Papers

ICMCTF1999 Session C4-2: Ellipsometry: Measurement and Modeling

Tuesday, April 13, 1999 8:30 AM in Sunset Room

Tuesday Morning

Start	Invited?	Item
8:30 AM		C4-2-1 Development of Model-Based Process Control of Complex Thin Film Structures C. Pickering, D.J. Robbins, A.D. Marrs, R.T. Carline (Defence Evaluation & Research Agency (DERA), United Kingdom); J. Russell, M. Sayed, M. Fearn, A. Dann (Defence Evaluation & Research Agency (DERA), Malvern, United Kingdom) This paper describes work to develop model-based process control of deposition as a generic method applicable to a range of thin film materials and structures. In-situ process monitoring and control require developments in (i) implementation of rapid accurate sensor measurements in the process chamber, (ii) process modelling, (iii) real-time data analysis and (iv) validation with off-line ex-situ measurements. Real-time measurements are generally made at a single point on the wafer, while in-line or off-line measurements may provide uniformity mapping data. The capabilities of in-line, on-line and real-time in-situ process control and their evolution from off-line monitoring are discussed. As an example of in-line control, the effectiveness of automated spectroscopic ellipsometry (SE) was demonstrated on product wafers, including ONO, OPO, nitride/metal and Si/SiGe structures, which were provided by a European consortium of IC manufacturers. For in-situ control, low-pressure Si/SiGe CVD is used as the demonstration process with real-time SE (RTSE) as sensor. A software suite is under development including (i) an epitaxy simulator tool based on multi-scale (reactor, process and atomistic levels) modelling, and (ii) advanced real-time data analysis algorithms. Virtual interface (VI) analysis and novel algorithms based on principal components and artificial neural networks (ANN) have been implemented in real time. The VI/ANN analysis has been demonstrated to be capable of following variable Ge concentration profiles, both step-wise and continuously graded, and the real-time results validated by off-line SIMS measurements. RTSE has been used to control the thickness of As-doped Si which has a growth rate which changes during the process and epi-Si on SOI which exhibits large emissivity excursions. Optimized software code to integrate the various elements for real-time control is under development.
9:10 AM		C4-2-3 Physical Properties of Reactively Sputtered Aluminum Nitride S.R. Kirkpatrick, D.M. Mihut, S. Long, S.L. Rohde (University of Nebraska) The physical properties of reactively sputtered Aluminum Nitride thin films were evaluated in terms of their stoichiometry, preferred orientation, microhardness, adherence, and optical properties, and these results were compared with published values for bulk crystalline and thin film Aluminum Nitride. The stoichiometry and impurity concentration, especially the oxygen content, were determined from SEM/EDAX measurements and confirmed using Auger. X-ray analysis was used to determine the diffracting crystallite size and preferred orientation of the film. The data gathered from chemical and x-ray analyses were used to generate a predictive model for the optical properties of the sputtered films. The sputtered films were analyzed using both in-situ and ex-situ ellipsometry. Thickness measurements were made using a Dektak profilometer, and confirmed with ellipsometry. The adhesion of the AlN on Si (100) wafers was assessed by determining the critical load at which the coatings failed when scratched with a Rockwell-C type diamond brale. The ellipsometry indicated a "n" value of approximately 2.06. Reactive aluminum sputtering produces an oriented film with a good deposition rate at low temperatures with physical properties that are similar to other thin film techniques.
9:30 AM		C4-2-4 Deriving the Kinetic Parameters for Pt-Silicide Formation From Temperature Ramped In Situ Ellipsometric Measurements T. Stark, H. Grünleitner, M. Hundhausen, L. Ley (Universität Erlangen-Nürnberg, Germany) In situ ellipsometry is employed to study the kinetics of Pt silicide formation by thermal annealing with constant heating rate up to 60 K/min for Pt layers of different thickness (10, 23, 100 nm) on Si (100). From spectroscopic ellipsometry data of the initial Pt/Si, the intermediate Pt₂Si, and the final PtSi phase an optimum photon energy of 3.5 eV was chosen for the kinetic study. Characteristic changes of the ellipsometric angles are observed as a function of temperature when the reaction fronts reach a depth below the surface that is related to the absorption length of the 3.5 eV photons. From an analysis of these transition temperatures based on the Kissinger formalism the activation energies for the formation of Pt₂Si and PtSi are obtained with an unprecedented accuracy of 1.55±0.05 and 1.72±0.05 eV, respectively. Modelling the evolution of Δ and Ψ as a function of temperature in the framework of a three layer model yields, in combination with the independently determined activation energies, the prefactors K₀ of the thermally activated reactions: 93cm²/sec ≤ K₀ ≤ 7.2x10³cm²/sec (for Pt to Pt₂Si) and 28cm²/sec ≤ K₀ ≤ 3.8x10⁴cm²/sec (for Pt₂Si to PtSi). Optical constants of the constituent materials (Pt, Pt₂Si, PtSi) have been determined as well in the energy range 1.5 to 4.5 eV.
10:30 AM		C4-2-7 Temperature Controlled Vacuum Arc Deposition D. Molenda, A. Ginovker, V. Cherepanov, L. Druker (Chessen Group Inc., Canada) Physical properties of hard coatings such as adhesion and wear resistance strongly depend on the substrate temperate during the deposition process. Therefore it is very important to control the surface temperature of tools in the process. The surface temperature strongly depends on the high voltage applied to the tools, on their shape and size, on the plasma density and content, and on some other parameters. To accurately measure the tool temperature we positioned a thermocouple on the table, where the tools are mounted, and applied the same high voltage to the thermocouple. This ensures that the energy flow to a surface unit of tools and of the thermocouple is the same. The high bias voltage and fluctuations in the arc plasma make direct measurements of the thermocouple current by gauges connected to the ground impossible. To avoid this difficulty, we suspended the thermocouple gauge at high voltage and transformed its readings into an optical signal. This signal is received by a photosensitive element connected to the ground. The second difficulty is to interpret the thermocouple data. The energy flow to the surface is the sum of the energy flow from plasma and the heater radiation. This energy heats tools and it is partially radiated back to the chamber. Therefore, the tool surface temperature depends on the shape and size of a tool. The surface temperature of large tools can be one to two hundred degrees lower than that of a thermocouple. To measure the tool temperature, we used two thermocouples of different sizes. We have developed software that computes the surface temperature using the temperatures of the two thermocouples. Thus the combination of a thermocouple subjected to the high voltage and software allows one to find the tool surface temperature on all stages of the vacuum arc deposition.
10:50 AM		C4-2-8 Process Monitoring in Low-Temperature PECVD of Silicon Oxide Films by IR-RAS Method Y. Inoue, H. Sugimura, O. Takai (Nagoya University, Japan) Recently coating of silicon dioxide films onto polymer has been strongly needed, so that plasma-enhanced chemical vapor deposition (PECVD) using organosilicon compounds, which is possible to lower the process temperature, has been extensively studied. At present, however, the deposition mechanism of silicon-oxide films at low temperature is not clear. In this study we investigated the reaction on the growing film surface by infrared reflection absorption spectroscopy (IR-RAS). We used a remote-type rf PECVD system. After the evacuation below 0.3 Pa, reactant organosilicon gas and oxygen gas were introduced from a gas inlet on the side wall and that at the top of the plasma source, respectively. Total pressure and rf power were kept at 10 Pa and 75 W. In situ observation of film surface was carried out by a Fourier transform infrared spectrometer (FT-IR). During deposition, the intensity of the absorption bands due to Si-O-Si and Si-OH increased linearly with deposition time.The dehydration condensation reaction of the Si-OH bonds in the deposited films was observed crearly in the IR absorption spectra.
11:10 AM		C4-2-9 Space-Polymer Materials Degradation in Oxygen Plasma and Ultraviolet Light Studied by In-Situ and Ex-Situ Spectroscopic Ellipsometryⁿ B.J. Dworak, M.D. Traudt, K.J. Brewer, A.D. Miller, C. Bungay, D.W. Thompson, J.A. Woollam, L. Yan (University of Nebraska-Lincoln) Most materials degrade or corrode when exposed to the low-earth-orbit (LEO) space environment. In this work we have exposed several polymers (Kapton^TM, Teflon^TM, and various silicones) to oxygen plasma and Ultraviolet light. The oxygen plasma is from an ECR source at 50 to 100W in close proximity to the sample under study. The AO flux for the system is up to 22 times greater than 4 x 10¹⁴ Atomic Oxygens/cm², that LEO spacecraft are exposed to. The purpose is to determine the degradation rate and chemical changes that take place due to atomic oxygen, ultraviolet light and other species in LEO. This research may allow corrective measures to be taken for future space flight missions. Diagnostics were made using fast in-situ visible spectroscopic ellipsometry, as well as ex-situ uv-vis, and infrared ellipsometry. The infrared covers characteristic resonant vibrational spectra in the 1.5 to 40 µm range and is sensitive to monolayer chemical changes at surfaces. Experiments on the polymers mentioned include tracking degradation of optical properties and their depth profile as a function of time for calibrated oxygen and ultraviolet exposures. ⁿResearch supported by NASA Lewis Research Center Grant Number NA63-2086
11:30 AM		C4-2-10 In-situ Spectroscopic Ellipsometry as a Surface Sensitive Tool to Probe Thin Film Growth Chian Liu, J Erdmann, A Macrander (Advanced Photon Source, Argonne National Laboratory) Sputtered thin film and multilayer x-ray mirrors are made routinely at the Advanced Photon Source (APS) for the APS users. Precise film growth control and characterization are very critical in fabricating high quality x-ray mirrors. Film thickness calibrations are carried out using in situ and ex situ spectroscopic ellipsometry, interferometry, and x-ray scattering. To better understand the growth and optical properties of different thin film systems, we have carried out a systematic study of sputtered thin films of Au, Rh, Pt, Pd, Cu, and Cr, using in situ ellipsometry. Multiple data sets were obtained in situ for each film material with incremental thicknesses and were analyzed with their correlation in mind. We found that in-situ spectroscopic ellipsometry as a surface-sensitive tool can also be used to probe the growth and morphology of the thin film system. This application of in situ spectroscopic ellipsometry for metal thin film systems will be discussed.