AVS2004 Session EM-MoP: Poster Session
Monday, November 15, 2004 5:00 PM in Room Exhibit Hall B
Monday Afternoon
Time Period MoP Sessions | Topic EM Sessions | Time Periods | Topics | AVS2004 Schedule
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EM-MoP-1 Oxidation of Epitaxial Al/Si(111) for Improved Josephson Tunnel Junctions
D.A. Hite, R. McDermott, R.W. Simmonds, K.B. Cooper, M. Steffen, S. Oh, S. Nam, J.M. Martinis, D.P. Pappas (NIST) One of the most promising candidates for a physical quantum bit (qubit) is the current biased Josephson junction. Quantized energy levels in the Josephson potential form the basis for the qubit and are manipulated by the application of currents at microwave frequencies. Recently, qubit spectroscopy (level spacing vs. dc bias current) has identified spurious resonances that have been shown to be a major source of qubit decoherence. Currently, all experimental evidence and modeling point to two-level fluctuators in the material system of the tunnel barrier as the origin of these spurious microwave resonances. In the present technology, tunnel junctions are grown as a trilayer by magnetron sputter deposition of Al with subsequent thermal oxidation for the tunnel barrier. In this talk, we will detail our efforts to identify and eliminate the spurious resonators by engineering epitaxial Josephson junctions with varying degrees of crystalline qualities and impurity concentrations. In particular, we will discuss the oxidation of ultra smooth Al films epitaxially grown on Si(111) as the base electrode of the tunnel junction. During each step in the Al/AlOx/Al trilayer growth, the structure has been investigated in situ by AES, AED and LEED. While tunnel junctions fabricated with these epitaxial base electrodes prove to be of non-uniform oxide thickness and too thin, I-V characteristics have shown a lowering of subgap currents by an order of magnitude. Transport measurements will be correlated with morphological structure for a number of devices fabricated with various degrees of crystalline quality. |
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EM-MoP-2 Nickel Silicide Formation and Strain Relaxation of SiGe Layers during Rapid Thermal Annealing of Ni/cap-Si/Si0.83Ge0.17/Si(001) Structure
C.H. Jang (Sungkyunkwan University, South Korea); Y.W. Kim (Seoul National University, Korea); M.R. Sardela Jr. (University of Illinois at Urbana-Champaign); Y.J. Song, K.-H. Shim (Electronics and Telecommunications Research Institute, Korea); N.-E. Lee (Sungkyunkwan University, South Korea) NiSi or NiSi1-yGey has been intensively investigated for contact applications in CMOS devices utilizing strained Si or SiGe layers for better device performance. Recently, NiSi1-yGey layers formed from the direct reaction of Ni/SiGe structure showed a better thermal stability but a rough interface compared to NiSi on Si substrate. Therefore, NiSi/SiGe structure with improved interface flatness for a better control of the ultra-shallow depth of contacts needs to be investigated. In this study, the electrical and structural characteristics of nickel silicides formed on p-Si0.83Ge0.17/Si (001) using a sacrificial Si capping layer (cap-Si) and strain relaxation of SiGe layers during nickel silicidation were investigated. The phase formation of nickel silicide and interface quality between nickel silicide and the SiGe layer were measured by XRD (X-ray diffraction) and TEM (transmission electron microscopy), respectively. Sheet resistance of nickel silicide on p-Si0.83Ge0.17 /Si(001) substrate was investigated by four-point probe measurements. Chemical composition and depth profile of nickel silicide was examined by AES (auger electron spectroscopy). The surface roughness of nickel silicide films was measured using AFM (atomic force microscope) and surface morphology by FE-SEM (field-emission scanning electron microscopy). Strain relaxation behaviors of SiGe layers during Ni silicidation were investigated by high-resolution XRD and reciprocal space mapping (RSM) study. The results showed the formation of nickel monosilicide at 400~550°C and the sheet resistance values of 6.533 ~7.918 Ω/sq. But, increase in sheet resistance values above TA ≥600°C is attributed to the formation of high-resistivity silicide phase and surface roughening by agglomeration of nickel silicides. Detailed changes in lattice parameters and mismatch in the SiGe layers will be presented. |
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EM-MoP-3 The Change of Microstructures in SiGe Film Grown on (001) Si Substrate using Solid Phase Epitaxy
S.G. Kim (ETRI, South Korea) SiGe films grown on Si substrate have a great interest for the application in high performance heterojunction bipolar transistors. In this system, study on the growth behavior and the microstructure is very important for the growth of defect-free SiGe film. In this work, we have investigated the growth behavior and the microstructure change of SiGe film on Si substrate grown by solid phase epitaxy (SPE) method. Amorphous Si1-xGex (x=0.2, x=0.35, x=0.5) films(~150nm) were deposited on (001) Si substrate by molecular beam epitaxy method and then crystallized (i.e SPE) at various anneal temperatures. These films were analyzed using glancing angle X-ray diffraction and transmission electron microscopy (TEM). For the Si0.8Ge0.2 sample annealed at 550â"f for 30 min, SiGe film was found to be amorphous. Single crystal SiGe film (~30 nm) with defects were formed in the sample annealed at 650â"f for 10 min, but very small amount of polycrystalline and amorphous SiGe layers still remained above the SiGe single crystalline layer. The preferred growth direction of polycrystalline SiGe layer was (111). For the Si0.8Ge0.2 film annealed at 750â"f for 10min, single crystalline SiGe layers was developed near SiGe/Si interface, and above the single crystalline layer, polycrystalline SiGe layer was formed with preferred growth direction of (220). For the Si1-xGex film with x>0.2, similar microstructure was formed but preferred growth direction changes with anneal temperature from (111) to (311) instead of (220). |
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EM-MoP-4 Investigation of Thermal Stability of Strained Si on Relaxed SiGe Layer
C.H. Jang, J.W. Lee, C.W. Yang (Sungkyunkwan University, South Korea); M.R. Sardela Jr. (University of Illinois at Urbana-Champaign); Y.J. Song, K.-H. Shim (Electronics and Telecommunications Research Institute, Korea); N.-E. Lee (Sungkyunkwan University, South Korea) MOSFET device utilizing a strained-Si channel on relaxed SiGe buffer layer is one of the most promising structure for the next-generation CMOS integration scheme below 50 nm technology node because of enhanced channel mobility and compatibility with conventional Si CMOS processes. For the practical adoption of strained-Si channels into nano-CMOS technology, fabrication methods of strained-Si/relaxed SiGe/Si structures and their compatibility with post-thermal processes are to be obtained. In particular, stability of strained-Si channels on relaxed SiGe layers is of great concern because formation of misfit and threading dislocations and increase of surface roughness can occur during elevated temperature processing due to thermal-induced instability of strained-Si layers. In this study, we investigated thermal stability of strained-Si on relaxed SiGe layer at elevated RTA (rapid thermal annealing) temperatures. Strained-Si channel layers on the relaxed Si1-xGex(x=0.2) buffer layer were deposited by reduced-pressure chemical vapor deposition (RP-CVD). In order to investigate the thermal stability of fabricated strained-Si/relaxed-SiGe/Si(001), RTA treatments were carried out at the temperature range of 700~950°C in N2 ambient for 60sec. Strain relaxation behaviors of strained-Si layer were investigated using Raman spectroscopy and reciprocal space mapping (RSM). Analyses of defect formation and structure of strained-Si were also performed by analytical transmission electron microscopy (AEM). And evolution of surface roughness and morphology upon RTA was measured using atomic force microscope (AFM) and field-emission scanning electron microscopy (FE-SEM). The combined results indicate that strained-Si is unstable due to strain relaxation leading to defect formation and increased surface roughness at the RTA temperature ï,³ 900 oC in the present experiments. Detailed results on strain relaxation behaviors of the strained-Si will be presented. |
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EM-MoP-5 Application of IR Variable Angle Spectroscopic Ellipsometry to the Determination of Free Carrier Concentration in n++ Germanium
D.W. Thompson, N.J. Ianno, K. Zhou (University of Nebraska-Lincoln) Free carrier concentration profiles were determined by Fourier Transform Infrared (FTIR) variable angle spectroscopic ellipsometry in arsenic doped n++ germanium. This technique exploits carrier absorption in the mid-infrared range and combines the sensitivity of ellipsometry with a simple Drude free carrier absorption model to determine the carrier profile. The germanium was doped from an arseno silica spin-on source in an open tube furnace under a reducing atmosphere. Peak dopant concentrations were in excess of 1019/cm3 over depths greater than 10 microns as determined by secondary ion mass spectrometry (SIMS). Shallower profiles were more effectively detected using ellipsometry. The optical modelling scheme approximated the depth profile of the carrier concentration using a large number of discrete layers. The effect of using different functional dependences such as Gaussian and error function was compared. |
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EM-MoP-6 Study on the Enhancement of the Etch Selectivity of Photoresist for Next Generation Lithography
C.H. Shin, J.Y. Yun, G.J. Min, C.J. Kang, H.K. Cho, J.-T. Moon (Samsung Electronics Co. Ltd., Korea) As device feature size shrinks to sub 100nm, process applications using 193nm ArF lithography are being increased in the semiconductor industry. However, as the resolution of photoresist increases, carbon ratio and phenyl group in the resist structure decrease (Ohnish parameter increases), with the reduction of dry etch resistance. Moreover, as industry turns to the NGL such as F2 and immersion ArF for sub-70nm patterning, limitations in the fabrication of patterning using NGL lie in both decreased physical thickness of photoresist below 2000Å and reduced hardness of materials. Dry etch resistances of immersion ArF and F2 photoresist were evaluated in line and space pattern. Etching was performed in the commercially available dual frequency plasma using O2, Ar, CF4, CHF3 and CH2F2 gas chemistries. It was found that dry etch resistances of NGL photoresist were weaker compared to the commercial ArF photoresist. Novel techniques forming a protective layer on photoresist will be discussed in this paper in order to improve dry etch resistance of new resist together with the enhancement of etch selectivity. |
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EM-MoP-7 Inductively Coupled Plasma Etching of Nano-Sized Magnetic Tunnel Junction Stack for MRAM Fabrication
S.W. Hwang, S.J. Jung, T.W. Kim, D.J. Ma (Samsung Advanced Institute of Technology, South Korea) There is a strong interest in the development of plasma etching processes for magnetic multilayer structures of the type used in sensores, magnetic random access memories(MRAM). MRAM offers high storage density, fast access time, and infinite rewrite capability. Therefore, there is trend towards nano-size to increase bit storage density. The method for patterning the magnetic tunnel junction(MTJ) stacks that comprise the MRAM is ion milling, which has problems such as sidewall redeposition, etc. In conventional reactive ion etching, the MTJ stack do not form sufficiently volatile etch products to allow efficient pattern transfer. One alternative would be to increase the substrate temperature during etch process in order to increase the vapor pressure of the etch products. This method is not a good option, because of the limited thermal stability of MTJ stacks. In this study, magnetic tunnel junction(MTJ) stacks on Si/SiO2 were etched using inductively coupled Cl2-based plasma and the effects of Cl2-based gas mixtures on the formation of reactive byproducts affecting on MTJ stack etching were investigated. When Cl2-based gas mixtures were used with Ar or O2, due to very low vapor pressure of the etch products, thick etch products remaining on the etched MTJ stack could be observed. However, these etch products were easily removed during the etching, especially when BCl3, C2F6 were added to Cl2/Ar. These results are interpreted as the formations of more reactive products when BCl3, and C2F6 were added to Cl2/Ar. Therefore, the physical and chemical properties of the etch products formed by the specific gas mixture appear to be important in nano-sized etching of MTJ cell stacks. |
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EM-MoP-8 Influence of Molybdenum on the Whisker Formation of Al Film
C.F. Lo, D. Draper, P. McDonald, P. Gilman (Praxair Electronics) This study was to understand if addition of Mo can minimize whisker formation of Al film. Four Al-Mo alloys with 5at%, 10at%, 15at% and 40at% Mo, respectively, plus one pure Al were deposited to glass substrates by physical vapor deposition. The as-deposited and 350C/1hour annealed films were characterized by the SEM-EDS and XRD. Many hillocks were observed on the as-deposited and annealed Al films, but no whisker was found. The as-deposited Al-5at% Mo film has a similar microstructure as that of the Al films. An enormous amount of whiskers with various shapes were formed after annealed. For the Al-10at%Mo and the other higher Mo content films, the hillocks were significantly reduced and no whisker was found. The XRD measurements showed that the Al and Al-10at% Mo films were (111) grain orientation dominant. The Al-5at% Mo, however, has the similar amount of (111) and (200) orientations. No grain orientation could be identified for the Al-15at%Mo and Al-40at% Mo films. Focusing on the whisker formation of the Al-5at% Mo film, a group of films annealed at 350C for 1 to 20 minutes were prepared. Increasing the holding time reduced the (111) oriented grains, while the (200) ones were not significantly changed. In addition, a new phase was formed after annealing. The results show that with at least 10at% addition of Mo, the hillock can be minimized and no whiskers will be generated. Addition of 5at% Mo, however, will generate whiskers by annealing at 350C. Formation of the whiskers on the annealed Al-5at% Mo was ascribed to the co-existence between the (111) and (200) oriented grains, which caused a higher internal stress as result of mismatch of the grain orientations. During annealing, to reduce the internal stress, the whiskers were generated. |
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EM-MoP-9 Change of Structural and Electrical Properties due to Phase Transition of Ge2Sb2Te5
Y.K. Kim, S.A. Park, J.H. Beack, M.K. Noh, K.H. Jeong, E.J. Jeong, D.-H. Ko (Yonsei University, Korea); M.-H. Cho (Korea Research Institute of Standards and Science, Korea) Ge 2Sb 2Te 5 ternary alloy film is used for phase-change nonvolatile memory device. This material shows electrical switching phenomena of resistance (~10 6 times) when phase transition occurs. In this research, we investigated the changes of structural and electrical properties after the phase of film transited from amorphous state to poly crystalline state. Phase transition of the alloy film grown by RF magnetron sputtering method was induced by post annealing treatment in N 2 ambient. XRD analysis showed that as-dep. film which was amorphous state crystallizes to NaCl fcc structure at 160~170 °C. As a result of DSC experiment, the effective activation energy for this crystallization is 2.5 ±0.11eV. Sheet resistance decreased from 10 9 to 10 3 Ω/sq. When it was annealed at 250 °C, phase transition from NaCl fcc structure to Hexagonal structure occurred. But not only hexagonal structure, other phases-Te and GeSb 2Te 4 hexagonal structures also appeared. This phase separation phenomenon also can be shown in SPEM(Scanning Photoemission Microscopy) data. In this phase, the sheet resistance decreased to 10 2 Ω/sq. AFM and XRR results show that while the crystallization occurs the surface roughening proceeds and thickness is decreased so that eventually the density increases. Hall measurement results indicate that resistance change is related to the change of hall concentration which is due to structure transition. |
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EM-MoP-10 On the Surface Morphology of CdTe Thin Films Evaporated onto Rotating Substrates
G.G. Rusu, M. Rusu (Al.I. Cuza University, Romania) CdTe thin films were prepared by thermal evaporation under vacuum by quasi-closed volume technique onto unheated glass substrates. During the evaporation process, the substrates holder were periodically passed (by rotational moving) over the evaporating source. As result of step by step deposition, multi-layered films were obtained. Depending on the rotating speed (varied between 20 and 210 rpm) and source temperature the thickness of the individual layers ranged from 0.75 nm to 7.60 nm. The total film thickness, ranged between 320 and 510 nm. For samples deposited in various conditions, AFM investigations were performed and the average roughness (a-r) and the root mean square surface (rms) roughness were calculated. The obtained results revealed a strong dependence of film surface morphology on the source temperature and rotational speed. At lower temperature source (925 K), the surface roughness decreases (from 2.30 to 0.57 nm) with increase of rotational speed, v, while at greater source temperature (1165 K) the surface roughness increase (from 0.50 to 2.10 nm) with v. Also, at greater source temperature, the films present a tellurium excess. The heat treatment of the films determines the increase of surface roughness and the precipitation of tellurium excess as nanocrystallites embedded in CdTe films. |
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EM-MoP-11 Future Super Conducting MeB2 Materials
I. Arvidssson, A. Pallas, K. Larsson (Uppsala University, Sweden) Metal diborides (MeB2) often have interesting thermal, mechanic and superconducting properties. MgB2 was put into focus some years ago for its high transition temperature (39 K) in combination with its simple AlB2-structure. The boron structure in MeB2, with interesting similarities to graphite structures, is much dependent of the electron transfer from the nearby metal atoms. An electronic and structural comparison has here been performed for various planar and puckered transition metal borides using quantum mechanical calculations. In comparison to MgB2 the transition metal diborides MoB2, ZrB2, RuB2, and PdB2 have been examined. The first two are planar with AlB2 structure and the latter two have in experiments been shown to have a structure similar to puckered CaSi2. The theoretical method used in the calculations is the density functional theory (DFT). Calculations were performed for each of the metal diborides as both planar AlB2-structures and as puckered CaSi2-structure. Extensive test calculations have been performed to ensure the accuracy of the model template and the calculation parameters. The results indicate that there are differences in stability for the planar and puckered structures. This variance in thermal stability was found to strongly correlate to differences in electron transfer between the metal atom and the boron skeleton. |
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EM-MoP-12 Optical properties of Zn1-xMnxS epilayers by Spectroscopic Ellipsometry
D.-J. Kim, S.-H. Eom, Y.-M. Yu, Y.D. Choi (Mokwon University, Korea); M.-Y. Yoon (Joongbu University, Korea); I.-H. Choi (Chung-Ang University, Korea) II-VI compounds with transition metal Mn are generally referred to as diluted magnetic semiconductors (DMS), and they can be crystallized in the NaCl, zincblende and wurzite structure defined by the binary host crystal structure. ZnMnS is one of the widely studied systems among the DMS groups and is led to a wide range of technological applications as functional layers in electronic and optoelectronic devices, solar cells and sensors. Therefore, these materials have attracted much interest because of their various structural and optical properties. ZnMnS epilayers were grown on GaAs (100) by hot-wall epitaxy. The grown films had zincblende structure, which was confirmed from x-ray diffraction spectra. The Mn composition ratios of the epilayers were determined using the electron probe x-ray micro analyzer. The surface morphologies with Mn compositions were observed by atomic force microscopy. And a spectroscopic ellipsometry was used to know the optical properties by dielectric constants. The measured dielectric function spectra reveal distinct structures at energies of E0, E0+δ0, E1, E1+δ1, and E2 critical points (CPs). The complex refractive index n*=n+ik, the absorption coefficient α, and the normal incidence reflectivity R were deduced from dielectric constants ε1 and ε2. Also, a shifting and a broadening of the CPs can be observed. A new CP appears in the vicinity of 7.0 eV with the increasing Mn composition. |
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EM-MoP-13 Effect of Mn Composition on Characterization of Zn1-xMnxS Epilayers
Y.-M. Yu, D.-J. Kim, S.-H. Eom (Mokwon University, Korea); K.-S. Lee, T.-H. Kim (Chungnam National University, Korea); Y.D. Choi (Mokwon University, Korea) ZnMnS is one of II-VI diluted magnetic semiconductors. The crystal structure of the bulk ZnMnS is cubic in the range of the Mn composition for x<0.1 and hexagonal for 0.1 |