Fabrication of lateral doping profiles by a computer-controlled focused ion beam

The advantages and throughput of a specialized focused-ion-beam technique—the creation of smoothly varying lateral doping profiles—are investigated. Calculated and experimental results are presented for the technique by which the log(gain) –gate-voltage characteristic of a GaAs FET can be linearized over four orders of magnitude. The throughput of the lateral tailoring process is estimated to exceed 1000 devices per hour based on the assumptions of a 10-mil2 (640-μm2) area per device, an average tailoring dose of 1012 ions/cm2 for a 5-μm-diam focused spot, an ion beam brightness of ∠50 A cm-2 sr for dopant ions at typical implantation voltages 50–150 kV, and a total overhead (i.e., positioning and registration) time of 1 sec per device. While a focused ion beam system with these capabilities will require development, the performance requirements including the ion-source brightness are well within the scope of present technology.