Interactions between sequential dopant diffusions in silicon-a review

Abstract

The trend towards very shallow, submicron diffusion depths in the fabrication of silicon-diffused devices has revealed a number of new diffusion phenomena which form the subject of this 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, which also show evidence for enhanced diffusion directly beneath certain diffused emitters.On the basis of the evidence reviewed, it is suggested that anomalies connected with phosphorus diffusion, namely the rapidly diffusing 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. The mechanism of generation, which has to account for enhancements in diffusivity of up to 100, and the identity of the defects are still in question, but it is argued that dislocation-related generation mechanisms can now be ruled out. 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. Finally, the causes of 'base retardation' are still not clear and the review suggests a number of areas for further study.

Diffusion of Gold in Silicon

“…Influence of phosphorus profile.--It is well known that a phosphorus profile acts as a getter layer during Au-diffusion (5)(6)(7). Moreover, the "emitter push effect" during a phosphorus diffusion has been widely investigated (18,19). While previously this has been explained by the generation of vacancies, Strunk etal.…”

Low Resistance Electrical Layer Formation: A Simulation Study of Diffusive Rapid Thermal Process on Implanted Dopant Species for Electronics Active Devices

“…2, flat-topped profiles of boron are produced through this simulation. Willoughby [9,10] showed that increasing the surface concentration changed the profiles from complementary error function to a flattop shaped. In this simulation, higher concentration of boron was used to match with boron SOD source in laboratory.…”

Interstitial Supersaturation And Climb Of Misfit Dislocations In Phosphorus‐Diffused Silicon

“…This result is in agreement with the conclusions drawn by Claeys et al (1978) and Tseng et al (1978) from differently designed experiments. The emitter-push effect and probably also other anamalous diffusion phenomena of Group I11 and Group V elements in silicon (Willoughby, 1977) are due to supersaturation of Si self-interstitials. The generation of this supersaturation can be understood in terms of a Kirkendall effect for an interstitial-type defect mechanism of diffusion.…”

“…The 'emitter-push effect' is one of the closely interrelated anomalous diffusion phenomena of Group I11 and Group V elements in silicon (Willoughby, 1977;Seeger et al, 1979). Its main feature is an extremely rapid diffusion of the base dopant near the emitter region of double diffused npn structures resulting in an enhanced movement of the base-collector boundary below the emitter (Fig.…”