Todd Henry

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.

Contact Resistance Reduction for Strained N-MOSFETs With Silicon-Carbon Source/Drain Utilizing Aluminum Ion Implant and Aluminum Profile Engineering

We demonstrate a novel technique to reduce the nickel silicide (NiSi) contact resistance Rcon in strained n-channel MOSFETs (n-FETs) with silicon carbon (Si:C) stressors, where a presilicide aluminum (Al) implant is performed and the Al profile is found to be affected by carbon (C). Al diffusion during silicidation is retarded by the presence of C and a high Al concentration is retained within the NiSi:C film, which is considered to be the main reason for electron barrier height ΦBn reduction in NiSi:C contacts. Ge preamorphization implant prior to Al implant further reduces the ΦBn to 0.44 eV. Integration of this technique in n-FETs with Si:C stressors achieves a 50% reduction in source/drain series resistance and 12% enhancement in saturation drive current. Negligible impact on the device short-channel effects is observed. When Al segregates at the NiSi/Si interface, the hole barrier height ΦBp is lowered, and such an Al profile can be used for the p-FETs. Al profile engineering shows a promise as a single-metal-silicide solution for selective Rcon optimization in CMOS.

Schottky barrier height tuning of silicides on p-type Si (100) by aluminum implantation and pulsed excimer laser anneal

We investigate the tuning of Schottky barrier height (SBH) of nickel silicide formed by pulsed excimer laser anneal of nickel on silicon implanted with aluminum (Al). A wide range of laser fluence was investigated, and it has been found that laser fluence influences the distribution of Al within the silicide and at the silicide/silicon interface. This in turn affects the effective whole SBH (ΦBp) at the silicide/silicon junction. High Al concentration at the silicide/silicon interface and high temperature for nano-second duration to achieve Al activation while keeping the Al concentration within the silicide low is vital for achieving low ΦBp. We demonstrate the achievement of one of the lowest reported ΦBp of ∼0.11 eV. This introduces a new option for forming nickel silicide contacts with reduced contact resistance at low thermal budget for possible adoption in future metal-oxide-semiconductor transistor technologies.

Benefits of Damage Engineering for PMOS Junction Stability

As CMOS devices continue to shrink, the formation of ultra shallow junction (USJ) in the source/drain extension remains to be a key challenge requiring high dopant activation, shallow dopant profile and abrupt junctions. The next generations of sub nano‐CMOS devices impose a new set of challenges such as elimination of residual defects resulting in higher leakage, difficulty to control lateral diffusion, junction stability post anneal and junction formation in new materials. To address these challenges for advanced technological nodes beyond 32 nm, it is imperative to explore novel species and techniques. Molecular species such as Carborane (C2B10H12), a novel doping species and a promising alternative to monomer Boron is of considerable interest due to the performance boost for 22 nm low power and high performance devices. Also, to reduce residual defects, damage engineering methodologies have generated a lot of attention as it has demonstrated significant benefits in device performance. Varian proprieta...

Impact of a Germanium and Carbon Preamorphization Implant on the Electrical Characteristics of NiSi/Si Contacts With a Presilicide Sulfur Implant

This letter reports the demonstration of preamorphization implant (PAI) using germanium (Ge) and carbon (C) and its combination with presilicide sulfur (S) implant for Schottky barrier height (SBH) tuning of nickel silicide (NiSi)-silicon contacts. Ge and C PAI increases the threshold temperature for agglomeration of a NiSi film, thus enhancing its thermal stability. A presilicide S implant and its segregation at metal/semiconductor interface effectively lowers the effective electron SBH ΦBn to 0.18 eV. In addition, the distribution of reverse current in the NiSi/n-type Si contact is improved with the introduction of Ge and C PAI.

Novel technique to engineer aluminum profile at nickel-silicide/Silicon:Carbon interface for contact resistance reduction, and integration in strained N-MOSFETs with silicon-carbon stressors

We report a new technique of achieving reduced nickel silicide contact resistance in strained n-FETs, where a pre-silicide Aluminum (Al) implant was introduced, and the Al profile was controlled/engineered by Carbon (C). C suppresses Al diffusion during silicidation, hence retaining high concentration of Al within the NiSi. Incorporating Al within NiSi reduces the Schottky barrier height for n-Si:C contact, leading to 18 % IOn improvement for Si:C S/D nFETs with no compromise on short channel effects.

Metal gate work function modulation by ion implantation for multiple threshold voltage FinFET devices

FinFET has emerged as a device structure to enable the device scaling at and beyond the 22nm technology node due to increasingly stringent demands for maximum device speed, lower leakage current and control of random dopant fluctuation effects. High-k dielectric (Hik)/metal gate (MG) technology makes it feasible to obtain improved Effective Oxide Thickness (EOT) scaling and reduced leakage. Replacement metal gate (RMG) flows have been used for high performance logic volume production at and beyond 45nm node [1]. Precise threshold voltage (Vt) control and multiple Vt are required for FinFET device architectures for future devices. This paper proposes an ion implantation approach for modulating metal gate work function for both n-metal and p-metal gate used in a HiK last and replacement gate process. This approach offers simplified integration flow where no additional mask is needed and resist mask can be used. The effective work function (eWF) was measured along with the EOT and Gate Leakage (Jg). Stress Induced Leakage Current (SILC) method was used for testing HiK stack reliability. The results showed up to 200mV eWF modulation by ion implantation with fine control and without EOT and Jg degradation. The effect of implant species and dose on the eWF was studied in this paper. SIMS analysis of HKMG stack on the blanket wafer was used to determine the dopant distribution and explore the possible mechanism for metal gate work function modulation by ion implantation.

An effective metals gettering process with a cryogenic carbon implant for CMOS image sensors

CMOS Image Sensors (CIS) can suffer from yield loss due to metal impurities, which act as generation and recombination centers, giving rise to higher dark currents than the original signal current, resulting in “White Pixel” defects. Metal impurities can enter the silicon surface during processing and diffuse during thermal steps to the vicinity of the photodiode device region. The goal of intrinsic gettering is to trap metallic impurities in a deep buried layer away from the device region. This paper describes a novel process for metals gettering with a cryogenic carbon implant, followed by a high temperature gettering anneal cycle, to form a much deeper buried and distinct defect layer. This technique also provides an effectively recrystallized, defect-free surface region after anneal, which is suitable for the subsequent growth of a defect-free epitaxial film for device fabrication. The physical mechanism involved in the gettering process will be discussed.

Schottky barrier height tuning using P+ DSS for NMOS contact resistance reduction

Nickel silicide (NiSi) contacts are adopted in advanced CMOS technology nodes as they demonstrate several benefits such as low resistivity, low Si consumption and formation temperature. But a disadvantage of NiSi contacts is that they exhibit high electron Schottky barrier height (SBH), which results in high contact resistance (Rc) and reduces the NMOS drive current. To reduce SBH for NMOS, we used phosphorous (P) ion implantation into NiPt silicide with optimized anneal in order to form dopant segregated Schottky (DSS). Electrical characterization was performed using test structures such as Transmission Line Model, Cross-Bridge Kelvin Resistor, Van der Pauw and diodes to extract Rc and understand the effects of P+ DSS on ΦBn tuning. Material characterization was performed using SIMS, SEM and TEM analysis. We report ∼45% reduction in Rc over reference sample by optimizing ion implantation and anneal conditions (spike RTA, milli-second laser anneals (DSA)).

“Abnormal” angle response curves of TW/Rs for near zero tilt and high tilt channeling implants

Angle control has been widely accepted as the key requirement for ion implantation in semiconductor device processing. From an ion implanter point of view, the incident ion direction should be measured and corrected by suitable techniques, such as XP-VPS for the VIISta implanter platform, to ensure precision ion placement in device structures. So called V-curves have been adopted to generate the wafer-based calibration using channeling effects as the Si lattice steer ions into a channeling direction. Thermal Wave (TW) or sheet resistance (Rs) can be used to determine the minimum of the angle response curve. Normally it is expected that the TW and Rs have their respective minima at identical angles. However, the TW and Rs response to the angle variations does depend on factors such as implant species, dose, and wafer temperature. Implant damage accumulation effects have to be considered for data interpretation especially for some “abnormal” V-curve data. In this paper we will discuss some observed “abnorma...