HINTS & TIPS

Q: How can external tools be run inside of Silvaco's run-time environment DeckBuild? Is it possible to include UNIX commands along with simulator syntax inside an input file?

A: The run-time environment for all Silvaco TCAD simulators, DeckBuild, allows users to include any UNIX command inside any simulator input file. The option uses the keyword SYSTEM before the UNIX command. Some users might find this option may need to be enabled using the OPTIONS category from the MAIN_CONTROL popup menu.

Any UNIX command or sequence of commands linked by ';' can be executed when preceded by the SYSTEM keyword. For example to remove a set of files before creating a diffusion movie:

system rm xxx* 
diffuse ..... dump=1 dump.pref=xxx

The only major exception to standard UNIX syntax is the use of the output redirect command '>' in UNIX. This cannot be used by SYSTEM since the output of the UNIX command will be redirected to the lower or run-time output window in DeckBuild. The following syntax can be used instead to output an extracted variable to a file.

#extract threshold voltage 
extract name="vth" \
xintercept (maxslope(curve(v."gate",i."drain"))) \
- ave(v."drain")/2.0 

# save Vth to a file called 
xxx.dat system echo $vth  | sed -n  "w xxx.dat"

 

The inclusion of any valid UNIX command within a simulator input file allows users to include their own simulators or other external routines inside DeckBuild. For example to call a program 'myprog' that reads and writes Silvaco format files might be called using:

# save ATHENA structure
structure outf=final.str
# run external program to create a new structure 
system  myprog final.str revised.str
#load new structure into ATHENA
init inf=revised.str

Q: Is it possible to model leakage current due to localized trap centers in the vicinity of depletion regions?

A: ATLAS version 4.3.0 includes a trap assisted tunneling model [1] that accounts for band-band tunneling assisted by traps. The model accounts for trap location, density and energies defined using the TRAP, DEFECT or DOPING statements. This model supercedes the TATUN model implemented in earlier ATLAS versions. To enable the model the syntax is:

MODEL TRAP.TUNNEL

With this model it is possible to simulate the effect of localized trap densities. Most commonly the effect of localized traps is seen when they are within the depletion region of a reverse biased diode, including in the drain junction area of MOSFETs. Figure 1 shows the reverse leakage current of a source/drain diode as a function of the location of trap centers. When the traps are wholly inside the source/drain region or deep enough in the substrate to be outside the depletion region the results are identical with the case including no traps at all. However when the traps are localized in the junction region the leakage current is 3 orders of magnitude higher. Traps located just deeper than the junction only have an effect when the depletion region extends deep enough to reach them as shown by the intermediate curves in Figure 1. Localized trap centers in devices might be caused by plasma etch damage, contamination or extended defects.

Figure 1. ATLAS simulation of leakge current based on traps located close to a pn junction.