Thin film fabrication using thermal evaporation

ppt

1. Thin Film Fabrication Using Thermal Evaporation Techniques By, V. Udhayasuriyan 116012305026 IV- M. Tech Nano ( Int ) PMIST 09-02-2020 1

2. content Introduction Principle Working Preparation of Films Substrate Cleaning Purity of the Evaporating Materials Advantage 09-02-2020 2

3. Introduction Thermal Evaporation is one of the simplest of the Physical Vapour Deposition (PVD) techniques. Basically, material is heated in a vacuum chamber until its surface atoms have sufficient energy to leave the surface. The coatings, also called films, are usually in the thickness range of angstroms to microns and can be a single material, or can be multiple materials in a layered structure . 09-02-2020 3

4. Cont.…. The materials to be applied with Thermal Evaporation techniques can be pure atomic elements including both metals and non metals , or can be molecules such as oxides and nitrides . The object to be coated is referred to as the substrate, and can be any of a wide variety of things such as: semiconductor wafers, solar cells, optical components , or many other possibilities. 09-02-2020 4

5. Principle A material in a high-vacuum environment is heated to its evaporation point by joule heating of the resistive boat in which it is located . The vaporized molecules then travel from the source to the substrate where they nucleate together, forming a thin film coating. 09-02-2020 5

6. working Preparation of film: T he material is heated to vapour form by means of resistive heating On heating the materials in vacuum, sublimation takes place and the atoms are transported and get deposited onto the cleaned substrates 09-02-2020 6

7. Substrate Cleaning T he substrates are cleaned using liquid detergent . I t is kept in dilute nitric acid . C leaned using distilled water and agitated in acetone . T hen rinsed in isopropyl alcohol and dried in hot air . 09-02-2020 7

8. Purity of the Evaporating Materials The deposited thin films will be contaminated if the evaporant itself is impure. Usually high purity materials are used. The purity of the evaporant material is further increased by sublimation . 09-02-2020 8

9. Production of Vacuum The evaporation of thin films with controlled properties requires an operating environment. Increase the mean free path of the evaporant atoms, to reduce surface as well as bulk contaminations and to protect the vapour source from oxidation and corrosion. 09-02-2020 9

10. Fig.2 Schematic diagram of the cross section of a diffusion pump 1. High vacuum intake 2. Jet cap 3. Throat 4. Vapour jet 5. To fore-vacuum 6. Heater 7. Boiler 8. Oil 9. Nozzle 10. Water cooled 09-02-2020 10

11. Heating methods in vacuum evaporation technique The evaporation of the material in a vacuum system requires a source to support the evaporant and to supply the heat of vaporization . The vacuum evaporation requires three things: Source Evaporate Substrate 09-02-2020 11

12. Source The simplest sources are resistance heated wires and metal foil of various size and shapes . Tungesten (W ) Molybdenum (Mo) Tantalum (Ta) are used as a resistance heated wires and metal foil. H igh melting point and low vapour pressure 09-02-2020 12

13. Why need of vaccum The material will heated at a lower temperature in vacuum. There will be reduction of the number of impurities in the deposit material. There is reduction to the effect of oxides formed on the boiling on the surface . The main advantage of the vacuum is that the adhesion to the film I ncrease in (mean free path) and better film can be formed . 09-02-2020 13

14. Vacuum evaporation method has the following advantages: Impurity concentration in the film will be minimum. Materials sublime at lower temperature under vacuum . Mean free path of the v apour atoms is considerably large at lower pressure and hence a sharp pattern of the film is obtained. Selection of the substrates is wide. 09-02-2020 14

15. Reference K. L. Chopra, Thin Film Phenomena, McGraw-Hills, New York (1969). Joy George, Preparation of thin films, Marcel Dekker, New York (1992). http://www.semicore.com/news/71-thin-film-deposition-thermal-evaporation https://angstromengineering.com/tech/resistive-thermal-evaporation / 09-02-2020 15