Abstract
Control of threshold voltage during gallium arsenide (GaAs) Metal Semiconductor Field Effect Transistor (MESFET) processing is critical. Variation in the dose rate during ion implantation has previously been demonstrated to affect sheet resistance and peak damage fraction for doses of 5 × 10 13 ions/cm 2 and higher. In this high dose regime, sheet resistance and damage increase as the dose rate increases. This paper describes dose rate effects in the low dose regime, where traditional channel implants are done, i.e., for 29Si + in the low 10 12 ions/cm 2 range. 29Si + was implanted at 3 × 10 12 ions/cm 2 followed by a co-implant of 9Be + at 1 × 10 12 ions/cm 2 into GaAs substrates. The silicon dose rate was varied from 3 nA/cm 2 to 44 nA/cm 2. The FET channel resistance varied by 4.0%, and was a direct function of the implanted beam current. Sheet resistance decreased as the beam current increased, which is in sharp contrast to results previously published for the high dose regime. Damage has been characterized and correlated to the electrical properties in the low dose regime. The results are compared to those for the high dose regime in order to more clearly define the differences associated with the inversion of the dose rate dependence between the low dose and high dose regimes.
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