Chemical beam epitaxy
The chamber itself is equipped with a liquid nitrogen cryoshield and a rotatable crystal holder capable of carrying more than one wafer.
It is worth noting that no chemical reaction is involved at the surface since the atoms are generated by thermal evaporation from solid elemental sources.
These diffuse through a stagnant boundary layer that exists over the heated substrate, after which they dissociate into the atomic group III elements.
[2] Selective growth through dielectric masking is readily achieved using CBE as compared to its parent techniques of MBE and MOCVD.
Selective growth is hard to achieve using elemental source MBE because group III atoms do not desorb readily after they are adsorbed.
With chemical sources, the reactions associated with the growth rate are faster on the semiconductor surface than on the dielectric layer.
No group III element can, however, arrive at the dielectric surface in CBE due to the absence of any gas phase reactions.
This makes it easier to perform selective epitaxy using CBE and at lower temperatures, compared to MOCVD or MOVPE.
[5] In recent developments patented by ABCD Technology, substrate rotation is no longer required, leading to new possibilities such as in-situ patterning with particle beams.
[6] This possibility opens very interesting perspectives to achieve patterned thin films in a single step, in particular for materials that are difficult to etch such as oxides.
It was observed that using TMGa for the CBE of GaAs led to high p-type background doping (1020 cm−3) due to incorporated carbon.
[4] CBE offers many other advantages over its parent techniques of MOCVD and MBE, some of which are listed below: So, a compromise should be found between high and low temperature for a good composition control.
