Germanium Ion Implantation Research Articles

Temperature dependence of germanium vacancy centers in high-quality diamond after 300 keV ion implantation

In this work, the temperature dependence of diamond GeV centers that were formed by germanium (Ge) ion implantation and annealed in a hydrogen atmosphere at 1000 °C was investigated by photoluminescence spectroscopy. It was found that the intensity of the GeV centers had a thermal quenching effect with the increase in temperature, and the activation energy was fitted at 62.32 meV. Then, the laser power dependence was mainly dependent on radiative recombination so that the diamond GeV center intensity increased with the laser power. Furthermore, the electron-phonon coupling and thermal softening effect were found between Ge ions and vacancies chemical bonds, which made the GeV center peak position red shift with the increase of temperature. Finally, the FWHM of the diamond GeV center exhibited both homogeneous (Lorentzian component) and inhomogeneous broadening (Gaussian component) at 80–280 K, indicating that the Lorentzian component was dominant in the FWHM of the GeV center.

Germanium ion implantation performance improvement on applied materials’ VIISta HCS high current implanter with use of germanium tetrafluoride (GeF4) and hydrogen (H2) mixture gases

Germanium ion implantation performance improvement on applied materials’ VIISta HCS high current implanter with use of germanium tetrafluoride (GeF4) and hydrogen (H2) mixture gases

Ge Ion Implanted Photonic Devices and Annealing for Emerging Applications.

Germanium (Ge) ion implantation into silicon waveguides will induce lattice defects in the silicon, which can eventually change the crystal silicon into amorphous silicon and increase the refractive index from 3.48 to 3.96. A subsequent annealing process, either by using an external laser or integrated thermal heaters can partially or completely remove those lattice defects and gradually change the amorphous silicon back into the crystalline form and, therefore, reduce the material’s refractive index. Utilising this change in optical properties, we successfully demonstrated various erasable photonic devices. Those devices can be used to implement a flexible and commercially viable wafer-scale testing method for a silicon photonics fabrication line, which is a key technology to reduce the cost and increase the yield in production. In addition, Ge ion implantation and annealing are also demonstrated to enable post-fabrication trimming of ring resonators and Mach–Zehnder interferometers and to implement nonvolatile programmable photonic circuits.

Silicon erasable waveguides and directional couplers by germanium ion implantation for configurable photonic circuits.

A novel technique for realization of configurable/one-time programmable (OTP) silicon photonic circuits is presented. Once the proposed photonic circuit is programmed, its signal routing is retained without the need for additional power consumption. This technology can potentially enable a multi-purpose design of photonic chips for a range of different applications and performance requirements, as it can be programmed for each specific application after chip fabrication. Therefore, the production costs per chip can be reduced because of the increase in production volume, and rapid prototyping of new photonic circuits is enabled. Essential building blocks for the configurable circuits in the form of erasable directional couplers (DCs) were designed and fabricated, using ion implanted waveguides. We demonstrate permanent switching of optical signals between the drop port and through the port of the DCs using a localized post-fabrication laser annealing process. Proof-of-principle demonstrators in the form of generic 1×4 and 2×2 programmable switching circuits were fabricated and subsequently programmed.

CuGa xSe y chalcopyrite-related thin films grown by chemical close-spaced vapor transport (CCSVT) for photovoltaic application: Surface- and bulk material properties, oxidation and surface Ge-doping

Device-grade ternary Cu–Ga–Se chalcopyrite thin films used for photovoltaic energy conversion have been prepared by a novel chemical close-spaced vapor transport (CCSVT) technique developed for a deposition on areas of up to 10×10 cm 2. A two-step process has been developed which allows the fine tuning of the film composition and the electronic properties. The extension of deposition times in the two-step process led to final film compositions with [Ga]/[Cu] ratios ranging from 0.9 to 5.7, allowing the study of the structural phase transitions. In this paper the main focus of interest is related to the material properties of the device-grade thin films prepared by CCSVT technique. We present our recent studies on (i) the growth, compositional, structural and electronic structural properties, (ii) the degradation under ambient conditions and (iii) the feasibility of n-type doping this p-type semiconducting material by germanium. Thin films were grown with chalcopyrite (1:1:2) and CuGaSe 2-related defect compound structures (DC) with stoichiometries of CuGa 3Se 5 and CuGa 5Se 8. In order to derive the DC structure, X-ray and neutron powder diffraction investigations have been carried out on powders of these CuGaSe 2-related compounds grown by elemental synthesis (powder) and CCSVT (thin films), respectively. We found no hints for an ordering of defects, as proposed in the past and giving name to the so-called Ordered Defect Compounds (ODC) in this and related structures. From our results a growth model is presented for CuGa 3Se 5 formation in gallium-rich CCSVT-grown CuGa x Se y films. The chemical and electronic surface and interface structure of CuGaSe 2 thin films with bulk [Ga]/[Cu] ratios between 0.94 and 1.39 is investigated by X-ray and UV-excited photoelectron spectroscopy (XPS and UPS, respectively). A transition of the Cu:Ga:Se surface composition from 1:1:2 for the Cu-rich bulk sample to 1:3:5 for the sample with the highest bulk [Ga]/[Cu] ratio is observed. Simultaneously, a downward shift of the valence band maximum position with respect to the Fermi energy is found. The comparison of the estimated conduction band minimum with that of CdS reveals the formation of a pronounced “cliff-like” conduction band offset at the respective interface. Furthermore, the CuGaSe 2 thin film degradation under ambient as well as under thermal conditions of CuGaSe 2 thin films has been studied by XPS. During thermal oxidation, the formation of predominantly Ga 2O 3 and some amount of SeO 2 were observed, but no copper oxides could be detected in the near-surface region of the thin films. The same oxides are found after native oxidation in air under ambient conditions. An additional sodium oxide compound formed at the thin film surface, Na x O and Na 2CO 3 after thermal and native oxidation, respectively. Germanium ion implantation technique of the near-surface region of CuGaSe 2 thin films has been used in order to prove the feasibility of n-type doping. In photoluminescence (PL) studies, the occurrence of a new emission line is identified as Ge related and explained as a donor–acceptor-pair (DAP) recombination. The precise role the Ge is playing in this doping of CuGaSe 2 is revealed by X-ray absorption spectroscopy (XANES and EXAFS) and ab initio calculations based on the density functional theory. The studies indicate that the incorporated Ge atoms preferentially occupy Ga sites when relaxation around the dopant is taken into account. Additionally, our corresponding theoretical band structure model predicts the existence of additional localized electronic acceptor and donor defect bands within the band gap of CuGaSe 2 originating from a strong covalent interaction between Ge 4s and Se 4p states for Ge atoms tetrahedrally surrounded by the Se nearest-neighbor atoms. A theoretically predicted anti-bonding Ge–Se4sp 3 defect band appearing well above the Fermi level for the Ge 1+ Ga point defect system can be directly linked to a Ge-dopant-related donor–acceptor-pair transition as observed in our photoluminescence spectra.

Properties of Phase Change Materials Modified by Ion Implantation

ABSTRACTIon implantation of germanium and carbon ions into thin films of Ge2Sb2Te5 (GST) and GeTe was applied to modify the properties of these phase change materials. It was found that it is possible to amorphize crystalline GST and GeTe using ion implantation for optimized ion doses and energies which depend on the film thickness, ion species and capping layer. A relatively low minimum dose is required for complete amorphization as judged by the absence of diffraction peaks in x-ray diffraction (XRD) scans. It is 4–5×1013 cm−2 for germanium implantation into GST, and slightly higher (1014 cm−2) for germanium implantation into GeTe. The properties of the re-amorphized films depend on ion species, dose and energy. The re-crystallization temperature of re-amorphized GST by ion implantation is comparable or higher than as-deposited amorphous GST. Carbon implantation in particular leads to a large increase in the crystallization temperature Tx. A carbon dose of 1016 cm−2 implanted into 20 nm amorphous GST yielded a crystallization temperature of 300 ºC, much higher than the crystallization temperature of 160 ºC we recorded for as-deposited, amorphous GST. Similarly, high dose carbon implantation into amorphous GeTe leads to large increase in Tx. We recorded a shift in Tx from 195 ºC for as-deposited GeTe to 400 ºC for C-implanted GeTe. Crystalline GeTe re-amorphized by a low dose germanium ion implantation exhibits a re-crystallization temperature below Tx of as-deposited amorphous GeTe and Tx increased with the implanted Ge dose to a crystallization temperature above that of unimplanted GeTe. Ion implantation can be regarded an additional tool to create phase change materials with different and improved switching properties that cannot be achieved by conventional sputter deposition.

Improvement of the Thermal Stability of NiSi by Germanium Ion Implantation

The thermal stability of nickel monosilicide (NiSi) is one of the important research topics in the area of nano-complementary metal oxide semiconductor. This paper reports the effect of germanium (Ge) ion implantation on the thermal stability of the structure. High dose Ge ion implantation can improve the thermal stability of the structure. Ge ion implantation before NiSi formation results in a very smooth interface due to Ge atom pileup at the interface. This high concentration Ge layer reduces the interface energy so that the thermal stability can be improved. Both the phase-transformation temperature and agglomeration temperature are improved by . The effects of Ge ion implantation on the NiSi-contacted and shallow junctions are also examined. Although fast Ni diffusion via the ion implantation induced defects is observed, better thermal stability can still be observed on the junction.

Formation of the intermediate semiconductor layer for the Ohmic contact to silicon carbide using Germanium implantation

By formation of an intermediate semiconductor layer (ISL) with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An array of transfer length method (TLM) test patterns is formed on N-wells created by P+ ion implantation into Si-faced p-type 4H-SiC epilayer. The ISL of nickel-metal Ohmic contacts to n-type 4H-SiC could be formed by using Germanium ion implantation into SiC. The specific contact resistance ρc as low as 4.23 × 10−5 Ωcm2 is achieved after annealing in N2 at 800 °C for 3 min, which is much lower than that (> 900 °C) in the typical SiC metallisation process. The sheet resistance Rsh of the implanted layers is 1.5 kΩ/□. The technique for converting photoresist into nanocrystalline graphite is used to protect the SiC surface in the annealing after Ge+ ion implantations.

Thermal Stability Improvement of NiSi on Gate by High Dosage Germanium Implantation

The thermal stability of nickel silicide (NiSi) on source/drain and gate is one of the important research topics in complementary metal oxide semiconductor technology. Here we report the effects of germanium-ion implantation (Gel/I) on the thermal stability of NiSi on poly-Si gates. Scanning electron microscope inspections and thin-film X-ray diffraction results show that agglomeration and NiSi 2 transformation can be suppressed by high dosage Ge implanted on poly-Si gates. The allowable process temperature of NiSi formation can be increased by 100°C.

New approach to remove crystal originated pits in Czochralski-grown silicon: combination of germanium ion implantation with solid-phase epitaxy

A two-step process is designed for removing crystal-originated pits (COPs) in the near-surface region of the Czochralski-grown silicon wafers. Firstly, Ge-ion implantation is used to acquire amorphous layer and thus disrupt COPs in the near-surface region. Following that, the annealing process is performed to boost solid-phase epitaxial growth (SPEG) and remove the implant damage. It is verified by cross-sectional transmission electron microscopy (XTEM), Rutherford backscattering spectroscopy (RBS), Raman spectroscopy and laser scattering technique that a refinement epitaxial layer of fewer COPs and excellent crystalline properties can be acquired by our method. Additionally, it is found that appropriate Ge-implant dose may be around 6×10 14/cm 2 and the corresponding annealing temperature should be above 600 °C. The two-step process may have some advantages, including relaxed conditions for pulling crystals, over previous methods.

Boron diffusion in amorphous silicon and the role of fluorine

We demonstrate that boron diffuses at high concentrations during low-temperature thermal annealing in amorphous silicon pre-amorphized by germanium ion implantation. For a typical boron ultrashallow junction doping profile, concentrations as high as 2×1020 cm−3 appear to be highly mobile at 500 and 600 °C in the amorphous silicon region before recrystallization. In crystalline silicon at the same temperatures the mobile boron concentration is at least two orders of magnitude lower. We also show that boron diffusivity in the amorphous region is similar with and without fluorine. The role of fluorine is not to enhance boron diffusivity, but to dramatically slow down the recrystallization rate, allowing the boron profile to be mobile up to the concentration of 2×1020 cm−3 for a longer time.

Dopant diffusion in amorphous silicon

ABSTRACTIn this work we investigate the diffusion of high-concentration ultrashallow boron, fluorine, phosphorus, and arsenic profiles in amorphous silicon. We demonstrate that boron diffuses at high concentrations in amorphous silicon during low-temperature thermal annealing. Isothermal and isochronal anneal sequences indicate that there is an initial transient enhancement of diffusion. We have observed this transient diffusion characteristic both in amorphous silicon preamorphized by germanium ion implantation and also in amorphous silicon preamorphized by silicon ion implantation. We also show that the boron diffusivity in the amorphous region is similar with and without fluorine, and that the lack of diffusion for low-concentration boron profiles indicates that boron diffusion in amorphous silicon is driven by high concentrations. Ultrashallow high-concentration fluorine profiles diffuse quite rapidly in amorphous silicon, and like boron, undergo a definite transient enhancement. In contrast, ultrashallow high- concentration phosphorus and arsenic profiles did not significantly diffuse in our experiments.

Damage removal and boron diffusion during solid phase epitaxial growth of SiGe alloy layers

SiGe/Si heterostructures have been fabricated using germanium ion implantation into silicon and subsequent solid phase epitaxy (SPE) growth. The damage removal and boron diffusion in the SiGe/Si heterostructures formed by high-dose Ge + preamorphized and BF 2 + implanted Si(0 0 1) during SPE growth have been investigated by double-crystal X-ray diffraction (DCXRD) and secondary ion mass spectrometry (SIMS). The results show that annealing at 600°C for 60 min can only remove a little damage induced by implantation and nearly no redistribution of Ge and B atoms has occurred during the annealing. Most damage induced by Ge + and BF 2 + ion implantation have been removed after annealing at 950°C for 60 min and accompanied by Ge diffusion, a boron diffusion has taken place. When annealing temperature rose to 1050°C, Ge diffusion has been slight while B diffusion has been deeper into the Si substrate with a very good distribution. The X-ray diffraction (0 0 4) rocking curves from the samples annealed at 1050°C for 60 min display two SiGe peaks, which may be related to the B and Ge concentration profiles.

Recrystallization behaviour and electrical properties of germanium ion implanted polycrystalline silicon films

The recrystallization behaviour of undoped and phosphorus-doped polycrystalline silicon films amorphized by germanium ion implantation at doses ranging from 1 × 1015 to 1 × 1016cm-2 are investigated, and the electrical properties of phosphorus-doped films after recrystallization are studied. The phosphorus doping concentration ranges from 3 × 1018 to 1 × 1020cm-3. It is found that the nucleation rate decreases for undoped films and increases for phosphorus-doped films with increasing germanium dose; the growth rates decrease for both doped and undoped films. The decrease in nucleation rate is caused by the increase in implantation damage. The decrease in growth rate is considered to be due to the increase in lattice strain. The grain size increases with germanium dose for undoped films, but decreases for phosphorus-doped films. The dependence of the electrical properties of the recrystallized films as a function of phosphorus doping concentration with different germanium doses can be explained in terms of the grain size, crystallinity and grain boundary barrier height.

Recrystallization characteristics of polycrystalline silicon films amorphized by germanium ion implantation : Myeon-Koo Kanget al., Solid-State Electronics, 38, 2, 383 (1995)

Recrystallization characteristics of polycrystalline silicon films amorphized by germanium ion implantation : Myeon-Koo Kanget al., Solid-State Electronics, 38, 2, 383 (1995)

Phosphorus and boron doping effects on solid phase recrystallization of polycrystalline silicon films amorphized by germanium ion implantation

Fig. 1 shows the density of grains as a function of annealing time for the undoped, P-doped and Bdoped films that were subjected to Ge + with a dose of 1 x 1015cm -2 and annealed at 600°C. The density of grains was obtained by directly counting the number of grains produced in the amorphized films after annealing through plan-view TEM observation. It is shown that the number of grains was very small at the beginning of the annealing step, but after a certain incubation time, which is the time for nuclei to grow to the critical size, the number of grains increased rapidly. It was found from this figure that the initial generation of nuclei for the doped films is faster than that for the undoped films. This is presumed to be due to the stress effects induced by a mismatch of atomic size between the implanated atoms and Si atoms [5]. Fig. 2 shows the nucleation rate as a function of reciprocal annealing temperature for the same films as shown in Fig. 1. The nucleation rates of these films were estimated from the slope of the line, as shown in Fig. 1. As can be seen from this figure, it was found that the nucleation rate was strongly dependent on the kind of doping, with B doping increasing the nucleation rate and P doping decreasing it. This is presumed to be due to the increase in the local stress for the B-doped films and the increase in the implantation-induced damage for the P-doped films [6].

Ultra-low Contact Resistivity by High Concentration Germanium and Boron Ion Implantation Combined with Low Temperature Annealing

AbstractA new formation method for an ultra-low resistivity contact and structural analysis are discussed. In this study, a minimum contact resistivity of 6.9× 10−9 Ω·cm2 has been successfully obtained in an AlSi(lwt%)Cu(0.5wt%) alloy / Si system by using heavy dose ion implantations of Ge and B combined with low temperature annealing as low as 550°C. Structural analysis on the Si surface layer has been carried out. As a result, it was found that the crystal lattice was expanded in-plane by 6% in the Si layer near the surface because of the high concentration of Ge and no relaxation of lattice strain at such a low temperature. It was also found that super-saturation of B was stably formed in this system. An ultra-low resistivity contact is considered to be a result of these combined effects.

Monte Carlo simulation of heavy species (Indium and Germanium) ion implantation into silicon

Monte Carlo ion-implant models for germanium and indium implantation into single-crystal silicon have been developed and are described in this paper. The models have been incorporated in the UT-MARLOWE ion implantation simulator, and have been developed primarily for use on engineering workstations. These models provide the required as-implanted impurity profiles as well as damage profiles, which can be used as inputs for transient enhanced diffusion simulation and subsequent multiple implant simulation. A comparison of simulation results with experimental data shows that the models predict both the impurity profiles and the damage profiles very successfully for a wide range of implant conditions. The damage profiles from germanium implant simulations have been used for subsequent multiple implant simulations and excellent agreement with experimental results has been achieved.

Recystallization characteristics of polycrystalline silicon films amorphized by germanium ion implantation

The recrystallization characteristics of polycrystalline silicon (poly-Si) films amorphized by germanium ion (Ge +) implantation on a SiO 2 layer are studied by TEM analysis, and the possibility of enlarging the final grain size is investigated. Also, the characteristics of Ge + implanted films with phosphorus doping are reported and discussed. The nucleation and growth rates of undoped Ge + implanted films are lower and higher, respectively, than those of silicon ion (Si +) implanted films, so that the former films achieve grain sizes about 2–3 times larger than the latter films, depending on annealing temperature. Phosphorus doping in Ge + implanted films effectively enhances the grain size, because of the retardation of random nucleation and the enhancement of grain growth. An average grain size of 12 μm is obtained in doped Ge + implanted films with a phosphorus concentration of 1 × 10 20 ions/cm 3 after annealing at 650°C for 5 h, which is about four times larger than that in undoped Ge + implanted films.

Waveguides Fabricated in Fused Silica by Germanium Ion Implantation at Varying Doses

AbstractThe implantation of MeV Ge3+ ions into fused silica has been used to fabricate single mode channel waveguides with a low propagation loss of 0.10–0.15 dB/cm. The loss coefficient, α, has been measured as a function of ion dose (8 × 1013 to 8 × 1016 ions/cm2) and annealing temperature (250 to 600 °C) at λ = 1300 nm. The value of cc for the as-implanted waveguides exhibited a minimum of -1.0 dB/cm at an intermediate range of dose from 8 × 1014 to 8 × 1015 ions/cm2. A progressive reduction in α occurred as the annealing temperature was increased from 300 to 500 °C. Annealing of the implanted waveguides at 500 °C for 1 h has produced an order of magnitude decrease in α to 0.1 dB/cm at 8 × 1014 ions/cm2. At doses which were outside of the intermediate range, the value of α was ≥ 10 dB/cm. This trend in α with ion dose has been attributed to the dominance of a residual nuclear component of damage after annealing.