**Hints, Tips and Solutions - August 2003**

**Q:** *EXACT* has powerful scripting
utilities for manipulating the final capacitance data and variables
but is there an easier graphical front end that would also allow
me to view the data?

**A:** Recent improvements to ** EXACT**
have included the addition of the Worksheet utility. When an experiment
has been completed within

**the Worksheet may be accessed from the “View-->Data” pulldown menu of the main**

*EXACT,***window shown in Figure 1. All the data from the experiment, including selected layers, process variables, layout variables and extracted capacitance data, will be sent to the Worksheet. An example of this is shown in Figure 2 where columns are shown for the test structure name, the chosen process layer names, the layout parameter that has been varied, and finally the calculated capacitance values from**

*EXACT***.**

*EXACT*

Figure 1. Once the ** EXACT**
experiment has been

run the data may be accessed through the Worksheet.

Figure 2. The ** EXACT**
Worksheet showing the data from the experiment.

The worksheet allows a number of operations to be performed which include;

- column/row selection
- inter-column or inter-row calculations into new columns or rows respectively
- selection of data for plotting in
*TonyPlot*

- selection of data that can then be sent to
for statistical analysis*SPAYN* - equation fitting through the use of the Silvaco Optimiser

The Worksheet allows a graphical approach to viewing
the variables and data that otherwise would be accessed only through
the ** EXACT** script utilities. As an example
of this we can select certain data, as shown in Figure 3, which
we wish to view. Once selected the Worksheet pulldown menu option
“Selection-->Tonyplot” will then send this data to

*. Figure 4 shows the selected data from Figure 3 where the measured capacitance values (B_Gnd_L1l, B_Gnd_L1p, B_Gnd_L1r, L1l_L1p, L1l_L1r and L1p_L1r) have been plotted against the layout variable LAYER1SPACE.*

**TonyPlot**Figure 3. Selection of data in
the

Worksheet to be sent to ** TonyPlot**.

Figure 4. Data from the Worksheet
plotted within ** TonyPlot**.

Many other features are available through this Worksheet which shall be described in future publications.

**Q.** *EXACT* allows
the measured data to be fitted to polynomial expressions using the
scripting utilities. Is there a way to instead optimise the fitting
interactively ?

**A.** Figure 5 shows a script which performs an interactve
optimization. A detailed description of the syntax in this script
is available in the *EXACT** User’s
Manual*. In step 1 in the script the capacitance database is
loaded and various selections are made that result in a table of
variables and data that we wish to work with, which in this case
is the NEARBODY capacitance (which is the capacitance effect between
two conductors edge-to-edge). The capacitance data from ** EXACT**
is in the units of Farads but for the purposes of fitting the script
scales these values into units of femtoFarads. In step 2 we define
an equation that will be used to fit the data to and in step 3 we
force the optimiser to come up in interactive mode.

Figure 5. EXACT script for performing

the analysis on the experiment data.

Figure 6 shows the Optimser window that appears within which the user can modify the equation, set up the optimization Control paramters and view the results of the ptimisation. In this case we show the variations of the equation coefficients (N0, N1, N2, N3, N4, N5) during the optimisation iterations.

Figure 6. The Optimizer window
that allows

interactive control of the fitting process.

When the optimisation has finished the original
data from * EXACT* and the fitted equation,
with the optimised parameters, may be plotted in

**. As shown in Figure 7 an excellent fit is obtained.**

*TonyPlot*Figure 7. Comparison of the original
*EXACT*

capacitance data and the equation used to fit the

data which has the optimised coefficents.

*Acknowledgments to Eric Guichard and his team
for these Hints and Tips.*