ICMCTF2003 Session C4/F2: Nondestructive and In-Situ Characterization Techniques and Process Monitoring

Wednesday, April 30, 2003 1:30 PM in Room Royal Palm 4-6

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	C4/F2-1 Real Time Control of the Deposition of Optical Coatings by Spectroellipsometry B. Drevillon, P. Bulkin (Ecole Polytechnique, France) In-situ spectroscopic ellipsometry is known to be very sensitive, non-invasive technique for monitoring and control of thin film growth. In the production of optical interference coatings the refractive index of the material is usually assumed to remain constant within a single layer. Under such assumption only the optical thickness of the layer can be efficiently controlled. For modern complex structures, however, even insignificant deviation from the design, due to shift in the refractive index, can be very detrimental to the resulting performance of the coating. Simultaneous real-time determination of refractive index and growth rate is necessary in order to comply with strict specifications. If the index departs from the target value, one has to adjust process parameters of the process and, ultimately, perform re-calculation of the filter structure. The talk will review the work performed at our laboratory during last few years. Development of several different control strategies will be discussed and their application to control of PECVD of optical interference coatings demonstrated. Latest work is concerned with advances in the closed-loop control of the fabrication of optical thin films by in-situ multi-wavelength phase-modulated kinetic ellipsometry using both, direct numerical inversion algorithm for the real-time reconstruction of refractive index and layer thickness and real-time fitting-based strategies. Those techniques are being tested on quarter-wave index optical filters as well as on graded refractive index profiles and demonstrate efficiency and robustness.
2:30 PM		C4/F2-4 Analysis and Control of TiO₂ Film Growth by PECVD Using In Situ Real-Time Spectroscopic Ellipsometry A. Amassian, P. Desjardins, L. Martinu (École Polytechique de Montréal, Canada) During the past decade, ex situ variable angle spectroscopic ellipsometry (VASE) has become a standard tool for high-precision thin film metrology in the FAB environment and in optical coatings (OCs). Today, in situ real-time spectroscopic ellipsometry (RTSE) is emerging as an important instrument for material develoment and optimization. In the present work, we describe the use of RTSE for the analysis of the deposition process of optical materials and for the control of the fabrication of optical filters by plasma-enhanced chemical vapor deposition (PECVD). We specifically focus on the investigation of the initial stages of TiO₂ growth on oxidized c-Si using both in situ and ex situ SE, and XRR (X-ray reflectivity). Dynamic analyses show that the growing TiO₂ films reach a critical coalescence thickness, d_c, that varies strongly with the growth rate, r, and substrate temperature, T_s. For T_s= 25°C, d_c varies from 20-25Å to 70-80Å and to ~ 150Å when r is increased from 0.3Å/s to 3Å/s and to >10Å/s, respectively. For comparison, at T_s= 150°C and r = 15Å/s, d_c= 80Å. This work correlates the film nucleation mechanism and the depth profile with process parameters, such as r, T_s, and plasma power. Examples of the growth of TiO₂ on SiO₂ and of SiO₂ on TiO₂ are also presented in the context of multilayer interference filter applications.
3:10 PM		C4/F2-6 Determination of Pore Size Distribution in Thin Mesoporous Oxide Films by Spectroscopic Ellipsometry A. Bourgeois, A. Brunet-Bruneau (University of Paris, France); S. Fisson (UMR CNRS 7601, France); D. Grosso, J. Rivory (University of Paris, France) Spectroscopic ellipsometry is a non destructive technique, well adapted to the determination of pore volume fraction, pore size distribution and accessible surface area of porous thin films, it is particularly attractive for low-k films. These quantities are deduced from the variation of the refractive index during adsorption and desorption of gas ^1,2. Several difficulties are encountered in the interpretation of the ellipsometric spectra, in particular the knowledge of the density and refractive index of the skeleton, its fraction of micropores, the variation of the film thickness during adsorption/desorption process. We present results obtained on mesoporous oxide films prepared by surfactant templating methods. A combination of spectroscopic ellipsometry measurements in the visible and in the infra red range is shown to solve part of the uncertainties mentioned above, in particular for silica films, where a realistic estimation of the skeleton refractive index can be obtained. ¹M. R. Baklanov, K. P. Mogilnikov, V. G. Polovinkin, F. N. Dultsev, J. Vac. Sci Technol B 18, (2000) 1385. ² C. Wongmanerod, S. Zangooie, H. Harwin, Appl. Surf. Sci.172, (2001) 117.
3:30 PM		C4/F2-7 Reactivity of Mesoporous Silica Films to Environment Pollution Studied by Infrared Ellipsometry A. Brunet-Bruneau, J. Rivory (University of Paris, France); S. Besson, T. Gacoin, J.P. Boilot (Ecole Polytechnique, France) This paper discusses the origin of the increase of the refractive index of mesoporous silica films during aging in air. Indeed spectroscopic ellipsometric measurements in the visible range show a strong increase of refractive index from 1.25 to 1.48, without significant thickness variation. Analysis of the infrared ellipsometry spectra allow us to conclude that silica skeleton remains unmodified during aging, whereas an important carbon and water contamination of pores is observed. This contamination leads to the increase of pores refractive index (from 1 to 1.5), while the skeleton refractive index and the pore volume fraction remain unchanged. This work also allows to point out that porosity can not be determined from the value of refractive index in the visible range without the knowledge of the skeleton refractive index and the pore content.
3:50 PM		C4/F2-8 Measurement of the Elastic Properties of Nanometer Thick Films: Comparative Assessment of Surface Brillouin Scattering and Laser-Induced Ultrasonics M.G. Beghi, C.E. Bottani (Politecnico di Milano, Italy); D. Schneider (Fraunhofer Institut, Dresden, Germany); A.C. Ferrari, J. Robertson (University of Cambridge, United Kingdom); R. Ohr, C. Shug (IBM Germany) Nanometer thick carbon films are of high interest for magnetic hard disk coatings and read-write heads. Next generation hard disk drives require carbon overcoats with thickness in the 1-2 nm range, to reach storage densities above 100 Gbit/in². As future head flying heights of about 6 nm promote head-disk contacts, the mechanical characterization of such films is of primary importance. For the measurement of the elastic moduli two techniques, both exploiting surface acoustic waves (SAWs), have been proposed: Surface Brillouin Scattering (SBS) and laser-induced SAWs (LISAW). In this work their performances have been assessed by a round robin test: two sets of carbon films, grown on silicon by two different cathodic arc systems, were independently measured by SBS and LISAW. Both techniques are non-destructive: they measure the velocity of SAWs, and derive from it the film properties. Their operation is however significantly different: while SBS relies on thermally excited SAWs, LISAW induces them by laser pulses, and allows significantly faster measurements. LISAW analyses pulse propagation in the time domain, while SBS is a spectroscopic technique. LISAW measures propagation in the MHz to hundreds of MHz frequency range, while SBS operates in the tens of GHz range, and is thus potentially more sensitive to perturbations by thin films. However velocity measurements by LISAW are more precise, and these two facts tend to compensate. The results of the round robin test show a good correlation between the Young's moduli measured by SBS and LISAW. This proves the ability of SAW based techniques to assess the Young's modulus in a thickness range not attainable by conventional techniques, such as nano-indentation. However, some systematic numerical differences are present between the sets of data provided by the two techniques. The causes for such differences are discussed and indications to improve measurements and data analysis are given.
4:10 PM		C4/F2-9 Adhesion Behaviour at Elevated Temperatures of CrN Coatings on Pretreated Metal Substrates Studied In-situ by PBA and ESEM R. Escobar Galindo, A. van Veen, H. Schut (Delft University of Technology, The Netherlands); J.Th.M. De Hosson (University of Groningen, The Netherlands) In this work we present a combined Positron Beam Analysis (PBA) and Environmental Scanning Electron Microscopy (ESEM) adhesion study on thin Chromium Nitride (CrN) coatings. Both techniques are equipped with a 4-point bending stage. PBA monitors the creation of open volume in the ceramic/metal interface prior to delamination while ESEM observations provide a picture of the delamination process itself. By varying the positron implantation energy, the coating layer or the coating/substrate interface can be studied separately. Coatings of 500 nm thickness were deposited via PVD on three types of steel (stainless (SS), tool (TS) and interstitial free (IFS) steel) and on polycrystalline copper. One TS and one IFS substrate were implanted with Zn ions at a flux of 10¹⁶ cm^-2 prior to the coating deposition. Samples were studied as deposited, after 30 minutes annealing at 973K and during 4-point bending test. After annealing the PBA results differ depending on the substrate. The S parameter ascribed to the nitride coating increases for both the implanted tool steel and the polycrystalline copper. This increase is observed all over the coating thickness. In the case of the IF steel there is a lower S parameter in the first 75 nm of the coating. With increasing depth S rises towards a value similar to the implanted TS and copper annealed samples. This 2-layer structure inside the coating is more pronounced for the implanted IFS sample. The different behaviour of the coating after annealing in dependence on the substrate is confirmed by ESEM observations and it is related to the adhesion properties of the coating. The S value ascribed to the interface increases in all samples after the annealing process confirming the creation of open volume at the interface. 4-point bending tests revealed a plastic deformation of the coating deposited on the soft IF substrate and a brittle delamination of the film when deposited on the hard tool steel. .
4:30 PM		C4/F2-10 Inhomogeneity of Titanium Oxide Film Studied with Spectroscopic Ellipsometry Technique L. Sun (SOPRA Inc); P. Hou (Nortel Networks) As a high refractive index film, titanium oxide (TiO₂) thin film has been widely used as optical coatings, generally when high-low index contrast is desired in multiple layer interference coatings. It is well known that structure and properties of TiO₂ films are highly dependent on processing technique. To study inhomogeneity formed in TiO₂ film, the destructive method such as the Scanning Electron Microscope (SEM) or Transmission Electron Microscope (TEM) is often used. In this paper, the non-destructive optical approach, spectroscopic ellipsometry (SE) technique is used for this purpose. It is found that SE technique can be successfully used to identify homogeneity information inside the film. Through closely monitoring the deposition process, the major reason for this inhomogeneity is the chamber temperature.