Unit 4 PS01CMTS53 Nuclration and condensation.pptx

Thia ppt Have a good enough content about nucleation and condenation of Thin film

1. Unit 4(PS01CMTS53)

2. What is Thin film Thin film is layered of materials deposited on a bulk substrate in order to impact properties of materials(less than about one micron or 1000nm) Thin = less than about one micron or 1000nm Film = Layer of materials on substracte Properties of materials change if we change the shape and size of material Aluminium block Aluminium foil

3. Nucleation “Phenomenon of formation of a stable nucleus called Nucleation ” The initial process that occurs in the formation of a crystal from a solution, a liquid or a vapor, in which a small number of ions, atoms or molecule become arranged in a patter characteristic of a crystalline solid forming a site upon which additional partical are deposited as the crystal growth Nucleation  is an important step in growth that helps determine the final structure of a thin film. Many growth methods rely on nucleation control such as atomic-layer epitaxy (atomic layer deposition). Nucleation can be modeled by characterizing surface process of  adsorption ,  desorption , and  surface diffusion . Adsorption and desorption Adsorption  is the interaction of a vapor atom or molecule with a substrate surface. The interaction is characterized the  sticking coefficient , the fraction of incoming species thermally equilibrated with the surface.  Desorption  reverses adsorption where a previously adsorbed molecule overcomes the bounding energy and leaves the substrate surface.

4. Condensation The surface mobility of ad-atoms is given by the substrate temperature, by their kinetic energy upon impingement and by the strength of interaction between a single atom and the substrate. If this interaction is strong one obtains a high nucleus density (nuclei per unit area). A weak interaction results in a low nucleus density. By the attachment of other adatoms the nuclei grow to islands (at constant nucleus density) which - depending on the given conditions - coalesce to a more or less connected film. The formation and growth process of thin films can be roughly divided into the stages of condensation, diffusion, nucleation, grain growth, combination, and connection of atoms or particle clusters into thin films on substrates. The formation and growth of thin films are not only related to the film materials and substrate materials, but also affected by the state and energy of atoms and ions, deposition rate, substrate temperature, impurities, and other factors. The growth process of the films will determine the microstructure and structure of the films, and the physical and chemical properties of the films are directly determined by the microstructure and structure of the films. 

5. Different thin film growth mechanisms. (a) island growth model, (b) the layer by layer model, and (C) the mixed growth model. 

6.   T hin film thickness measurement Thickness is the single most significant film parameter. It may be measured either by in-situ monitoring of the rate of deposition, or after the film is taken out of the deposition chamber. (1) Film Resistance This simple method , applicable to metallic and low resistivity semiconductor film, rests on the fact that the resistance is related to the film thickness. Resistance of metal film can be measured very easily by making the film one arm of a dc or ac Wheatstone bridge.

7. (2) Capacitance Monitor The Thickness of dielectric film may be determined by directly monitoring the capacitance of a capacitor configuration type. Rate of evaporation by measuring changes in the capacitance of parallel-plate condenser due to change in the dielectric constant resulting from the presence of vapor of the evaporant. The method is not very sensitive and required careful measurement.

8. The thickness of a single-layer film can be measured easily using a spectrophotometer. Note, however, that this is possible only for film thickness in a range of approximately 0.3 to 60 μm , and that the refractive index of the film material is required for measurement. Some light is reflected from the top surface of the thin film and some transmits into the film. There is another reflection when the transmitted light reaches the bottom interface of the film. The light from each of these reflections recombines to generate varying levels of constructive or destructive interference depending on the wavelength of light and the optical distance the light travels. (3) S pectrophotometer

9. Thin film is a two dimensional material layer deposited on a substrate in order to achieve properties that cannot be easily achieved or not realized at all by the same material in its bulk form. The distinct property of a thin film is resulting from the unique way of making it, in the form of progressive addition of atoms or molecules. The phenomenal rise in thin film researches is no doubt due to their extensive applications in the diverse fields of electronics, optics, space science, aircrafts, defense and other industries.   Thin film thickness and its properties

10. Deposition rate control u sing  Quartz Crystals The key concept of this type of measurement and control involves mounting of an oscillator crystal within a vacuum chamber in order to receive deposition in real time and the crystal is affected by the deposition in a measurable way. In particular, there will be a drop in the oscillation frequency when there is an increase in the mass of the crystal caused by the material being deposited onto it. The changes in the oscillation frequency is continuously recorded by an electronic instrument, which then converts the frequency data into Thin Film Deposition thickness data by performing appropriate mathematical functions. The data includes both instantaneous rate and cumulated thickness.