Cryogenic Implantation Research Articles

Cryogenic implantation to boost PFET performance and reduce variability in 3D NAND flows

Cryogenic implantation to boost PFET performance and reduce variability in 3D NAND flows

Contact Resistance Improvement for Advanced Logic by Integration of Epi, Implant and Anneal Innovations

ABSTRACTAs advanced CMOS scaling with FinFETs continues beyond the 10/7nm nodes, contact resistance (Rc) remains a dominant component affecting device performance. The FinFET Source/Drain (S/D) contact area has become smaller with fin pitch scaling, resulting in drastically increased Rc. To achieve higher drive currents and fully realize the performance gain from FinFET architectural changes, it is critical to continue to reduce contact resistivity (ρc) < 1.0x10-9 Ω.cm2 for both NMOS and PMOS. In this paper, we review the recent trends for ρc reduction for advanced CMOS devices and discuss approaches that have demonstrated reduction in ρc, such as in-situ heavily doped epitaxial films for S/D, advanced ion implantation and laser anneals. The implant techniques include pre-amorphization implants (PAI), dopant boosting implants, cryogenic (-100°C) implants for damage engineering and plasma doping (PLAD) for conformal doping of high aspect ratio (HAR) contacts. With such high levels of doping from epi and implants, advanced laser anneals are key for epitaxial regrowth and formation of metastable alloys for dopant supersaturation or segregation in top layers. Millisecond laser anneal (MSA) improves dopant activation and nanosecond laser anneal (NLA) permits superactivation, and both have become key enablers for ρc reduction. This paper also reviews two alternative contact approaches: dual silicide scheme and wrap-around contact (WAC), as potential pathways to further reduce Rc for advanced CMOS nodes.

Investigating Helium Bubble Nucleation and Growth through Simultaneous In-Situ Cryogenic, Ion Implantation, and Environmental Transmission Electron Microscopy.

Palladium can readily dissociate molecular hydrogen at its surface, and rapidly accept it onto the octahedral sites of its face-centered cubic crystal structure. This can include radioactive tritium. As tritium β-decays with a half-life of 12.3 years, He-3 is generated in the metal lattice, causing significant degradation of the material. Helium bubble evolution at high concentrations can result in blister formation or exfoliation and must therefore be well understood to predict the longevity of materials that absorb tritium. A hydrogen over-pressure must be applied to palladium hydride to prevent hydrogen from desorbing from the metal, making it difficult to study tritium in palladium by methods that involve vacuum, such as electron microscopy. Recent improvements in in-situ ion implantation Transmission Electron Microscopy (TEM) allow for the direct observation of He bubble nucleation and growth in materials. In this work, we present results from preliminary experiments using the new ion implantation Environmental TEM (ETEM) at the University of Huddersfield to observe He bubble nucleation and growth, in-situ, in palladium at cryogenic temperatures in a hydrogen environment. After the initial nucleation phase, bubble diameter remained constant throughout the implantation, but bubble density increased with implantation time. β-phase palladium hydride was not observed to form during the experiments, likely indicating that the cryogenic implantation temperature played a dominating role in the bubble nucleation and growth behavior.

Reduction in number of crystal defects in a p+Si diffusion layer by germanium and boron cryogenic implantation combined with sub-melt laser spike annealing

To reduce the number of crystal defects in a p+Si diffusion layer by a low-thermal-budget annealing process, we have examined crystal recovery in the amorphous layer formed by the cryogenic implantation of germanium and boron combined with sub-melt laser spike annealing (LSA). The cryogenic implantation at −150 °C is very effective in suppressing vacancy clustering, which is advantageous for rapid crystal recovery during annealing. The crystallinity after LSA is shown to be very high and comparable to that after rapid thermal annealing (RTA) owing to the cryogenic implantation, although LSA is a low-thermal-budget annealing process that can suppress boron diffusion effectively. It is also shown that in the p+Si diffusion layer, there is high contact resistance due to the incomplete formation of a metal silicide contact, which originates from insufficient outdiffusion of surface contaminants such as fluorine. To widely utilize the marked reduction in the number of crystal defects, sufficient removal of surface contaminants will be required in the low-thermal-budget process.

Boron diffusion layer formation using Ge cryogenic implantation with low-temperature microwave annealing

It is shown that a low-sheet-resistance p-type diffusion layer with a small diffusion depth can be fabricated efficiently by cryogenic boron and germanium implantation combined with low-temperature (400 °C) microwave annealing. Compared with the conventional annealing at 1000 °C, a much smaller diffusion depth is obtained at the same sheet resistance. The low sheet resistance at 400 °C is due to microwave absorption in the surface amorphous layer, which is formed by cryogenic germanium implantation. However, the pn junction leakage was worse than that in conventional annealing, because crystal defects remain near the amorphous/crystal interface after microwave annealing. It is found that the pn junction leakage is improved greatly by cryogenic germanium implantation. These results show that a suitable combination of cryogenic implantation and microwave annealing is very promising for p-type diffusion layer technology.

Enhanced Ge n+/p Junction Performance Using Cryogenic Phosphorus Implantation

In this paper, we present a detailed study of temperature-based ion implantation of phosphorus dopants in Ge for varying dose and anneal conditions through fabricated n+/p junctions and n-type MOSFETs (nMOSFETs). In comparison with room temperature (RT) (25 °C) and hot (400 °C) implantation, cryogenic (−100 °C) implantation with a dose of 2.2e15 $\mathrm{cm}^{-2}$ followed by a (400 °C) rapid thermal annealing leads to 1) lower junction leakage with higher activation energy and 2) lower sheet resistance with higher dopant activation and shallower junction depth. Gate-last Ge nMOSFETs fabricated using cryogenic implanted n+/p source/drain junction (2.2e15 $\mathrm{cm}^{-2}$ ) exhibit lower off-current (upto $5\times )$ and higher ON-current compared with RT (25 °C) and hot (400 °C) implanted nMOSFETs. This paper demonstrates that cryogenic implantation (−100 °C) can enable high-performance Ge nMOSFETs by alleviating the problems of lower activation and high diffusion of phosphorus in Ge.

High Performance 400 °C p+/n Ge Junctions Using Cryogenic Boron Implantation

We report high performance Ge p + /n junctions using a single, cryogenic (-100 °C) boron ion implantation process. High activation>4 × 10 20 cm -3 results in specific contact resistivity of 1.7 × 10 -8 Ω-cm 2 on p + -Ge, which is close to ITRS 15 nm specification (1 × 10 -8 Ω-cm 2 ) and nearly 4.5× lower than the state of the art (8 × 10 -8 Ω-cm 2 ). Cryogenic implantation is shown to enable solid-phase epitaxial regrowth and lower junction depth through amorphization of the surface Ge layer. These improvements in Ge p + /n junctions can pave the way for future high mobility Ge p-MOSFETs.

Reduction of surface roughness and defect density by cryogenic implantation of arsenic

A defect-free diffusion layer is found to be formed by the cryogenic ion implantation technique for arsenic dopants. The following thermal annealing completely recrystallizes amorphous layers through solid-phase growth, eliminating dislocation growth. Furthermore, substrate cooling drastically suppresses the melting of the substrate surface. It is considered that, owing to the ability to absorb thermal energy brought about by cooling the substrate, the number of local microvoids formed by vacancy clusters is reduced and interstitial clusters are not easily enlarged, leading to surface roughness reduction. The substrate-cooling technique is very effective for suppressing recrystallization bought about by the self-annealing effect, and it is a very effective technology not only for reducing the defect density but also for improving the Si/SiO2 interface state density.

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.

Germanium and Silicon: A Comparative Study of Hydrogenated Interstitial and Vacancy Defects by IR Spectroscopy

Vibration modes of cryogenically H-implanted germanium in the specific case of cryogenic implantation were detected by Fourier transform IR spectroscopy. Multiple internal reflection apparatuses were used; this optical configuration allowed enough sensitivity to detect small absorption bands. By making an analogy with the "well-known" silicon modes, hydrogenated interstitial and multivacancy defects and hydrogen-terminated were identified. The peaks at ( after annealing) and ( after annealing) can be attributed to modes in germanium, those at ( after annealing) and ( after annealing) to , those at ( after annealing) to , and those at to .

Ion implantation of semiconductors

Abstract Ion implantation was first applied to semiconductors over 30 years ago as a means of introducing controllable concentrations of n- and p-type dopants at precise depths below the surface. It is now an indispensable process in the manufacture of integrated circuits. This review gives a brief and selected overview of ion beam modification of semiconductors, treating both fundamental and technological issues of current interest. Damage introduction during ion irradiation and its removal during a thermal annealing step are key issues which are highlighted. Some semiconductors are easily damaged and amorphised (e.g. silicon) whereas others (e.g. gallium nitride) are quite resistant to damage production due to efficient dynamic defect annihilation during implantation. The conditions needed to remove implantation damage also vary dramatically from one semiconductor to another: amorphous layers in silicon can be recrystallised to completely remove disorder at ∼600°C, whereas extended defects in gallium nitride require temperatures of >1400°C to remove them. High dose implantation can result in the formation of supersaturated solid solutions, alloys and compounds, often with intriguing properties as a result of the non-equilibrium aspects of ion implantation. Formation of silicon dioxide layers directly during oxygen bombardment of silicon, even under cryogenic implantation conditions, is given as an example. From the standpoint of semiconductor technology, there are several current issues under intense study. Two of these are highlighted with respect to silicon technology: the problems of transient enhanced diffusion of dopants during low temperature annealing due to residual implantation-induced defects, and the need to remove extremely low concentrations of metals from active device regions. Finally, some recent novel applications of implantation in compound semiconductors are treated.

Temperature processing effects in proton-implantedn-type GaAs

Characterization of the effects of thermal processing on the optical and electronic properties of proton implantedn-type GaAs is reported in this paper. The thermal processing includes variations in the substrate temperature during implantation and postimplantation thermal annealing. Infrared reflectivity data indicate that the depths to which the optical changes extend in the as-implanted samples are greatest in the cryogenic implants. Carrier concentration profiles derived from capacitance-voltage measurements are shown to have significant differences depending upon processing history. Existence ofn-type surface layers are noted in high fluence level implants.