**HINTS & TIPS**

**Q: **How can the lateral implant
straggle be tuned separately to the vertical implant profile?

**A:** When using the analytical implant tables
in **ATHENA** the default model for the lateral implant range
assumes a gaussian profile with a standard deviation equal to the
vertical standard deviation (delta Rp) read from the table. This
approximation is reasonable for amorphous implant substrates. This
includes cases where the implant beam has been amorphised by a screen
oxide or is implanted at a high angle.

Tuning of the lateral implant range can be done by specifying the lateral standard deviation prior to the implant:

MOMENTS ...... LSTD.DEV=<value>

IMPLANT ......

However this is cumbersome to use in many
cases since the `MOMENTS` statement
requires explicit definition of the implant dose and energy and
all the vertical implant parameters. Therefore it is more convenient
to use a unit less scaling parameter `LAT.RATIO1 `on
the` IMPLANT` statement to multiply
the default lateral straggle by a factor. The default for
`LAT.RATIO1` is 1.0 so to slightly
increase the lateral straggle of an arsenic implant the following
syntax might be used:

IMPLANT ARSENIC DOSE=<v> ENERGY=<v> LAT.RATIO1=1.2 PRINT.MOM

This `PRINT.MOM` parameter
is included as a useful check. It prints the implant moments used
into the run-time output. Figure 1 shows the effect of adjusting
only `LAT.RATIO1.` The vertical
implant depth is constant while the lateral implant straggle can
be tuned to match electrical results.

Figure 1. Using the LAT.RATIO1 parameter to tune lateral implant range.

For implants that are normally modeled with
a dual pearson distribution (eg. the SVDP Model) a separate lateral
straggle is used for each of the two Pearson distributions. This
means for an implant using the SVDP Model there is a separate lateral
straggle for the main and secondary dopant distributions. Since
the secondary distribution in the Dual Pearson is from ion channeled
through the lattice, the lateral straggle of these ions is much
reduced. By default it is equivalent to 0.2 times the standard deviation
of the secondary Pearson distribution (`SSTD.DEV`).
For most implants the lateral range of the
two Pearson distributions are difficult to distinguish in 2D, an
artificial case in Figure 2 is used to demonstrate.

Figure 2. Demonstration f different lateral straggle of channeled and non-channeled ions.