Extraction of Implant Moments from Measured Data

ancaex08.in : Extraction of Implant Moments from Measured Data

Requires: SSuprem 4 and OPTIMIZER
Minimum Versions: Athena 5.22.3.R

This example shows how the general purpose OPTIMIZER can be used for extraction of dual-Pearson implant parameters from an experimental profile. This technique could be useful when Athena's implant look-up tables do not include moments for a specific implant (e.g. 0 degrees angle, very high or low energy, "exotic" ion-material combination, etc.) or when it appears that a simulated profile does not match an experimental one. This example can also be used as a tutorial for setting up an optimization procedure with a so-called curved target.

An experimental profile for 1e13 ion/cm**2, 15 keV, 0 degrees Boron implant into <100> crystalline silicon is used in this example. This SIMS profile published by H. Kinoshita of the Microelectronic Research Center (Austin, TX). The profile is in a simple XY format which can be read into the OPTIMIZER ancaex08_4256.opt .

To load and execute this example, display this text and select the Load example button while this text is displayed. This will copy the input file and several support files including ancaex08_4256.dat and ancaex08_4256.opt will be copied to your current working directory at this time.

Selection of initial values for optimization is usually very important in the setup of the optimization task. In thr case of implantation one can use parameters available for a similar implant. To demonstrate the flexibility of this approach, parameters corresponding to the same implant but at 7 degrees are used. It can be performed by using default a SVDP model and PRINT.MOM parameter in the IMPLANT statement.

If you want to compare this initial approximation with the experimental one, just select the run button to execute the example. In the end the two profiles will be overlaid in TonyPlot, so one can see that the experimental profile has a much bigger and deeper channeling peak than the default 7 degrees profile.

The Optmizer is used to find a better set of dual-Pearson parameters range, std.dev, gamma, etc. that will result in a simulated profile which better match the experimental one. In order to achieve this, select Optimizer... from the Main Control menu. The Deckbuild: Optimizer screen will appear in a moment. Unlike the first example ancaex08.in, this example does not use a special optimizer file with preset parameters and targets, so you should repeat the following steps in order to set the optimization task.

First, select Parameters from the Mode menu, this will display the Parameter worksheet. Select (highlight) the MOMENTS statement and choose Add from the Edit pull-down menu. The Parameter define pop-up will appear. Check all check-boxes excluding the first two which correspond to dose and energy, then press Apply . Nine new rows will be inserted into the Parameter worksheet. By default all min/max values for parameters are +-50%. This should be changed for some parameters. For example, we may expect a wider range for skewness (asymmetry) for Pearson distributions, therefore we set {bold} {newline}Minimum value to -1.0 and Maximum value to +3.0 for gamma and sgamma parameters. Also, the intervals for the fourth moment kurtosis of both first and second Pearson functions should be wider (2.7,10.0). dratio should not be higher than 1.0 therefore its maximum value should be set to 1.0. To edit any of these numeric values position the pointer over the corresponding cell of the worksheet, click the left-hand mouse button, edit the value, and do not forget to push the return button after finishing the editing.

The next step is setting the curved target. Select Targets from the Mode menu. Highlight the extract line. This line extracts the Boron chemical concentration profile which corresponds to the SIMS measured profile. After that choose Add from the Edit pull-down menu. A new row will be inserted into the Target worksheet. The target name will correspond to the name in the extract statement. Now, to insert experimental profiles as a curved target select the only row in the worksheet by double-clicking the left-hand button while the pointer is positioned anywhere in the row, then choose Edit > X/Y Data > Insert > From File . The Optimizer X/Y Target Data pop-up will appear. Select ancaex08_4256.opt file and then press Load .

The next step is to change the response type of the curved target from log to linear . Otherwise the estimated error would be very small because Optimizer would take the log of the result and target at each point before computing the error. Select the Edit > Select all . All the rows will appear raised. Then choose Lin/Log from the same menu and all row's response type will be toggled.

Now, once the parameters, targets, and setup information have been defined, the Optimization process can be started by pressing the Optimize button. During the optimization run, the Graphics mode shows real-time updates of parameter, target, and error values. After optimization is completed you may execute TonyPlot which will plot the comparison between optimized and measured profiles.