Ion Implantation and Synthesis of Materials - Studium

230 15 Ion Implantation in CMOS Technology: Machine ChallengesFig. 15.11. The effective total scan area for a serial wafer endstation can be described by arectangle with sides equal to the sum of twice the wafer radius 2R w , the beam diameterd beam , and twice the effective turn around distance d t a required for the beam to decelerateand reaccelerateSingle-Wafer Endstation: Dual Mechanical Scan (Linear) withUnscanned Spot BeamThe utilization equation for this design is identical to (15.4) except that theturnaround distances correspond to those of the mechanically moving endstations.Using the formulations above, it is possible to compare the relative productivityof the multi- and single-wafer endstations (see Fig. 15.12).15.4.2 Implanters Commercialized in the Past 35 YearsIt is useful to arrange various types of implanter platforms according to themethods by which the ions are distributed uniformly across the wafer(s), i.e., thescanning methods. Over 100 variants of the basic implanter design have beenintroduced in the past 35 years.The first commercial implanters, available in the early 1970s, were eitherelectrostatically scanned, uncollimated single-wafer systems or mechanicallyscanned multiwafer machines. The electrostatically scanned “spot” beam systemswere viable for single-wafer low current and medium current machines into theearly 1980s but were phased out due to unacceptable beam angle variations acrossnewer and larger 150 and 200 mm substrates. Ulvac attempted to extend theconcept with electrostatic collimation beamline elements for parallelism in theearly 1990s, but this was not widely adopted. Eaton addressed angle control by“wobbling” the wafer in synchronization with the scanned beam, but this was notadopted either. Instead, hybrid systems with electric or magnetic scanning pluscollimation in only one direction were adopted and dominate the market today.Since modern implanters no longer use two-dimensional beam scanning, thisdesign was not included in the previous section on beam utilization.