ICMCTF2005 Session F1/E3-1: Mechanical Properties and Adhesion

Monday, May 2, 2005 10:30 AM in Room California

Monday Morning

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10:30 AM F1/E3-1-1 Thin Film Stress Measurement by Fiber Optic Strain-Gage
M. Cremona, W.G. Quirino, S.M.M. Quintero, A.L.C. Triques (Pontificia Universidade Catolica do Rio de Janeiro, Brazil); L.C.G. Valente (Gavea Sensors - Genesis, Brazil); C.A. Achete (Coppe - UFRJ, Brazil)

Many coating applications depend on the monitor and control of film's physical properties. Particularly important are the thermal and/or residual stresses, which mainly occur in the hard coating deposition process. These stresses can affect the optical, electrical, magnetic and mechanical properties of the film. The need to measure and control the stress it is vital for the success of the final device. The development of in situ analysis not only provides the possibility of a feedback control during deposition, but also give a more efficient evaluation of the best conditions to achieve particular properties. Recently, a considerable research has been focused on fiber Bragg gratings (FBG), particularly on systems using these devices for sensing applications. FBG which can be operated in a wavelength-coding manner has become an important component for optical sensing devices in measuring temperature and stress principally in systems where electrical measurements are not allowed. In this work, we present a new optical FBG strain sensor which can be utilized to measure in situ the induced substrate strain caused by the film stress. The fiber optical sensor is interfaced to an analyzer to determine the wavelength shift of the reflected signal due to strain and temperature effect. The technique was used during the deposition of silicon carbide (SiC) and Indium Tin Oxide (ITO) thin films by rf magneto sputtering, onto silicon and glass substrates. The direct measurement of the wavelength shift (Δλ = 0.7 nm) for the ITO films provides a strain value ε = 5.8e-4 which can be used to found the tensile stress σ = 70 MPa presents in the film/substrate interface. These preliminary results are in agreement with other works reported in the literature. The research is under way to improve the accuracy and study the possibility to develop a more compact device.

This work is supported by RENAMI, CNPq, and FAPERJ.

10:50 AM F1/E3-1-2 Tensile and Compressive Stress in Hard Metal Films
G.C.A.M. Janssen (TU Delft, Netherlands); J.-D. Kamminga (NIMR, Netherlands)
Thin films on substrates are usually in a stressed state. An important, but trivial, contribution to that stress stems from the difference in thermal expansion coefficient of substrate and film. Much more interesting are the intrinsic stresses, resulting from the growth and/or microstructure of the film. We explain the occurrence of tensile stress in non-recrystallizing metal films. The explanation is based on modern grain growth models and accurate stress measurements. The key ingredient to the explanation is the proof of the existence of a stress gradient in non-recrystallizing metal films. From a comparison of stress versus thickness to average grain size versus thickness we infer that tensile stress is generated at the grain boundaries. Furthermore it is shown that the tensile stress caused by grain boundary shrinkage and the compressive stress caused by ion-peening are additive. In polycrystalline hard metal films the grain structure evolves during growth, leading to wider grains higher up in the film. The tensile component of the stress in the film is generated at the grain boundaries and therefore depends on film thickness. The effect of ion bombardment is independent of grain size, therefore compressive stress does not depend on film thickness. As a result in polycrystalline films deposited under a bias voltage a stress gradient exists from tensile at the interface to compressive at the top of the film.
11:10 AM F1/E3-1-3 Determination of Cohesive Strength of DLC Film on 316L Stainless Steel by Four Point Bend Test in Conjunction with Finite Element Analysis Method
M.M. Morshed, B.J. Mac Donald, D.C. Cameron, M.S.J. Hashmi (Dublin City University, Ireland)
The mechanical performance of DLC coating on 316L stainless steel deposited by saddle field fast atom beam source has been evaluated using the four point bend (FPB) test. Two different deposition parameters, pressure and current were considered to deposit the film. Load-displacement measurements were carried out during the bend test to determine the load corresponding to crack initiation. This load designated as the cohesive strength of the coating which is also called the cracking resistance of coating and provides a measure of the strength of the coating. The cohesive strength of the coating was calculated based on elementary beam theory. SEM was used to determine the location of crack. Finite element analysis was used to predict the stress distribution across the coating thickness. The experimental work of FPB has been used to support the numerical (finite element) model for the determination and prediction of film cohesive strength. It was observed that at lower deposition current, the cohesive strength increases with increased deposition pressure whereas, for higher deposition current, these values do not increase with increasing deposition pressure. The model takes into account the film Young’s modulus, thickness and deposition pressure and current, and has shown that it is capable of predicting film cohesive strength when combined with a theoretical formulation for brittle fracture. It has been observed that the maximum stress develops at the outer surface of the film and propagates through the film-substrate interface. This result is only been validated for films with a higher Young’s modulus compared to that of the substrate material.
11:30 AM F1/E3-1-4 Residual Stresses in Titanium Nitride Thin Films Deposited by DC and Pulsed DC Unbalanced Magnetron Sputtering
M. Benegra (University of Sao Paulo, Brazil); D.G. Lamas, M.E. Fernández de Rapp (CINSO, Argentina); N. Mingolo (Comision Nacional de Energia Atomica, Argentina); A.O. Kunrath (Colorado School of Mines); R.M. Souza (University of Sao Paulo, Brazil)
This work presents a study on the effect of deposition parameters on the residual stresses developed in titanium nitride thin films deposited onto cemented carbide (WC-Co) substrates. Depositions were conducted with a single titanium target placed in an unbalanced magnetron sputtering chamber. Six different conditions were selected; varying parameters such as bias (0, -50 or -100 V), type of target power (DC or pulsed DC) and, in the cases were substrate bias was zero, substrate condition (ground or floating). Pulsed power was applied at a frequency of 50 kHz and with a reverse pulse time of 1 microsecond. Residual stresses were evaluated through X-Ray diffraction, using the sin2ψ method. Results confirmed the effect of substrate bias on the residual stresses of thin films. Additionally, it was possible to observe that pulsed target power results in residual stress variations consistent with the difference in ion energy obtained with this type of target power.
11:50 AM F1/E3-1-5 Determination of the Adhesion and Hermiticity between Encapsulation Polymer and Insulating Layers via a Capacitance-Voltage Technique
Y.-S. Lin, J.-M. Ting (National Cheng Kung University, Taiwan)
To develop a micro-sensing chip for in vitro use,packaging is extremely critical in that there are areas which must be exposed to a fluid for purpose of sensing.One of the micro-sensing chips that is under our investigation is a molecular imprinting micro-sensing chip.In this type of chips,a well-like open sitting on top of a field effect transistor (FET) is used for the sensing.The bottom of the well-like open is a dielectric layer that is exposed to a KCl electrolyte;while the wall is a polymeric material. Therefore,the penetration or absorption of the liquid through the interface between the dielectric and the polymeric material has to be prevented.In this study,we have examined such an issue through the use of a capacitance-voltage (C-V) technique.Using the C-V techniques,the penetration or absorption of the liquid can be monitored by observing the variations in the capacitance.The specimens studied are a three-layer structure consisting of Si,a dielectric,and a polymer (with an open) from the bottom to the top.The dielectric layers investigated include silicon oxide and silicon nitride;while the polymeric materials include epoxy, polyimide,and MIP (molecular imprinting polymer,which is high selectivity to CRP,cholesterol,bilirubin,morphine and so on.).The silicon oxide and silicon nitride layers were prepared using a thermal oxidation method and a chemical vapor deposition (CVD) technique,respectively.The polymer layer was applied by spin coating.Both the thickness of the polymeric materials and the dimensions of the open were varied.Various materials characterizations,including electron spectroscopy for chemical analysis (ESCA), residual stress measurements,and scanning electron microscopy (SEM) were performed on the specimens prior to the C-V measurements.Long term C-V measurements,exceeding 3 months,were conducted to allow data acquisitions at different times during the measurements.The results are explained using a equivalent circuit model.
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