Activation and redistribution of implanted P and B in polycrystalline Si by rapid thermal processing

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Abstract
Rapid thermal processing (RTP) allows electrical activation of implanted semiconductors to be carried out at high temperature in times so short (∼10 s) that minimal dopant redistribution occurs. Use of RTP to activate implanted species in single‐crystal Si is well documented, but relatively little has been reported for poly‐Si. In this paper, we present measurements on 0.4 μm thick poly‐Si films implanted with n‐type (31P+) or p‐type (11B+) dopants. RTP was carried out in vacuo (∼1×10−5 Torr) by exposing samples for 5–30 s to the blackbody radiation of a graphite heater at 1150–1300 °C. Dopant activation and redistribution following RTP was measured by spreading resistance and four‐point probe. In poly‐Si, unlike similarly implanted and rapidly annealed single‐crystal Si, we find considerable redistribution for both dopants. For P, significant dopant loss occurred from the uncapped poly‐Si surface; however, a thin (600 Å) SiO2 cap prevented this outdiffusion. For B, on the other hand, uncapped poly‐Si surfaces exhibited minimal dopant loss. The time evolution of carrier concentration profiles depended both on implant dose and RTP conditions.

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