Depth profile characterization of ultra shallow junction implants

A need for analysis techniques, complementary to secondary ion mass spectrometry (SIMS), for depth profiling dopants in silicon for ultra shallow junction (USJ) applications in CMOS technologies has recently emerged following the difficulties SIMS is facing there. Grazing incidence X-ray fluorescence (GIXRF) analysis in the soft X-ray range is a high-potential tool for this purpose. It provides excellent conditions for the excitation of the B-K and the As-L _iii,ii shells. The X-ray standing wave (XSW) field associated with GIXRF on flat samples is used here as a tunable sensor to obtain information about the implantation profile because the in-depth changes of the XSW intensity are dependent on the angle of incidence. This technique is very sensitive to near-surface layers and is therefore well suited for the analysis of USJ distributions. Si wafers implanted with either arsenic or boron at different fluences and implantation energies were used to compare SIMS with synchrotron radiation-induced GIXRF analysis. GIXRF measurements were carried out at the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II using monochromatized undulator radiation of well-known radiant power and spectral purity. The use of an absolutely calibrated energy-dispersive detector for the acquisition of the B-Kα and As-Lα fluorescence radiation enabled the absolute determination of the total retained dose. The concentration profile was obtained by ab initio calculation and comparison with the angular measurements of the X-ray fluorescence.     

Modification of catheter materials by coating with polymer layers containing silver

The surface of polyurethane based catheter material or of silicon wafers as model surfaces were modified by spin coating of solutions of poly(ethylene oxide) or poly(vinyl alcohol) in water. For the incorporation of silver ions, silver nitrate was added to some of the solutions or the as-cast surfaces were dipped into AgNO₃ solution. Furthermore, samples coated with a thin layer of metallic silver were prepared by deposition of silver vapor in vacuum. The as-prepared surfaces were studied by atomic force microscopy and X-ray photoelectron spectroscopy. During the spin coating of the solutions containing AgNO₃, clusters of the silver component were formed. They were well dispersed in a poly(vinyl alcohol) matrix but act as nucleation agents in poly(ethylene oxide) where then large spherulites are formed. The surface compositions of coated samples and the depth profiling were carried out by angle dependent X-ray photoelectron spectroscopy.     

Applications of total reflection X-ray fluorescence spectrometry in trace element and surface analysis

Total reflection X-ray fluorescence spectrometry (TXRF) is presented as a genuine surface analytical technique. Its low information depth is shown to be the characteristic feature differentiating it from other energy dispersive X-ray fluorescence methods used for layer and surface analysis. The surface sensitivity of TXRF and its analytical capability together with the limitations of the technique are discussed here using typical applications including the contamination control of silicon wafers, thin layer analysis and trace element determination. For buried interfaces and implantation depth profiles in silicon a combination of TXRF and other techniques has been applied successfully. The TXRF method has the particular advantage of being calibrated without the need for standards. This feature is demonstrated for the example of the element arsenic.     

Industrial applications of instrumental neutron activation analysis

Neutron activation analysis is shown as a useful diagnostic technique in semiconductor industry. A better acceptance of the method for applications in industry has been achieved through a specialized analytical service. Its main application is the characterization of high purity silicon in all stages of production. Irradiation of large sample volumes allowes a very sensitive detection of impurities in silicon with detection limits down to 10^–16 g/g. Other applications discussed are the analysis of silicon carbide, quartz, pure water and titanium. Special techniques described are autoradiography, depth profiling and surface analysis. In semiconductor process technology NAA was used to monitor contamination of silicon wafers.     

TOF-SIMS depth profiling and element mapping on oxidized AlCrVN hard coatings

V-alloyed AlCrN hard coatings were deposited on silicon wafers (Si (100)) by reactive arc evaporation in a commercial coating system at 500 °C for 10 min, resulting in a coating thickness of ∼500 nm. The chemical composition of the stoichiometric coatings is constant at approximately Al_0.70Cr_0.05V_0.25N regardless of the applied bias voltage during deposition. Coatings synthesized at a low bias of −40 V show a dual-phase structure (hexagonal close-packed and face-centered cubic (fcc)), whereas coatings deposited at a high bias of −150 V have a metastable single-phase structure (face-centered cubic). All samples were oxidized for 15 min under 20 mbar O₂ atmosphere and at four different temperatures (550, 600, 650, and 700 °C). The oxidized coatings were subject to depth profiling and element mapping by a time of flight secondary ion mass spectrometry instrument, equipped with a Bi-cluster analysis gun and Cs⁺-sputter gun. The evaluation of the in-depth distribution of several elements and species points out distinctive differences in the oxidation behavior of the two different coatings, whereas element mapping shows the formation of islands made of oxidized vanadium and aluminum species as the top-most layer of the single-phase (fcc) coating at temperatures above 650 °C.     

Antireflective sol–gel TiO2 thin films for single crystal silicon and textured polycrystal silicon

In this paper, antireflective TiO₂ thin films have been prepared on single crystal silicon, and textured polycrystal silicon by sol–gel route using the dip-coating technique. The thickness and the refractive index of the films have been optimised to obtain low reflexion in the visible region, by controlling both the concentration of the titanium isopropoxide (Ti(ⁱOPr)₄), and the annealing temperature. We showed that the use of a TiO₂ single layer with a thickness of 64.5 nm, heat-treated at 450 or 300 °C, reduces the reflection on single crystal silicon at a level lower than 3% over the broadband spectral ranges 670–830 nm and 790–1010 nm, respectively. In order to broaden the spectral minimum reflectance as much as possible, we have proposed to texture polycrystal silicon wafers, and to coat these wafers by a TiO₂ single layer with a thickness of 73.4 nm. In this case, the reflectance has been reduced from 27 to 13% in the spectral range 460–1000 nm.     

Depth profiles of Al impurities implanted in Si wafers determined by means of the high-resolution grazing emission X-ray fluorescence technique

The synchrotron radiation based high-resolution grazing emission X-ray fluorescence (GEXRF) technique was used to extract the distribution of Al ions implanted with a dose of 10¹⁶ atoms/cm² in Si wafers with energies ranging between 1 and 100 keV. The depth distributions of the implanted ions were deduced from the measured angular profiles of the Al-Kα X-ray fluorescence line with nanometer-scale precision. The experimental results were compared to theoretical predictions of the depth distributions resulting from ion implantation. A good agreement between experiment and theory was found which proved that the presented high-resolution grazing emission X-ray fluorescence technique is well suited to perform depth profiling measurements of impurities located within the extinction depth, provided the overall shape of the distribution can be assumed a priori.     

Experimental shift allowance in the deconvolution of SIMS depth profiles

We study the deconvolution of the secondary ion mass spectrometry (SIMS) depth profiles of silicon and gallium arsenide structures with doped thin layers. Special attention is paid to allowance for the instrumental shift of experimental SIMS depth profiles. This effect is taken into account by using Hofmann's mixing‐roughness‐information depth model to determine the depth resolution function. The ill‐posed inverse problem is solved in the Fourier space using the Tikhonov regularization method. The proposed deconvolution algorithm has been tested on various simulated and real structures. It is shown that the algorithm can improve the SIMS depth profiling relevancy and depth resolution. The implemented shift allowance method avoids significant systematic errors of determination of the near‐surface delta‐doped layer position. Copyright © 2013 John Wiley & Sons, Ltd.     

Low energy X-ray radiation impact on coated Si constructions

Low energy X-ray radiation impact on the coated Si structures is discussed in this paper. Experimental sandwich structures consisting of amorphous hydrogenated a:C–H or SiO_x-containing DLC films were synthesized on Si 〈1 1 1〉 wafers using direct ion deposition method and exposed to low energy (medical diagnostic range) X-ray photons. Irradiation of samples was performed continuously or in sequences and protective characteristics of the irradiated DLC films were investigated. Experimental data were used as the input data for Monte Carlo modelling of X-ray scattering effects in the coated silicon constructions, which affect significantly the “signal to noise ratio” in DLC-coated Si structures proposed for their application in medical radiation detectors. Modelling results obtained in the case of DLC coatings were compared to the results of calculations performed for other commonly used combinations coating–detector material.The evaluation method of coated structures for their possible application in medical radiation detector constructions has been proposed in this paper. It is based on the best achieved compatibility between the appropriate mechanical characteristics, coating’s resistance against the radiation damage and the lowest estimated scattering to total dose ratio in the coated radiation sensitive volume.     

X-ray microanalysis of thin film layered specimens containing light elements

Analysis of thin film layers on bulk substrates is carried out using a technique based on the (z) model of the depth distribution of X-ray emission. Both the composition and thickness of individual layers can be determined provided that the same element is not present in more than a single layer.The application of this method to the analysis of thin titanium-boron nitride bilayers on silicon or molybdenum substrates is discussed. X-ray intensities were measured by energy dispersive spectroscopy with a windowless or ultra thin window detector. The thickness of a 10 nm titanium layer could be estimated to within about ±1 nm, which is comparable with the depth resolution attainable by Auger sputter profiling.     

Replica multichannel polymer chips with a network of sacrificial channels sealed by adhesive printing method

Replica microchips for capillary array electrophoresis containing 10 separation channels (50 microm width, 50 microm depth and 100 microm pitch) and a network of sacrificial channels (100 microm width and 50 microm depth) were successfully fabricated on a poly(methyl methacrylate) (PMMA) substrate by injection molding. The strategy involved development of moving mask deep X-ray lithography to fabricate an array of channels with inclined channel sidewalls. A slight inclination of channel sidewalls, which can not be fabricated by conventional deep X-ray lithography, is highly required to ensure the release of replicated polymer chips from a mold. Moreover, the sealing of molded PMMA multichannel chips with a PMMA cover film was achieved by a novel bonding technique involving adhesive printing and a network of sacrificial channels. An adhesive printing process enables us to precisely control the thickness of an adhesive layer, and a network of sacrificial channels makes it possible to remove air bubbles and an excess adhesive, which are crucial to achieving perfect sealing of replica PMMA chips with well-defined channel and injection structures. A CCD camera equipped with an image intensifier was used to simultaneously monitor electrophoretic separations in ten micro-channels with laser-induced fluorescence detection. High-speed and high-throughput separations of a 100 bp DNA ladder and phi X174 Hae III DNA restriction fragments have been demonstrated using a 10-channel PMMA chip. The current work establishes the feasibility of mass production of PMMA multichannel chips at a cost-effective basis.     

Nanometric resolution in glow discharge optical emission spectroscopy and Rutherford backscattering spectrometry depth profiling of metal (Cr,Al) nitride multilayers

In this work, we address the capability of glow discharge optical emission spectroscopy (GDOES) for fast and accurate depth profiling of multilayer nitride coatings down to the nanometer range. This is shown by resolving the particular case of CrN/AlN structures with individual thickness ranging from hundreds to few nanometers. In order to discriminate and identify artefacts in the GDOES depth profile due to the sputtering process, the layered structures were verified by Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM). The interfaces in the GDOES profiles for CrN/AlN structures are sharper than the ones measured for similar metal multilayers due to the lower sputtering rate of the nitrides. However, as a consequence of the crater shape, there is a linear degradation of the depth resolution with depth (approximately 40 nm/μm), saturating at a value of approximately half the thickness of the thinner layer. This limit is imposed by the simultaneous sputtering of consecutive layers. The ultimate GDOES depth resolution at the near surface region was estimated to be of 4–6 nm.     

Surface interpenetrating networks of polyacrylamide in poly(ethylene terephthalate) as a means of surface modification

Surface interpenetrating network (IPN) polymers are emerging hybrid materials in which the surface of existing polymers can be modified to preserve their chemical structure and bulk properties. A detailed structural characterization of poly(ethylene terephthalate) (PET) thin films on nanoscopically flat silicon wafers has been carried out by Scanning Probe Microscopy (SPM) and X-ray photoelectron spectroscopy (XPS). Examination of the surface of spin-coated annealed PET film by the SPM in tapping mode revealed a two-phase structure. One phase appeared as a dense crystalline fraction of the polymer while the other was identified as amorphous. These findings were supported by Differential Scanning Calorimetry (DSC), which recognized the crystallinity of annealed PET film at 30%. Modification of the PET surface with interpenetrating polyacrylamide (PAM) increased the roughness of the surface with uniform properties. The depth profiling with XPS revealed that PAM interpenetration extended down to 7.2 nm, confirming a three-dimensional character of the polymer modification, with a relative mass concentration of PAM at about 30.7% in the IPN interface.     

Atomic and electronic structure of the surface of porous silicon layers

Atomic and electronic structure of the surface layers of porous silicon was studied by the methods of the near fine structure spectroscopy at the edge of X-ray absorption and ultrasoft X-ray emission spectroscopy. The thickness of the oxide layer and the degree of distortion of silicon-oxygen tetrahedra in this layer were estimated. The thickness of the surface oxide layer on the amorphous layer covering the nanocrystals of porous silicon that was kept during one year is several times greater than the thickness of the natural oxide in the single crystal silicon wafers. Distortion of the silicon-oxygen tetrahedron, the basic structural units of the silicon oxide, is accompanied by elongation of Si-O bonds and an increase in the Si-O-Si bond angles.     

100 Jahre Einkristallzucht aus der Schmelze

Cars, television, mobile phones, digital cameras, cash machines: Daily life is strongly affected by microchips produced from high purity silicon single crystals via thin wafers. Most of these single crystals are prepared by a process invented by the German‐Polish scientist Jan Czochralski in 1916 in the “Kabelwerk Oberspree (KWO)” of the “Allgemeine Elektricitätsgesellschaft (AEG)” in Berlin‐Oberschöneweide. Czochralski discovered the famous method to pull single crystals by accident: Deep in thought, he dipped his pen not into an ink pot but into a crucible with liquid tin, both standing next to one another on his desk. Quickly he pulled his pen out and observed a thin thread of tin emerging from the tip. After etching, the thread was identified as a single crystal of tin. This observation is probably one of the most important technical inventions of the first half of the 20^th century. In 1917, he left the AEG in Berlin and worked in the metal research laboratory, later belonging to the “Metallgesellschaft”, in Frankfurt/Main. Until today, wafers of high‐purity silicon are prepared by the Czochralski method. Silicon wafers with 200 mm diameter were produced in 1990, 300 mm wafers in 2001. The production of wafers with 450 mm diameter was expected for 2016. Siltronic produced in 2009 the first dislocation‐free silicon single crystal with 450 mm diameter, and other companies followed. However, until now, the 450 mm technology is not standard. This is due to a combination of very high investment costs needed to establish the 450 mm technology and very low prices of microchips.     

Fabrication of arrays of sub-20-nm silica walls via photolithography and solution-based molecular coating

We report herein fabrication of arrays of sub-20-nm silica walls via photolithography and the surface sol-gel process. A photolithographically fabricated line template on a silicon wafer was coated with a silica nanolayer using the surface sol-gel process, and then the topmost portion of the silica layer and the template were successively removed using CHF(3) and oxygen plasma, respectively, leaving the sidewalls of the silica layers remaining on the substrate. These walls were fully self-supporting, and the thicknesses of silica wall were 6, 8, and 12 nm at 20, 30, and 60 cycles, respectively. The height/width ratio of the wall was 38 at the 30-cycle coating. This ratio is surprisingly high when compared to that of the conventional photolithography processes. Successive formation of the silica, polymer, and silica layers yielded a trilayer sidewall, and the spacer polymer layer could be selectively removed to form a doubled sidewall. Size reduction and proliferation of sub-20-nm silica wall was thus achieved. The reported method is simple and cost-efficient and opens a gateway to further miniaturization of nanostructures.     

Simple,Rapid, and Large-Scale Fabrication of Multi-Branched Hydrogels Based on Viscous Fingering for Cell Culture Applications

Hydrogels are widely used in cell culture applications. For fabricating tissues and organs, it is essential to produce hydrogels with specific structures. For instance, multiple-branched hydrogels are desirable for the development of network architectures that resemble the biological vascular network. However, existing techniques are inefficient and time-consuming for this application. To address this issue, a simple, rapid, and large-scale fabrication method based on viscous fingering is proposed. This approach utilizes only two plates. To produce a thin solution, a high-viscosity solution is introduced into the space between the plates, and one of the plates is peeled off. During this procedure, the solution's high viscosity results in the formation of multi-branched structures. Using this strategy, 180 mm × 200 mm multi-branched Pluronic F-127 hydrogels are successfully fabricated within 1 min. These structures are used as sacrificial layers for the fabrication of polydimethylsiloxane channels for culturing human umbilical vein endothelial cells (HUVECs). Similarly, multi-branched Matrigel and calcium (Ca)-alginate hydrogel structures are fabricated, and HUVECs are successfully cultured inside the hydrogels. Also, the hydrogels are collected from the plate, while maintaining their structures. The proposed fabrication technique will contribute to the development of network architectures such as vascular structures in tissue engineering.     

Structure and dielectric properties of HfO<Subscript>2</Subscript> films prepared by a sol–gel route

Mono- and multilayer HfO₂ sol–gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 °C for 0.5 h (after drying at 100 °C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 °C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 °C the films are totally crystallized. The HfO₂ grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO₂ layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.     

AFM study of defect-induced depressions of the smectic-A/air interface

The smectic-A/air interface of liquid-crystal droplets with antagonistic boundary conditions is studied by atomic force microscopy (AFM). The droplets are prepared on coated silicon wafers on which a planar alignment is preferred in contrast to the homeotropic alignment at the air interface. As a result, focal conic defects appear in the smectic-A phase causing a characteristic pattern of depressions in the droplet surface. The dimensions of the defect-induced depressions are measured by AFM as a function of temperature for two different compounds possessing a smectic-A-isotropic and a smectic-A-nematic transition. Whereas the results are independent of temperature in the smectic-A-isotropic case, reflecting the first-order nature of the transition, a pronounced temperature dependence is observed for the second compound, where the depth of the defect-induced depressions decreases continuously with increasing temperature and vanishes at the second-order transition to the nematic phase. These observations can be qualitatively explained through the behavior of the layer compressional elastic constant at the smectic-A-nematic transition.     

Investigation of infill-patterns on mechanical response of 3D printed poly-lactic-acid

This paper presents the effect of infill patterns (IPs) on the mechanical response of 3D printed specimens by conducting the low-velocity impact test (LVI) and compression test. The poly-lactic acid (PLA, purity 98 wt% >) material has selected and printed using fused deposition modeling (FDM, speed 20 mm/s, layer height 0.2 mm, no of layers 30, extruded at 200 °C) with four different IPs: triangle, grid, quarter cubic, and tri-hexagon. The LVI test on velocity-time, energy-time and force-displacement, and the compression responses have examined and presented in this study. The LVI test was carried out to determine the penetration energy level, energy absorption capacity (toughness), stiffness, and strength of PLA porous parts (60% infill density) for implant/tissue/recyclable product applications. The results have shown that the triangular pattern has produced the highest absorbed energy in LVI test (penetration energy 7.5 J, and stiffness 668.82 N/mm) due to more sheared/contact layers’ perpendicular to impactor (hemispherical insert); while the grid pattern exhibited the highest compressive strength (72 MPa) due to more layers aligned along the compressive loading direction The SEM fracture surface image of Triangular IP has produced effective raster and layer bonding, less number of voids, more amount of circular beach markings, and absence of ratchet lines leading to possess improved mechanical properties.