If the number of generated point defects is very high a crystalline material undergoes a phase transition to an amorphous state where neither long range nor short range order of the atoms can be found.
A widely used method to model this phase transition is to assume a threshold
level for amorphization
. An area where the sum of the interstitial
concentration
and the vacancy concentration
is above this
amorphization threshold level, is considered as being completely
amorphous. The point defect concentrations that are required to determine the
phase transition can be calculated either by the Follow-Each-Recoil method or by
the Kinchin-Pease damage model.
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(3.172) |
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(3.173) |
If a simulation is performed with a point defect concentration threshold level
of
cm
simulated amorphous areas in crystalline silicon agree very well
with measured amorphization thicknesses for implantations performed at room
temperature. Since the generation of amorphous areas strongly depends on the
wafer temperature the threshold point defect concentration for amorphization
is only valid for room temperature. In order to determine the
amorphization also for a wider temperatures range
had to be modeled
as a function of the wafer temperature.
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