal ion slicing in potassium tantalate (KTaO3). Deep-ion implantation is used to create a buried sacrificial layer in (001) single-crystal wafers of KTaO3. 10-μm-thick single-crystal films have been fabricated by adjusting the stress level in the implantation damage layer to induce room-temperature etchless exfoliation. Crack propagation is found to depend critically on implantation dose, with a threshold dose for exfoliation near 1×1016 cm−2. A significant implantation-induced etch selectivity between the sacrificial layer and the rest of the sample is also found. Capacitance measurements show that the films exhibit a bulk-like dielectric constant and loss tangents below 0.01 at low temperatures.

Raman investigation of damage caused by deep ion implantation in diamond

Raman microscopy has been employed to investigate the nature of damage created when natural type-IIa diamond is irradiated with MeV alpha particles. Three features appear in the Raman spectrum due to damage, viz., (i) the first-order diamond Raman line is broadened and downshifted, (ii) broad features appear which are a measure of the vibrational density of states of ion-beam-amorphized diamond, and (iii) the damage causes the appearance of sharp defect-induced Raman peaks at 1490 and 1630 cm-1. For damage below an amorphization threshold, a linear relationship exists between the full width at half maximum and frequency shift, which shows that these are Kramers-Kronig related. The annealing behavior of the sharp Raman feature at 1490 cm-1 suggests that this peak is associated with vacancies with an activation energy for annealing of 4.06 eV, while the 1630-cm-1 peak is due to an interstitial related defect with an activation energy of 1.2 eV. For sub-MeV ion irradiation, damage beyond the critical amorphization level usually leads to relaxation of the diamond structure to graphite upon thermal annealing. However, for MeV ion irradiation, it was found that annealing, even when the ion induced damage level is well above the amorphization threshold, could restore the original diamond structure. We attribute this result to the high internal pressure the damaged layer is subjected to which does not allow relaxation to graphitically bonded structures.

Direct wafer bonding and transfer of 10-μm-thick magnetic garnet films onto semiconductor surfaces

Bonding between liquid-phase-epitaxy-grown yttrium iron garnet films and various semiconductors is realized by direct wafer bonding. The semiconductor substrates can serve as a platform for integration or as a “handle” platform for the transfer of mesoscopic garnet films. To effect film transfer, a sacrificial layer is formed in the garnet by deep ion implantation prior to bonding. Shear stress at the garnet/semiconductor interface can be controlled by temperature tuning during the bonding process. A debonding temperature threshold of ∼400 °C is found and related to the interfacial thermal stress due to difference in thermal expansion coefficients of the bonded materials. Film separation is realized by the application of thermally induced stress at the sacrificial layer.

Fabrication of single-crystal lithium niobate films by crystal ion slicing

We report on the implementation of crystal ion slicing in lithium niobate (LiNbO3). Deep-ion implantation is used to create a buried sacrificial layer in single-crystal c-cut poled wafers of LiNbO3, inducing a large etch selectivity between the sacrificial layer and the rest of the sample. 9-μm-thick films of excellent quality are separated from the bulk and bonded to silicon and gallium arsenide substrates. These single-crystal films have the same room-temperature dielectric and pyroelectric characteristics, and ferroelectric transition temperature as single-crystal bulk. A stronger high-temperature pyroelectric response is found in the films.

Crystal ion slicing of single-crystal magnetic garnet films

Epitaxial liftoff has been used for achieving heterogeneous integration of many III-V and elemental semiconductor systems. However, it has been heretofore impossible to integrate devices of many other important material systems. A good example of this problem has been the integration of single-crystal transition metal oxides on semiconductor platforms, a system needed for on-chip thin film optical isolators. We report here an implementation of epitaxial liftoff in magnetic garnets. Deep ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG (Bi-YIG) epitaxial layers grown on gadolinium gallium garnet (GGG). The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. Ten-micron-thick films have been lifted off from the original GGG substrates by etching in phosphoric acid. Millimeter-size pieces of excellent quality have been transferred to the silicon and gallium arsenide substrates. Study of the magnetic domain structure in the detached epilayers by Faraday contrast shows no changes in film anisotropy. Optical insertion loss measurements are also presented.

Epitaxial liftoff of thin oxide layers: Yttrium iron garnets onto GaAs

We report on the implementation of epitaxial liftoff in magnetic garnets. Deep-ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG epilayers grown on gadolinium gallium garnet. The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. 10-μm-thick films of excellent quality are lifted off and bonded to silicon and GaAs substrates. No noticeable degradation in magnetic coercivity due to domain pinning is observed. Stress-induced microfracturing in the thin oxide layers is also addressed.