Design & construction of a high vacuum thermal evaporator

Abstract

Thin-film deposition is the process of depositing a thin film of material onto a substrate and can be done by physical or chemical methods. The Physical Vapour Deposition (PVD) coating process has the ability to apply diverse films at various process temperatures. This flexibility allows coatings to be applied to a variety of substrates. The aim of this project was to design and construct a high vacuum thermal evaporator, enabling physical deposition techniques to take place. A high vacuum system was available that created an environment appropriate for physical deposition. The high vacuum system makes use of two pumps with the ability to reach pressures down to 10-7mbar in few seconds. The system has all the necessary feedthroughs installed inside the chamber. These feedthroughs consist of high and low current lead-ins, thermocouple and a rotary transmission. Combining all these together it was possible to construct the thermal evaporator. The work on the system was divided into two parts, the construction inside and that outside the chamber. The heating resistance together with all the fixturing necessary were installed inside the chamber. The work outside the chamber consisted mainly in the apparatus required to control the system. The system was initially operated and tested in order to identify design or construction faults. Physical deposition was then carried out using glass substrates coated with aluminium or silver. Measurements of thickness and adhesion were made and used as indicators of the thermal evaporator function. A study of the effect of substrate heating on adhesion was also carried out. This resulted in further improvements and following this it was confirmed that the system operated correctly.