2 - Technologies

The process of film formation by vacuum evaporation consists of several physical stages: transformation of the material to be deposited by evaporation or sublimation into the gaseous state; transfer of particles to the substrate; deposition onto the substrate; rearrangement of particles on the surface. In the vacuum evaporation technique, the material to be deposited is heated, usually by putting small lumps of it in an electrically heated "boat" made of tungsten or molybdenum, in an ultra-high vacuum (i.e., 10^-4 Pa). In the case of metals, the deposition starts when the material has formed a liquid pool in the boat and the shutter is opened. The difference between the various evaporation methods is in the heating method and in the type of evaporation sources.

Cathode sputtering: The material to be sputtered is used as a cathode target in a system in which a glow discharge is established in an inert gas (e.g., argon or xenon) at a pressure of 1 to 10 Pa and a voltage of several kilovolts. The substrate on which the film is to be deposited is placed on the anode of the system. The positive ions of the gas created by the discharge are accelerated towards the cathode (target). Under the bombardment of the ions, the material is removed from the cathode (mostly in the form of neutral atoms and, in part, also in the form of ions). The liberated components condense on surrounding areas and consequently on the substrate placed on the anode. In RF (radio frequency) sputtering, AC discharges of 5-30 MHz are employed. In the case of the DC process described in the previous paragraph, problems are encountered in initiating the process and with sputtering insulating materials. In the RF process, one electrode is coupled capacitively to a RF generator. It then develops a negative DC bias with respect to the other electrode. This is related to the easier response of electrons than ions to an applied RF field.

The film application method of thick films is basically a screen printing technique. The circuit is fabricated by successively printing each layer until the desired circuitry is achieved. The basic tools used in printing are the squeegee and the screen. The system that incorporates these basic tools and provides adequate means for controlling them precisely in the fabrication is the screen printer.

The holes of the stainless steel, polyester, or nylon screen are filled with a photolithographically shaped emulsion, which has openings according to the layout pattern. The substrate is placed under the screen and the squeegee presses the paste through the screen mask openings while traveling along.