Ion Implantation and Synthesis of Materials - Studium

15.4 Low Energy Productivity: Beam Utilization 229Single-Wafer Endstation: Linear Mechanical Scan with ScannedSpot BeamA processing chamber in which only one wafer is implanted at a time is typicallyemployed for medium current implanters. The endstation consists of a singlescanning arm capable of linear motion of up to 140–200 mm s −1 . over a range ofup to 400 mm. The wafer is typically held on an electrostatic chuck which may begas-cooled to maintain adequate wafer temperature.The wafer can usually be tilted at angles of up to 60° and rotated through a full360° either while on the chuck or prior to being placed there. When operating atmaximum throughput, a typical single-wafer architecture can process up to350 wph.For the single-wafer endstation described above, (15.2) can be rewritten as:πRϒ=(2R + d + 2 d )(2R + d + 2 d )2ww beam ta−xw beam ta−y(15.4)where d beam refers to the beam diameter, and d ta−x,y refers to the effective distancefor the beam to decelerate and reaccelerate for the x and y directions, seeFig. 15.11. It should be apparent from (15.5) and Fig. 15.11 that a relativelysimple way to improve beam utilization (and hence throughput) for the singlewaferplatform is to “paint” not a rectangular region but a circular region only, theradius of which would be R = R w + 1/2d beam + d ta−effective . This eliminates wastingbeam on the “corners” of the rectangular region.Equation (15.2) now becomes2wRϒ=⎛ 1⎜R + d + 2d⎝ 2w beam ta−effective2⎞⎟⎠(15.6)Single-Wafer Endstation: Linear Mechanical Scan with UnscannedRibbon BeamAchieving uniformity with this type of a system necessarily requires a beambroader than the wafer. Assuming a beam 10% wider than the wafer, (15.2) nowbecomesw2wπRϒ=2(1.1 R )( h + d )beamta(15.7)