Optimization of the Ion-Cut Process in Si and SiC Page: 4 of 10
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height after cycling at 3500C is not. This "reverse" annealing indicates that the damage level
somehow increases during thermal cycling. Since elimination or reduction of lattice damage
normally minimizes the free-energy of the lattice, the apparent increase in damage seems to be
thermodynamically improbable. Others have reported a similar effect and even have noted a ten-
fold increase in the height of the damage peak after post-implantation annealing [7,8]. It is clear
that the presence of hydrogen substantially affects the thermal evolution of the damage
microstructure. This is seen in Fig. 4 where the damage or displacement field, extracted from the
spectral data, is compared with TRIM simulated profiles of the implanted ions and the deposited
energy. It is immediately clear that the displacement field correlates strongly with the hydrogen
profile in the sample rather than the deposited energy.
* TRIM: HYDROGEN =
o 10-2 + TRIM: DAMAGE -3
*. "" DISPLACEMENT 0
++++ " '+ ' t1
U " 1
0.2 0.4 0.608
Figure 4. Comparision of the displacement field (from the annealed sample in Fig. 3) with
computer-simulated profiles of the implanted hydrogen and the as-implanted defect production.
The similarity between the displacement field and the hydrogen profile suggests that this
field may be monitored to gauge the hydrogen activity within the lattice. To this end, it is
important to understand the specific nature of the hydrogen activity responsible for the behavior
of the displacement field (e.g., the large enhancement produced by thermal cycling). The
temperature range that evokes the largest response in the displacement field closely matches the
range where a large fraction of the hydrogen undergoes a transition between bound and unbound
states as observed by Weldon . As discussed earlier, the thermal evolution of hydrogen into
unbound states involves the formation of pressurized gas inclusions within platelet that cause
microcracking. Cracking produces a relative displacement between regions on either side of the
platelet by an arbitrarily amount (i.e., not an integral number of lattice spacings). This disrupts
the registry within the lattice making it impossible for an ion beam traversing a crack to remain
channeled. An ion beam aligned with the lattice on one side of the crack will, in general, be
misaligned in the other. The existence of these misaligned regions (relative to the ions) can
easily account for the anomalous increase in the scattering yield associated with microcracking.
Based upon these arguments, it is reasonable to conclude that the thermal response of the
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Holland, O.W. Optimization of the Ion-Cut Process in Si and SiC, article, January 5, 2001; Tennessee. (digital.library.unt.edu/ark:/67531/metadc716261/m1/4/: accessed June 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.