Physical Vapor Equation

Cleanliness and yield are of great importance in microfabrication, therefor conditions in the cleanroom are very strictly controlled: a constant circulating purified airflow, control of temperature, humidity and vibrations. Because of the small scale of the fabricated microstructures, they are very sensitive to any contamination by dust or other particles. Experiments are conducted under strict operating conditions: no fluctuations in temperature, vibrations or humidity. Most of the contamination issues can be retraced to human sources, stressing the importance of correct working methods while in the cleanroom. For this reason, persons who work in the cleanroom always wear a protective suit to reduce skin particle emission as much as possible.

A thin film has at least one small dimension, usually the thickness, and a lower density than bulk materials. Many of the thin-film properties, such as resistivity, dielectric constant, thermal expansion coefficient and refractive index, are dependent on the thickness. The deposition processes will also have an influence on the properties of the film.

1.2.1 Physical Vapor Deposition

The principle of Physical Vapor Deposition (PVD) consist of the ejection of material from a solid target, transportation of this material in vacuum to the substrate surface and finally deposition as a thin film. Ejection is achieved by resistive heating, electron beam heating, ion bombardment or laser beam bombardment (also called laser ablation). All aluminium films are deposited with PVD. Other examples of materials used in PVD are refractive metals and metal alloys like TiW, WN, TiN or ZnO.

1.2.1.1

A glow discharge plasma will provide positively charged argon ions. On impact with the negatively biased target, these argon ions will trigger the ejection of one atom from the target material. After ejection, the atoms are transported in vacuum to the substrate. The ejected atoms display a high energy and hit the surface with a considerable amount of energy. Sputtering rates lie between 1 and 10 nm/s, significantly higher than for evaporation. Because of the high sputtering pressures (1-10 mTorr), the sputtered atoms will collide several times before reaching the substrate. This gives rise to both beneficial and detrimental effects: loosely bound atoms will be kicked out and a more dense film is obtained, on the other hand the substrate or film may be damaged if too much energy is