Ultra-shallow Junctions Research Articles

A Comparison of Short-Channel Control in Planar Bulk and Fully Depleted Devices

The short-channel effects (SCEs) of planar bulk and fully depleted finFET devices have been compared using the same junction overlap and lateral gradient, and it is shown that, for finFET devices, a significant component of electrostatic control arises from a naturally present shallow extension junction. When such shallow junctions are applied to a bulk device, we show that the SCE becomes comparable to that of a finFET. Furthermore, we show that, if an embedded source/drain stressor is incorporated in a bulk device, it will not degrade the short-channel benefit of the ultrashallow junctions. The ability to span a wide power/performance range by doping and the improvement in SCEs by the use of ultrashallow extension junctions can potentially extend the life of bulk-type technologies.

PureGaB p+n Ge diodes grown in large windows to Si with a sub-300 nm transition region

Ultrashallow junction Ge-on-Si p+n diodes have been fabricated using an epitaxial growth technique of crystalline Ge on Si substrates in a standard ASM Epsilon 2000 CVD reactor. An As-doped Ge is first deposited selectively at the temperature of 700°C where most of the lattice mismatch-defects are trapped at the interface of Ge and Si and vanish within the first 300nm of Ge growth. Under this condition, good quality single crystal Ge is grown within a layer thickness of approximately 1μm on different window sizes up to hundreds of μm2. For p+n junction fabrication, the process is followed in the same reactor with a sequence of pure-Ga and then pure-B depositions, to form an ultrashallow p-doping of As-doped Ge-islands that can be metallized by Al. The term PureGaB is introduced for this technology. The I–V and C–V characterization the diodes confirms the good quality of the ultrashallow junction Ge diodes with ideality factors of less than 1.1 and reliable low saturation currents. The doping levels are shown to be such that the depletion over the diodes falls within the Ge region.

Germanium Doping, Contacts, and Thin-Body Structures

Interest in Ge has risen sharply in since the turn of the century, as it has enabled applications ranging from field-effect-transistors, solar cells, photonics, and sensors. In this paper the state-of-the-art will be reviewed in the areas of (i) dopant behavior and ultrashallow junction performance metrics, (ii) thin-body structure formation, and (iii) contact methodologies in Ge.

Achieving Ultra-Shallow Junctions in Future CMOS Devices by a Wet Processing Technique

The continued scaling of CMOS devices to the sub-16 nm technology node will likely be achieved with new architectures, such as FinFETs and high mobility substrates, including compound semiconductors (III-V). At these technology nodes, abrupt channel doping profiles with high dopant activation will be needed under low thermal budget environments for III-V materials. Ion implantation into III-V materials presents a problem as it induces crystal damage, which can alter the stoichiometry in a manner that is difficult to recover. The residual damage can lead to higher junction leakage and lower dopant activation. This paper presents a potentially defect-free alternative, mono-layer doping (MLD), which utilizes wet processing techniques.

Physical understanding of cryogenic implant benefits for electrical junction stability

We investigate the effect of cryogenic temperature implants on electrical junction stability for ultra shallow junction applications for sub-32 nm technology nodes and beyond. A comprehensive study was conducted to gain physical understanding of the impact of cryogenic temperature implants on dopant-defect interactions. Carborane (C2B10H12) molecule, a potential alternative to monomer boron was implanted in carbon preamorphized silicon substrates at cryogenic implant temperatures. Results indicate implants at cryogenic temperatures increase dopant activation with reduced diffusion, resulting in lower sheet resistance for a lower junction depth. Further, this study emphasizes the benefits of co-implants performed at cryogenic temperatures as alternative to traditional preamorphizing implants.

Development of an industrial tool to make passivation layers for UV sensors improvement

Today, the collection of generated charges is a limiting problem for the realization of UV sensors. Indeed, the native silicon oxide of the surface acts as a region of recombination centers [1]. Then, the sensors exhibit a low sensitivity in the UV wavelengths. An approach to overcome this drawback is the realization of a few nanometers thick passivation layer at the surface by creating an ultra-shallow junction (USJ) with a high activation level.The realization of such junctions requires two steps: first, the implantation of dopants which consists in introducing impurities at the surface of the substrate, then the thermal activation of these dopants to obtain the electrical characteristics of the junction. The Plasma Immersion Ion Implantation (PIII) process allows us to implant dopants in a very thin layer (10–20nm) into the silicon substrate [2–4]. These impurities are located in interstitial sites in the silicon, and need an activation process to modify the electrical properties of the layer. The step is performed by means of an excimer laser annealing process (ELA) [5–8] to melt a very thin layer of the silicon substrate and then activate the dopants without diffusion. In the framework of the ALDIP project (Laser Activation of Dopants implanted by Plasma Immersion), IBS Company has developed with its partners a cluster to realize these two steps with industrial production rates and cleanliness.Four-point probe measurements and SIMS analyzes have been used to characterize the junctions realized with this process. We have reached a sheet resistance lower than 500Ω/sq for a junction depth of 29nm and an abruptness of 3nm/dec. Nevertheless, electrical measurements on diodes have revealed a significant leakage current of around 10−5A/cm2, revealing the presence of defects inside the junction. Light Beam Induced Current (LBIC) [9–12] characterization has shown that these defects are localized at the edge of the laser beam.

Codiffusion of Phosphorus and Carbon in Preamorphized Ultrashallow Junctions

Codiffusion of Phosphorus and Carbon in Preamorphized Ultrashallow Junctions

Thermal budget control for processes with spike-shaped temperature profiles: Application to rapid thermal annealing

The spike-shaped temperature profile in thermal treatments is widely used in the IC industry for providing precise thermal budgets. This thermal budget control issue becomes more crucial as the technology node progressively shrinks. Therefore, rapid thermal processing (RTP), such as spike annealing has the ability to yield ultra-shallow junctions. With its exceptionally stringent performance requirements (for example, high temperature uniformity and high temperature ramp-up/down rate), temperature control in RTP systems is a challenging task. In this study, a novel methodology for designing a control system to provide a precise thermal budget is presented. By tuning controller parameters and designing the set-point profile, the method targets thermal budget indices instead of temperature servo control. Two types of controllers, PI and PI 2D, are considered. Practical issues, such as the feasibility range for temperature ramp-up/down rate and the effect of model mismatch, are also discussed. The results show that the simple PI controller performs well in spike RTP systems. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Challenges and opportunity in performance, variability and reliability in sub-45 nm CMOS technologies

In this paper, we present a detailed discussion related to the consequences on CMOS process flow for the high-speed race required by electronics applications. Key process elements for CMOS circuits speed enhancement are reported such as process stressors, high-k metal gate (HK/MG) stack, and low resistivity ultra-shallow junctions. Physical description and electrical interests are deeply discussed. Beside pure performance benefit, side effects of new process steps implementation are presented. Key transistor parameters variability as threshold voltage and drive current and reliability have been investigated for CMOS transistor. Finally a first risk evaluation is proposed for sub-28nm CMOS technologies with more aggressive architectures introduction.

Improvement of Heavy Dopant Doped Ni-Silicide Using Ytterbium Interlayer for Nano-Scale MOSFETs with an Ultra Shallow Junction

In this paper, a novel Ni silicide with Yb interlayer (Yb/Ni/TiN) on a boron cluster (B18H22) implanted source/drain junction is proposed for the first time, and its thermal stability characteristics are analyzed in depth. The proposed Ni-silicide exhibits a wider RTP temperature window for uniform sheet resistance, surface roughness and better thermal stability than the conventional structure (Ni/TiN). In addition, the cross-sectional profile of the proposed Ni-silicide showed less agglomeration despite the high temperature post-silicidation annealing, and it can be said that the proposed structure was little dependence on the temperature post-silicidation annealing. The improvement of Ni silicide properties is analyzed and found to be due to the formation of the rare earth metal--NiSi (YbNi2Si2), whose peaks were confirmed by XRD. The junction leakage current of the p + -n junction with Yb/Ni/TiN and B18H22 implantation is smaller than that with Ni/TiN by almost one order of magnitude as well as improving the thermal stability of ultra shallow junction.

Molecular monolayers for conformal, nanoscale doping of InP nanopillar photovoltaics

Semiconductor nanopillar arrays with radially doped junctions have been widely proposed as an attractive device architecture for cost effective and high efficiency solar cells. A challenge in the fabrication of three-dimensional nanopillar devices is the need for highly abrupt and conformal junctions along the radial axes. Here, a sulfur monolayer doping scheme is implemented to achieve conformal ultrashallow junctions with sub-10 nm depths and a high electrically active dopant concentration of 1019–1020 cm−3 in arrays of InP nanopillars. The enabled solar cells exhibit a respectable conversion efficiency of 8.1% and a short circuit current density of 25 mA/cm3. The work demonstrates the utility of well-established surface chemistry for fabrication of nonplanar junctions for complex devices.

Nonthermal illumination effects on ultra-shallow junction formation

In this letter, we present direct and unambiguous experimental evidence for nonthermal illumination effects in boron or arsenic implanted silicon. Both, dopant diffusion and activation vary significantly with illumination. Depending on annealing temperature, diffusion is either enhanced or inhibited. The results have significant implications for modeling and formation of ultrashallow junctions.

Effect of Fluorine Co-Implant on Boron Diffusion in Germanium Preamorphized Silicon During Post-LSA Rapid Thermal Annealing

Fluorine co-implant has been shown to reduce boron transient enhanced diffusion and deactivation when coupled with conventional spike rapid thermal anneals (RTA). For ultrashallow junction formation beyond the 45 nm technology node, non-melt laser spike anneal (LSA) is a promising diffusion-less annealing candidate. In this paper, the effect of fluorine co-implant on boron diffusion during LSA and the subsequent post-LSA thermal budget is evaluated. Silicon wafers were implanted with germanium, fluorine, and subsequently boron ions. Non-melt LSA was carried out at a temperature range from 1150 to 1350°C, followed by RTA at 825°C for 30 s. Secondary ion mass spectrometry confirms that in the presence of fluorine, retarded boron diffusion is observed at LSA temperatures below 1250°C. As the LSA temperature is increased or when a subsequent soak RTA is carried out, enhanced boron diffusion is observed. The reduced boron diffusivity at LSA temperatures below 1250°C is attributed to the efficient capture of interstitials released from the end-of-range defects by fluorine-vacancy clusters during the millisecond anneal. As the thermal budget is increased, excess interstitials caused by the fluorine implant are released, thus increasing the boron diffusion.

Comparison of Boron Diffusion in Silicon during the Formation of Shallow p+/n Junction with KrF and Green Laser Annealing

A combination of Ge pre-amorphization implantation (Ge-PAI), low-energy B implantation and non-melt laser annealing is a promising method to form highly-activated, abrupt and ultra-shallow junctions (USJ). In this work, shallow p+/n junction was formed by annealing the implanted sample with two different laser sources, i.e. by using excimer laser, KrF (λ= 248nm, pulse duration : 37ns) and green laser (λ= 527nm, pulse duration : 110ns) in order to compare the diffusion of boron during the formation of shallow p+/n junction. Experimental results show that remarkable boron diffusion occurred during annealing of the samples subjected to KrF laser annealing with a very short annealing time. Meanwhile, boron diffusion is controlled in the samples subjected to green laser annealing. We considered that the penetration depth and the pulse duration are the important factor that may caused the difference in boron diffusion during annealing process.

Problems of N-type Doped Regions in Germanium, their Solutions, and How to Beat the ITRS Roadmap

In this paper the authors discuss the issues surrounding the formation of ultrashallow n-type junctions in Ge. In general the n-type dopants are relatively difficult to activate and diffuse quickly, leading to high access resistances and limited capability to reduce the device dimensions, respectively. Sheet resistance (Rs) was calculated for n-type box-like profiles in Si and Ge. To achieve ITRS Roadmap targets in Si an active doping concentration of 1.5-2×1020 cm-3 is required, but due to the enhanced electron mobility it is predicted approximately 6×1019 cm-3 is sufficient in Ge.

(Invited) Advances in Si and Ge Millisecond Processing: From SOI to Superconductivity and Carrier-Mediated Ferromagnetism

This paper reviews the advances that millisecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, namely silicon and germanium, thus enabling the fabrication of novel microelectronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. Opportunities in ultra-shallow junction formation for silicon-on-insulator, superconducting Ge and Si, and diluted ferromagnetic Ge, along with the technical reasons for using annealing times in the ms range are discussed in the context of state-of-the-art materials processing. Whereas these examples are based on solid phase processing, the more sophisticated approach regards on working with the liquid phase at the surface of solid substrates. As a recent example the controlled surface melting of a Ge enriched silicon substrate is reported.

Activation of As Atoms in Ultrashallow Junction during Milli- and Microsecond Annealing Induced by Thermal-Plasma-Jet Irradiation

We irradiated a micro-thermal-plasma-jet (µ-TPJ) to an As-implanted Si wafer surface to form an ultrashallow junction (USJ). A high-power-density TPJ for microsecond rapid thermal annealing (RTA) was generated by using a small orifice of 0.8 mm diameter instead of 2.0 mm to concentrate the TPJ. The µ-TPJ could anneal the Si wafer surface at a temperature as high as 920 K for 340 µs. By reducing the annealing duration (ta) from 1.2 ms to 340 µs, the sheet resistance (RS) of the As2+-implanted Si wafer decreased from 1520 to 1287 Ω/sq. In addition, the chemical bond states of As at the very surface were measured by X-ray photoelectron spectroscopy (XPS) and the fraction of activated As was estimated to be ∼15% larger than that in the case of millisecond annealing. Surface As atoms in Si wafers were more efficiently activated by a microsecond annealing than a millisecond annealing owing to the suppression of diffusion and clustering.

Activation of As Atoms in Ultrashallow Junction during Milli- and Microsecond Annealing Induced by Thermal-Plasma-Jet Irradiation

Activation of As Atoms in Ultrashallow Junction during Milli- and Microsecond Annealing Induced by Thermal-Plasma-Jet Irradiation

Precise Control of Spike Anneal Process for Advanced CMOS

Aggressive scaling of planar bulk CMOS device has resulted in the need for ultra-shallow junctions (USJ) formation. This represents some special concern are not only integration solution, but also the individual process precise control to meet the evolutional requirements. In the USJ particular, as junction thickness (depth) decreases, the series resistance of the junction increases. Therefore, the dopants concentration must to be increased to improve the resistance. Dilemma, the diffusion is an important issue in shallow junction technology. The spike anneal process was widely adopted at advanced CMOS fabrication to meet the device requirements. In this paper, how to precisely control the processes of spike anneal is discussed. The two major interacted process factors, peak-temperature and residence-time must be separately tunable, not only to meet the requirements of device parameter, but also to achieve an operational precise controlling for process setup, optimization and maintenance.

Electronic Structures of Donor-Acceptor-Donor Trimer Codopants in Silicon

The total energies of donor-acceptor-donor D2A trimer codopants (D = As and Sb, A = B, Al, Ga, In and Tl) in Si and their electronic geometrically stable structures were studied using ab initio calculations in order to propose new dopants for the formation of ultra shallow junctions with high carrier concentrations in the source/drain regions. The results of the calculations indicated that the trimer codopants were formed in Si and were stable. The trimer codopants are also able to activate the inactive complexes As2V and Sb2V by codoping acceptor atoms that occupy vacant sites. In particular, As2Al, As2Ga, Sb2B and Sb2Ga resulted in both shallower donor levels and higher solid solubility compared to traditional single donor atoms such as As and Sb.