– Full process control and advanced data logging
– Customised design
– Multilayer depositions – several crucibles or boats with individual shutters
– Dedicated thermal evaporation systems or mixed source systems
– Special organic evaporators
– Implementation in Roll-to-roll process
WHAT IS THERMAL EVAPORATION?
Not good at alloys
Nearly all metal layers in the early semiconductor technologies were deposited by thermal evaporation. All though evaporation is still used in many research labs, the technique is today replaced by sputtering in most silicon technologies for two reasons. The first is the problem of covering steps. As the lateral dimensions of transistors have increased the thickness of the metal layers has remained nearly constant. As a result of this the topography that the metal must cover has become more severe. Thermal evaporated films have a very poor ability to cover these structures which yields a discontinued film on the vertical walls. Besides this it is also difficult to produce well-controlled alloys by evaporation. The poor ability to cover steps can be used as an advantage when using thermal evaporation for e.g. lift-off processes.
Here the film is deposited on top of a patterned layer of photo resist. The films naturally tend to break at the edges of the resist so that when the resist is subsequently dissolved, the layer on top of the resist is easily lifted.
The thermal evaporation process:
The material to be deposited is loaded into a heated container called a crucible or a boat.
The crucible is resistively heated by applying a large current.
As the material in the crucible becomes hot it gives of a vapour which atoms travel in straight lines until they strike a surface where they accumulate as a film.