ICMCTF2000 Session C4: Precision in Process Control

Tuesday, April 11, 2000 3:30 PM in Room Sunset

Tuesday Afternoon

Start	Invited?	Item
3:30 PM	Invited	C4-7 Numerical Methods for the Design of Optical Multilayer Coatings with a Special Emphasis on the Manufacturability of the Solutions J.A. Dobrowolski (National Research Council of Canada) The two main numerical approaches to the design of optical multilayer coatings with a proscribed performance are refinement and synthesis. In the former a starting design that is a first approximation of the required performance is used for numerical optimization in which the construction parameters of the system are gradually adjusted until an acceptable performance is achieved. Synthesis methods are used whenever the problem is so complicated that a reasonable starting design cannot be found. Some typical refinement and synthesis methods will be mentioned. The solutions that can be obtained by these techniques depend very much on the optical constants of the available coating materials. The effect on the solutions of limitations on the optical constants will be discussed at some length. Normally the solutions will consist of inhomogeneous layers, or of homogeneous multilayer systems composed of two or more coating materials. Which of these types of solutions is chosen will depend on the equipment available in the manufacturing facility. The successful experimental implementation of the solutions will depend on the extent to which the properties of real layers fulfill the assumptions made about the films during the design. It will also depend on the ability to control the thicknesses of the layers during the deposition process. This too will be discussed. It will be shown that the use of deposition techniques that allow for real-time evaluation of the thicknesses of the deposited layers will result in a much higher yield of successful filters. This is because the thicknesses of the layers yet to be deposited can be adjusted to correct for the errors in the thicknesses of the layers already produced.
4:10 PM		C4-9 In-situ Spectroscopic Ellipsometry and Photometry for Magnetron Sputter Process Control M. Vergöhl, N. Malkomes, T. Matthée, G. Bräuer (Fraunhofer Insitute for Surface Engineering and Thin Films, Germany) Today, most optical coatings for architectural glass are deposited by reactive magnetron sputtering. Powerful tools for stabilizing the magnetron sputter process by plasma monitoring are necessary, an optical in-situ monitor is required for a real time control of the optical film properties. Within the scope of this contribution, results of ex-situ and in-situ spectroscopic ellipsometry as well as photometry are applied for monitoring the optical properties of magnetron sputtered single films and multilayers on transparent substrates. The capabilities and limits of the two methods are compared for different layer systems (e.g. low-e, antireflex, spectral selective reflecting coatings) with respect to an implementation in in-line coaters.
4:30 PM		C4-10 In sStu Interferometry Measurements Through Transparent Magnetron Sputter Deposited Films : a Powerful Tool for Optical Properties Determination and Process Control F. Perry (L.s.g.s, Umr 7570, Inpl, France); P. Pigeat (Ecole des Mines, France); A. Billard (L.s.g.s, Umr 7570, Inpl, France); A. Lelait, C. Frantz (Ecole des Mines, France) For single layer or multi-layer transparent films dedicated to applications in optics, the optical properties and the thickness of each layer must be controlled precisely during the synthesis of the film. In reactive magnetron sputtering, the deposition is usually monitored by means of optical emission spectroscopy, which is also known to constitute a powerful tool for plasma diagnostic. Although the emission line intensity of the sputtered metal, assumed to be quite proportional to the sputtering rate of the target, can be used as a convenient control parameter of the process, this method doesn't give direct information about the nature of the synthesised film. In this paper, we present a method of optical interferometry measurement as a process control and for in situ determination of the optical indexes of the transparent growing film. For this, an optical fibre sending the collected signal to a monochromator is placed behind a glass slide in order to measure the evolution of the transmission intensity, characteristic of the film optical properties and of the deposition rate, during the growth of the coating. This method is very sensitive and also constitutes a convenient technique to determine the transient sputtering operation just preceding the steady state stage. In this technique, either excited argon emission or a halogen lamp can be used as light source, the former being very attractive for applications in industrial plants. The fitting of the experimental transmittance evolution by the calculated one is performed with a MATLAB routine of roots mean square minimisation. This parameters determination, by the inverse problem resolution with the simplex method, leads rapidly to the optical indexes, n and k, and to the thickness of the growing film. By means of this technique, bi-layers of transparent oxides have been synthesised with a good accuracy of optical parameters and a precisely controlled thickness.
4:50 PM		C4-11 Chrome Nitride Growth via Ellipsometric Process Monitoring and Control J.H. Perales, D.M. Hornyak, J. White, S.R. Kirkpatrick, S.L. Rohde (University of Nebraska) A combination of single layer and multilayer Cr, CrN and Cr2N thin film coatings was deposited on (100) silicon substrates using ion assisted reactive magnetron sputtering. Real-time in situ ellipsometry was used in tandem with target voltage monitoring techniques to control the deposition process. These coatings were characterized post-deposition using X-ray diffraction (XRD) and spectroscopic ellipsometry (SE), in some cases X-ray Photoelectron Spectroscopy (XPS). The refractive indices of Cr, Cr2N, and CrN were determined from the analysis of the SE data. To test the effectiveness of the ellipsometric control techniques the predicted compositions and phase percentages for the resulting films were compared with those determined from post deposition analysis. In most cases, accurate control of the film chemistry could be obtained by first predicting optical constants of the desired film composition, and then setting the reactive gas flow to achieve these optical properties, as determined through real-time spectroscopic ellipsometry. The control technique was found to be most accurate for nearly pure phases of CrN, Cr2N, and Cr as these were the standards used to generate the optical models for the mixed phase films