Annealing technology under arsenic overpressure for GaAs LSI–influence on dislocation and threshold voltage

Abstract

AbstractSince the microscopic uniformity of the threshold voltage (Vth) of an FET is important to obtain GaAs LSI, the cause of the threshold voltage uniformity was researched by investigating the annealing dependencies of the dislocations in the semiinsulating substrate of LEC GaAs and the microscopic uniformity of Vth. Annealing under arsenic overpressure decreased the dislocation density on the substrate surface and formed a uniform distribution of dislocations. This is believed to be caused by the supply of arsenic to the substrate surface. When annealing was carried out under low arsenic pressure, Vth shifted toward the negative direction at the area with clustered pits, and a clear dislocation network was formed. On the other hand, when annealing was carried out under arsenic overpressure using arsene, the shift of Vth in a negative direction becomes small and Vth was distributed uniformly. When annealing was carried out using a protective PCVD SiNx film, the distribution of Vth was consistently uniform, regardless of the dislocation distribution. As described in the preceding, it was found that a high concentration of AsGa exists in the area of the clustered pits, the uniformity of Vth is independent of the dislocation density but dependent on the stoichiometry of the substrate prior to or after annealing, and the distribution of Vth becomes more uniform with an increase of arsenic concentration.