High current implantation

Fig. 15.1. Plan view (dispersive plane) schematic of a batch mode high current implanter, the Axcelis HC3...

Fig. 15.2. A 300 mm high current implanter showing (left to right) gas delivery system, ion source, analyzer magnet, process chamber, and wafer handling system...

Ion implanter-both medium high current Furnaces-diffusion annealing oxidation... 

Along with electronic transport improvements must come attention to substrate transport in such porous structures. As discussed above, introduction of gas-phase diffusion or liquid-phase convection of reactants is a feasible approach to enabling high-current-density operation in electrodes of thicknesses exceeding 100 jxm. Such a solution is application specific, in the sense that neither gas-phase reactants nor convection can be introduced in a subclass of applications, such as devices implanted in human, animal, or plant tissue. In the context of physiologically implanted devices, the choice becomes either milliwatt to watt scale devices implanted in a blood vessel, where velocities of up to 10 cm/s can be present, or microwatt-scale devices implanted in tissue. Ex vivo applications are more flexible, partially because gas-phase oxygen from ambient air will almost always be utilized on the cathode side, but also because pumps can be used to provide convective flow of any substrate. However, power requirements for pump operation must be minimized to prevent substantial lowering of net power output. 

A recent result on Al-implanted 4H-SiC, which is in sharp contrast to the common opinion that amorphization should be avoided, has been reported by E. Kalinina from the Ioffe Institute in St. Petersburg [124]. She showed that very good activation could be achieved by RT implantation of Al at doses in excess of 10 cm . This completely amorphized material is shown to be fairly well recrystallized by an RTA process that also causes some of the Al to diffuse into the low-doped n-type epilayer, forming the p n junction at a larger depth than the highly defective implanted area. Nearly ideal forward IV-characteristics were also shown for current densities of several kA cm . Even if the stability of such heavily implanted devices may be questioned this result shows that there is still a long way to go before a fully optimized implantation technology is at hand. 

Tang, Y., J. B. Fedison, and T. P. Chow, An Implanted-Emitter 4H-SiC Bipolar Transistor with High Current Gain, Technical Digest of 58th Device Research Conference, Denver, CO, June 19-21, 2000, pp. 131-132. 

The various implants are typically serviced by distinct types of tools, each engineered to provide a solution for a specific segment of the implant application space. Traditionally, these segments have been called high current, medium current, and high energy, and can be characterized mainly by the dose and the energy of implanted ions. 

Most ion implanters with the simple fixed-spot beamline described above also make use of a multiwafer, mechanically scanned type endstation to provide adequate wafer cooling and improve overall tool productivity (discussed in more detail in Sect. 15.4). A rendered drawing of a typical high current tool with a multiwafer batch endstation is shown in Fig. 15.2. 

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