Modeling Dopant Diffusion in Gallium Arsenide

We have been developing models for our process simulators, SUPREM 3.5 and SUPREM-IV, for processes used in the fabrication of GaAs devices. Our initial experiments led to relatively simple models for diffusion of common dopants in GaAs, usually dependent only on temperature and the local dopant or carrier concentration. These models were incorporated into our first GaAs simulator, SUPREM 3.5. While these simple models were adequate for some process conditions, there are many cases where anomalous diffusion occurs and these models break down. The generally accepted diffusion mechanisms for n- and p-type dopants in GaAs have been shown to be the same as, or indistinguishable from, the models used for diffusion in silicon, and are therefore compatible with the diffusion algorithms used in SUPREM-IV. These algorithms include the effects of point defects. GaAs and eight of its dopants have recently been incorporated into SUPREM-IV and we have modeled, or are attempting to model, many of the anomalous diffusion phenomena using this simulator. These phenomena include uphill diffusion of implanted dopants, time dependent diffusion, implant energy dependent diffusion, and abnormal diffusion of grown-in dopants in MBE and MOCVD material.