ICMCTF1998 Session F4/B3-2: Microstructural Characterization - Microanalytical and Imaging Characterization (2)

Thursday, April 30, 1998 8:30 AM in Room San Diego

Thursday Morning

Start	Invited?	Item
8:30 AM	Invited	F4/B3-2-1 Atomic Scale Characterization by Cross-sectional Scanning Tunneling Microscopy E.T. Yu, S.L. Zuo, A.Y. Lew (University of California, San Diego); R.H. Miles (SDL, Inc.); W.G. Bi, C.W. Tu (University of California, San Diego) We will describe the applications of Cross-sectional scanning tunneling microscopy (STM) to the elucidation of atomic-scale structure, and it scorrelation with materials properties and device behavior, in a variety of III-V semiconductor materials systems. Studies in our laboratory of InAs/GainSb superlattices have yielded detailed, quantitative measurements of atomic-scale interface roughness. Phenomena occurring during epitaxial growth have been found to produce a dependence of interface roughness on both growth sequence and crystallorgaphic direction. In addition, measurements of mobility anisotropy in these structures have been found to be quantitatively consistent with modeling of interface roughness scattering using roughness parameters obtained by STM, demonstrating a direct, quantitative correlation between atomic-scale device structure. Studies of InP/InAsP heterostructures have yielded direct, atomically resolved images of ananometer-scale phase separation in InAsP alloy layers grown by gas-source molecular-beam epitaxy, with the boundaries between As-rich and P-rich regions occurring primarily within {111} planes. Imaging of both (110) and (1-10) cross-sectional planes has yielded information about the three-dimensional structure of phase-separated regions within the alloy.
9:10 AM	Invited	F4/B3-2-3 Secondary Electron Imaging of Nucleation and Growth of Semiconductors for Nanostructure Fabrication Y. Homma (NTT Basic Research Laboratories, Japan) Observing growing surfaces with atomic-layer sensitivity together with nanometer-scale lateral resolution is useful for controlling nanostructure fabrication on semiconductor surfaces. We have shown that scanning electron microscopy (SEM) in ultrahigh vacuum (UHV) can image surface atomic layers, such as reconstructed surface domains and nucleating 2D-islands, and that it enables dynamic characterization of growth processes. In this paper, we present the results of in situ observations for Ge solid phase epitaxy (SPE) on Si(111) and GaAs molecular beam epitaxy (MBE) on GaAs and Si substrates, and discuss control of grown structures. paragrahhGermanium shows typical Stranski-Krastanov islanding on a Si substrate. Surface reconstruction affects the crystallization temperatures of Ge on Si(111) surfaces during SPE. On the steps or at the out-of-phase boundaries (OPBs) of 7x7 domains, islanding takes place at a lower temperature than on 7x7 regions. Thus, Ge islands align along steps and OPBs when deposited materials are almost fully consumed in the initial stage of islanding. This enables regular arrangement of Ge islands. paragrahhIn GaAs MBE on GaAs, 2D-island nucleation and coalescence processes has successfully observed in real time. Different growth stages, nucleation of islands, coalescence of islands, and completion of a monolayer, are clearly imaged during monolayer growth. On a patterned Si(111) surface, which was heated in UHV to obtain equilibrium step structures, it is possible to grow GaAs selectively at step bands eliminating any growth on (111) terraces. Large-scale complex networks of GaAs can be fabricated using such a patterned Si substrate. paragrahhThe lateral resolution of secondary electron imaging can be improved to 1-2 nm, which is high enough to resolve most nanostructures. UHV-SEM is, thus, a promising technique for monitoring quantum structure fabrications on semiconductor surfaces.
9:50 AM		F4/B3-2-5 Investigation of Borophosphosilicate Glass Roughness and Planarization with the Atomic Force Microscope S.K. Tang (Nanyang Technological University, Singapore); V.Y. Vassiliev (Chartered Semiconductor Manufacturing Ltd., Singapore); S. Mridha (Nanyang Technological University, Singapore); L.H. Chan (Chartered Semiconductor Manufacturing Ltd., Singapore) Borophosphosilicate glass (BPSG) films have been widely used in the fabrication of Ultra Large Scale Integrated (ULSI) semiconductor devices as an interlayer dielectric between the gate and first metal level due to its excellent planarization and gettering properties ¹. BPSG films can be deposited by various chemical vapor deposition (CVD) techniques such as atmospheric and sub-atmospheric pressure CVD, low pressure CVD and plasma-enhanced CVD ². It is well known that because of the process chemistry and instability of the complex glass material, BPSG films are prone to contain surface defects due to the phenomena of moisture absorption from the ambient. In our previous works ³, ⁴, ⁵ devoted to BPSG defect formation, we concluded that surface defects can exist in the liquid state in the form of small droplets and have proposed the mechanism of these defect formation and growth. In this study, the capability of the atomic force microscope (AFM) technique to detect and characterize surface roughness of as-deposited and thermally densified BPSG films deposited using atmospheric and subatmospheric pressure TEOS-ozone based CVD as well as atmospheric and low pressure silane-based CVD were demonstrated. It was found that surface roughness of as-deposited BPSG films deposited with both atmospheric pressure techniques is higher than BPSG films created at reduced pressure. Thermal treatment of BPSG glass film, however, removed the difference in the roughness of the films. It was found that the immediate appearance and growth of liquid defects on the surface of BPSG films affect the accuracy of the BPSG roughness measurements. Issues regarding the application of the atomic force microscope on BPSG surface roughness will be discussed. The effectiveness of BPSG film planarization on the step model of device structure by flowing of film during thermal treatment is usually controlled using scanning electron microscopy (SEM) cross-section techniques. There was an attempt to use non-destructive profilometric technique ⁶ which showed the potential attraction of such an approach. In this work, AFM was used as a quick non-destructive technique for characterization of BPSG planarization in terms of the flowing angle on the step model of integrated semiconductor circuit device. Correlation dependence between AFM flowing angle and SEM analysis of the same device areas showed a linear dependence for angles less than 70 degrees. ¹ W. Kern and G. L. Schnable, RCA Review, 43(3), 423 (1982). ² T. G. Duhanova, V.Y. Vassiliev, and Y. I. Veretenin, in Reviews on Electronic Technology / (Russian), Series 3, 1370, Institute -Electronics-, Moscow, Russia (1988). ³ V. Y. Vassiliev, L. Wei, Z. J .Zheng, H. R. Wang, and L. Chan, Proc. of Third Dielectrics for ULSI Multilevel Int. Conf., 171 (1997). ⁴ S. K. Tang, S. Mridha, V. Y. Vassiliev, J. Z. Zheng and L. H. Chan, 7th International Symposium on IC Technology, Systems & Appl. 1997 (in press). ⁵ S. K. Tang, V. Y. Vassiliev, S. Mridha, L. Chan, 44th AVS National Symposium, 1997. ⁶ D. S. Williams and E. A. Dein, J. Electrochem. Soc., 134, 657 (1987).
10:10 AM	Invited	F4/B3-2-6 X-ray Diffraction and Reflection Techniques for Thin Film Analysis J.S. Spear (Philips Electronic Instruments) Thin films are importatn in many industries. The trend is toward thinner and thinner films. There are many film properties that are desirable to characterize which can be characterized with x-ray diffraction and reflection techniques. These include crystalline phase determination, crystallite size, texture, residual stress, film thickness, and interface roughness. Many of these techniques are well understood for bulk materials, but not for thin films. Thin films present many challenges for obtaining these types of data because of the smaller quantity of materials and because they often have strong preferred orientation. This presentation will give an overview of the information that can be collected with x-ray diffraction and reflection techniques on thin film materials. The hardware and analysis requirements for thin films, which differ from bulk materials, will also be discussed.
10:50 AM		F4/B3-2-8 The Effect of Transverse Current Injection on the Structural and Electrical Properties of Ti Films During Post-deposition Annealing in Air N. Parkansky, B. Alterkop, Y. Rosenberg, R.L. Boxman, S. Goldsmith (Tel Aviv University, Israel) Amorphous 0.1microm thick Ti films were deposited on glass substrates by vacuum arc deposition. Post-deposition annealing of the films was carried out at 200-400 ⁰C for 3 h in air. The film structure was examined by XRD, SEM, and EDX after each 1 h annealing. The same procedure was carried out with transverse current injection through the films. A current density of J~3.3 A/cm² was injected parallel to the film surface when a d.c. field of 1.4 V/cm was applied using silver paint contacts during annealing. After 3 h of annealing and regardless of the current injection XRD did not show any Ti lines. Crystalline phases of TiO and a small quantity of Ti₄O₇ were found in the films annealed without current injection. The quantity of TiO increased with annealing time. The same Ti films annealed with current injection contained only the TiO crystalline phase. The X-ray intensity of this phase did not change with annealing time after 1 h of annealing. After 3 h of annealing the TiO intensity was approximately an order of greater in the J=0 films than in the films annealed with current injection. Some quantity of nitrogen was found in the films after 3 h annealing with current injection. The room temperature electrical resistance of the film annealed with current injection was a factor of 3 less than without the current injection.
11:10 AM		F4/B3-2-9 Surface Morphology of Co-sputtered Alloy Thin Films J.H. Hsieh (Gintic Institute of Manufacturing Technology); Y. Liu (Gintic Institute of Manufacturing Technology, Singapore) Three alloy thin films were deposited on Si (100) by co-sputtering of various metals to investigate the formation of amorphous phase which may lead to featureless surface and structure morphologies. These thin films, including Nb-Cr, Ti-Nb, and Cr-Zr, were examined using AFM, XRD and SEM. It was found that the tendency of forming amorphous thin films by co-sputtering lay in the difference in atomic size of the paired metals. The results also showed that the degree of amorphization in these films was directly reflected on their surface and structure morphology. By controlling deposition rate of these elements, an alloyed thin film with ultra-low surface roughness and featureless structure can be developed. It was also found that the addition of nitrogen or oxygen can further reduce surface roughness to a certain extent.
11:30 AM		F4/B3-2-10 Structural and Electrochromic Properties of InN Thin Films N.A. Asai, Y. Inoue, H. Sugimura, O. Takai (Nagoya University, Japan) Indium nitride (InN), one of the III-V compound semiconductors with the wurtzite crystal structure, shows electrochromism. It is important to correlate the structural properties of InN thin films with their electrochromic properties in order to make the electrochromic mechanism clear. This paper reports on the correlation between the structural properties and the electrochromic properties of InN thin films. InN thin films were prepared by rf reactive ion plating. The structural properties of the InN films were characterized by using TEM, AFM and XRD. The electrochromic properties were measured with double-beam spectroscopy combined with an electrochemical measurement system. The chemical bonding states were determined by XPS. The InN films were prepared on glass plates and copper grids covered by collodion. The InN film which had the preferred orientation of (101) showed fine electrochromic performance. AFM image of this sample indicated granular surface morphology composed of small elliptic grains less than 100nm in diameter. These elliptic grains, which indicated the orientation of (101), grew in parallel with the substrates. This formed porous structure which provided a lot of active sites for the electrochromic reaction.
11:50 AM		F4/B3-2-11 Superlattices of Semiconductor Microstructures: Experimental Methods of Characterisation by the Third Order Non-linear Dielectric Susceptibility B.S.V. Gopalam (Indian Insitute of Technology, Madras, India) Non-linear optical properties are useful in the field of optronics. The third order non-linear dielectric susceptibility at optical frequencies increases over orders of magnitude as the dimensionality decreases, as in quantum wells, wires and dots. Some experimental methods of determination of this are examined for superlattices made out of these microstructures.
12:10 PM		F4/B3-2-12 Characterization by TEM of the Crystalline and Quasicrystalline Phases Observed During the In-Situ Heating of Al-Mn Thin Films J. Reyes-Gasga, @um A@ Pita (UNAM, Mexico) Structural characterization by TEM of the phases observed during the in-situ heating of Al-Mn thin films is presented in this work. These films were produced by evaporation of different alloys concentrations of the Al-Mn system on NaCl substrates which were hold in N₂ temperature during evaporation. The obtained amorphous phase is changed to a consecutive number of crystalline phases during the heating experiment. These series of phases include Al₆Mn, Al₄Mn, AlMn and quasicrystalline phases, all of them with a variable density of defects. The quasicrystalline phases correspond the decagonal and approximant phases. We thank the technical help of C. Zorrilla, S. Tehuacanero, P. Mexia, R. Hernandez, J.A. Ramierz and L. Rendon. This work was supported by CONACYT under project 3271P-A9608.