Beam-line Ion Implantation Research Articles

Doping of ultra-thin Si films: Combined first-principles calculations and experimental study

This paper presents comprehensive density functional theory-based simulations to understand the characteristics of dopant atoms in the core and on the surface of ultra-thin sub-5 nm Si films. Quantum confinement-induced bandgap widening has been investigated for doped Si films considering two different doping concentrations. Thickness-dependent evolution of dopant formation energy is also extracted for the thin films. It is evident from the results that doping thinner films is more difficult and that dopant location at the surface is energetically more favorable compared to core dopants. However, the core dopant generates a higher density of states than the surface dopant. Projecting the carrier states in the doped Si film onto those of a reference intrinsic film reveals dopant-induced states above the conduction band edge, as well as perturbations of the intrinsic film states. Furthermore, to experimentally evaluate the ab initio predictions, we have produced ex situ phosphorus-doped ultra-thin-Si-on-oxide with a thickness of 4.5 nm by the beam-line ion implantation technique. High-resolution transmission electron microscopy has confirmed the thickness of the Si film on oxide. Transfer length method test structures are fabricated, and the temperature-dependent electrical characterization has revealed the effective dopant activation energy of the ion-implanted phosphorus dopant to be ≤ 13.5 meV, which is consistent with our theoretical predictions for comparable film thickness. Ultra-thin Si films are essential in the next generation of Si-based electronic devices, and this study paves the way toward achieving that technology.

Plasma‐immersion ion implantation: A path to lower the annealing temperature of implanted boron emitters and simplify PERT solar cell processing

AbstractIon implantation is a suitable and promising solution for the massive industrialization of boron doping, which is a crucial process step for most next‐generation solar cells based on crystalline silicon (c‐Si). However, the use of ion implantation for boron doping is limited by the high temperature (in the 1050°C range) of the subsequent activation anneal, which is essential to dissolve the boron clusters and reach a high‐emitter quality. In this work, we propose the use of plasma‐immersion ion implantation (PIII) from B2H6 gas precursor instead of the standard beamline ion implantation (BLII) technique to decrease this temperature down to 950°C. PIII and BLII boron emitters were compared with annealing temperatures ranging from 950°C to 1050°C. Contrary to BLII, no degradation of the emitter quality was observed with PIII implants annealed at 950°C along with a full activation of the dopants in the emitter. At 1000°C, emitter saturation current densities (J0e) below 21 fA/cm2 were obtained using the PIII technique regardless of the tested implantation doses for sheet resistances between 110 and 160 Ω/sq. After metallization steps, the metal/emitter contact resistances were assessed, indicating that these emitters were compatible with a conventional metallization by screen‐printing/firing. The PIII boron emitters' performances were further tested with their integration in n‐type passivated emitter rear totally diffused (PERT) solar cells fully doped by PIII. Promising results already show a conversion efficiency of 20.8% using a lower annealing temperature than with BLII and a reduced production cost.

Exploring conductivity in ex-situ doped Si thin films as thickness approaches 5 nm

Silicon (Si) has been scaled below 10 nm in multigate and silicon-on-insulator (SOI) device technologies, but clearly Si thickness cannot be reduced indefinitely, as we will run out of atoms eventually. As thickness approaches 5 nm, surfaces and interfaces will significantly impact the electrical behavior of Si, and surface physics cannot be discounted. Below that, bulk material properties will be altered considerably in the few-monolayer limit. One of the most basic defining properties of a semiconductor is its conductivity. To improve conductivity, while inducing a channel by appropriate biasing, it is necessary to define an accurate impurity doping strategy to reduce parasitic resistance. In this paper, we investigated the changing electrical conductivity of SOI films as a function of the Si thickness, in the range of 3–66 nm. SOI films were ex situ doped using three different approaches: liquid/vapor phase monolayer doping of phosphorus using allyldiphenylphosphine, gas-phase doping of arsenic using arsine (AsH3), and room-temperature beam-line ion implantation of phosphorus. The circular transfer length method and micro-four-point probe measurements were used to determine the resistivity of the Si films, mitigating the contribution from contact resistance. The resistivity of the Si films was observed to increase with decreasing Si film thickness below 20 nm, with a dramatic increase observed for a Si thickness at 4.5 nm. This may drastically impact the number of parallel conduction paths (i.e., nanowires) required in gate-all-around devices. Density functional theory modeling indicates that the surface of the Si film with a thickness of 4.5 nm is energetically more favorable for the dopant atom compared to the core of the film.

Diagnosis of phosphorus monolayer doping in silicon based on nanowire electrical characterisation

The advent of high surface-to-volume ratio devices has necessitated a revised approach to parameter extraction and process evaluation in field-effect transistor technologies. In this work, active doping concentrations are extracted from the electrical analysis of Si nanowire devices with high surface-to-volume ratios. Nanowire resistance and Si resistivity are extracted, by first extracting and subtracting out the contact resistance. Resistivity (ρ) is selected as the benchmark parameter to compare different doping processes with each other. The impacts of nanowire diameter scaling to 10 nm and of nanowire spacing scaling to <20 nm are extracted for monolayer doping and beam-line ion implantation. Despite introducing significant crystal damage, P beam-line ion implantation beats allyldiphenylphosphine (ADP) P monolayer doping with a SiO2 cap in terms of lower Si resistivity and higher dopant activation, with dependencies on the nanowire width greater than on nanowire spacing. Limitations in ADP P monolayer doping with a SiO2 cap are due to the difficulties in dopant incorporation, as it is based on in-diffusion, and P atoms must overcome a potential barrier on the Si surface.

Development and experimental study of large size composite plasma immersion ion implantation device

Plasma immersion ion implantation (PIII) overcomes the direct exposure limit of traditional beam-line ion implantation, and is suitable for the treatment of complex work-piece with large size. PIII technology is often used for surface modification of metal, plastics and ceramics. Based on the requirement of surface modification of large size insulating material, a composite full-directional PIII device based on RF plasma source and metal plasma source is developed in this paper. This device can not only realize gas ion implantation, but also can realize metal ion implantation, and can also realize gas ion mixing with metal ions injection. This device has two metal plasma sources and each metal source contains three cathodes. Under the condition of keeping the vacuum unchanged, the cathode can be switched freely. The volume of the vacuum chamber is about 0.94 m3, and maximum vacuum degree is about 5 × 10−4 Pa. The density of RF plasma in homogeneous region is about 109 cm−3, and plasma density in the ion implantation region is about 1010 cm−3. This device can be used for large-size sample material PIII treatment, the maximum size of the sample diameter up to 400 mm. The experimental results show that the plasma discharge in the device is stable and can run for a long time. It is suitable for surface treatment of insulating materials.

Homojunction silicon solar cells doping by ion implantation

Production costs and energy efficiency are the main priorities for the photovoltaic (PV) industry (COP21 conclusions). To lower costs and increase efficiency, we are proposing to reduce the number of processing steps involved in the manufacture of N-type Passivated Rear Totally Diffused (PERT) silicon solar cells. Replacing the conventional thermal diffusion doping steps by ion implantation followed by thermal annealing allows reducing the number of steps from 7 to 3 while maintaining similar efficiency.This alternative approach was investigated in the present work. Beamline and plasma immersion ion implantation (BLII and PIII) methods were used to insert n-(phosphorus) and p-type (boron) dopants into the Si substrate. With higher throughput and lower costs, PIII is a better candidate for the photovoltaic industry, compared to BL. However, the optimization of the plasma conditions is demanding and more complex than the beamline approach.Subsequent annealing was performed on selected samples to activate the dopants on both sides of the solar cell. Two annealing methods were investigated: soak and spike thermal annealing. Best performing solar cells, showing a PV efficiency of about 20%, was obtained using spike annealing with adapted ion implantation conditions.

Plasma Doping of InGaAs at Elevated Substrate Temperature for Reduced Sheet Resistance and Defect Formation

Plasma doping (PLAD), a high-throughput ion implantation technique capable of achieving ultrashallow junctions and conformal doping of 3-D structures such as fin field-effect transistors, is investigated as an alternative to conventional beam-line ion implantation for InGaAs at advanced technology nodes. The PLAD at an elevated substrate temperature (ET-PLAD) is studied and reported for InGaAs for the first time. The ET-PLAD can give lower sheet resistance than room-temperature PLAD due to enhanced dopant incorporation. More crucially, an ET can help to prevent amorphization. After dopant activation anneal, residual corner defects are observed in small fins that are amorphized during plasma ion implantation, whereas fins that remain crystalline during plasma ion implantation are free of corner defects.

Liquid Phase Epitaxy (LPE) Formation of Localized High Quality and Mobility Ge & SiGe by High Dose Ge-Implantation with Laser Melt Annealing for 10nm and 7nm Node CMOS Technology

We investigated using high dose (5E16/cm2) Ge beam-line ion implantation in combination with laser melt annealing as an alternative to Ge-epi by CVD to form high quality single crystal Ge-epilayer by LPE (liquid phase epitaxy) that is very uniform, thin 10-25nm and localized for high mobility Ge-channels. The implant resulted in 7nm amorphous Ge deposition by a method called dose controlled deposition (DCD). A 515nm laser was used to vary the melt depth from 9nm to 500nm based on laser anneal pulse duration and power level. Ellipsometer was used to measure the surface amorphous layer thickness while therma-wave (TW) analysis was used to monitor Ge implant damage recovery after LPE. SIMS depth profiles showed Ge surface concentration varied from 100% down to 2% based on the laser melt depth. X-TEM analysis showed the transformation of deposited amorphous Ge surface layer to single crystal Ge after laser melt and LPE. Sb implantation at two dose levels of 3E15/cm2 and 3E13/cm2 was used to examine laser melt annealing effects on n-type dopant activation and electron mobility in Ge. Special Hx-probe tips on the 4PP system was required to measure sheet resistance and CAOT/DHE method was used for Differential Hall Effect measurements.

Liquid Phase Epitaxy (LPE) Formation of Localized High Quality and Mobility Ge & SiGe by High Dose Ge-Implantation with Laser Melt Annealing for 10nm and 7nm Node CMOS Technology

Localized Ge and SiGe high quality/mobility device surface material region on bulk-Si and SOI wafers are needed for 10nm and 7nm node CMOS technology. Traditionally SiGe and Ge device surface material on bulk-Si or SOI wafers are realized by CVD epitaxial growth or Vapor Phase Epi (VPE) at elevated temperatures. Selective deposition can be achieved with hard mask. To reduce defects strain relaxed buffer (SRB) or aspect ratio trapping (ART) have been employed with bulk-Si or layer transfer wafer bonding for SiGeOI or GeOI. An alternative to VPE is to use either SPE (solid phase epitaxy) or LPE (liquid phase epitaxy) to form SiGe or Ge epitaxial surface layers. Using high dose Ge implantation >E16/cm2 with photoresist soft mask as proposed in 2004 by Borland et al [1,2]. Localized amorphous Ge surface regions can be formed after Ge-infusion doping by Gas Cluster Ion Beam (GCIB) technique followed by low temperature SPE to form single crystal thin surface Ge epitaxial layers but residual end-of-range (EOR) damage remained. Today, laser melt annealing of implanted junctions are currently being used in production for high quality back-side illuminated CMOS image sensors used in smart phone cameras by several IC and foundry semiconductor manufacturers to completely eliminate any residual implant damage/defects with 100% dopant activation provided the melt depth exceeds the implant damage depth [3]. Last year at IWJT-2013 Borland et al [4] reported using Ge-plasma ion implantation at 1E16/cm2 and 1E17/cm2 doses with laser melt annealing to realize up to 55% SiGe by LPE with >4x higher mobility at 160cm2/Vs. One limitation they noted with plasma implantation was poor retained dose due to surface sputtering at low energies which limited the Ge content to <55% for 1E17/cm2 dose. Therefore to overcome this retained dose problem we investigated Ge beamline ion implantation in this paper which should give 100% retained dose. The Ge surface amorphous layer thickness measured by elipsometry was 15nm while the Ge-SIMS depth profile measures 7nm Ge at 100%. Therma-wave analysis was used to monitor the Ge-implant damage recovery and Ge or SiGe recrystallized epitaxial surface layer after various laser melt annealing conditions of varying power level and pulse duration. The Ge-SIMS depth profiles shows we could vary the melt depth for LPE Ge layer from 10nm to >400nm and the Ge layer content from 97% down to 2% respectively. We will also show X-TEM of the Ge-LPE regions. Sb implantation was used to investigate n-type dopant activation in Ge at low and high doses of 3E13/cm2 and 3E15/cm2. Rs measurements were done using a special Hx 4 point probe and SRP (spreading resistance profile) depth profiles. In summary, using high dose beam-line Ge-implantation we realized >7nm amorphous Ge deposition. Epitaxial growth of Ge was achieved by liquid phase epitaxy using shallow laser melt annealing between 10nm and >400nm melt depths.

Effect of $\hbox{B}_{2}\hbox{H}_{6}$ Plasma Doping on the Shallow Trench Isolation in CMOS Image Sensor Device

We evaluate the electrical and optical properties of a complementary metal-oxide-semiconductor (CMOS) image sensor with shallow trench isolation (STI) sidewall doped by plasma-doping (PLAD) method using B2H6. PLAD can be used to fabricate an STI sidewall junction depth shallower than that fabricated using conventional beamline ion implantation. The use of B2H6 for the STI sidewall doping by PLAD facilitates the concurrent doping of numerous hydrogen atoms around the STI sidewall, thus improving the optical properties, such as temporal noise, crosstalk, and saturation, of the 1.75-μm pixel CMOS image sensor. Although the dark current performance was slightly degraded, it could be improved under more heavily doped conditions.

Advantage of Plasma Doping for Source/Drain Extension in Bulk Fin Field Effect Transistor

The impact of plasma doping (PD) on the formation of source/drain extension (SDE) is demonstrated for a p-type bulk fin field effect transistor (FinFET). The impurity distribution in a narrow fin (15 nm) was analyzed with atom probe tomography (APT) and secondary ion mass spectroscopy (SIMS). The lateral distribution of boron in the Si fin by the PD is similar to the case with conventional beam-line ion implantation (BL). However, the vertical distribution of boron by the PD is much steeper than that by the conventional BL. TCAD simulations show that the driving current of the FinFET fabricated by the PD is 34% higher than that of the FinFET fabricated by the BL under the same off-leakage current. Therefore, the PD is a key technology for fabricating the SDE of narrow bulk-FinFETs in the future.

High temperature oxidation resistance of fluorine-treated TiAl alloys: Chemical vs. ion beam fluorination techniques

The modification of the alloy surface by halogens significantly improves their oxidation behaviour at high temperature. It corresponds to the preferential reaction of the aluminium with the applied fluorine at the oxide/alloy interface and it promotes the growth of an adherent and stable alumina layer. Well-defined fluorine profiles beneath the surface of the material can be achieved by either fluorine beam line ion implantation (BLI 2) or plasma immersion ion implantation (PI 3). As an alternative to the implantation-based approach, chemical fluorination techniques such as gas-phase treatment and dipping in F-based solutions were also investigated. The fluorine depth-profiles were measured before and after oxidation at 900 °C using non destructive ion beam analyses: Proton Induced Gamma-ray Emission (PIGE), Rutherford Backscattering Spectroscopy (RBS) as well as Elastic Recoil Detection Analysis (ERDA). It enables to control and to optimise the fluorination conditions of technical TiAl alloys for an industrial application.

Plasma immersion ion implantation of polymers and silver–polymer nano composites

Biocompatibility and wear resistance are the outstanding properties of hydrogenated diamond like carbon (a-C:H), making it a very suitable material for medical applications, especially as a coating for joint replacing implants. Recently the demand for additional antimicrobial features of such coatings is becoming more and more pronounced. One possibility is the introduction of silver particles, which has already been done for a variety of polymer based products. We have developed a hybrid synthesis method to produce silver nano particle containing a-C:H based on the ion induced transformation of silver–polymer nano composites into Ag containing a-C:H. Now those results have been transferred to plasma immersion ion implantation (PIII), which allows a 3D treatment and thus is the next step towards industrial application. PIII experiments have been conducted with a mixture of CH 4 and Ne as well as Ar with a pulsed bias of 40 kV. From beam line ion implantation experiments, the correlation of fluence and ion energy with film properties is well known, so this work is focused on the investigation of plasma etching and sputtering effects, caused by direct exposure to the plasma. It will be shown, that these effects can be compensated by adding hydrocarbon species to the plasma. Using this method, film properties like density, hydrogen content and sp 3 fraction comparable to those of typical a-C:H can be achieved. RBS, ERD and Raman spectroscopy are used to investigate and to understand the densification process.

Pulsed Inductively-Coupled Plasma Doping of Phosphorus for N+-P Junction Fabrication

Plasma doping is an attractive technology that may be capable of producing ultra-shallow junctions with high productivity. We used a pulsed inductively-coupled plasma (ICP) to increase the plasma density and to reduce particulates and deposits. We doped phosphorus ions at a low substrate bias voltage (0.2 to 2 kV) by using PH3 as the process gas. An n+-p junction with low sheet resistance was then formed by spike rapid thermal annealing (RTA). We investigated the density of the pulsed plasma as a function of time to determine the optimal delay time for the substrate pulse bias after the RF power of the ICP antenna had been switched on. The pulse width of the substrate bias was optimized to 50 s to maximize the throughput. We compared the plasma doping with a traditional beam-line ion implantation and found that it resulted in a lower junction depth and a higher sheet resistance at the same voltage. A junction depth of 34 nm and a sheet resistance of 590 / were obtained by plasma doping at 0.5 kV with spike RTA at 950 C.

Comparison of oxidation resistance of copper treated by beam-line ion implantation and plasma immersion ion implantation

Copper which has many favorable properties such as low cost, high thermal and electrical conductivity, as well as easy fabrication and joining is one of the main materials in lead frames, interconnects, and foils in flexible circuits. Furthermore, copper is one of the best antibacterial materials. However, unlike aluminum oxide or chromium oxide, the surface copper oxide layer does not render sufficient protection against oxidation. In this work, in order to improve the surface oxidation resistance of Cu, Al and N were introduced into copper by plasma immersion ion implantation (PIII) and beam-line ion implantation (BII). The implantation fluences of Al and N were 2 × 10 17 ions cm −2 and 5 × 10 16 ions cm −2, respectively. The implanted and untreated copper samples were oxidized in air at 260 °C for 1 h. The X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as X-ray photoelectron spectroscopy (XPS) results indicate that both implantation methods can enhance the oxidation resistance of copper but to different extent. PIII is superior to BII in enhancing the oxidation resistance of copper. The effects and possible mechanisms are discussed.

SIMS/ARXPS—A New Technique of Retained Dopant Dose and Profile Measurement of Ultralow-Energy Doping Processes

A newly developed surface analysis technique, which combines secondary ion mass spectrometry with angle-resolved X-ray photoelectron spectroscopy, was used to achieve more accurate results of the retained impurity doses and profiles for ultralow-energy implants, including conventional beamline implant and plasma immersion ion implantation (PIII). Using this method, it has been found that the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (diborane) PIII demonstrates thicker native oxide and much more B dose loss during rapid thermal processing and surface-cleaning treatments than conventional beamline ion implantation, due to the higher surface B concentration. In order to match the electrical parameters of the device, PIII must consider higher nominal dose to compensate the B loss.

Comparison of tribological behaviour and biocompatibility of Ti6Al4V alloy after ion implantation or thermal oxidation

AbstractThis paper describes improvements of the tribological properties and the biocompatibility of Ti6Al4V alloy implanted by oxygen plasma immersion (PIII) in comparison with other treatments like thermal oxidation, conventional beamline ion implantation (II) of nitrogen and a combination of both thermal oxidation and II of nitrogen.Ball‐on‐disc friction and wear tests were performed to investigate the modifications introduced for each treatment. Biocompatibility tests were carried out by controlling Al and V ion migration in a Hank's solution simulating the human body fluid. The reported results indicate that PIII provide a promising method to improve the characteristics of the Ti6Al4V alloy to be used in human body implants. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Improving the oxidation resistance of TiAl-alloys with fluorine

The technical TiAl-alloy γ-MET (Ti–46.5Al–4(Cr, Nb, Ta, B)) was oxidised thermocyclically (24 h-cycle-test) at 900 °C in wet and dry air. In this paper results of untreated and fluorine treated TiAl-samples are presented. Their oxidation behaviour will be shown. Several methods were used to apply the halogens to the surface, e.g. beamline ion implantation, spraying of or dipping into a halogen containing liquid. A pure protective alumina scale was found, e.g. after treatment with a fluorine containing polymer and thermocyclic oxidation up to 1 year at 900 °C in laboratory air. On the other side thick fast growing and non-protective mixed oxide scales were found on the untreated samples.

Oxygen plasma treatment to restrain nickel out-diffusion from porous nickel titanium orthopedic materials

Porous nickel–titanium (NiTi) shape memory alloy is a prospective orthopedic biomaterial due to its porous structure that allows bone tissue and blood vessel ingrowth during fixation of implants. Unfortunately, the higher probability of Ni release from the increased surface area of a porous surface compared to conventional dense NiTi shape memory alloys causes more serious health concerns. In order to mitigate leaching of harmful Ni ions, we create a firm barrier layer on the surface by conducting oxygen plasma immersion ion implantation (PIII) into the porous structure. The non-line-of-sight capability of PIII allows more uniform treatment of all exposed areas compared to beam-line ion implantation. Our simulated body fluid immersion test indicates that Ni leaching is significantly reduced after oxygen PIII. X-ray photoelectron spectroscopy profiles illustrate that the thickness of the barrier layer is almost unchanged after immersion in SBF for 4 weeks, demonstrating the excellent durability of the layer in a biological medium.

Ultra shallow P+/N junctions using plasma immersion ion implantation and laser annealing for sub 0.1 μm CMOS devices

Classical beam line ion implantation is limited to low energies and cannot achieve P+/N junctions requested for <45nm ITRS node. RTA (rapid thermal annealing) needs to be improved for dopants activation and damage reductions. Spike annealing process also induces a large diffusion mainly due to TED (transient enhanced diffusion).Compared to conventional beam line ion implantation limited to a minimum energy implantation of 200eV, plasma immersion ion implantation (PIII) is an emerging technique to get ultimate shallow profiles (as-implanted) due to no lower limitation of energy and high dose rate. On the another hand, laser thermal processing (LTP) allows to obtain very shallow junction with no TED, abrupt profile and activated depth control.In this paper, we show the implementation of the BF3 PIII associated with the LTP. Ions from BF3+ plasma have been implanted in 200mm n-type silicon wafers with energies from 100eV to 1keV and doses from 3E14 to 5E15at/cm2 using PULSION® (IBS PIII prototype). Then, wafers have been annealed using SOPRA VEL 15 XeCl excimer lasers (l=308nm, 200ns, 15J/pulse) with energy density from 1 to 2.5J/cm2 and 1, 3 or 10 shots. The samples have been characterized at CEA LETI by secondary ion mass spectrometry (SIMS) combined with four points probe sheet resistance measurements.