Papers

AVS1997 Session TF1-ThA: Ex-Situ Characterization

Thursday, October 23, 1997 2:00 PM in Room B3/4

Thursday Afternoon

Start	Invited?	Item
2:00 PM		TF1-ThA-1 An XPS Analysis of Several Co_3-y Fe_y O₄ Films and Their Optical Properties. P. Ruzakowski Athey (PPG Industries Inc.); P.H. Holloway (University of Florida, Gainesville); E.G. Goralski (PPG Industries Inc.) A series of Co_3-y Fe_y O₄ films has been analyzed with x-ray photoelectron spectroscopy (XPS) to determine film composition through a deconvolution process. These films were deposited onto soda-lime-silica substrates by spray pyrolysis of metal acetylacetonates. Five compositions were chosen by varying the starting molar ratios of metal acetylacetonates. The XPS core level spectra of the mixed-metal oxides are compared to their single metal oxide counterparts and discussed. The composition was also determined with x-ray fluorescence (XRF) and is compared to that determined from XPS deconvolution analysis. X-ray Diffraction (XRD) was used to monitor the lattice shift expected in the XRD patterns as a function of composition. Each film s optical constants and thickness were determined from reflectance (frontside (R1) and backside (R2)) and transmittance(T) measurements as a function of composition.
2:20 PM		TF1-ThA-2 A High Resolution XPS Investigation into the Oxidation Resistance of Ti_1-xAl_xN Based Layers C.J. Blomfield, B.J. Tielsch (Kratos Analytical Limited, United Kingdom); D.J. Surman (Kratos Analytical Inc.); L.A. Donohue, I.J. Smith, W.D. Munz (Sheffield Hallam University, United Kingdom) Ti_1-xAl_xN PVD coatings are commonly used in high temperature wear resistance applications such as dry machining and forming. Recently cation substituted alloys of Ti_1-x-y-zAl_xCr_yY_zN with y = 0.03 and z = 0.02 have been shown to offer enhanced high temperature oxidation resistance when compared with TiN and Ti_1-xAl_xN layers. Such films were deposited by a combined steered arc evaporation/unbalanced magnetron sputter deposition process on austenitic stainless steel and subsequently analysed with high resolution monochromatic XPS. The detection limits of XPS would often preclude surface chemical analysis of such low atomic concentrations of Cr and Y however such problems are overcome by the high sensitivity of the Axis Ultra electron spectrometer. Analysis at both normal and glancing angles revealed the presence of a complex passive oxide layer on the as-deposited films. High resolution chemical state imaging and small area XPS have been employed to investigate the surface oxide distribution and the role played by Cr and Y in the improved oxidation resistance of the Ti_1-x-y-zAl_xCr_yY_zN films.
2:40 PM		TF1-ThA-3 An Investigation of the Optical Properties and Composition of Three Binary Metal Oxide Films: Co_3-y Fe_y O₄, Co_3-x Cr _x O₄, and Cr_x Fe_yO₄. P. Ruzakowski Athey (PPG Industries Inc.); P.H. Holloway (University of Florida, Gainesville) Three optically absorbing mixed-metal oxide films, Co_3-yFe_y O₄, Co_3-xCr_xO₄, and Cr_xFe_yO₃, have been characterized with a variety of analytical techniques to determine their optical properties and composition. These films were deposited onto soda-lime-silica substrates by spray pyrolysis of metal acetylacetonates in an aqueous suspension. Three specific compositions were chosen based on a previous optical characterization study of a mixed-metal oxide film, Co_3-x-yCr_xFe_yO₄, where the starting metal acetylacetonate mole ratios are equivalent in the binary and ternary metal oxide systems. The optical constants and film thickness were determined from reflectance (frontside (R1) and backside (R2)) and transmittance(T) measurements. For these types of samples, this optical procedure is a major improvement over a previous method. With the current method, surface roughness information (previously obtained from AFM) was not necessary, and the modeling time is substantially reduced. The film composition was investigated with x-ray photoelectron spectroscopy (XPS), x-ray fluorescence (XRF) and sputtered neutral mass spectrometry (SNMS).
3:00 PM		TF1-ThA-4 Infrared and Ellipsometric Analysis of Ion Implanted SiO₂ Y.S. Tung, R. Mu, A. Ueda, Z. Gu, D.O. Henderson (Fisk University); C.W. White, J.G. Zhu, R.A. Zuhr (Oak Ridge National Laboratory) This paper presents a spectroscopic study of ion implanted SiO₂ characterized by external infrared reflectance and ellipsometry. The infrared reflectance spectra are processed by the Kramer-Kronig transformation to obtain the LO and TO spectra. Ellipsometry is used to measure the refractive index of the implanted SiO₂. The Si-O-Si asymmetric bond stretching vibration at 1100 cm^-1 is found to be red shifted as compared to virgin SiO₂. The implantation induced densification and Si-O-Si bond breaking are the mechanisms for the peak position shift. The densification effect is examined by the relationship of infrared peak position, Si-O-Si bond angle, and refractive index. The bond breaking is examined by the formation of a peak located at 960 cm^-1 which is attributed to the Si-O--- dangling bond. This peak disappears after annealing at 600°C for 30 minutes. The red shifted 1100 cm^-1 peak blue shifts after annealing. Therefore, the annealing is believed to lead to the recovery of the broken Si-O-Si bonds. Due to the Gaussian nature of the implanted profile, chemical etching is performed on the implanted samples to obtain infrared spectra and the refractive index of SiO₂ at different implantation depths from the surface. The implanted profile characterized by this method is correlated with the results from Rutherford Backscattering Spectrometry (RBS).
3:20 PM		TF1-ThA-5 Negative Ion Assisted Silicon Oxidation at Low Temperature H. Shindo, T. Koromogawa, Y. Sawa (Tokai University, Japan); T. Ichiki, Y. Horiike (Toyo University, Japan) Low temperature and low damage silicon oxidation technique is highly required in various ULSI processes. Especially for trench isolation of memory cell, the oxidation should be ion-assisted for directionality but with low damage. For this purpose, a new method of negative ion assisted silicon oxidation was experimentally studied employing a microwave O₂ plasma. A feasibility of high rate and low temperature silicon oxidation by negative ion was examined.The plasma produced in a 6 inch stainless-steel chamber was employed and the downstream plasma was mainly concerned because the negative ion was highly populated. Ion mass and energy analysis showed that the dominant negative ion was O^- and its density was more than one order higher than O₂ ^-. Silicon oxidation was made on a stage in the downstream at 20 cm from the microwave window, and the stage was biased by DC voltage to irradiate both negative and positive ions. The oxide film quality thus produced was analyzed by XPS, FTIR and ellipsometer. The oxide film thickness was measured by two methods of XPS and ellipsometer, and they were very consistent. The oxidation rate at the positive bias showed as high as 100 A/min at +100 V and it was one order higher than those at the negative bias of -100 V or at no bias. This high rate of oxidation at the positive bias is due to its high chemical reactivity which comes from the fact that the negative ion O^- is atomically like the O radical. The activation energy for the oxidation by the negative ion was obtained as about 0.11 eV, this value is very close to that obtained by the radical oxidation⁽¹⁾, supporting the interpretation of high rate. Since the oxidation is ion-assisted, this method provides a powerful technique to preform a directional oxidation of the silicon at low temperature. (1) T.Fuyuki: Jpn. J. Appl. Phys. 33(1994)440.
3:40 PM		TF1-ThA-6 Infrared Spectroscopy and UV-Visible Ellipsometry Analysis of SiO₂ Films Deposited from O₂/TEOS Plasmas A. Goullet, C. Vallée, K. Aumaille, G. Turban (Institut des Matériaux de Nantes, France) Silicon dioxide thin films have been deposited at low pressure (a few millitorr) on silicon substrates in oxygen/tetraethoxysilane (O₂/TEOS) helicon diffusion plasmas. The reactor is operated at 300 W rf power without heating or biasing the sample. In earlier studies the plasmas have been characterized by different complementary diagnostics. The films are analysed by combined use of ex situ infrared spectroscopy and in situ spectroscopic UV-Visible ellipsometry. Complementary chemical etching (p-etch) and density measurements have been performed. Changes in the film properties are observed varying the TEOS fraction in the O₂/TEOS mixture. As the TEOS fraction increases the growth rate and the chemical etching rate increase while the density of the film decreases. This behavior corresponds to the incorporation of voids during the growth and is related to water absorption by postdeposition exposure to air. In addition, silanol groups incorporate during the growth within the films. Normalized infrared absorbance spectra between 2800 and 3800 cm^-1 are deconvoluted to quantify the silanol and water content. For porous films, the water band clearly dominates in the infrared spectra whereas the absorption peak is shifted to silanol band for denser films. The Bruggeman effective medium approximation is used both in the UV-Visible and infrared range to determine the fraction of voids included within the films. Films close to a thermal oxide exhibit efficient moisture barrier properties which allowed , using a two layer deposited sample,to estimate part of in situ and ex situ incorporated water and silanol groups in a porous film.
4:00 PM		TF1-ThA-7 Structure of the Interfacial Region between Polycarbonate and Plasma-Deposited SiN_1.3 and SiO₂ Optical Coatings. A. Bergeron, D. Poitras, J.E. Klemberg-Sapieha, L. Martinu (Ecole Polytechnique, Canada) Optical coatings are used in increasingly demanding applications. In particular, optical films on plastic substrates present a considerable challenge due to the necessity to control adhesion and the properties of the interface. In our laboratory, we use dual-mode microwave/radiofrequency (MW/RF) PECVD of silicon compound films for optical coatings ¹. We have shown earlier an evidence that an extended interfacial region exists between the PECVD films and the polymeric substrate ². In the present work, we investigate the structural characteristics of this interfacial region for the particular case of Si-compound films on polycarbonate (PC), using different plasma conditions for surface pretreatment in order to enhance adhesion. We characterize the films, the substrates and the interfaces by non-destructive optical methods using variable angle spectroscopic ellipsometry and in situ spectrophotometry, and by other techniques such as AFM, XPS and cross-sectional TEM. We found that the interfacial region consists of a crosslinked layer about 15 to 50 nm thick (depending on the pretreatment conditions). We correlate the depth profile of the refractive index, the interface roughness and the chemical composition gradient at the interface with the adhesion strength and with the optical response of SiN_1.3/PC and SiO₂/PC systems. We point out the importance of including the interface structure in the optical design of thin film multilayer systems on plastic substrates. ¹D. Poitras, J.E. Klemberg-Sapieha, S.C. Gujrathi and L. Martinu, Optical Engineering, 35 (1996) 2693. ²J.E. Klemberg-Sapieha, D. Poitras, L. Martinu, N.L.S. Yamasaki and C.W. Lantman, J. Vac. Sci. Technol. A., 15 (1997) May/June.
4:20 PM		TF1-ThA-8 Heterogeneity in Hydrogenated Silicon: Evidence for a Linear Chain-like Structure D.V. Tsu, B.S. Chao, S.J. Jones, S.R. Ovshinsky (Energy Conversion Devices, Inc.); J. Yang, S. Guha (United Solar Systems Corp.); R. Tsu (University of North Carolina, Charlotte) The microstructure of thin 50 nm Si films, made by PECVD under a wide range of hydrogen dilution of disilane gas is investigated using high resolution TEM as well as Raman spectroscopy. As the dilution level increases from none to moderate, the position of the broad TO Raman peak (associated with "amorphous" Si) increases from 475 to 483 cm^-1. At high dilution levels, both Raman and TEM reveal micro-crystalline inclusions, while the micro-crystalline phase predominates at the highest dilution levels. However, the TEM results show that even the so called "amorphous" phase is neither homogeneous nor completely amorphous, e.g., as described by a continuous random network (CRN). In addition to the short range order of the CRN-like phase, we identify the presence of a new structural component that is neither completely amorphous, nor completely ordered as in the micro-crystallites. This intermediate phase has a linear chain-like structure (1 to 2 nm wide, lengths 10's of nm's) that shows evidence of order along its length. As the dilution increases, so do the length and volume % of the chains. TEM shows the chains are present even in films produced with no dilution. Raman measurements show enhanced scattering at 490 cm^-1 that we believe is a signature of these chains, and that the shift in the TO peak position with dilution is associated with the enhancement of this 490 cm^-1 band. Deconvolution analysis allowed us to quantify the relative volumetric content of the chain-like phase: it ranges from ~ 5 % in the no dilution films to ~ 15 - 20 % for films made at moderately high levels (where micro-crystallites exist but do not predominate). For very high dilution levels, the 490 band is distinctly evident. The presence of the 490 band is not solely limited to the very high H₂ dilution levels normally associated with the deposition of poly-crystalline material, but in fact exists in materials made at all dilution levels.
4:40 PM		TF1-ThA-9 Texture Formation and Surface Roughening of Ni Thin Films Deposited by Magnetron Sputtering onto SiO₂/Si, MgO and SiC Surfaces E.B. Svedberg, P. Sandström, J.-E. Sundgren, L.D. Madsen (Linköping University, Sweden) Epitaxial growth often provides homogeneous and smooth surfaces important for diverse applications such as ultra-high density microelectronic device structures, and for buffer layers in magnetic multilayers and superlattices. Ni films of 200 nm thickness were ultra high vacuum (UHV) sputter deposited at 200 and 400 C onto oxidized silicon, MgO (001) and offcut 4H SiC wafers. The structure and morphology of the films were analyzed using XRD and AFM. Prior to growth the MgO and SiC substrates were in situ pretreated at ~950 C for 15 min to obtain clean substrate surfaces. The MgO(001) showed a 1x1 reconstruction and the SiC surface exhibited a √3x√3 reconstruction. In all cases the deposited Ni films were cubic and highly oriented. On the oxidized Si wafers, x-ray diffraction pole figures showed the Ni to have a <111> fiber texture regardless of deposition temperature. On SiC, the films were highly oriented with Ni [111]//SiC [0001]. The in-plane-orientation showed a 6-fold symmetry resulting from growth of two 111-oriented domains. Atomic force microscopy (AFM) revealed grains 40 nm in diameter with an rms roughness of 1.2 nm for the 200 C film. The 400 C films showed no pronounced grain structure whilst maintaining a similar rms roughness (1.3-1.5 nm). On MgO, the texture varied considerably with temperature. At 200 C, smooth, single-crystal layers with a complete (200), cube-on-cube, texture were obtained (despite a 16% mismatch), whereas at 400 C, a (751) texture formed that was four-fold degenerate and twinned. This change in texture was accompanied with a transition to a pronounced faceted surface as shown by AFM.
5:00 PM		TF1-ThA-10 Determining Thickness of Thin Metal Films with Spectroscopic Ellipsometry for Applications in Magnetic Random-Access Memory (MRAM) H.G. Tompkins, T. Zhu, E. Chen (Motorola, Inc.) Metal thicknesses can be determined using optical methods such as spectroscopic ellipsometry when the thickness of the film is small enough that the light penetrates to the bottom of the film. In order to use ellipsometry, it is necessary to determine the optical constants of the film material accurately. In this work, we describe the determination of the optical constants and thicknesses of single metal layers of NiFe, Cu, Co, Ta, and FeMn deposited with two different deposition methods. The thicknesses range from about 6 nm to about 20 nm thick. We have also investigated the ex situ measurement of multiple metal layers, and discuss the conditions where the thicknesses of the individual layers can be determined and the conditions were they cannot be distingushed from each other.