DEPOSITION OF THIN ALUMINUM FILM ON ACRYLIC SUBSTRATE USING PHYSICAL VAPOR DEPOSITION TECHNIQUE (PVD)

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1 DEPOSITION OF THIN ALUMINUM FILM ON ACRYLIC SUBSTRATE USING PHYSICAL VAPOR DEPOSITION TECHNIQUE (PVD) Marwa A. Elajel *, Sana M. Sbeta ** Plasma Research Lab., Tripoli Libya * marwa_ali_77@yahoo.com, ** sbeta_62@yahoo.com Abstract A pure thin aluminum films were deposited on poly methyl meta acrylic (PMMA) substrates using physical vapor deposition technique based on thermal evaporation method. Surface roughness of deposited films was investigated using scanning electron microscopy (SEM). The image indicated that the deposited film has a smooth surface. The effect of substrate thickness on the theoretical and experimental capacitance was also investigated in this work. The results indicated a good agreement between the theoretical and experimental capacitance. 1. INTRODUCTION Physical Vapor Deposition (PVD) comprises a group of surface coating technologies used for decorative coating, tool coating, and other equipment coating applications, and also some self-supporting shapes. It is fundamentally an evaporative process in which the basic mechanism is an atom by atom transfer of material from the solid phase to the vapor phase and back to the solid phase, thus gradually building film thickness. Coatings produced by PVD processes have the advantages of high temperature strength, good impact strength, excellent abrasion resistance, and the capability to be deposited onto surfaces with complex shapes [1]. There are three basic processes considered PVD technology: ion plating, evaporation, and sputtering, all of which are normally carried out under vacuum. All three techniques must follow the same fundamental steps to develop a deposit, but they generate and deposit materials in somewhat differing manners, thus requiring equipment unique to each process [1]. PVD is pervasive in many applications, including microelectronics, optics, magnetic, hard and corrosion resistant coatings, micro-mechanics, etc. Progress in each of these areas depends upon the ability to selectively and controllably deposit thin films - thickness ranging from tens of angstroms to micrometers - with specified physical properties. This, in turn, requires control - often at the atomic level - of film microstructure and microchemistry [1]. One of the main applications of the thermal evaporation method is used in the electrical applications such as capacitors. The capacitor is a simple device for storing charge. It consists of two conductors separated by small space as shown in Fig.1. Each conductor carries a net charge. The charges are equal in magnitude but opposite in sign thus the net charge on the inter capacitor is zero [2].

2 The capacitance of any capacitor is a constant, the value of which depends on the geometry of the capacitor. For the parallel plate capacitor, capacitance depends on the area A of the plate and the distance d between them. One can increase capacitance by either increasing A or decreasing d [3]. The capacitance C of any capacitor is calculated using the equation [3] C k ε 0 A d = (1) where k is a dielectric constant and ε 0 is a permittivity of vacuum. In this work, thermal evaporation method was used to deposit pure aluminum on the acrylic substrate on two surfaces. The deposited film used as conductive layers, while the acrylic used as insulator. Surface morphology of deposited films were investigated using scanning electron microscope (SEM). For comparing between the theoretical capacitance and the experimental capacitance, the theoretical capacitance calculated using equation (1) and the experimental capacitance measured using capacitance meter. 2. EXPERIMENTAL WORK Fig 1 Parallel plate capacitor The experimental setup employed in this work, is schematically depicted in Fig.2, essentially is a thermal evaporation based system consisted of three main components. The components are as follows: [1] home made stainless steel cylindrical vessel used as a vacuum chamber to carry out deposition process; [2] a vacuum system used to maintain a preset pressure inside the reactor using a rotary pump to bring the pressure down to 10-3 torr and then by a turbo molecular pump. Base pressure reaches 10-5 torr which is low enough to provide good quality depositions. The chamber pressure is monitored by a widerange manometer, composed by a Ion and Capacitive gauges; [3] a tungsten wire used as an electric heater connected with potential organizer power supply (VARIAC) 10 kw.

3 Chamber Power supply VARIAC Vacuum System Fig.2 Experimental apparatus employed for film deposition. The acrylic samples were used in this study have a constant area (6 x 6 cm) and different thicknesses (2, 3, 6, 10, and 14 mm). The samples were cleaned ultrasonically using distilled water and then dried by air. After placing the substrate in the vacuum chamber, the deposition process was carried out at base pressure of 10-5 torr. Figure 3 shows the substrates before and after deposition. The capacitance was measured using capacitance meter FUKE DM-6013A, and the theoretical capacitance was calculated from equation (1), where k = 3.3 [4] and ε 0 = 8.85 x F/m 3. RESULTS AND DISCUSSION Fig. 3 Acrylic substrates before and after deposition Table (1) shows the experimental (C E ) and theoretical (C T ) capacitance for all the samples. It is clear that the capacitance increases with decreasing the thickness. A good agreement between the theoretical and experimental capacitance was achieved as shown in Fig.4.

4 Table (1) Theoretical (C T ) and Experimental (C E ) capacitance at various substrate thicknesses (d). d (mm) C T (nf) C E (nf) C ( n F ) Theoretical Capacitance Experimental Theoritical Capacitance Capacitance Experimental Capacitance d (mm) Fig. 4 The effect of substrate thickness on theoretical and experimental capacitance Figure 5 shows the surface morphology of the aluminum deposited film, it is clear that the surface is a smooth. Fig. 5 SEM image of deposited film

5 4. CONCLUSION A Pure aluminum films were deposited on acrylic substrates of different thicknesses on both sides using PVD technique based on the thermal evaporation method. SEM image indicates that the deposited films have smooth surfaces. A good quality capacitors can be obtained using films deposited by PVD technique. Also the thickness of the substrate has inverse proportion with the capacitance of the capacitor and there is a good agreement between the theoretical and experimental capacitance. 5. ACKNOWLEDGMENT This work is financially supported by the National Bureau for research and development and the plasma research laboratory, Libya. 6. REFERENCES [1] HANDBOOK of Deposition Technologies for Films and Coatings, 1994, 2 nd Edition,, Noyes Publications, Park Ridge, New Jersey. [2] U. P. COLETTA, 1994, "College Physics", James M. Smith Publisher, Mc Graw. Hill. [3] R. L. BOYLESTAD, 2000, "Introductory Circuit Analysis", 9 th Edition, Prentice-hall, Inc, Upper Saddle River, New Jersey. [4] H. DOMININGHAUS, 1993, "Plastics for Engineers Materials, Properties, Applications", 3 rd Edition, Hanser Publishers.