Janusz Bogdanowicz

Active dopant characterization methodology for germanium

In order to reach the ITRS goals for future complementary metal-oxide semiconductor technologies there is a growing interest in using germanium as an alternative substrate material in view of its higher mobility. Different species and thermal budgets are presently being investigated in order to determine the most likely candidates for the required junction formation. A key issue is the accurate determination of the achievable electrical activation, i.e., the reliable measurement of the sheet resistance and electrical depth profile. In order to be applicable to Ge-based junctions, standard techniques such as the spreading resistance probe and scanning spreading resistance microscopy (SSRM) need to be reevaluated in terms of their performance and operational conditions. First, the significantly different behavior of germanium calibration curves (versus silicon) will be discussed. Next, the shape and characteristics of the probe imprints (Ge is softer than Si) and the differences in raw data behavior will be...

Light absorption in conical silicon particles

The problem of the absorption of light by a nanoscale dielectric cone is discussed. A simplified solution based on the analytical Mie theory of scattering and absorption by cylindrical objects is proposed and supported by the experimental observation of sharply localized holes in conical silicon tips after high-fluence irradiation. This study reveals that light couples with tapered objects dominantly at specific locations, where the local radius corresponds to one of the resonant radii of a cylindrical object, as predicted by Mie theory.

Advances in optical carrier profiling through high-frequency modulated optical reflectance

As indicated by the ITRS roadmap, obtaining accurate information on the electrically active dopant profile for sub-30-nm structures is a key issue. Presently, however, there is no conventional, probe-based (destructive) technique available satisfying the ITRS targeted depth (3%) and carrier level (5%−10%) reproducibility and accuracy. In this work, the authors explore the promising capabilities of nondestructive photomodulated optical reflectance (PMOR) techniques, based on the localized (micrometer beam size) detection of variations in the reflectivity of the sample, due to thermal and plasma (excess carrier) effects as can be generated by a modulated pump laser such as the Therma-Probe® (TP) system. Earlier and more recent work using low modulation (1 kHz) frequencies has shown that it is possible, but rather tedious, to extract the electric junction depth (at about 1018 cm−3) and carrier concentration of chemical vapor deposition grown (CVD) (boxlike) structures based on so-called power curves (where t...

Nondestructive extraction of junction depths of active doping profiles from photomodulated optical reflectance offset curves

The ITRS Roadmap highlights the electrical characterization of the source and drain extension regions as a key challenge for future complimentary-metal-oxide-semiconductor technology. Presently, an accurate determination of the depth of ultrashallow junctions can routinely only be performed by time-consuming and destructive techniques such as secondary ion mass spectrometry (SIMS). In this work, the authors propose to use the fast and nondestructive photomodulated optical reflectance (PMOR) technique , as implemented in the Therma-Probe® (TP) dopant metrology system, for these purposes. PMOR is a pump-probe technique based on the measurement of the pump-induced modulated change in probe reflectance, i.e., the so-called (photo) modulated reflectance. In this article, the authors demonstrate that the absolute junction depths of boxlike active dopant structures can be extracted in a very simple and straightforward way from the TP offset curves, which represent the behavior of the modulated reflectance as a f...

Photovoltage versus microprobe sheet resistance measurements on ultrashallow structures

Earlier work [T. Clarysse et al., Mater. Sci. Eng., B 114–115, 166 (2004); T. Clarysse et al., Mater. Res. Soc. Symp. Proc. 912, 197 (2006)] has shown that only few contemporary tools are able to measure reliably (within the international technology roadmap for semiconductors specifications) sheet resistances on ultrashallow (sub-50-nm) chemical-vapor-deposited layers [T. Clarysse et al., Mater. Res. Soc. Symp. Proc. 912, 197 (2006)], especially in the presence of medium/highly doped underlying layers (representative for well/halo implants). Here the authors examine more closely the sheet resistance anomalies which have recently been observed between junction photovoltage (JPV) based tools and a micrometer-resolution four-point probe (M4PP) tool on a variety of difficult, state-of-the-art sub-32-nm complementary metal-oxide semiconductor structures (low energy and cluster implants, with/without halo, flash- and laser-based millisecond anneal). Conventional four-point probe tools fail on almost all of thes...

Electrothermal theory of photomodulated optical reflectance on active doping profiles in silicon

The electrical characterization of the source and drain extension regions of complementary metal oxide semiconductor (CMOS) transistors is highlighted in the international technology roadmap for semiconductors (ITRS) as a major challenge for future technology nodes. In practice, there is a clear need for techniques which are simultaneously accurate, nondestructive, fast, local, and highly reproducible. The photomodulated optical reflectance (PMOR) technique has shown to be a very promising candidate to solve this need. However, even though this technique has been widely studied on homogeneous bulk material and on as-implanted (i.e., unannealed) doping profiles, the extension toward active doping profiles requires a detailed investigation (due to the presence of a built-in electric field). In this paper, after performing an in-depth investigation of the optical and transport models involved in a PMOR experiment, we derive an analytical theory to explain the PMOR signal behavior observed on active doping pr...

Atom probe tomography analysis of SiGe fins embedded in SiO2: Facts and artefacts

We present atom probe analysis of 40nm wide SiGe fins embedded in SiO2 and discuss the root cause of artefacts observed in the reconstructed data. Additionally, we propose a simple data treatment routine, relying on complementary transmission electron microscopy analysis, to improve compositional analysis of the embedded SiGe fins. Using field evaporation simulations, we show that for high oxide to fin width ratios the difference in evaporation field thresholds between SiGe and SiO2 results in a non-hemispherical emitter shape with a negative curvature in the direction across, but not along the fin. This peculiar emitter shape leads to severe local variations in radius and hence in magnification across the emitter apex causing ion trajectory aberrations and crossings. As shown by our experiments and simulations, this translates into unrealistic variations in the detected atom densities and faulty dimensions in the reconstructed volume, with the width of the fin being up to six-fold compressed. Rectification of the faulty dimensions and density variations in the SiGe fin was demonstrated with our dedicated data treatment routine.

On the interplay between relaxation, defect formation, and atomic Sn distribution in Ge(1−x)Sn(x) unraveled with atom probe tomography

Ge(1−x)Sn(x) has received a lot of interest for opto-electronic applications and for strain engineering in advanced complementary-metal-oxide-semiconductor technology, because it enables engineering of the band gap and inducing strain in the alloy. To target a reliable technology for mass application in microelectronic devices, the physical problem to be addressed is to unravel the complex relationship between strain relaxation (as induced by the growth of large layer thicknesses or a thermal anneal) and defect formation, and/or stable Sn-cluster formation. In this paper, we study the onset of Sn-cluster formation and its link to strain relaxation using Atom Probe Tomography (APT). To this end, we also propose a modification of the core-linkage [Stephenson et al., Microsc. Microanal. 13, 448 (2007)] cluster analysis method, to overcome the challenges of limited detection efficiency and lateral resolution of APT, and the quantitative assessment for very small clusters (<40 atoms) embedded in a random distr...

Impact of band gap narrowing and surface recombination on photoelectrothermal modulated optical reflectance power curves

Photomodulated optical reflectance is a well established technique for surface and near surface characterizations. In this work, the nonlinear behavior of the differential reflectance as a function of the pump irradiance (104–106W∕cm2) is studied on uniformly and nonuniformly (p‐n∕p+‐p junctions) doped silicon structures, with a particular emphasis on the impact of band gap narrowing (BGN) and of surface recombination velocities (SRVs). We show that the BGN induced by the presence of excess carriers substantially influences the excess carrier profile. We also explain the unexpected shape of power curves on lowly doped substrate by a time-dependent variation of the SRVs during illumination.

Nanofocusing of light into semiconducting fin photonic crystals

This letter demonstrates experimentally and investigates theoretically the possibility for enhanced light coupling into periodic arrays of nanoscale semiconducting fins. Using Raman spectroscopy, we show that an electromagnetic field impinging upon such periodic structures can be confined into the semiconducting regions when the ratio W/λ0 of the fin width to the incident wavelength is sufficiently small and when the incident light polarization is parallel to the fin edges. As we demonstrate based on band structure calculations and finite-element simulations, this corresponds to the availability and excitation of a dielectric-band mode of the constituted photonic crystal waveguide, i.e., a mode guided inside the semiconducting fins. The understanding of this nanofocusing behavior opens the way to a plethora of applications including the optical metrology of deep-subwavelength non-planar semiconductor devices.