Real Time Applications

Real time monitoring of the interaction of Si (100) with atomic hydrogen: The "H-insertion/Si-etching" kinetic model explaining Si surface modifications
Authors: G.V. Bianco, M. Losurdo, M.M. Giangregorio, P. Capezzuto, G. Bruno
APPLIED PHYSICS LETTERS 95 161501 (2009)
Abstract: The interaction of p- and n-type crystalline silicon [c-Si (100)], with atomic hydrogen produced by a remote radiofrequency (13.56 MHz) H-2 plasma has been investigated in real time using in situ spectroscopic ellipsometry. The effects of substrate doping, temperature and time on the c-Si surface modifications are discussed. A thicker hydrogenated surface layer forms for n-type Si. This hydrogenated layer is subsequently etched by further exposure to hydrogen. A kinetic model based on the competition between hydrogen insertion and silicon etching is proposed to explain modifications of c-Si, and the rate constants of the hydrogen insertion and silicon etching processes are determined.
Email: maria.losurdo@ba.imip.cnr.it, giovanni.bruno@ba.imip.cnr.it
Analysis of controlled mixed-phase, amorphous plus microcrystalline. silicon thin films by real time spectroscopic ellipsometry
Authors: N.J. Podraza, J. Li, C.R. Wronski, E.C. Dickey, R.W. Collins
Abstract: Engineered thin films consisting of periodic arrays of silicon microcrystallites in a hydrogenated amorphous silicon host matrix have been prepared by plasma-enhanced chemical vapor deposition where the hydrogen dilution of silane is modulated in multiple cycles. These types of films have been guided by a phase evolution diagram, depicting the deposition conditions and film thickness at which the material exhibits amorphous, microcrystalline, or mixed-phase (amorphous+microcrystalline) characteristics, developed for intrinsic Si: H prepared with varying H-2 dilution on unhydrogenated a-Si: H. Real time spectroscopic ellipsometry (RTSE) has been used in situ to noninvasively determine the phase evolution of the resulting hydrogenated mixed-phase (amorphous+microcrystalline) silicon thin films and corroborated with dark-field transmission electron microscopy. Such tailored microstructures are of growing interest as components of thin film photovoltaic devices, and RTSE is shown to be a key technique for structure verification.
Email: njp140@psu.edu
Real-time evaluation of thickness, optical properties and stoichiometry of SiOx gas barrier coatings on polymers
Authors: M. Gioti, S. Logothetidis, J. Schroeder, G. Steiniger
THIN SOLID FILMS 517 6230-6233 (2009)
Abstract: Silicon oxide (SiOx) coatings have been exploited for packaging applications due to their exceptional properties. They can be fabricated by a number of techniques, including Electron Beam Evaporation (EBE); an easily applicable method in industrial scale. The SiOx films' thickness and stoichiometry are the key parameters for the achievement of the final functional properties of the systems. The need to reduce material waste as well as the time required for the evaluation of the systems, make real-time monitoring and control requisite. This work highlights a methodology based on real-time Multi-Wavelength Ellipsometry for the monitoring of the EBE processes of SiOx coatings on poly(ethylene terephthalate) membranes. It is presented a thorough correlation between the basic optical parameters, such as refractive index and Penn gap, and the SiOx films' thickness, stoichiometry. composition and functional properties, such as oxygen permeation.
Email: mgiot@physics.auth.gr
In situ spectroscopic ellipsometry as a versatile tool for studying atomic layer deposition
Authors: E. Langereis, S.B.S. Heil, H.C.M. Knoops, W. Keuning, M.C.M. van de Sanden, W.M.M. Kessels
JOURNAL OF PHYSICS D-APPLIED PHYSICS 42 073001 (2009)
Abstract: In this paper recent work on the application of in situ spectroscopic ellipsometry (SE) during thin film synthesis by atomic layer deposition (ALD) is reviewed. In particular, the versatility of this all-optical diagnostic is demonstrated by results obtained on Al2O3, HfO2, Er2O3, TiO2, Ta2O5, TiN and TaNx films with thicknesses ranging from 0.1 to 100 nm. By acquiring SE data in between the ALD cycles and by analysing the film thickness and the energy dispersion of the optical constants of the films, the layer-by-layer growth and material properties of the films can be studied in detail. The growth rate per cycle and the ALD saturation curves can be determined directly by monitoring the film thickness as a function of the number of cycles, while also the nucleation behaviour of the films on various substrates and submonolayer surface changes during the ALD half-cycles can be probed. The energy dispersion relation provides information on the optical properties, the crystalline phase and the material composition of the films. For metallic films, electrical properties can be calculated from the Drude absorption yielding insight into the electrical resistivity and electron scattering effects in ultrathin films.
Email: w.m.m.kessels@tue.nl
Monitoring plasma etching of biomolecules by imaging ellipsometry
Authors: H. Rauscher, K. Stapelmann, O. Kylian, B. Denis, F. Rossi
VACUUM 84 75-78 (2009)
Abstract: Low-pressure plasma discharges can be applied to remove various biomolecules from surfaces. However, the knowledge on the interaction between plasma and biomolecules and the kinetics of their removal is still rather poor, which is a major limiting factor for the optimization of this type of plasma treatment. This is, among other reasons, because of the restrictions of currently used techniques for the evaluation of the rates of biomolecule removal during plasma treatment. Therefore, an alternative method based on imaging ellipsometry is applied in this study. It is shown that this method allows reliable semi-quantitative comparison of the treatment efficiency of plasma discharges sustained in different gas mixtures.
Email: hubert.rauscher@jrc.it
Analysis of the early growth mechanisms during the chemical deposition of CdS thin films by spectroscopic ellipsometry
Authors: M.G. Sandoval-Paz, R. Ramirez-Bon
THIN SOLID FILMS 517 6747-6752 (2009)
Abstract: Chemically deposited CdS thin films were analyzed in this work by means of the spectroscopic ellipsometry technique. The CdS thin films were deposited from an ammonia-free process at short durations in order to obtain information about the layer microstructure and kinetic growth process. We found that the conditions of the ammonia-free reaction solution promote the ion-by-ion deposition process at the early growth stages yielding a compact, high refraction index and highly crystalline oriented CdS layers. Using a concentration of 1.82 mg/ml of cadmium in the reaction solution, the resulting films possess a double layer microstructure which consists of an inner compact layer and an external porous one. The inner layer is developed during the first 15 min of deposition time and it reaches a thickness around of 80 nm. After this time and on this inner layer of CdS, it grows an external porous layer whose thickness increases with the deposition time. The formation of the CdS compact layer at the early stages is related with the ion-by-ion growth mechanism. The subsequent CdS porous layer is formed during the cluster-by-cluster growth stage at longer deposition times. By reducing the cadmium concentration in reaction solution down to 0.76 mg/ml, maintaining constant molar ratio concentrations of Cd/complexing and Cd/thiourea, the chemically deposited CdS films develop only the inner compact layer with a thickness of about 80 nm after 35 min of deposition time.
Email: myrnasandoval@udec.cl
Application of wide angle beam spectroscopic ellipsometry for quality control in solar cell production
Authors: C. Major, G. Juhasz, P. Petrik, Z. Horvath, O. Polgar, M. Fried
VACUUM 84 119-122 (2009)
Abstract: Wide angle beam ellipsometry developed by our group uses non-collimated illumination with a special light source and arrangement giving multiple-angle-of-incidence and multiwavelength information. Our aim was to make our wide angle beam ellipsometer suitable for spectral measurement and to obtain the spectra of many points along a long line (presently 0.2 m but it could be increased up to 1 m if necessary) of an entire sample simultaneously. The prototype uses a xenon lamp as a light source with film polarizers and a concave optical grating to reach the desired 6 nm spectral resolution over the range of 360-630 nm. This new technique mixed with an appropriate ellipsometric model has the capability to make "in situ" control in solar cell fabrication. In order to demonstrate the ability of our instrument, wide angle beam spectroscopic ellipsometry measurements were carried out on Al-doped ZnO samples, which have different physical properties such as specific resistance and transparency.
Email: major@mfa.kfki.hu
In-situ spectroscopic ellipsometry: optimization of monitoring and closed-loop-control procedures
Authors: Humlicek J
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (4) 793-796 (2008)
DOI: 10.1002/pssa.200777798
Abstract: We discuss optimized extraction of information contained in a series of complex reflectance ratios in a series of consecutive, in-situ SE measurements during the growth of thin films. We present a general computational scheme and discuss guidelines for the optimum data treatment. As an example, we analyze several hundreds of spectra recorded during the growth of diamond-like carbon on TiCN/steel substrate.
Email: humlicek@physics.muni.cz
Analysis of Compositionally and Structurally Graded Si:H and Si1-xGex:H Thin Films by Real Time Spectroscopic Ellipsometry
Authors: Podraza NJ, Li J, Wronski CR, Horn MW, Dickey EC, Collins RW
AMORPHOUS AND POLYCRYSTALLINE THIN-FILM SILICON SCIENCE AND TECHNOLOGY-2008 Book Series: MATERIALS RESEARCH SOCIETY SYMPOSIUM PROCEEDINGS 1066 253-258 (2008)
Abstract: Hydrogenated silicon (Si:H) and silicon-germanium alloy (Si1-xGex:H) thin films have been prepared by plasma enhanced chemical vapor deposition of SiH4 and GeH4 and measured during growth using real time spectroscopic ellipsometry (RTSE). A two-layer virtual interface analysis has been applied to study the structural evolution of Si:H films prepared in multistep processes utilizing alternating layers of high and low H-2-dilution materials, which have been designed to produce predominantly amorphous silicon (a-Si:H) films with a controlled distribution of microcrystallites. The compositional evolution of alloy-graded a-Si1-xGex:H has been studied as well using similar methods. In each study, the depth profile of the microcrystalline silicon (pc-Si:H) content f(mu c), or the Ge content, x, has been extracted. Additionally, RTSE has been used to monitor post-deposition exposure of a-Si:H, a-Si1-xGex:H, and a-Ge:H films to hydrogen plasmas in situ in order to study the sub-surface modification and etching that would be anticipated when a highly H-2-diluted layer is deposited on a layer prepared with lower dilution. These analyses provide guidance for enhancing the performance of Si:H based solar cells through controlled fractions of microcrystallites in bulk amorphous i-layer materials using modulated H-2 dilution, through controlled bandgap profiling using compositionally graded a-Si1-xGex:H, and through a better understanding of the modification of underlying layers during the deposition of subsequent layers in multilayer stacks.
Indium adlayer kinetics on the gallium nitride (0001) surface: Monitoring indium segregation and precursor-mediated adsorption
Authors: Choi S, Kim TH, Wolter S, Brown A, Everitt HO, Losurdo M, Bruno G
PHYSICAL REVIEW B 77 (11) 115435 (2008)
DOI: 10.1103/PhysRevB.77.115435
Abstract: Indium kinetics and evidence for indium segregation on the GaN (0001) surface are investigated via in situ spectroscopic ellipsometry. Indium deposition exhibits two stable states at coverages of 1.0 and 1.7 ML within the temperature range of 630-688 degrees C. Formation of each layer is governed by two kinetic processes: nuclei formation and nuclei-mediated layer adsorption. The measured desorption activation energies of nuclei of the first (2.04 eV) and second (2.33 eV) monolayers are lower than the desorption activation energies of the aggregated first (2.64 eV) and second (2.53 eV) monolayers, respectively. This suggests that adatoms preferentially interact with the nuclei and laterally aggregate.
Email: maria.losurdo@ba.imip.cnr.it
Transient growth and thinning of the barrier oxide layer on iron measured by real-time spectroscopic ellipsometry
DOI:10.1016/j.electacta.2008.05.021
Authors: Zijie Lu and Digby D. Macdonald
Abstract: The transient growth and thinning of the passive film on iron was investigated in ethylenediaminetetraacetic acid, disodium salt (EDTA) containing borate buffer solutions of pH 8.4 using real-time spectroscopic ellipsometry under potentiostatic control. EDTA effectively suppressed the formation of the outer layer of the passive film, thereby rendering the barrier layer amenable to direct examination. It was shown that the barrier layer growth was completed in about 10 s upon potential stepping in the anodic direction. On the other hand, the thinning of the barrier oxide layer upon potential stepping in the cathodic direction occurred at a rate that was two orders in magnitude lower than the growth rate. The steady-state barrier layer thickness varied linearly with applied potential, whereas the steady-state current density did not depend on the formation potential. These spectroscopic ellipsometric measurements are qualitatively explained by the point defect model (PDM).
Plasma-enhanced chemical vapour-deposited silicon nitride films; The effect of annealing on optical properties and etch rates
Authors: Wright DN, Marstein ES, Rognmo A, Holt A
SOLAR ENERGY MATERIALS AND SOLAR CELLS 92 (9) 1091-1098 (2008)
DOI: 10.1016/j.solmat.2008.03.013
Abstract: The optical properties and etch rates of silicon nitride (SiNx:H) deposited by plasma-enhanced chemical vapour deposition (PECVD) and their correlation with bond concentrations have been studied. By varying the silane-to-total gas ratio, films with refractive index (n) between 1.92 and 3.00 were deposited. Higher n films had increased absorption and decreased etch rates. Annealing the samples at different temperatures revealed that all films were thermally stable up to 750 degrees C, above which all experienced a rise in it, attributed mainly to mass densification. The etch rate correlated well the N-H bond concentration for both annealed and as-deposited films.
Ultrafast dynamic ellipsometry measurements of early time laser ablation of titanium thin films
Authors: Bolme CA, Funk DJ
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 92 (4) 761-766
DOI: 10.1007/s00339-008-4612-1
Abstract: The dynamics of laser ablated titanium thin films are investigated using a recently developed technique that measures time-resolved and one-dimensional spatially-resolved ablation dynamics in a single shot. Ultrafast dynamic ellipsometry, a technique based on space-shifted spectral interferometry, uses the time-dependent frequency of a chirped laser pulse to provide time encoding, allowing the picosecond probing of material dynamics in a single shot. With this technique, the sample is probed at two different incident angles with both s- and p-polarized light, which measures the motion of the material and any change in its complex refractive index. Ultrafast dynamic ellipsometry is applied to study the mechanism of initiation by laser-based optical detonators that employ the ablation of titanium thin films. The resulting data indicate that the titanium is ablated as a fragmented flyer and not as an expanding plasma.
Real-time study of a-Si : H/c-Si heterointerface formation and epitaxial Si growth by spectroscopic ellipsometry, infrared spectroscopy, and second-harmonic generation
Authors: Gielis JJH, van den Oever PJ, Hoex B, van de Sanden MCM, Kessels WMM
PHYSICAL REVIEW B 77 (20) 205329 (2008)
DOI: 10.1103/PhysRevB.77.205329
Abstract: The performance of many devices based on Si thin films deposited on crystalline Si (c-Si) is highly governed by interface quality. For many of these applications, only fully epitaxial films or fully amorphous films having an abrupt interface with the substrate are desired. However, the realization of these perfectly sharp interfaces and the mechanisms governing their formation are not fully understood yet. In this study, the interface formation between Si thin films and c-Si has been investigated by simultaneously applying three complementary optical techniques in real time during low temperature Si film growth. The films were deposited in a hot-wire chemical vapor deposition process by using both native oxide covered and H terminated Si(100) substrates. The formation of hydrogenated amorphous Si (a-Si:H), epitaxial Si, and mixed phase Si has been detected with spectroscopic ellipsometry, by measuring the optical properties of the growing films. The evolution of the hydrogen content and hydrogen bonding configurations in the films has been monitored by attenuated total reflection infrared spectroscopy. A clear dependence of the hydrogen content on film morphology is observed with the amorphous films containing significantly more hydrogen. The surface and interface sensitive technique of second-harmonic generation (SHG) has been applied both spectroscopically and in real ;time. The SHG spectra of a-Si:H films on Si(100) obtained in the SHG photon energy range of 2.7-3.5 eV revealed a dominant contribution originating from the film/substrate interface related to E-0'/E-1 critical point (CP) transitions of c-Si. The real-time behavior of the SHG response is shown to strongly depend on differences in initial film morphology, which allows for identification of direct a-Si:H/c-Si heterointerface formation, nanometer-level epitaxial growth, and fully epitaxial growth at a very early stage of film growth. On the basis of the results obtained by the three optical techniques, the c-Si surface passivation mechanism by a-Si:H thin films is addressed and it is demonstrated that the combination of the techniques provides a profound method to control processes occurring during Si thin film growth.
M-plane III-nitride materials for polarization sensitive devices grown by PAMBE with real time analysis by spectroscopic ellipsometry
Authors: Misra P, Boney C, Pillai R, Starikov D, Bensaoula A .
PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS 5 (6) 2286-2289 (2008)
Abstract: In this paper we present a study of the growth of M-plane GaN epilayers on LiAlO2 substrates under Ga rich conditions and growth at Ga stable conditions by plasma assisted molecular beam epitaxy (PAMBE) coupled with in-situ spectroscopic ellipsornetry (SE). Previous studies on M-plane materials have suggested that, optimum growth conditions with respect to surface morphology, are those giving rise to Ga tri-layer coverage at low growth temperature. By studying Ga ption/desorption in vacuum and in the presence of active nitrogen we find that the total coverage for M-plane material is distinctly different for these two conditions. Under vacuum, the stable Ga coverage corresponded of 0.48 nm, while a thicker Ga stable coverage of 0.7 ma was determined N plasma. Using these GaN growth conditions, M-plane InGaN layers were grown and fabricated into polarization-sensitive photodetectors.
Ellipsometry studies of the kinetic of deprotection of thin 193 nm positive tone resist film
Authors: Ridaoui H, Derrough S, Sourd C, Trouve H, Pikon A, Tortai JH
ADVANCES IN RESIST MATERIALS AND PROCESSING TECHNOLOGY XXV, PTS 1 AND 2
Book Series: PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS (SPIE) 6923, pages: 92326-92326, part 1-2 (2008)
Abstract: A new methodology that allows monitoring the deprotection kinetic of UV sensitive thin resist films was recently developed at LTM. This tool measures by ellipsometry changes in optical properties of thin resist films heated at a PEB temperature and exposed to UV.
This article presents results of the deprotection kinetic of model resist supplied by Rohm and Haas. Films thicknesses range from 58nm to 150nm. Two thermal protocols were used to check an impact of the film thickness on the deprotection kinetic. The first one is a thermal ramp were temperature increases at a given rate. Prior to this ramp the sample was exposed to UV for 60s with the help of a broadband Xe lamp. This protocol allows detecting the temperature that initiates the deprotection reaction into the film. The second test consists in heating the samples at a fixed temperature for a given time and to expose to UV the film at this temperature. This studies supplies information on the deprotection kinetic occurring in the film at this temperature.
The work we did on 193 nm resist films clearly shows that this technique can monitor both the thermal initiation of the deprotection and the real time measurement of the compaction kinetic of the film during the PEB. The initial film thickness impact on the deprotection kinetic is presented in this paper to check whether lithography processes should be adapted to the film thickness.
Pyrolysis, crystallization, and sintering of mesostructured titania thin films assessed by in situ thermal ellipsometry
Authors: Bass JD, Grosso D, Boissiere C, Sanchez C
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (25) 7882-7897 (2008)
DOI: 10.1021/ja078140x
Abstract: In-situ thermal ellipsometric analysis is used to elucidate new and fine-scale details on the thermally driven densification, pyrolysis, crystallization, and sintering of dense and ordered mesoporous titania thin films prepared by evaporation-induced self-assembly. The role of the heating schedule, initial film thickness, nature of the substrate and templating agent, solution aging, and presence of water and other additives in the calcination environment is examined. Each of these parameters is shown to have unique and often substantial effects on the final film structure, while the technique itself provides detailed insight into the chemical origin and evolution of these effects. In-situ monitoring and control over the governing chemical processes, such as high-temperature adsorption phenomena that impact nanocrystal growth, is also demonstrated. The evolution of both the porosity and chemical processes occurring inside these materials are evaluated, including extraction of kinetic parameters for the pyrolysis of the template and crystallization of the matrix walls. The latter is shown to be strongly dependent on the presence of mesoscale ordering with ordered cubic films indicating a 1D diffusion-limited crystallization process and dense films following a 3D diffusion-limited process. Less well-ordered mesoporous films, despite similarities in pore volume and pore size distributions, are kinetically more reminiscent of dense films in terms of crystallization. In-situ thermal ellipsometry, by detailing the evolution of the thermally driven chemistry and ceramization that dictate the final film properties, provides immensely important insight into the synthesis and optimization of advanced functional materials based on titania and other metal oxide thin films.
In-situ polarimetry of illumination for 193-nm lithography
Authors: Nomura H, Furutono Y
OPTICAL MICROLITHOGRAPHY XXI, PTS 1-3
Book Series: PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS (SPIE) 6924, pages: T9241-T9241, part 1-3 (2008)
Abstract: Ellipsometry is defined as a technique for determining the properties of a bulk material or a thin film, such as optical index and thickness, from the measurement of a polarization state of a reflected light or a change of polarization states between the incident and reflected lights. On the other hand, polarimetry is defined as a technique for determining a polarization state of a light. In other words, ellipsometry uses polarization as a probe and polarimetry measures polarization itself.
We have constructed a theory of polarimetry of illumination used in lithography equipments, fabricated a polarimeter mask, and demonstrated it for a hyper-NA (numerical aperture) immersion lithography scanner. The polarimeter mask comprises polarizers and quarter-wave (lambda/4) plates that are crammed into a narrow space with a height of 6.35 mm. The thin plate polarizers available at a wavelength of 193 nm are made of calcite, and the lambda/4-plates insensitive to angle of incidence are made of four thin plates, two of which are crystalline quartz; the other two are sapphire. A light traveling through a window of the polarimeter mask reaches an image detector at the wafer level through projection optics. Stokes parameters of the illumination light can be measured without any influence from polarization characteristics of the projection optics between the mask and the image detector.
Dielectric functions of a growing silver film determined using dynamic in situ spectroscopic ellipsometry
Authors: Oates TWH, Ryves L, Bilek MMM
OPTICS EXPRESS 16 (4) 2302-2314 (2008)
Abstract: The dielectric functions of plasma deposited silver on SiO2 through all stages of Volmer-Weber growth at room temperature and 150 degrees C were determined unambiguously by applying a model-independent inversion method to dynamic in situ spectroscopic ellipsometric data. The results show large differences in the localized plasmon resonance and the percolation threshold at the two temperatures. Using these model-independent dielectric functions we assess the effectiveness of modelling the plasmon resonance by fitting a Lorentz oscillator. The methods show agreement for the position of the plasmon resonance below the percolation threshold and for the effective film thickness up to 5.6 nm at room temperature and 11.5 nm at 150 degrees C, however the line shape of the resonance is described by the Lorentzian only in the early stages of film growth.
Email: oates@physics.usyd.edu.au