| |
| |
Wafer Technology Ltd
34 Maryland Road
Tongwell
Milton Keynes
Bucks
MK15 8HJ
United Kingdom
Telephone:
+44 (0)1908 210444
Facsimile:
+44 (0)1908 210443
Email: sales@wafertech.co.uk
|
|
|
|
Growth
Several different growth techniques are
used for production of III-V compound semiconductor crystals
at Wafer Technology. The growth method used depends on the required
material type and properties. Basic details of the processes
used are given below.
|
|
Horizontal
Synthesis
Used for producing stoichiometric
polycrystalline bars of the compounds
High purity elements (Ga, As, In and/or P) are contained within
a quartz boat, sealed in a quartz ampoule and placed into
a furnace chamber. The furnace chamber is heated up and a
temperature gradient is then moved along the boat. Temperatures
and pressures are dependant on the compound being synthesised.
Liquid Encapsulated Czochralski
Used for the manufacture of single
crystals
The starting materials (either pre-synthesised polycrystalline
chunks or, in the case of semi-insulating GaAs, elemental
Ga and As) are placed in the growth crucible along with a
pellet of boron trioxide. The crucible is placed inside a
high pressure crystal puller and heated up.
At 460°C the boron trioxide melts to form a thick, viscous
liquid which coats the entire melt, including the crucible
(hence, liquid encapsulated). This layer, in combination with
the pressure in the crystal puller, prevents sublimation of
the volatile group V element.
The temperature is increased until the compound synthesises
(temperatures and pressures are varied depending on which
material is being produced). A seed crystal is then dipped,
through the boron trioxide layer, into the melt. The seed
is rotated and slowly withdrawn and a single crystal propagates
from the seed.
Crystal growth is monitored by the use of CCTV cameras and
measurements of weights, temperatures and pressures are made
at regular intervals.
Vertical Gradient Freeze
Used for producing low dislocation
density GaAs crystals
Chunks of polycrystalline GaAs, produced by horizontal synthesis,
are placed in a crucible with a seed crystal of the required
orientation. The crucible is then placed vertically in a furnace
and a temperature gradient is moved up the length of the crystal
(away from the seed).
Single crystal growth propagates from the seed crystal and,
because the crystal forms in the shape of the crucible, diameter
control of the ingot is relatively simple.
|
 |
|
|
|
