Interactions between sequential dopant diffusions in silicon-a review

The diffusion characteristics of some of the individual dopants involved (phosphorus, arsenic, boron and gallium) are first briefly surveyed, and then interactions between sequential diffusions are described in detail. The effects discussed include 'emitter-push' or 'push-out', which is the enhanced penetration of a base dopant, such as boron, directly beneath an emitter diffusion, and 'base retardation' which is where the diffused base-collector junction away from the emitter advances more rapidly than that directly beneath it. Also discussed are effects associated with buried marker layers. It is suggested that anomalies connected with phosphorus diffusion, namely the rapidly diffusion phosphorus 'tail', the 'push-out' effect and the movement of buried marker layers are all linked and are consistent with the generation of a high supersaturation of point defects. Another general conclusion emerging from the review is that a 'depletion' or 'dip' is found in the base profile (boron or gallium) under either a phosphorus or arsenic emitter diffusion, and that most observations are consistent with that caused by the electric field generated by the diffusing emitter dopant.