A thin film is a layer of material ranging from fractions of a nanometre (monolayer) to several micrometres in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many applications. A familiar example is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices, LEDs, optical coatings (such as antireflective coatings), hard coatings on cutting tools, and for both energy generation (e.g. thin-film solar cells) and storage (thin-film batteries). It is also being applied to pharmaceuticals, via thin-film drug delivery. A stack of thin films is called a multilayer.
PECVD Deposition System
The technique of radio frequency plasma enhanced chemical vapour deposition (RF-PECVD) is commonly used for the deposition of hydrogenated amorphous or microcrystalline silicon and its alloys such as silicon carbide and silicon nitride; more recently other techniques such as VHF-PECVD, ECR-PECVD, MW-PECVD, HWCVD are being increasingly used for the deposition of these materials.
- RF Plasma Process Chamber
- Radio frequency plasma excitation.
- Substrate temperature up to 600 °C.
- Substrate to electrode distance 1-5 cm.
- MW PECVD System
- Microwave plasma excitation
- Substrate temperature up to 1000 °C
- Substrate to source distance 1-30 cm
- Water cooled chamber
Sputtering Deposition System
E Beam Deposition System
Electron beam evaporation is a well-established technique extensively used both in industries and in research laboratories for the deposition of optical materials, metals and semiconductors. Single crucible and multi crucible electron beam sources with power supplies of 6, 10 and 15 kW maximum power are available. The use of multi crucible electron beam sources allows the deposition of multilayers of four or more materials; a quartz crystal thickness controller is used for programming multilayers as well as for the automatic control of the thickness and of the deposition rate in each layer.
As an option, electron beam evaporation system can be equipped with an additional ion beam source for bombarding the substrates during deposition (Ion Beam Assisted Deposition – IBAD).
Ion Beam Deposition System
Thin film optical devices are formed by several layers of oxides of different materials with different index of refraction. The technique of Dual Ion Beam Sputtering allows the deposition of optical coatings with good and stable mechanical (abrasion resistance, adhesion) and optical (low absorbance, refraction index homogeneity) properties.
The Dual Ion Beam Sputtering System consists of a high vacuum chamber with two Ion Beam Sources (IBS’s). One of the IBS’s is used to sputter optical materials of different index of refraction (such as SiO , Ta O , TiO ) mounted on a rotating substrate holder; the second IBS is used for substrate pre-cleaning and for oxygen ionization and bombardment of the oxide films during deposition. A control system allows automatic operation of vacuum and deposition cycles with a fine thickness control of each layer.
Thermal Evaporation System
The technique of hot wire chemical vapour deposition (HWCVD) is being increasingly used for the deposition of materials such as hydrogenated amorphous or microcrystalline silicon and its alloys and as diamond films. The main part of a deposition system consists in a vacuum chamber evacuated by a pumping unit to some appropriate vacuum level. After achieving the desired ultimate vacuum, the process gas mixture is introduced via Mass Flow Controllers and the pressure is kept constant by a variable conductance valve. Process gas is then decomposed by the heat generated by a hot filament of tungsten, tantalum or other material into radicals which are then deposited as thin films.
The important figure of merit for any vacuum system, and in particular for a deposition chamber, is the total leak and degassing rate when the reactor is at deposition temperature: the ratio of this parameter to the process gas flow rate will largely determine the achievable purity of films deposited in that reactor. In order to optimize the properties of each layer and therefore the characteristics of the electronic devices, it is desirable to deposit each layer, and in particular the active semiconductor layer, in high purity conditions; it is therefore necessary to minimize all external sources of contamination and in particular any contamination by the wire. The general vacuum and pressure control features of a HWCVD are similar to those of a PECVD reactor.