Impact of Endstation Design and Beam Scan Mechanism

2 Impact of Endstation Design and Beam Scan Mechanism 

The choice of endstation design and the mechanism of beam scan can also compromise angle control. We consider several examples below. 

Travel Path Length Effect for a Ribbon Beam on a Single-Wafer Endstation 

Implanters utilizing a fast-scanned beam with a one-dimensional mechanical scan can be further divided into a vertical scan and a plane-of-wafer scan, see Fig. 15.16. In the former, the mechanical scan direction is always perpendicular to the ion beam vector. In the latter, the mechanical scan direction is adjusted with the wafer tilt, so that it is always in the plane of the wafer. It is clear that, for the case of a zero-degree implant, the two methods are identical. However, for tilted implants, the vertical scan method results in the beam travel distance (and hence the beam size in the case of highly divergent beams) becoming a function of vertical position on the wafer. The degree of across-wafer variation increases with the 

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