Cedric Huyghebaert

Fabrication and analysis of a Si/Si0.55Ge0.45 heterojunction line tunnel FET

This paper presents a new integration scheme to fabricate a Si/Si0.55Ge0.45 heterojunction line tunnel field effect transistor (TFET). The device shows an increase in tunneling current with gate length. The 1- μm gate length device shows on current in excess of 20 μA/μm at VGS=VDS=1.2 V. Low-temperature measurements, performed to suppress trap-assisted tunneling (TAT), reveal the point subthreshold swing as low as 22 mV/dec at 78 K. Field-induced quantum confinement effects are found to increase the tunneling onset voltage by ~ 0.35 V. Variation of the tunneling onset voltage measured experimentally is correlated to variation in the pocket thickness and its doping concentration. Small geometry devices were found to be more susceptible to microvariations in the pocket thickness and doping concentration.

EUV lithography imaging using novel pellicle membranes

EUV mask protection against defects during use remains a challenge for EUV lithography. A stand-off protective membrane – a pellicle – is targeted to prevent yield losses in high volume manufacturing during handling and exposure, just as it is for 193nm lithography. The pellicle is thin enough to transmit EUV exposure light, yet strong enough to remain intact and hold any particles out of focus during exposure. The development of pellicles for EUV is much more challenging than for 193nm lithography for multiple reasons including: high absorption of most materials at EUV wavelength, pump-down sequences in the EUV vacuum system, and exposure to high intensity EUV light. To solve the problems of transmission and film durability, various options have been explored. In most cases a thin core film is considered, since the deposition process for this is well established and because it is the simplest option. The transmission specification typically dictates that membranes are very thin (~50nm or less), which makes both fabrication and film mechanical integrity difficult. As an alternative, low density films (e.g. including porosity) will allow thicker membranes for a given transmission specification, which is likely to improve film durability. The risk is that the porosity could influence the imaging. At imec, two cases of pellicle concepts based on reducing density have been assessed : (1) 3D-patterned SiN by directed self-assembly (DSA), and (2) carbon nanomaterials such as carbon nanotubes (CNT) and carbon nanosheets (CNS). The first case is based on SiN membranes that are 3D-patterned by Directed Self Assembly (DSA). The materials are tested relative to the primary specifications: EUV transmission and film durability. A risk assessment of printing performance is provided based on simulations of scattered energy. General conclusions on the efficacy of various approaches will provided.

VO2, a Metal-Insulator Transition Material for Nanoelectronic Applications

Nanoelectronic Applications K. Martens, I. P. Radu, G. Rampelberg, J. Verbruggen, S. Cosemans, S. Mertens, S. Xiaoping, M. Schaekers, C. Huyghebaert, C. Detavernier, S. De Gendt, M. Heyns, J. Kittl a IMEC, Kapeldreef 75, Leuven, Belgium b ESAT Dept., KULeuven, Leuven, Belgium c Physics Dept., K. U. Leuven, Leuven, Belgium d Dept. of Solid State Sciences, UGent, Gent, Belgium e Chemistry Dept. KULeuven f Materials Engineering Dept., KULeuven

Properties and performance of EUVL pellicle membranes

EUV mask protection during handling and exposure remains a challenge for high volume manufacturing using EUV scanners. A thin, transparent membrane can be mounted above the mask pattern so that any particle that falls onto the front of the mask is held out of focus and does not image. The fluoropolymer membranes that are compatible with 193nm lithography absorb too strongly at the 13.5nm EUV exposure wavelength to be considered. Initially, the industry planned to expose EUV masks without any pellicle; however, the time and cost of fabricating and qualifying an EUV mask is simply too high to risk decimating wafer yield each time a particle falls onto the mask pattern. Despite the challenges of identifying a membrane for EUV, the industry has returned to the pellicle concept for protection. EUVL pellicles have been in development for more than a decade and reasonable options exist. Meeting all pellicle requirements is difficult, so this type of risk-mitigation effort is needed to ensure that there is a viable high-volume manufacturing option. This paper first reviews the desired membrane properties for EUVL pellicles. Next, candidate materials are introduced based on reported properties and compatibility with fabrication. Finally a set of candidate membranes are fabricated. These membranes are screened using a simplified set of tests to assess their suitability as an EUV pellicle. EUV transmission, film stress, and film durability data are included. The results are presented along with general guidelines for pellicle membrane properties for EUV manufacturing.

Capacitive actuation and switching of add–drop graphene-silicon micro-ring filters

We propose and experimentally demonstrate capacitive actuation of a graphene–silicon micro-ring add/drop filter. The mechanism is based on a silicon–SiO2–graphene capacitor on top of the ring waveguide. We show the capacitive actuation of the add/drop functionality by a voltage-driven change of the graphene optical absorption. The proposed capacitive solution overcomes the need for continuous heating to keep tuned the filter’s in/out resonance and therefore eliminates “in operation” energy consumption.

SHG/2PF microscopy of single and multi-layer graphene

Since the discovery of graphene in 2004 by Novoselov and Geim, a lot of research emphasis has been directed towards its characterization. Most of the important scientific breakthroughs have been obtained on exfoliated graphene (produced via the well known ‘scotch tape’ method), nowadays, different synthetic routes have been developed to obtain largescale graphene. Among several optical techniques, Raman spectroscopy is the one most often employed to characterize the defects, number of graphene layers and other properties of the graphitic films regardless of their fabrication method. In this work, we will report on the microscopic imaging of the two-photon fluorescence (2PF) properties and the second harmonic generation (SHG) in both single layer and few layer graphene.

CNTs in the context of EUV pellicle history

In the early 2000s, membranes both thin enough to transmit EUV light and strong enough to be free-standing at mask dimensions did not exist. The lithography community assumed that defect control for photomasks would be achieved, not with a pellicle, but with a clean scanner environment, thermophoretic protection and a removable pellicle.1 In 2006, Intel published their research on an EUV pellicle.2 Since then, an international development effort on EUV pellicle membranes has spanned a range of materials and fabrication approaches. Not only materials, but also the requirements of the EUV pellicle membrane have evolved over time. Imec’s pellicle work based on carbon nanotubes (CNTs) started in 2015, and is placed in relation to the rich history of EUV pellicles. CNTs are one-atom-thick carbon sheets rolled into tubes. The CNTs can be single- or multi-walled and can vary in diameter and in length. These engineered CNTs can be arranged in different configurations to form membranes of different densities. Thus, the CNT membrane’s properties can be fundamentally changed to meet the EUV pellicle targets for properties like transmittance. The historical trends in EUV pellicle membrane development are presented and the CNT membranes are described in that context.

New materials for modulators and switches in silicon photonics (Conference Presentation)

In this presentation we will report on our recent work on new materials that can be monolithically integrated on high-index contrast silicon or silicon nitride photonic ICs to enhance their functionality. This includes graphene and other 2D-materials for realizing compact electro-absorption modulators and non-linear devices, ferroelectric materials for realizing phase modulators and adiabatic couplers for realizing bistable switches.

Novel membrane solutions for the EUV pellicle: better or not?

A protective membrane – a pellicle – must be used to prevent yield loss during EUV lithography exposure, just as it was for 193nm lithography. The pellicle must be thin enough to transmit EUV light, yet strong enough to withstand the scanner environment. Membrane solutions for ~ 80W exposure exist. Our focus is developing a membrane solution for 250W exposure power. The main pellicle challenge here is still the identification of a membrane material that has very high transmission at EUV wavelengths. Additionally, absorption during lithographic exposure results in high thermal and mechanical load for the pellicle, which can cause yield problems. The current candidates for pellicle membranes such as poly-silicon and silicon nitride cannot withstand 250W power conditions, therefore alternative materials will be required for the future HVM pellicle. At imec, a variety of novel membrane material options are investigated for the HVM pellicle application. One promising approach is based on carbon nanotubes (CNT). In this paper we outline different CNT based process options, and report results on their optical, thermal, and mechanical performance. In addition, we will report on their uniformity and robustness towards scanner application. Finally, the family of CNT-based membrane options will be compared to promising candidates fabricated using conventional film approaches that do not have a CNT layer.

CNT EUV pellicle: moving towards a full-size solution

Development of a pellicle membrane to protect the reticle from particles for EUV source powers beyond 250 W is a subject of intensive research and is in great demand to support high volume manufacturing with EUV lithography. Identifying a membrane with high EUV transmission, mechanical integrity, thermal stability and chemical resistance within the scanner environment is extremely challenging; yet these properties are required to realize next-generation EUV pellicle solutions. This paper proposes free-standing carbon nanotube (CNT) film as an alternative next generation core pellicle material. Most of the desired pellicle characteristics can be achieved by tuning the properties of freestanding CNT films. We demonstrate that free-standing CNT films possess very high EUV transmission (up to 99%) and good transmission uniformity (0.4% half range), mechanical stability (maximum deflection ~0.08 mm at 2 Pa), thermal stability (no change under greater than 500 W equivalent EUV exposure in vacuum without hydrogen radicals) and scalability to a full pellicle size. Other important CNT membrane properties are presented and are favourable for the pellicle application: low EUV scattering, low EUV reflectivity and high transmission under DUV. The ability of the CNT film to stop particles is analysed. The only known failure of the CNT membrane is instability to hydrogen radical/ion environment within the current reticle chamber of the scanner. If changing that environment to limit hydrogen radicals near the pellicle surface is not an option, there is a need to coat the CNT structures for protection. The challenges and considerations for coating the free-standing CNT membranes are discussed.