Implantation Damage Annealing
dopants into a substrate by directly
bombarding the substrate with
high-energy ions of the
chemical being deposited. This process involves the collision of the
highly-energetic bombarding ions
with the atoms of the substrate, and is therefore destructive to the
material structure of the substrate being bombarded.
damage caused by ion implantation include: 1) the formation of
such as Frenkel defects, vacancies, di-vacancies, higher-order
vacancies, and interstitials; 2) the
within its supposedly
crystalline structure; and 3) formation of
as the localized amorphous regions grow and overlap. Damage types 1 and
2 are categorized together as 'primary crystalline damage'. Restoring
the ion-implanted substrate to its pre-implant condition requires the
substrate to be subjected to a reparative thermal process known as annealing.
Implantation Damage Annealing
has five (5) major components: 1) electrical activation of the
implanted impurities; 2) primary crystalline damage annealing; 3)
annealing of continuous amorphous layers; 4) dynamic annealing; and 5)
diffusion of implanted impurities. It is conducted in a neutral
environment, such as in Ar or N2
of the implanted impurities refers to the process of increasing the
electrical activity of newly implanted impurity atoms during annealing,
which usually don't occupy substitutional sites after being implanted.
The temperature range up to 500 deg C remove trapping defects, releasing
carriers to the valence or conduction bands in the process. Electrical
activity decreases again at 500-600 deg C, because of the formation of
dislocations. Beyond 600 deg C, however, electrical activation
increases until it peaks at around 800-1000 deg C.
crystalline damage annealing
basically consists of: 1) recombination of vacancies and
self-interstitials in the low temperature range (up to 500 deg C); 2)
formation of dislocations at 500-600 deg C which can capture impurity
atoms; and 3) dissolution of these dislocations at 900-1000 deg C.
the continuous amorphous layers
that extend to the surface has been shown to occur by solid-phase
epitaxy between 500-600 deg C. Under this phenomenon, the crystalline
substrate beneath the amorphous layers initiates the recrystallization
of the amorphous layers, with the regrowth proceeding towards the
substrate surface. Factors affecting the recrystallization rate include
crystal orientation and the implanted impurities. Amorphous layers
that don't extend to the surface anneals differently, with the
solid-phase epitaxy occurring at both amorphous-single crystal
interfaces and the regrowth interfaces meeting below the surface.
simply refers to the healing of implant damage even as the implantation
process is still occurring. This takes place because the heat
applied to the wafer during implantation makes the point defects more
pertains to the mass transport of implanted species across a
concentration gradient within an implanted layer during the annealing
process. The presence of implant damage makes this diffusion process
more complex than what would occur in an undamaged single-crystal
substrate. Diffusion of implanted impurities during annealing can
degrade devices that have shallow junctions or narrow base and emitter
regions if the thermal processing is not done rapidly enough.
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