Si Multilayers Research Articles

Phase change observation in reflection multilayers by total electron yield and reflection spectra

Precise optical elements for use in the extreme ultraviolet region are necessary for controlling both the uppermost layer thickness and the reflection phase in a reflection multilayer system. In this study, a phase value corresponding to both the uppermost layer thickness and the reflection phase was derived from the reflectance and total electron yield (TEY) intensity. Mo∕Si multilayers were fabricated on a silicon wafer with various thicknesses of the uppermost Mo layer. Phase values obtained from the reflection and TEY measurements were found to change in accordance with increases in the thickness of the uppermost Mo layer and a concomitant change in the reflection phase.

High-speed strained-single-crystal-silicon thin-film transistors on flexible polymers

We fabricate thin-film transistors (TFTs) on both strained and unstrained single-crystal Si membranes transferred to flexible-polymer substrates. The active layer is transferred from the starting silicon on insulator (SOI) using a simple, fast, and reliable dry-printing method. When a multilayer Si∕SiGe∕Si structure is pseudomorphically grown on SOI and the buried oxide is selectively removed, strained Si with a negligible density of dislocations is achieved via elastic strain sharing between the SiGe alloy layer and the Si layers. Both the drain current and the transconductance of TFTs fabricated on this strained Si∕SiGe∕Si membrane after its transfer to the flexible polymer are much higher than of TFTs fabricated on the unstrained-Si counterpart.

Temperature effects on the magnetic properties of antiferromagnetically coupled amorphous Co0.74Si0.26/Si multilayers

AbstractThe effect of temperature on the magnetic properties of antiferromagnetically coupled amorphous Co0.74Si0.25/Si multilayers has been investigated by Magneto‐Optical Transverse Kerr Effect and Superconducting Quantum Interference Device. The studied temperature range has been varied between 5 K (15 K for Kerr loops) and room temperature. The results show that the Curie temperature of the multilayers is close to room temperature and that the antiferromagnetic exchange coupling can only be detected at temperatures close to the Curie temperature. When the temperature is decreased, the coercive field of the single films composing the multilayer increases, masking the antiferromagnetic coupling below 250 K. Field‐Cooling and Zero‐Field‐Cooling measurements suggest the presence of a small superparamagnetic contribution. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal stability of nanoscale silver metallization in Ag/W/Co/Si(100) multilayer

Abstract In this work, we have studied thermal stability of nanoscale Ag metallization and its contact with CoSi2 in heat-treated Ag(50 nm)/W(10 nm)/Co(10 nm)/Si(1 0 0) multilayer fabricated by sputtering method. To evaluate thermal stability of the systems, heat-treatment was performed from 300 to 900 °C in an N2 ambient for 30 min. All the samples were analyzed by four-point-probe sheet resistance measurement (Rs), Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and atomic force microscopy (AFM). Based on our data analysis, no interdiffiusion, phase formation, and Rs variation was observed up to 500 °C in which the Ag layer showed a (1 1 1) preferred crystallographic orientation with a smooth surface and Rs of about 1 Ω/□. At 600 °C, a sharp increase of Rs value was occurred due to initiation of surface agglomeration, WSi2 formation, and interdiffusion between the layers. Using XRD spectra, CoSi2 formed at the Co/Si interface preventing W silicide formation at 750 and 800 °C. Meantime, RBS analysis showed that in this temperature range, the W acts as a cap layer, so that we have obtained a W encapsulated Ag/CoSi2 contact with a smooth surface. At 900 °C, the CoSi2 layer decomposed and the layers totally mixed. Therefore, we have shown that in Ag/W/Co/Si(1 0 0) multilayer, the Ag nano-layer is thermally stable up to 500 °C, and formation of W-capped Ag/CoSi2 contact with Rs of 2 Ω/□ has been occurred at 750–800 °C.

3-D Integration Technology for High Performance Detector Arrays

ABSTRACTThis paper describes a technology for three-dimensional (3-D) integration of multiple layers of silicon integrated circuits. The technology promises to dramatically enhance on-chip signal processing capabilities of a variety of detector devices hybridized with Si electronics. The focus of the paper is on high performance infrared focal plane arrays based on HgCdTe, which offer the ultimate in infrared sensitivity and find application in high performance military systems. Performance data from test FPA devices with integrated multilayer Si stacks are discussed in this paper.

Strain-induced ordering of small Ge islands in clusters at the surface of multilayered Si–Ge nanostructures

Classical molecular-dynamics simulations based on the Tersoff potential are used to compute at the atomic level the strain-induced potential well generated at the surface of the capping layer by a buried, three-dimensional Ge island on Si(001). A simple model is outlined in order to predict the configurational arrangement for the nucleation of small Ge islands in such a potential well. The theoretical predictions are compared with atomic force microscope images of multilayered SiGe nanostructures grown by chemical vapor deposition. The cluster configuration is shown to be strongly dependent on the capping layer thickness, and to closely mimic the behavior predicted by the model.

Depth-graded multilayers for application in transmission geometry as linear zone plates

Fresnel zone plates for x-ray focusing optics are typically made using lithographic techniques. To achieve optimum efficiency for hard x rays, a depth of several microns is required, which limits the minimum zone width and hence minimum focal spot size achievable using lithography. We are exploring the fabrication of zone plates by an alternative technique that surmounts these limitations: the growth of a multilayer film to be used in transmission (Laue) diffraction geometry, in which the thickness of consecutive layers gradually increases according to the Fresnel zone formula; the film is sectioned after growth to the required depth. For a planar multilayer, this produces a linear zone plate that can focus x rays in one dimension. Here we report the growth and characterization of a depth-graded multilayer suitable for use as a zone plate for hard x-ray focusing. The multilayer has a total of 470 alternating layers of WSi2 and Si with thicknesses increasing monotonically from 15 to 60 nm, for a total thickness of 11.33μm. One of the major challenges is to understand and select the right material system for this kind of thick multilayer. We have found that WSi2∕Si is a promising system. A comparison between WSi2∕Si and W∕Si multilayers is presented.

Investigation of multilayer structural changes in phase and amplitude-defects correction process

Controlling defects on the extreme ultraviolet lithography (EUVL) mask has become a critical issue among many EUVL element technologies. We have conducted experiments to investigate the correctability of two kinds of major defect types, phase and amplitude defects. Phase defects correctability was addressed by using the electron-beam local heating method and amplitude defects correctability were done by using the focused ion-beam (FIB). Additionally, two kinds of multilayers, Mo∕Si and Mo∕Ru∕Si, were used as substrates to inspect the behavior in a comparative way. As a result, the sink brought by electron-beam (e-beam) localized heating on a planar multilayer surface was about 8 and 13.6 nm in Mo∕Si and Mo∕Ru∕Si multilayers, respectively, under the e-beam dose of 250μC∕cm2. However, the heating effect was limited to within a few layers from the surface. FIB etching was also conducted on a planar surface of a multilayer. There are two types of FIB correction methods, image mode and spot mode. The etched area was relatively large (∼3μm×3μm) in image mode. But in the spot mode, the etched area could be confined to a few tens of nanometers in diameter. This FIB method also caused some damage on the multilayer surface.

Angle-dependent photovoltaic effect in Al–Si multilayers

Al–Si multilayer stacks have been prepared by an alloying process from aluminum and silicon platelets. Irradiation of a stack with infrared to visible laser radiation generates photovoltaic signals depending on the angle of incidence of the laser beam with respect to the layer planes, with zero signal and a polarity reversal for beam and layers in parallel. Results are explained in terms of photoactive layers connected in series and symmetrically aligned along the stack axis. For light beams inclined with respect to the layer planes, asymmetry is introduced by fractional shadowing of photoactive regions due to the intransparent metallic layers.

Varistors made of indium tin oxide∕Si multilayers on p-type GaN substrates

Varistors are important devices in the prevention of electric circuits from electric surges or in the stabilization of the operation current. Instead of the conventional granular type, varistors consisting of conductor/semiconductor multilayers grown on p-type semiconductor substrates are developed. In this work, the conductor used is indium tin oxide (ITO), the semiconductor is Si and the substrate is of p-type GaN. It was found that symmetric and nonlinear current-voltage curves are available by cascading two (ITO∕Si)N∕p-GaN films with a bridging Ag film. Furthermore, the current-voltage characteristics can be manipulated by depositing various periods of ITO∕Si multilayers on the p-type GaN substrates. The details of the design principle and the characterizations of the cascading (ITO∕Si)N∕p-GaN thin-film varistors are also discussed.

Uniform CoSi 2 nano-nucleus formation by oxide mediated silicidation with a Ti capping layer

The nucleation stage toward CoSi 2 with average island size of about 4 nm and uniform island size distribution is obtained from a TiN/Co/Ti/Co/SiO x /Si multilayer with the SiO x as a mediated layer by annealing at 460 °C for 240 s followed by 600 °C 240 s. It is found that Ti capping layer can enhance Co diffusion into the Si substrate at higher temperature (600 °C 240 s) annealing, which results in larger nucleus size (average grain size about 12 nm) but nonuniform nucleus size distribution. However, two-step annealing for 460 °C 240 s followed by 600 °C 240 s results in a smaller average nucleus size with better nucleus size distribution. The mechanism responsible for the discrepancy is discussed in the paper.

MeV Si ion bombardments of thermoelectric BixTe3/Sb2Te3 multilayer thin films for reducing thermal conductivity

BixTe3/Sb2Te3 multilayer thin films were grown as thermoelectric (TE) materials using electron-beam evaporation. Solid antimony (III) telluride and bismuth (III) telluride were used for the growth of BixTe3 and Sb2Te3 layers. Rutherford backscattering spectroscopy (RBS) analysis shows that the grown antimony telluride film has the stoichiometry of Sb2Te3 and the bismuth telluride film is Bi1.1Te3. The grown multilayer films have a periodic structure consisting of alternating Bi1.1Te3 and Sb2Te3 layers. The Bi1.1Te3/Sb2Te3 multilayer thin films with five or seven layers were analyzed by RBS. The grown Bi1.1Te3 and Sb2Te3 monolayer thin films and Bi1.1Te3/Sb2Te3 multilayer thin films were bombarded by 5MeV Si ions. The thermal conductivity of the grown films was measured by a 3ω-method thermal conductivity measurement system. The multilayer structure and MeV Si ion bombardment made the films to have a lower thermal conductivity.

High-efficiency diffractive x-ray optics from sectioned multilayers

We investigate the diffraction properties of sectioned multilayers in Laue (transmission) geometry, at hard x-ray energies (9.5 and 19.5keV). Two samples are studied, a W∕Si multilayer of 200×(29nm) periods, and a Mo∕Si multilayer of 2020×(7nm) periods, with cross-section depths ranging from 2to17μm. Reflectivities as high as 70% are observed. This exceeds the theoretical limit for standard zone plates operating in the multibeam regime, demonstrating that all of the intensity can be directed into a single diffraction order in small-period structures.

Temperature dependence of transport properties of high mobility holes in Ge quantum wells

The transport properties of a two-dimensional hole gas (2DHG), with very high room-temperature drift mobilities, formed in 7.5- (2540cm2V−1s−1) and 20-nm (2940cm2V−1s−1) strained Ge quantum wells of multilayered Si∕Si0.33Ge0.67∕Ge∕Si0.33Ge0.67∕Si0.73Ge0.27∕Si(001) p-type modulation-doped heterostructures were investigated experimentally in the temperature range of 10–295K. For both samples the drift mobility of the 2DHG behaves in the same way as the Hall mobility, increases as the temperature decreases. The sheet carrier density of the 2DHG increases with decreasing temperature, which is opposite to the behavior of Hall-effect sheet carrier density. We found that the 2DHG formed in the thicker Ge quantum well has a higher drift mobility at 295K but a lower one at low temperatures. For both samples the Hall factor increases with decreasing temperature, reaching unity at 10K, when carriers in parallel conducting layers completely freeze-out. The interpretation of these results is carried out and the scattering mechanisms limiting the 2DHG mobility are discussed.

Nanotribological properties of CN/TiCN/TiN/Si multilayer as determined byAFM

In this work, the mechanical properties of new hard coatings based on a multilayerstructure have been investigated at the nanometre scale. A multilayer structure ofCN/TiCN/TiN on silicon substrate has been deposited by dual-ion-beam sputtering. Thenanomechanical properties have been determined measuring nanoindentation, friction andwear by means of an atomic force microscope (AFM) on the multilayer after deposition ofeach layer. Nanoindentation and wear experiments were performed with the AFM using adiamond tip whereas the friction behaviour of each layer was evaluated taking AFMfriction images with silicon nitride tips while the normal force was increased during thescanning.The hardness and the resistance to wear of the system are observed to increaseas the next layer is deposited and the multilayer is completed. In contrast, thefriction is shown to decrease in the same way. All these results indicate that themultilayer combines ultrahard behaviour with good tribological and wear properties.

비정질 n형 Si 박막을 이용한 자기터널링 트랜지스터 제작과 특성

Magnetic tunneling transistor (MTT) device using the amorphous n-type Si semiconductor film for base and collector consisting of the [CoFe/NiFe](free layer) and Si(top layer) multilayers was used to study the spin-dependent hot electron magnetocurrent (MC) and tunneling magnetoresistance (TMR) at room temperature. A large MC of 40.2 % was observed at the emitter-base bias voltage ( ) of 0.62 V. The increasing emitter hot current and transfer ratio ( / ) as are mainly due to a rapid increase of the number of conduction band states in the Si collector. However, above the of 0.62 V, the rapid decrease of MC was observed in amorphous Si-based MTT because of hot electron spin-dependent elastic scattering across CoFe/Si interfaces.

Cleaning of extreme ultraviolet lithography optics and masks using 13.5nm and 172nm radiation

Under extreme ultraviolet (EUV) exposure, the surfaces of the imaging optics and mask, which are coated with a Mo∕Si multilayer, become contaminated with organic compounds. Thus, an efficient method of removing carbon contamination from masks and the imaging optics is required. Then, we propose two methods as a removal method of contamination: one is in situ cleaning method without heating a sample by synchrotron radiation irradiation that is mainly targeted at the imaging optics, and another is cleaning method without heating a sample using by 172nm light irradiation that is targeted at an EUV lithography finished mask. For in situ cleaning so called online cleaning, the contamination removal rate is 0.24nm∕min in the condition of O2-rich-vacuum environment at a pressure of 5.0×10−2Pa and an electron beam current of 130mA of 1.0GeV electron storage ring. For offline cleaning using 172nm light, the contamination removal rate is 2nm∕min in the O2-rich-vacuum environment at the pressure of 2×10−3Pa. Both two methods restore the reflectivity of a Mo∕Si multilayer to its original level without causing any surface damage. The effectiveness of both in situ and offline contamination removal are confirmed.

Structural and Magnetic Characteristics of Fe∕Si Bilayer and Multilayer Films Obtained by Thermal Deposition in Ultrahigh Vacuum

The structural and magnetic characteristics of Fe/Si bilayer and multilayer films with nanometer-thick layers obtained by thermal deposition in ultrahigh vacuum have been studied by methods of small-angle X-ray scattering, electron spectroscopy, and magnetometry. It is established that the mechanisms involved in the formation of Fe/Si and Si/Fe interfaces are different.

Optical properties of SiO 2/nanocrystalline Si multilayers studied using spectroscopic ellipsometry

Using variable-angle spectroscopic ellipsometry, we measure the pseudo-dielectric functions of as-deposited and annealed SiO 2/SiO x multilayers. The SiO 2(2 nm)/SiO x (2 nm) multilayers are prepared under various deposition temperatures by ion beam sputtering. Annealing at temperatures above 1100 °C leads to the formation of Si nanocrystals (nc-Si) in the SiO x layer of multilayers. Transmission electron microscopy images clearly demonstrate the existence of nc-Si. We assume a Tauc–Lorentz lineshape for the dielectric function of nc-Si, and use an effective medium approximation for SiO 2/nc-Si multilayers as a mixture of nc-Si and SiO 2. We successfully estimate the dielectric function of nc-Si and its volume fraction. We find that the volume fraction of nc-Si decreases after annealing, with increasing x in as-deposited SiO x layer. This result is compared to expected nc-Si volume fraction, which is estimated from the stoichiometry of SiO x .

Enhanced ordinary magnetoresistance in Co∕Si systems

The enhancement of the ordinary magnetoresistance (OMR) in Si has been attempted by constructing two type of Co∕Si systems; one is the sputter-deposited current perpendicular to plane-type Co∕Si multilayers and the other is the sputtered-Co∕anodized-porous-Si system. The Co∕Si multilayers show the sharp OMR at a low field and the negative granular-type giant magnetoresistance at higher fields. At 50K, however, only the OMR appears with the ratio of about 3.0% for an in-plane field of 10kOe. In the Co∕anodized-Si system, a very large OMR of about 60% is observed at 50K for perpendicular field of 10kOe.