High-dose Implantation Research Articles

Effects of oxygen-inserted layers on diffusion of boron, phosphorus, and arsenic in silicon for ultra-shallow junction formation

The effects of oxygen-inserted (OI) layers on the diffusion of boron (B), phosphorus (P), and arsenic (As) in silicon (Si) are investigated, for ultra-shallow junction formation by high-dose ion implantation followed by rapid thermal annealing. The projected range (Rp) of the implanted dopants is shallower than the depth of the OI layers. Secondary ion mass spectrometry is used to compare the dopant profiles in silicon samples that have OI layers against the dopant profiles in control samples that do not have OI layers. Diffusion is found to be substantially retarded by the OI layers for B and P, and less for As, providing shallower junction depth. The experimental results suggest that the OI layers serve to block the diffusion of Si self-interstitials and thereby effectively reduce interstitial-aided diffusion beyond the depth of the OI layers. The OI layers also help to retain more dopants within the Si, which technology computer-aided design simulations indicate to be beneficial for achieving shallower junctions with lower sheet resistance to enable further miniaturization of planar metal-oxide-semiconductor field-effect transistors for improved integrated-circuit performance and cost per function.

Structural and optical investigations of 120 keV Ag ion implanted ZnO thin films

Structural as well as optical modifications in zinc oxide (ZnO) thin film with Ag ion implantation were carried out in the present study. The pure ZnO thin films were synthesized by RF-magnetron sputtering technique at room temperature. 120 keV Ag ion beam was used for Ag ion implantation with different implantation dose from 3 × 1014 to 3 × 1016 ions/cm2 by negative ion implantation facility. The thickness and composition of pure ZnO and Ag implanted film at higher dose 3 × 1016 ions/cm2 were estimated by Rutherford backscattering spectroscopy. The change in surface stoichiometry was estimated by using X-ray photoelectron spectroscopy with Ag ion implantation. The modifications in structural features with Ag ion implantation in ZnO films were observed by X-ray diffraction technique (XRD). The pure ZnO thin film was preferentially grown in c-axis direction with crystallite size ~10.6 nm confirmed by XRD. Surface morphology of the pure and Ag implanted ZnO thin films was estimated by atomic force microscopy and revealed the roughness and grain size were increased with increasing the implantation dose. The transmittance of the films was decreased drastically at higher implantation dose as corroborated by UV–visible spectroscopy. Raman spectroscopy of the films was used to understand the lattice defects and disordering during Ag ion implantation. At the higher dose, the film was entirely oriented in c-axis confirmed by X-ray pattern, which can be beneficial for device fabrication.

Porous germanium formed by low energy high dose Ag+-ion implantation

A technical approach is proposed for the synthesis of thin porous PGe layers with Ag nanoparticles based on low-energy high-dose implantation of single-crystal c-Ge metal ions. To demonstrate a successes of this technique, we performed an Ag+-ion implantation of a polished c-Ge substrates with an energy of 30 keV at a dose of 1.5⋅1017 ion/cm2 and a current density of 5 μA/cm2. Methods of scanning electron and atomic force microscopy, as well as EDX analysis and electron backscattered diffraction was shown that as a result of the implantation on the c-Ge surface a porous amorphous PGe layer is formed of a spongy structure consisting of a network of intersecting Ge nanowires with an average diameter of ∼10–20 nm. At the ends of the nanowires, the synthesis of Ag nanoparticles is observed. It was found that the formation of pores during Ag+-ion implantation is accompanied by efficient spattering of the Ge surface.

High-intensity implantation of aluminium ions into VT1-0 titanium alloy

Structural and phase state of VT1-0 titanium alloy surface layers with different initial grain sizes before and after ion implantation with aluminum ions at the high-dose implantation mode was studied. Implantation of aluminum ions into VT1-0 titanium alloy made it possible to form surface layers with improved performance properties.

Влияние высокодозной имплантации углерода на фазовый состав, морфологию и автоэмиссионные свойства кристаллов кремния

AbstractThe study of high-dose carbon-ion implantation without post-process annealing reveals significant modification of the morphology, surface-layer phase composition, and field-emission properties of silicon wafers. The effect of the electrical conductivity type on the evolution of the silicon-crystal surface morphology, upon a variation in the irradiation dose, and a high content of diamond-like phases in the region of microprotrusions at the maximum dose regardless of the electrical conductivity type are found. It is demonstrated that the high-dose implantation of carbon in silicon wafers with a pre-structured surface increases the maximum density of field-emission currents by more than two orders of magnitude.

Создание пористых слоев германия имплантацией ионами серебра

AbstractWe propose a method for the formation of porous germanium ( P -Ge) layers containing silver nanoparticles by means of high-dose implantation of low-energy Ag^+ ions into single-crystalline germanium ( c -Ge). This is demonstrated by implantation of 30-keV Ag^+ ions into a polished c -Ge plate to a dose of 1.5 × 10^17 ion/cm^2 at an ion beam-current density of 5 μA/cm^2. Examination by high-resolution scanning electron microscopy (SEM), atomic-force microscopy (AFM), X-ray diffraction (XRD), energy-dispersive X-ray (EDX) microanalysis, and reflection high-energy electron diffraction (RHEED) showed that the implantation of silver ions into c -Ge surface led to the formation of a P -Ge layer with spongy structure comprising a network of interwoven nanofibers with an average diameter of ∼10–20 nm Ag nanoparticles on the ends of fibers. It is also established that the formation of pores during Ag^+ ion implantation is accompanied by effective sputtering of the Ge surface.

Effect of dose and size on defect engineering in carbon cluster implanted silicon wafers

Carbon-cluster-ion-implanted defects were investigated by high-resolution cross-sectional transmission electron microscopy toward achieving high-performance CMOS image sensors. We revealed that implantation damage formation in the silicon wafer bulk significantly differs between carbon-cluster and monomer ions after implantation. After epitaxial growth, small and large defects were observed in the implanted region of carbon clusters. The electron diffraction pattern of both small and large defects exhibits that from bulk crystalline silicon in the implanted region. On the one hand, we assumed that the silicon carbide structure was not formed in the implanted region, and small defects formed because of the complex of carbon and interstitial silicon. On the other hand, large defects were hypothesized to originate from the recrystallization of the amorphous layer formed by high-dose carbon-cluster implantation. These defects are considered to contribute to the powerful gettering capability required for high-performance CMOS image sensors.

Characterization of photoresist films exposed to high-dose implantation conditions

Alternative approaches are now required to fulfill the strict requirements of photoresist (PR) dry strip process after high-dose implantation. A better understanding of the PR degradations induced by the ion bombardment during the implantation is thus required. In this study, in-depth characterizations of PR films after arsenic and phosphorus-high-dose implantation have been made. The influence of the dopant species (As or P) as well as the implantation energy has been investigated. The experimental results have then been confronted to simulations performed with stopping and range of ions in matter (SRIM). The experimental results show the formation of a “crust layer” enriched in carbon and depleted in oxygen and hydrogen whose density, hardness, and elastic modulus are higher than the nonimplanted PR (pristine). SRIM simulations confirm that the PR degradation is mainly due to crosslinking phenomenon. Chemical analyses have revealed that the dopants are present in their elemental and oxidized forms in the PR and that they are also linked to the PR carbon atoms. The knowledge of the dopants' chemical environment is key information to understand the presence of residues after dry strip processes and develop alternative processes to avoid their formation.

Positron and nanoindentation study of helium implanted high chromium ODS steels

AbstractThree oxide dispersion strengthened (ODS) steels with different chromium content (MA 956, MA 957 and ODM 751) were studied as candidate materials for new nuclear reactors in term of their radiation stability. The radiation damage was experimentally simulated by helium ion implantation with energy of ions up to 500 keV. The study was focused on surface and sub-surface structural change due to the ion implantation observed by mostly non-destructive techniques: positron annihilation lifetime spectroscopy and nanoindentation. The applied techniques demonstrated the best radiation stability of the steel ODM 751. Blistering effect occurred due to high implantation dose (mostly in MA 956) was studied in details.

Point defects in Ga-implanted SiC: Experiment and theory

We present an experimental and theoretical study of the electronic properties of Ga implanted silicon carbide (SiC). The dose of implanted Ga was selected to simulate the implant-tail region, typical of high-dose box-profile p-type doping implantation employed for device manufacture. Samples were electrically characterized by capacitance-voltage (C-V), deep level transient spectroscopy, and minority carrier transient spectroscopy. The thermal stability of the detected levels (seven majority carrier traps, five minority carrier traps) was investigated by performing an isochronal annealing prior to each characterization step. Density functional theory was employed to study both isolated (substitutional and interstitial Ga) and complex Ga-related defects (N- and vacancy-related) in order to gain more insight in the nature of the detected levels. Finally, based on the experimental and theoretical results, the possible role of Ga in the nature of the detected levels is discussed.

An Electrical and Physical Study of Crystal Damage in High-Dose Al- and N-Implanted 4H-SiC

In this paper, an investigation into the crystal structure of Al-and N-implanted 4H-SiC is presented, encompassing a range of physical and electrical analysis techniques, with the aim of better understanding the material properties after high-dose implantation and activation annealing. Scanning spreading resistance microscopy showed that the use of high temperature implantation yields more uniform resistivity profiles in the implanted layer; this correlates with KOH defect decoration and TEM observations, which show that the crystal damage is much more severe in room temperature implanted samples, regardless of anneal temperature. Finally, stress determination by means of μRaman spectroscopy showed that the high temperature implantation results in lower tensile stress in the implanted layers with respect to the room temperature implantation samples.

(Invited) Challenges for Ion Implantation in Power Device Processing

In power device technologies distinct challenges have to be addressed. These are partly in contrast to needs and developments in advanced DRAM and Logic products that dominantly strive for ultrafast switching speed provided by lowest nm node technologies. Power devices in general are facing the main demand to lower dissipation losses caused by increased current density at decreasing structure sizes and optimized performance of device switching behavior at the same time. Today modern power device fabs are facing a variety of wafer sizes ranging from 100mm to 300mm, mainly depending on the availability of distinct base materials for power devices. For minimizing static and dynamic power losses of high voltage switches the main keys are local control of charge carrier lifetime and the use of thin and ultrathin wafers. Besides that, high dose implants with energies higher than the actually supported 60 keV to 80 keV on modern implanters are and will be necessary for source and p+ implantations in power devices. In mainstream power technologies the main application driven key factors are lowest RDSon for compensation devices as well as minimal power dissipation for high voltage switches. Advanced in-situ metrology will be demanded for charge compensation devices of the next generation. The shrinkage of the pitch size and the related demand for a limitation of the lateral out-diffusion is driving the need for reliable energy stability as well as careful tuning of secondary process parameters. Implantations for material modification purposes are gaining relevance. As of today the vast majority of power devices are still fabricated on silicon substrates. However, other semiconductors like SiC and GaN obtain superior material characteristics compared to silicon. That is why considerable development effort is put into the understanding of how to fabricate devices based on those materials. One ingredient is the knowledge how ion implantation can affect and tailor their semiconductor properties. An overview on effects of ion implantation into these materials will be given. Overall, a summary of today’s challenges towards ion implantation for power device technology as well as an outlook to next generation demands will be presented.

Self-assembly of magnetic nanoclusters in diamond-like carbon by diffusion processes enhanced by collision cascades

Mono-energetic cobalt implantation into hydrogenated diamond-like carbon at room temperature results in a bimodal distribution of implanted atoms without any thermal treatment. The ∼100 nm thin films were synthesised by mass selective ion beam deposition. The films were implanted with cobalt at an energy of 30 keV and an ion current density of ∼5 μA cm−2. Simulations suggest the implantation profile to be single Gaussian with a projected range of ∼37 nm. High resolution Rutherford backscattering measurements reveal that a bimodal distribution evolves from a single near-Gaussian distribution as the fluence increases from 1.2 to 7 × 1016 cm−2. Cross-sectional transmission electron microscopy further reveals that the implanted atoms cluster into nanoparticles. At high implantation doses, the nanoparticles assemble primarily in two bands: one near the surface with nanoparticle diameters of up to 5 nm and the other beyond the projected range with ∼2 nm nanoparticles. The bimodal distribution along with the nanoparticle formation is explained with diffusion enhanced by energy deposited during collision cascades, relaxation of thermal spikes, and defects formed during ion implantation. This unique distribution of magnetic nanoparticles with the bimodal size and range is of significant interest to magnetic semiconductor and sensor applications.

Ohmic contact on n- and p-type ion-implanted 4H-SiC with low-temperature metallization process for SiC MOSFETs

The ohmic contact on n- and p-type SiC regions with the same contact metal is a key process in regard to creating high-performance MOSFETs and insulated gate bipolar transistors (IGBTs). The dependence of the contact resistance on n- and p-type SiC regions on ion species, dose, and implantation temperature was investigated. The results of such an investigation revealed that the amorphization of the SiC surface and the generation of 3C-SiC produce a low contact resistance without the need for a high-temperature metallization process. The contact resistances of 2.1 × 10−6 Ω cm2 on the n-type SiC region and 1.3 × 10−3 Ω cm2 on the p-type SiC region were obtained with high-dose ion implantation at room temperature on the n-type SiC region, high-dose ion implantation at high temperature on the p-type SiC region, and a titanium-based contact electrode. A SiC MOSFET was fabricated with the low-temperature ohmic contact process. The positive-bias gate leakage current markedly increased. It can be deduced that high-dose ion implantation at room temperature on the n-type SiC region degrades surface roughness on the N+ source region.

Distinct enhancement of sub-bandgap photoresponse through intermediate band in high dose implanted ZnTe:O alloys

The demand for high efficiency intermediate band (IB) solar cells is driving efforts in producing high quality IB photovoltaic materials. Here, we demonstrate ZnTe:O highly mismatched alloys synthesized by high dose ion implantation and pulsed laser melting exhibiting optically active IB states and efficient sub-gap photoresponse, as well as investigate the effect of pulsed laser melting on the structural and optical recovery in detail. The structural evolution and vibrational dynamics indicates a significant structural recovery of ZnTe:O alloys by liquid phase epitaxy during pulsed laser melting process, but laser irradiation also aggravates the segregation of Te in ZnTe:O alloys. A distinct intermediate band located at 1.8 eV above valence band is optically activated as evidenced by photoluminescence, absorption and photoresponse characteristics. The carrier dynamics indicates that carriers in the IB electronic states have a relatively long lifetime, which is beneficial for the fast separation of carriers excited by photons with sub-gap energy and thus the improved overall conversion efficiency. The reproducible capability of implantation and laser annealing at selective area enable the realization of high efficient lateral junction solar cells, which can ensure extreme light trapping and efficient charge separation.

Effect of thermal and laser annealing on the atom distribution profiles in Si(111) implanted with P+ and B+ ions

The results of studying the effect of thermal and laser annealing on the distribution profiles of phosphorus and boron atoms in Si(111), implanted with different energies and radiation doses, are presented. It is demonstrated that an almost uniform distribution of impurity atoms can be obtained in the near-surface region of Si(111) by means of high-dose ion implantation and thermal and laser annealing. By the phased ion implantation of P+ and B+ into different sides of Si(111) with a gradual decrease in energy and radiation dose, p–i–n structures with a controlled thickness of the p and n regions are obtained, which is of great practical importance in the establishment of various device structures.

Complementary study of the internal porous silicon layers formed under high-dose implantation of helium ions

The surface layers of Si(001) substrates subjected to plasma-immersion implantation of helium ions with an energy of 2–5 keV and a dose of 5 × 1017 cm–2 have been investigated using high-resolution X-ray reflectivity, Rutherford backscattering, and transmission electron microscopy. The electron density depth profile in the surface layer formed by helium ions is obtained, and its elemental and phase compositions are determined. This layer is found to have a complex structure and consist of an upper amorphous sublayer and a layer with a porosity of 30–35% beneath. It is shown that the porous layer has the sharpest boundaries at a lower energy of implantable ions.

Molybdenum Concentration Depth Profile in Aluminum Implanted by Multi-charged Molybdenum Ions

In addition to the accelerating voltage of ions, ion charge state, ion sputtering, diffusion and phase change will all affect the concentration depth distribution. In order to distinguish the influence degree of the various factors, appropriate computational and experimental approaches must be put forward. Molybdenum ions from a metal vapor vacuum arc (MEVVA) ion source are implanted into aluminum to investigate the influence factors of the concentration depth profiles. The results of high voltage electron microscopy (HVEM) have showed that phase change are not induced by molybdenum ion implantation of an average current density of lower than 20μA/cm2. Rutherford backscattering spectroscopy (RBS) is used to investigate the Mo concentration depth profile in the Mo-implanted Al. RBS from Mo-implanted Al is converted to Mo concentration depth distribution considering the change of stopping cross section induced by high dose ion implantation. The measured concentration depth profile is compared with the calculation result of the TRIDYN program, in which sputtering and multi-charged state can both be considered dynamically. The deviation of the experiment and simulation results could be attributed to radiation enhanced diffusion or intense pulse beam current density implantation.

Study of Oxide Hardmask Effect on High Dose Implant Process for ISFET Fabrication

The study of the effects of photoresist thickness and the use of PECVD deposited oxide hard mask layer during source/drain high dose ion implantation process in the fabrication of ion-sensitive field effect transistor (ISFET) is presented. Implementation of the new optimized process for the source/drain implant mask together with the improved process module have been successful in improving the threshold voltage (Vt) of the ISFET device from negative to more than 0.3V. Consistent high ISFET yields of more than 90% were possible to achieve.

Formation of ZnSe nanoclusters in the layers of silicon dioxide by high-fluence ion implantation and annealing

In this work we used the method of hot implantation of zinc and selenium ions into SiO2/Si structures in combination with subsequent heat treatment in order to form nanosized phases. Implantation modes for ionic synthesis chosen in such a way that the concentration of the embedded impurity is maximum approximately at the middle of the thickness of the dielectric layer. For the subsequent clustering of the impurity, it is necessary to create a high concentration of the implanted impurity at the maximum of the depth profile. The computer stimulation to select Implantation modes was carried out using the SRIM- 2013 program. Also we calculated the thickness of the silicon dioxide layer sprayed during high-dose implantation of zinc ions was. In this way, we have studied the formation of ZnSe precipitates in silicon dioxide by means of Zn (150 keV, 4×1016 cm−2) and Se (170 keV, 4×1016 cm−2) implantation at 550 °C and subsequent annealing at 1000 °C for 3 min. From analysis of XTEM images it has been showen that the use of hot implantation leads to the formation of small nanoclusters with sizes from 2 to 15 nm. Subsequent annealing results in the redistribution of nanoclusters within the implanted layer and the formation of large crystallites (up to 80 nm). To analyze the distribution of the introduced impurity throughout the sample depth the Rutherford backscattering (RBS) method was used. The band at 251-256 cm-1 associated with LO phonons of crystal ZnSe was registered in Raman spectra.