In-plane Microstructure Research Articles

ICP-CVD 비정질 실리콘에 형성된 처리온도에 따른 저온 니켈실리사이드의 물성 변화

ICP-CVD(inductively-coupled Plasma chemical vapor deposition)를 사용하여 $250^{\circ}C$ 기판온도에서 140 nm 두께의 수소화된 비정질 실리콘( ${\alpha}$ -Si:H)을 제조하였다. 그 위에 30 nm-Ni을 열증착기를 이용하여 성막하고, $200{\sim}500^{\circ}C$ 사이에서 $50^{\circ}C$ 간격으로 30분간 진공열처리하여 실리사이드화 처리하였다. 완성된 실리사이드의 처리온도에 따른 실리사이드의 면저항값 변화, 미세구조, 상 분석, 표면조도 변화를 각각 사점면저항측정기, HRXRD(high resolution X-ray diffraction), FE-SEM(field emission scanning electron microscope), TEM(transmission electron microscope), SPM(scanning probe microscope)을 활용하여 확인하였다. $300^{\circ}C$ 에는 고저항상인 $Ni_3Si$ , $400^{\circ}C$ 에서는 중저항상인 $Ni_2Si$ , $450^{\circ}C$ 이상에서 저저항의 나노급 두께의 균일한 NiSi를 확인되었다. SPM결과에서 저저항 상인 NiSi는 $450^{\circ}C$ 에서 RMS(root mean square) 표면조도 값도 12 nm이하로 전체 공정온도를 $450^{\circ}C$ 까지 낮추어 유리와 폴리머기판 등 저온기판에 대응하는 저온 니켈모노실리사이드 공정이 가능하였다. 【We fabricated hydrogenated amorphous silicon(a-Si:H) 140 nm thick film on a $180\;nm-SiO_2/Si$ substrate with an inductively-coupled plasma chemical vapor deposition(ICP-CVD) equipment at $250^{\circ}C$ . Moreover, 30 nm-Ni film was deposited with a thermal-evaporator sequently. Then the film stack was annealed to induce silicides by a rapid thermal annealer(RTA) at $200{\sim}500^{\circ}C$ in every $50^{\circ}C$ for 30 minuets. We employed a four-point tester, high resolution X-ray diffraction(HRXRD), field emission scanning electron microscope(FE-SEM), transmission electron microscope(TEM), and scanning probe microscope(SPM) in order to examine the sheet resistance, phase transformation, in-plane microstructure, cross-sectional microstructure evolution, and surface roughness, respectively. We confirmed that nano-thick high resistive $Ni_3Si$ , mid-resistive $Ni_2Si$ , and low resistive NiSi phases were stable at the temperature of $350{\sim}450^{\circ}C$ , and > $450^{\circ}C$ , respectively. Through SPM analysis, we confirmed the surface roughness of nickel silicide was below 12 nm, which implied that it was superior over employing the glass and polymer substrates.】

나노급 다결정 실리콘 기판 위에 형성된 니켈실리사이드의 물성과 미세구조

10nm Ni/30 nm와 70nm poly Si/200nm <TEX>$SiO_2/Si(100)$</TEX> 구조로부터 니켈실리사이드의 열적안정성을 연구하기 위해서 쾌속열처리기를 이용하여 실리사이드화 온도 <TEX>$300{\sim}1100^{\circ}C$</TEX>에서 40초간 열처리하여 실리사이드를 제조하였다. 준비된 실리사이드의 면저항값 변화, 미세구조, 상 분석, 표면조도 변화를 각각 사점면저항측정기, FE-SEM, TEM, HRXRD, SPM을 활용하여 확인하였다. 30 nm 다결정실리콘 기판 위에 형성된 실리사이드는 <TEX>$900^{\circ}C$</TEX>까지 열적안정성이 있었다. 반면에 70 nm 다결정실리콘 기판 위에 형성된 실리사이드는 기존연구결과와 동일한 <TEX>$700^{\circ}C$</TEX> 이상에서 고저항상인 <TEX>$NiSi_2$</TEX>로 상변화 하였다. HRXRD로 확인한 결과, 30 nm 두께의 기판 위에 니켈실리사이드는 <TEX>$900^{\circ}C$</TEX> 고온에서도 NiSi상이 유지되다가 <TEX>$1000^{\circ}C$</TEX>에서 <TEX>$NiSi_2$</TEX>로 상변화 하였다. FE-SEM 과 TEM 관찰결과, 30 nm 두께의 다결정실리콘 기판에서는 <TEX>$700^{\circ}C$</TEX>의 저온처리에는 잔류 다결정실리콘 없이 매우 균일하고 평탄한 40 nm의 NiSi가 형성되었고, <TEX>$1000^{\circ}C$</TEX>에는 선폭 <TEX>$1.0{\mu}m$</TEX>급의 미로형 응집상이 생성됨을 확인하였다. 70 nm 두께의 다결정실리콘 기판에서는 불균일한 실리 사이드 형성과 잔류 다결정실리콘이 존재하였다. SPM결과에서 전체 실험구간에서의 RMS 표면조도 값도 17nm 이하로 CMOS공정의 FUSI게이트 적용의 가능성을 보여주었다. 다결정실리콘 게이트의 높이를 감소시키면 니켈실리사이드는 상안정화가 용이하며 저저항구간을 넓힐 수 있는 장점이 있었다. We fabricated thermally-evaporated 10 nm-Ni/30 nm and 70 nm Poly-Si/200 nm-<TEX>$SiO_2/Si$</TEX> structures to investigate the thermal stability of nickel silicides formed by rapid thermal annealing(RTA) of the temperature of <TEX>$300{\sim}1100^{\circ}C$</TEX> for 40 seconds. We employed for a four-point tester, field emission scanning electron microscope(FE-SEM), transmission electron microscope(TEM), high resolution X-ray diffraction(HRIXRD), and scanning probe microscope(SPM) in order to examine the sheet resistance, in-plane microstructure, cross-sectional microstructure evolution, phase transformation, and surface roughness, respectively. The silicide on 30 nm polysilicon substrate was stable at temperature up to <TEX>$900^{\circ}C$</TEX>, while the one on 70 nm substrate showed the conventional <TEX>$NiSi_2$</TEX> transformation temperature of <TEX>$700^{\circ}C$</TEX>. The HRXRD result also supported the existence of NiSi-phase up to <TEX>$900^{\circ}C$</TEX> for the Ni silicide on the 30 nm polysilicon substrate. FE-SEM and TEM confirmed that 40 nm thick uniform silicide layer and island-like agglomerated silicide phase of <TEX>$1{\mu}m$</TEX> pitch without residual polysilicon were formed on 30 nm polysilicon substrate at <TEX>$700^{\circ}C\;and\;1000^{\circ}C$</TEX>, respectively. All silicides were nonuniform and formed on top of the residual polysilicon for 70 nm polysilicon substrates. Through SPM analysis, we confirmed the surface roughness was below 17 nm, which implied the advantage on FUSI gate of CMOS process. Our results imply that we may tune the thermal stability of nickel monosilicide by reducing the height of polysilicon gate.

Macroscopic modelling of structured materials: Relationship between orthotropic Cosserat continuum and rigid elements

The macroscopic modelling of in-plane elastic behaviour of composite solids made with regular orthotropic texture is the object of the present study. At the macro-scale, the effect of heterogeneity can be included by adopting an homogenisation toward a generalised continuum on which specific finite element codes are based. As an alternative, a specific rigid element approach has been recently proposed [Casolo, S., 2004. Modelling in-plane micro-structure of masonry walls by rigid elements. International Journal of Solids and Structures 41(13), 3625–3641] based on a discrete mechanistic formulation. This paper presents a sequel of such research, and expounds the theoretical relationship between the orthotropic Cosserat continuum and the proposed rigid elements. Then, referring to two different masonry-like textures, the constitutive parameters of the corresponding Cosserat continuum and of the rigid element model are calculated. Numerical analyses compare their performance, and display the impact of the composite texture in the case of a concentrated load. The capability to discern the behaviour of different structured materials at the macro-scale is pointed out by observing how the local rotation of the blocks and the consequent different deformation of vertical and horizontal joints have influence on the strain field maps.

Induced thermal stress fields for three-dimensional distortion control of Si wafer topography

Localized, controlled heating can induce a thermal stress field in silicon wafers and displace the surface topography in three dimensions, which is useful for nanoscale regulation of overlay in microcontact printing systems. Simulation and experimental results are presented to demonstrate the use of a thermal array consisting of a dense distribution of independent heating elements to locally displace silicon wafer alignment microstructures. An experimental apparatus comprised of a 7×7 array of thermal cycling sources is used to control the absolute three-dimensional position of surface microstructures. The system is used to demonstrate out-of-plane sensitivity of 1.4 μm/°C by thermomechanical displacement contributions from thermal expansion of the heating element. Rolloff in out-of-plane displacement of 200 nm/mm/°C in silicon at the boundary between heated and nonheated regions in this apparatus is exhibited. Dynamic real-time control of the substrate flatness is thus feasible and is demonstrated with the apparatus using feedback from three alignment microscopes, to sub-100 nm levels of regulation. Control of the in-plane microstructure position is achieved by stabilizing the vertical displacement with a mechanical nanopositioning stage, while establishing a thermal stress field to produce displacement sensitivity of 70 nm/°C. Real-time feedback control of the in-plane microstructure position is demonstrated, also within sub-100 nm of the target regulation level.

Modelling in-plane micro-structure of masonry walls by rigid elements

This paper proposes rigid elements for a specific simplified model of the in-plane behaviour of masonry walls made of regular textures. The elements are plane, quadrilateral and connected by two normal springs and one shear spring on each side. The mechanical characteristics of these connections are defined in consideration of the texture effects arising due to the mechanical degradation of mortar. The present approach has proved effective when transferring the essential texture information from micro-scale to macro-scale. In particular, the “local rotation” of the blocks is obtained by assigning different stiffness to the shear springs, according to their orientation, while the in-plane bending stiffness can be reproduced by properly disposing the two normal springs. Depending on the geometry of the textures, these aspects are significant in case of large differences in the elastic modulus of the constituents, as is the case of masonry walls subjected to heavy seismic loading. Numerical simulations have proved that it is possible to deal with these aspects with a very reduced computational effort which is promising for non-linear dynamical analyses applications.

(La1−xPrx)0.7Ca0.3MnO3 colossal magnetoresistive thin films on yttria stabilized zirconia

Thin epitaxial films of (La1−xPrx)0.7Ca0.3MnO3 (x=0,0.25,0.5,0.75,1) were grown on (001) ZrO2(Y2O3) substrates by aerosol MOCVD at 750°C. The structure and electronic properties of the films were compared with those of the films on perovskite substrates and with ceramics of the same composition. The films on ZrO2(Y2O3) are (110) oriented and possess a varying in-plane orientation microstructure giving rise to an extremely high density of the large-angle boundaries (∼1011cm−2). Above the maximum resistivity temperature Tp, the microstructure results in a ∼30meV increase of the hopping energy of small polarons (∼130meV) and suppression of the maximum of d(logρ/T)/d(1/T) at the transition from Arrhenius like (logρ∝T−1) to Mott like (logρ∝T−1/4) temperature dependence of resistivity (ρ). Below Tp an empirical law logρ=αT 2+logρ′ was derived indicating a thermally activated trapping of the itinerant charge carriers. Large-angle boundaries in the films on ZrO2(Y2O3) destabilize the ferromagnetic state and cause residual resistivity (ρ′) higher by a factor of 100 compared to the films on the perovskite substrates. They provide a reservoir for the tunnel magnetoresistance owing to the spin-polarized tunneling.

Anisotropic magnetoresistance of (0 0 h), (0 h h) and ( h h h) La 2/3Sr 1/3MnO 3 thin films on (0 0 1) Si substrates

The epitaxial growth of magnetoresistive La 2/3Sr 1/3MnO 3 thin films with different orientations on (0 0 1) Si substrates has been successfully achieved by a suitable choice of the buffer heterostructure. The out-of-plane and in-plane microstructure has been carefully analysed and related to the magnetocrystalline anisotropy. The dependence of the magnetoresistance (MR) as a function of the angle between the current and the applied field has been explored in a wide field range. At high field the magnetisation is saturated whatever the direction of the field and we observe the intrinsic anisotropic magnetoresistance (AMR) effect having a uniaxial anisotropy while at low field the magnetocrystalline anisotropy induces higher-order angle dependence of the magnetoresistance.

Correlations of Microstructure and TEM Observations of Plasticity in Metallic Nanolaminates

ABSTRACTNanolaminate materials exhibit increases in hardness and yield strength beyond those expected according to rule of mixtures calculations. Several models have been proposed to explain this enhancement of strength, but conclusive experimental verification is hindered by the complex interaction between ingrown defects, in-plane microstructure and compositional modulation. In this study, mechanisms of plastic deformation in nanolaminates are investigated by in situ TEM straining of epitaxial Cu/Ni nanolaminates grown on Cu (001) single crystal substrates. Two distinct types of deformation are observed. Initial plastic deformation is accommodated by motion of “Orowan” and threading dislocations in a uniform and random fashion. As the stress levels increase, fracture occurs creating a mixed mode crack. Subsequent observations suggest that intense plastic deformation occurs over many bilayers in the direction of crack growth, but is contained to within one or two bilayers in a direction normal to the crack faces.

Effect of ion bombardment on in-plane texture, surface morphology, and microstructure of vapor deposited Nb thin films

Niobium films were deposited by physical vapor deposition (PVD) and ion-beam-assisted deposition (IBAD) using ion energies of 0, 250, 500 and 1000 eV, and R ratios (ion-to-atom arrival rate ratio) of 0, 0.1, and 0.4 on (100) silicon, amorphous glass, and (0001) sapphire substrates of thickness 50–1000 nm. Besides a {110} fiber texture, an in-plane texture was created by orienting the ion beam with respect to the substrate. The in-plane texture as measured by the degree of orientation was strongly dependent on both ion-beam energy and the R ratio. In fact, the degree of orientation in the films followed a linear relationship with the energy per deposited atom, En. The grain structure was columnar and the column width increased with normalized energy. The surface morphology depended on both the normalized energy of the ion beam and the film thickness. All films had domelike surface features that were oriented along the ion-beam incident direction. The dimension of these features increased with normalized energy and film thickness. Surface roughness also increased with normalized energy and film thickness, with the root-mean-square roughness increasing from 1.6 nm for the PVD sample (100 nm thick) to 36.7 nm for the IBAD film (1000 eV, R=0.4, 800 nm thick). Both the surface morphology evolution and in-plane texture development in these films were the result of the different ion sputter rates among differently oriented grains.

Self-alignment of metallic nanowires in CaF2-based composite films grown on stepped NaCl substrates

Self-aligned metallic nanowires have been formed in CaF2-based composite films grown on stepped NaCl (101) substrates. The nanowires were columns standing perpendicular to the {100} facets of the substrates, and have in-plane anisotropic microstructure with respect to the films.

In-plane microstructure of plasma-sprayed MgAl spinel and [formula omitted]-mullite based protective coatings: An electron microscopy study

Planar specimens prepared from thin plasmasprayed Mg-Al spinel and 2 1 -mullite layers are investigated via conventional and analytical transmission electron microscopy in order to evaluate the constraints of rapid solidification on the in-plane microstructure at different scales of resolution. Despite intrinsic differences in the nature and density of structural defects between the two materials studied, their gross-scale microstructures share a characteristic sequence starting from (i) large, spherical core grains, followed by (ii) a radial chillzone exhibiting columnar to dendritic grain morphologies, which eventually leads to (iii) an impingement zone formed by the intersection of different chillzones. Relief of thermomechanical strain from the core grains and chill zones gives rise to an equiaxed subgrain architecture and intensive microcracking in the impingement zone. Moreover, the impingement zone represents the region of highest and most varied lattice defect density.

In-plane remanence and microstructure in Co—Cr—Ta thin films

The in-plane remanence properties of Co—Cr—Ta thin films have been investigated in order to quantify interaction effects parallel and transverse to the transfer sputter deposition direction prepared at two substrate temperatures. The in-plane remanence properties of the films produced at the lower temperature were found to exhibit a Δ I peak height of 2 — the maximum possible value. These strong positive interactions were attributed to the more homogeneous structure resulting from the lower temperature of deposition.

X-ray investigation of porous silicon under angles of grazing incidence and exit

Porous silicon (PS) was prepared from p-type Si wafers (1–5Ωcm) by electrochemical etching at 50mA/cm 2. The in-plane microstructure of PS was investigated by X-ray diffraction under grazing incidence and exit (GID). In the as-etched sample we find the shape of the (220) Bragg peak to consist of two components which have the same Bragg angles, both corresponding to the lattice parameter of crystalline Si. There is a very sharp reflection with a width of the instrumental resolution and a second peak which is about 30 times broader. In explanation of these features we propose a structural model for PS in which the Si particles have crystalline cores which are coherently connected to each other and to the Si substrate. After rapid thermal oxidation (RTO) of PS only the sharp line remains, showing that the coherent matrix of small particles survived the oxidation. From other investigations it is known that RTO PS still shows photoluminescence.

Combined microstructure x-ray optics

Multilayers are man-made microstructures which vary in depth and are now of sufficient quality to be used as x-ray, soft x-ray, and extreme ultraviolet optics. Gratings are man-made in-plane microstructures which have been used as optic elements for most of this century. Joining of these two optical microstructures to form combined microstructure optical elements has the potential for greatly enhancing both the throughput and the resolution attainable in these spectral ranges. The characteristics of these new optic elements will be presented and compared to the experiment with emphasis on the unique properties of these combined microstructures. The results reported are general in nature and not limited to the soft x-ray or extreme ultraviolet spectral domains and also apply to neutrons.

Combined Microstructure X-Ray Optics; Multilayer Diffraction Gratings

ABSTRACTMultilayers are man-made microstructures engineered to vary in depth that are now of sufficient quality to be used as x-ray, soft x-ray and extreme ultraviolet optics. Gratings are in-plane man-made microstructures which have been used as optic elements for most of this century. Joining of these two optical elements to form combined microstructure optics has the potential for greatly enhancing both the resolution and the throughput attainable in these spectral ranges. Experimental results for multilayer gratings are presented and discussed. It will be demonstrated that multilayer diffraction gratings act as x-ray prisms and are high efficiency dispersion elements.