Essay On Thermal Evaporation

PVD processes can be used to deposit films of elements and alloys as well as compounds using reactive deposition processes. In reactive deposition processes, compounds are formed by the reaction of depositing material with the ambient gas environment. Quasi-reactive deposition is the deposition of films of a compound material from a compound source. During the transport and condensation process, having a partial pressure of reactive gas in the deposition environment can compensate the loss of more volatile species or less reactive species. A couple of examples representative of the physical deposition are given below:

Molecular beam epitaxy Molecular beam epitaxy (MBE) is a beam of molecules or atoms which emanate from an evaporation or effusion source. The beam of particles travels across an evacuated chamber with few if any collisions, and deposits onto a

In this way, chemical reaction byproducts can not be incorporated as impurities as can be the case with CVD methods.

Thermal evaporation is one of the oldest techniques of depositing thin films. Evaporation uses a heater to melt the material and raises its vapor pressure to a useful range. The vapor pressure is a pressure at which the vapor of the targeted substance is in equilibrium with its liquid or solid forms. Employing the thermodynamic principle, the number of molecules departing a unit area of evaporant per second, or flux F, is given by: Equation 7

Where is a slowly variable function of the temperature (T) and is the activation energy (in eV) needed to evaporate cone molecule of the material. The activation energy for evaporation is associated with the enthalpy of the formation of the evaporant, H,