Thin film deposition
To generate functional layers such as electrodes and conductors, optical reflectors and waveguides, membrane materials as well as masking layers we have several fabrication processes. Besides wafer substrates we can apply these layers on various other substrates such as glass or even plastic.
Evaporation:
In the case of thermal evaporation, the materials are either heated in a vacuum by resistance heating or electron beam until they vaporize or sublimate. The material vapor then moves straight to the substrate where it condenses and forms a layer.
Typical properties:
- Thickness: a few nm – a few 100 nm
- Low coverage of vertical edges > permits Lift-off
Materials:
Many metals such as Ag, Al, Au, Cu, Cr, Fe, Pd, Pt, Ni ... and oxides thereof.
Sputtering:
During the sputtering process an inert noble gas is ionized and accelerated towards the target that contains the coating material. Atoms and molecules of the material are ejected, which are then deposited on the substrate and form a layer.
Typical properties:
- Thickness: few nm – ca. 1µm
- Good coverage of edges
Materials:
Many metals such as Ag, Al, Au, Cu, Cr, Pd, Pt, Ni, V, W ... but also alloys and compounds such as for example AlNd, AlSi, ITO, WSi2 ...
PECVD:
In plasma-enhanced chemical vapor deposition, the reaction gases are split up by plasma and combine as a layer on the substrate.
Typical properties:
- Film thickness: a few 10 nm – a few µm
- Good edge coverage
Materials:
Silicon oxide (SiO2), Silicon nitride (Si3N4), Silicon oxy-nitride (SiON), silicon carbide (SiC)
Thermal / wet oxidation:
The silicon substrate is directly oxidized, ie, oxygen diffuses into the silicon and compounds with the silicon to silicon dioxide.
Typical properties:
- Film thickness: a few nm – a few µm
- Excellent step coverage, even jagged surfaces and overhangs are oxidized
- Excellent film thickness homogeneity
LPCVD:
Reactant gases decompose at the hot surface of a substrate and form the desired materials as deposited layer.
Typical properties:
- Film thickness: a few 10 nm – a few µm
- Good step coverage
- Deposition of stoichiometric layers
Possible films:
Silicon nitride (Si3N4), stress optimized silicon nitride, poly silicon
Micro electroplating:
By applying a voltage between a metal anode and the substrate, dissolved metal ions in an electrolyte deposit on a substrate.
Typical properties:
- Film thickness: a few µm – some 100µm
Materials:
Au, Cu, Ni
Ion implantation:
During ion implantation, doping atoms are ionized and implanted into the silicon substrate with high energy.
Typical properties:
- Generation of n-or p-type regions in silicon
- The specific resistance of silicon can be adjusted between 0.01 and 10 Ohm cm
- Doping depth after annealing up to about 5µm
as function of dopant concentration