Germanium Implantation Research Articles

Controlled localised melting in silicon by high dose germanium implantation and flash lamp annealing

High intensity light pulse irradiation of monocrystalline silicon wafers is usually accompanied by inhomogeneous surface melting. The aim of the present work is to induce homogeneous buried melting in silicon by germanium implantation and subsequent flash lamp annealing. For this purpose high dose, high energy germanium implantation has been employed to lower the melting temperature of silicon in a predetermined depth region. Subsequent flash lamp irradiation at high energy densities leads to local melting of the germanium rich buried layer, whereby the thickness of the molten layer depends on the irradiation energy density. During the cooling down epitaxial crystallization takes place resulting in a largely defect-free layer. The combination of buried melting and dopant segregation has the potential to produce unusually buried doping profiles or to create strained silicon structures.

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.

Buried melting in germanium implanted silicon by millisecond flash lamp annealing

Flash lamp annealing in the millisecond range has been used to induce buried melting in silicon. For this purpose high dose high-energy germanium implantation has been employed to lower the melting temperature of silicon in a predetermined depth region. Subsequent flash lamp treatment at high energy densities leads to local melting of the germanium rich layer. The thickness of the molten layer has been found to depend on the irradiation energy density. During the cool-down period, epitaxial crystallization takes place resulting in a largely defect-free layer.

Understanding Ion Implantation Defects in Germanium

The recent interest in germanium as an alternative channel material for PMOS has revealed major differences from silicon in relation to ion implantation. In this paper we describe some initial results of a fundamental study into defect creation and removal in ion implanted germanium. In this stage of the work we have used silicon and germanium implants into germanium and into germanium rich silicon-germanium. The defect evolution in these samples is compared with electron and neutron irradiated material using annealing studies in conjunction with deep level transient spectroscopy, positron annihilation and Rutherford back scattering. It is proposed that both vacancy and interstitial clustering are important mechanisms in implanted germanium and the likely significance of this is discussed.

Impact of an As implant before CoSi 2 formation on the sheet resistance and junction breakdown voltage

Germanium implantation for silicon amorphization before silicide formation, for both titanium and cobalt, and its impact on morphological and electrical properties has been reported in literature. The benefits in terms of improved silicide formation on narrow lines are stress relaxation and silicided junction leakage current reduction. In this work the results of arsenic implantation instead of germanium are reported in the case of Cobalt Salicide technology for its scaling below 90 nm technology node. A baseline process without implant has been compared with arsenic implantation performed at different process conditions. As implantation before CoSi 2 growth can improve the diode breakdown voltage although a slight increase in sheet resistances is observed. Electrical results are in agreement with morphological evidences by TEM, SEM and AFM techniques showing a reduction of the silicide grain size and a smoothening of the silicide by increasing the implant energy.

Effects of germanium and carbon coimplants on phosphorus diffusion in silicon

The authors have studied the interactions between implant defects and phosphorus diffusion in crystalline silicon. Defect engineering enables ultrashallow n+∕p junction formation using phosphorus, carbon, and germanium coimplants, and spike anneal. Their experimental data suggest that the positioning of a preamorphized layer using germanium implants plays an important role in phosphorus diffusion. They find that extending the overlap of germanium preamorphization and carbon profiles results in greater reduction of phosphorus transient-enhanced diffusion by trapping more excess interstitials. This conclusion is consistent with the end-of-range defects calculated by Monte Carlo simulation and annealed carbon profiles.

Selective SiGe Etching Formed by Localized Ge Implantation on SOI

The fully depleted SOI devices present lateral isolation issues due to the shallow trench isolation (STI) process. We propose in this paper to study a new fabrication process for integrating local isolation trenches. Germanium (Ge) implantation is used to create SiGe (Silicon-Germanium) layer on thin SOI (silicon on insulator) that can be selectively etched. The advantage is the capability of implantation to localize the SiGe area on this substrate and to avoid STI process issues. Aggressive dimensions and geometries are studied and resulting material transformation (crystallization and Ge diffusion) are apprehending via SEM (Secondary Electron Microscopy) or AFM (Atomic Force Spectroscopy) to understand the etching kinetics. After optimization, we demonstrate the capability of fabricating localized trenches on SOI without degrading the neighboring Si layer or consuming the thin BOX (buried oxide).

Structural properties of Ge-implanted SiO 2 layers and related MOS memory effects

Recently, the feasibility of using ion implantation of germanium and high temperature annealing to fabricate a near-interface nanocrystal (nc) layer into a silicon dioxide (SiO 2) on Si film has been demonstrated. In this work, the influence of ion implantation parameters on the nc layer formation in SiO 2 is studied. Transmission electron microscopy and Rutherford backscattering spectroscopy have been used to study the Ge-redistribution in the SiO 2 films. Depending on the ion implantation energy and dose, the formation of a bulk nc layer in addition to the desired near-interface layer can be observed. A maximum near-interface Ge-nc density of 1.7 × 10 12 cm −2 has been measured. Capacitance–voltage measurements have been used to study electrical properties of metal-oxide-semiconductor structures containing such implanted SiO 2 films. The results indicate a strong memory effect due to the presence of near-interface Ge-nc. As an example, flat-band shifts of 4.5 V have been obtained at a programming voltage of 7 V for 1 s. For the first time, long retention properties have been demonstrated on a memory structure containing a single near-interface Ge-nc layer.

Poly-Si gate engineering for advanced CMOS transistors by germanium implantation

Standard gate materials are compared to Ge implanted poly-Si and deposited poly-SiGe. It is demonstrated in this paper that the electrical resistance of the gate is significantly reduced via the use of poly-SiGe (from 30% to 40% decrease in resistance). Similarly, we show via specific optimization that localized Ge implantation is also suitable to reduce gate resistance. Physical characterizations are performed to determine the “root” causes at the origin of these improvements. In line with future publications showing strong benefits on CMOS device performance, grain size effects seem to be the main mechanisms explaining the measured improvement.

Impact of the end of range damage from low energy Ge preamorphizing implants on the thermal stability of shallow boron profiles

A fundamental understanding of the effect of scaling amorphous layers on the thermal stability of active concentrations is required for the formation of ultrashallow junctions. A study on the influence of boron on the evolution of the end of range defects for samples containing shallow amorphous layers formed by low energy germanium implants is conducted. Czochralski grown (100) silicon wafers are preamorphized with 1×1015cm−2, 10keV Ge+ and subsequently implanted with 1×1015cm−2, 1keV B+ such that high boron levels are attained in the end of range region. A sequence of anneals are performed at 750°C, under nitrogen ambient for times ranging from 1s to 6h and the end of range defect evolution is imaged via plan-view transmission electron microscopy (TEM). Defect analyses are conducted utilizing quantitative TEM which indicates substantial differences in the defect evolution for samples with boron in the end of range. The extended defects observed are very unstable and undergo a fast dissolution. In contrast, stable defects are observed in the experimental control in which the evolution follows an Ostwald ripening behavior. Secondary ion mass spectroscopy analyses confirm the ephemeral nature of the defects observed and also demonstrates drastic reductions in interstitial supersaturation. In addition, uphill-type diffusion is observed to occur for a short time frame, which emphasizes a transient interstitial supersaturation. Correlation of this data with sheet resistance and active dose measurements conducted on a Hall measurement system strongly indicates the formation of boron interstitial clusters. The high boron concentrations and supersaturation levels attained at the anneal temperature enables the cluster formation. An estimate of the boron concentrations trapped in the clusters is determined from the active dose obtained from the Hall measurements and indicates concentrations much higher than those available in the end of range. This suggests an interstitial migration from the end of range to regions of higher boron levels. Since the end of range is in the vicinity of the highly doped layer it is not isolated from the strain effects induced by the high initial activation levels. Hence it is proposed that the tensile strain stimulates the interstitial migration from the end of range to the boron-doped layer. Consequently, the end of range defects dissolve as the interstitial supersaturation falls below levels required to sustain their evolution.

Electrical characterization and modelling of high energy pre-amorphized P+N silicon junctions

Shallow P+N junctions were obtained using germanium pre-amorphization step to reduce the high diffusivity of boron implanted in silicon. The germanium implantation step was performed under different conditions of temperature: ambient temperature and nitrogen temperature. P-type doping was obtained by boron implantation at relatively low energy. To characterize and simulate the electrical behaviour of such samples, steady state current–voltage measurements have been performed at different temperatures varying between 172 and 294 K. The results show a close dependence between the current–voltage characteristics of the samples and their technological parameters of manufacturing. The pre-amorphization step at ambient temperature seems to improve the electrical behaviour of the junction. To simulate the electrical characteristics of the studied samples, a reliable model has been developed based on the classical Spice formulas and taking into account additional phenomena. The simulated curves satisfactorily fit the experimental results for all the samples.

Defect evolution of low energy, amorphizing germanium implants in silicon

The defect evolution upon annealing of low energy, amorphizing germanium implants into silicon was studied using plan-view transmission electron microscopy. Implants with energies of 5–30 keV at an amorphizing dose of 1×1015 Ge+ cm−2 were annealed at 750 °C from 10 s to 360 min. For the implant energies of 10 and 30 keV, the defects form clusters which evolve to {311} defects that subsequently dissolve or form stable dislocation loops. However, as implant energy drops to 5 keV, the interstitials evolve from clusters to small, unstable loops which dissolve within a small time window and do not form {311}’s. To determine the effect of the free surface as an interstitial recombination sink for 5 keV implants, the amorphous layer of a 10 keV implant was lapped to less than the thickness of a 5 keV amorphous layer and then annealed. We found that the defect dissolution observed for the 5 keV implant energy was dependent on the implant energy and not the proximity of the end-of-range damage to the surface. The activation energy of the observed rapid defect dissolution at 5 keV was calculated to be 1.0±0.1 eV.

Germanium diffusion in polysilicon emitters of SiGe heterojunction bipolar transistors fabricated by germanium implantation

A study is made of germanium diffusion in polysilicon emitters of SiGe heterojunction bipolar transistors made by germanium implantation. Implanted Ge is found to diffuse from the single-crystal silicon substrate into deposited polysilicon emitter layers during rapid thermal anneal at 1045 °C. Measurements of germanium diffusivity in polycrystalline silicon are reported at temperatures between 800 and 900 °C and modeled by an Arrhenius relationship with a preexponential factor of Do=0.026±0.023 cm2/s and an activation energy of E=2.59±0.36 eV. The measured diffusivity in polycrystalline silicon is ≈104 times larger than that reported for single-crystal silicon. It is hypothesised that germanium diffusion in polysilicon occurs by diffusion along grain boundaries.

Influence of Ge implantation on the mechanical properties of polycrystalline silicon microstructures

Polycrystalline silicon (poly-Si) based microstructures, with boron doping (B-doping), are studied, with reference to their built-in stress, for different germanium implantation (Ge-implantation) doses. The microstructures are studied free standing and under static and dynamic deformations, by a combination of macroscopic (pull-in voltage, resonance frequency) and microscopic (micro-Raman) experimental techniques, in comparison with numerical calculation methods. The counterbalancing effect of Ge-implantation versus the B-doping, with respect to the built-in stress, is examined in poly-Si. Measurements, with three different experimental methods, and calculations, on bridges designed and fabricated for micromachining applications, show, consistently, the same maximization trend for the built-in stress, with a maximum at a Ge-dose of 1015 ions/cm2, in agreement with a similar non-monotonic Ge-dependence of the growth rate and the crystalline quality of poly-Si, from the literature.

A technique to reduce the contact resistance to 4H-silicon carbide using germanium implantation

The effects of implanted Ge on the resistance of nickel-metal contacts to n-type and p-type 4H-SiC are reported. The Ge was implanted with an energy of 346 keV and a dose of 1.7 × 1016 cm-2, and the wafer was annealed up to 1700°C for 30 min. Contact resistance measurements using the transfer length method (TLM) were performed on etched mesas of n-type and p-type 4H-SiC, with and without the Ge. For the annealed-Ni metal contacts, the Ge lowered the specific contact resistivity from 5.3 × 10-4 Ωcm2 to 6.0 × 10-5 Ωcm2 for n-type SiC and from 1.2 × 10-3 Ωcm2 to 8.3 × 10-5 Ωcm2 for p-type SiC. For the as-deposited (unannealed) Ni, the Ge produced ohmic contacts, whereas the contacts without Ge were rectifying. These results suggest that the addition of Ge can be an important process step to reduce the contact resistance for SiC-device applications.

Ion Beam Doping of Chlorinated Copper Phthalocyanine Thin Films

Ion beam implantation of energetic nickel, germanium, and tin ions was studied for the purpose of altering the properties of the film structures of chlorinated copper phthalocyanine. Changes in the surface topology, conductivity, electron absorption spectra, and current response to ammonia were shown to be due to both ion bombardment of the samples and the subsequent thermal annealing.

Modeling Dislocation Loop Nucleation and Evolution in Germanium, Arsenic and Boron Implanted Silicon

AbstractA loop nucleation and evolution model in Si+ implanted Silicon was previously introduced [1]. In this study, the model is extended to predict end of range (EOR) and projected range defect nucleation and evolution created by different ion implant species such as Germanium, Arsenic and Boron. The model assumes that all the nucleated loops come from {311} unfaulting and the loop density and average loop radius follow a log normal distribution. The model is verified with the experimental data obtained from literature for Germanium [2], Arsenic [3] and Boron [4] implanted Silicon for different implant doses and energies. Modeling results are in agreement with the experimental results.

Strained SiC: Ge Layers in 4H SiC formed by Ge Implantation

ABSTRACTThe ion implantation of germanium into 4H-SiC at 1000 °C resulted in crystalline SiC:Ge layers that are coherently strained to the (0001) oriented 4H-SiC substrates. Germanium implantation energies of 140 keV and 50 keV were chosen to form approximately 100nm thick step-like SiC:Ge layers with Ge atomic fractions ranging from 0.0007 to 0.006. High-resolution x-ray diffraction (HRXRD) and reciprocal space mapping reveal a high-quality, compressively strained SiC:Ge layer. High-temperature annealing resulted in partial relaxation of the macroscopic layer strain, however the SiC:Ge layer remained strained with a coherent interface for annealing up to at least 1650°C. Because Ge is a group-IV atom like Si and C, its incorporation into the lattice is expected to act as an isoelectronic impurity, rather than a charged donor or acceptor. Thus, high-quality, SiC:Ge layers have the potential for bandgap and strain engineered electronics such as SiC-based high electron mobility transistors (HEMTs) for RF-power electronics. Currently there is no established heterojunction pair in SiC material technology for fabricating HEMTs and other heterojunction devices.

Germanium implantation into amorphous carbon films

The effects of Ge incorporation into amorphous carbon films by ion implantation were studied, with special attention to the modifications of the friction properties. Amorphous carbon films were deposited by dc-sputtering and implanted, at room temperature, with Ge ions at an energy of 20 and 50 keV. The doses ranged from 10 13 to 10 17 atoms cm −2 and the ion fluence was 1 μA cm −2. The samples were analyzed by Rutherford backscattering spectrometry (RBS), infrared transmission spectroscopy (IR), and atomic force and lateral force microscopy (AFM and LFM, respectively). The presence of oxygen contamination was revealed by IR measurements. While the surface roughness always decreases with the increase of the ion dose, in the case of the samples implanted with 20-keV Ge + a decrease of the friction coefficient was observed with the increase of the ion dose. For samples implanted with 50-keV Ge +, the friction coefficient remained constant. These results can be understood as a combination of two effects: the formation of defects due to the ion implantation and the graphitization of the surface layers.

Defect Evolution from Low Energy, Amorphizing, Germanium Implants on Silicon

ABSTRACTPlan-view transmission electron microscopy (PTEM) was used to characterize defect evolution upon annealing of low-to-medium energy, 5-30 keV, germanium implants into silicon. The implant dose was 1 × 1015 ions/cm2, sufficient for surface amorphization. Annealing of the samples was done at 750 °C in nitrogen ambient by both rapid thermal annealing (RTA) and conventional furnace, and the time was varied from 10 seconds to 360 minutes. Results indicate that as the energy drops from 30 keV to 5 keV, an alternate path of excess interstitials evolution may exist. For higher implant energies, the interstitials evolve from clusters to {311}'s to loops as has been previously reported. However, as the energy drops to 5 keV, the interstitials evolve from clusters to small, unstable dislocation loops which dissolve and disappear within a narrow time window, with no {311}'s forming. These results imply there is an alternate evolutionary pathway for {311} dissolution during transient enhanced diffusion (TED) for these ultra-low energy implants.