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4.5.4 Multiple Implantations with Varying Rotation Angles

If implantations are performed with large tilt angles to introduce dopants underneath a mask edge, regions of the active area at the opposite side of the mask edge can be shielded by the mask as illustrated in Fig. 4.16.

Figure 4.16: Illustration of the shielding effect by a mask edge.
\begin{figure}\begin{center} \resizebox{0.95\linewidth}{!}{\rotatebox{0}{\includegraphics{fig/monte/shield.eps}}}\end{center}\end{figure}

To overcome this unwelcome effect the wafer can be rotated during the implantation either gradually or continuously. In order to approximately keep the channeling behavior just the twist angle is changed by this rotation while the tilt angle is kept constant.

It is possible to simulate such a rotating implantation with one simulation run. An arbitrary number of ion beam directions can be used for one implantation % latex2html id marker 21166 \setcounter{footnote}{11}\fnsymbol{footnote}. The total number of simulated ions is uniformly subdivided among the different ion beam directions. Starting with a specified twist angle % latex2html id marker 21166 \setcounter{footnote}{12}\fnsymbol{footnote} the angle is changed by

$\displaystyle \Delta \mathrm{twist} = \frac{360\,^\circ}{\text{Number of Beam Directions}}$ (4.7)

after

$\displaystyle \frac{\text{Total Number of Requested Ions}}{\text{Number of Beam Directions}}$ (4.8)

have been simulated.

Besides this gradual rotation it is also possible to define a continuous rotation % latex2html id marker 21166 \setcounter{footnote}{13}\fnsymbol{footnote}. In that case the twist angle is selected randomly for each simulated ion just considering that the rotation angles are equally distributed.


Footnotes

... implantation% latex2html id marker 21166 \setcounter{footnote}{11}\fnsymbol{footnote}
The command-line option nbRotation specifies how many different ion beam directions are used during the implantation process.
... angle% latex2html id marker 21166 \setcounter{footnote}{12}\fnsymbol{footnote}
The twist angle is specified by the command-line parameter twist.
... rotation% latex2html id marker 21166 \setcounter{footnote}{13}\fnsymbol{footnote}
The command-line parameter revolving determines a continuous rotation.
previous up next contents Previous: 4.5.3 Point Response Interface Up: 4.5 Special Features Next: 4.6 Speedup Algorithms
A. Hoessiger: Simulation of Ion Implantation for ULSI Technology