Vacancy Species Produced by Rapid Thermal Annealing of Silicon Wafers

Abstract

Rapid thermal annealing (RTA) of Czochralski silicon wafers at around 1260°C installs a depth profile of some vacancy species. Subsequent oxygen precipitation in such wafers is vacancy-assisted. The data on RTA-installed vacancy profiles - and the corresponding precipitate density profiles - suggest that there is a slow-diffusing vacancy species (Vs) along with two fast-diffusing species: a Watkins vacancy (Vw) manifested in irradiation experiments and fast vacancy (Vf) responsible for the high-T vacancy contribution into self-diffusion. The Vs species are lost during cooling stage of RTA, and the loss seems to occur by conversion of Vs into Vf followed by a quick out-diffusion of Vf. A model based on this scenario provides a good fit to the reported profiles of oxide precipitate density in RTA wafers for different values of TRTA and different cooling rates.

Trap‐Limited Vacancy Diffusion in Silicon at High Temperatures

“…Although the present analysis assumed a single kind of V, the concept of several quasi‐independent forms of a free vacancy cannot be dismissed altogether. The monitored vacancy in RTA wafers seems to disappear by conversion into a faster vacancy form (denoted V f ) with subsequent quick out‐diffusion of V f to the wafer surface . This additional loss channel of V + V* (apart from their own out‐diffusion and recombination with self‐interstitials) is not manifested in the presently discussed donor profiles.…”

“…The apparent vacancy diffusivity D deduced by various techniques in silicon wafers is systematically smaller than the expected free vacancy diffusivity, and the values of D seem to be random. Previously, it was suggested that a vacancy can exist in several structural forms, of strongly different diffusivities (slow forms and fast forms), with a relatively slow exchange between these forms. Different kinds of vacancy (or a mixture of them) can be manifested depending on the experimental conditions, for different time scales of observation.…”

“…The data on high‐temperature vacancy diffusivity seem to be contradictory . 1) By the density and size of voids that are formed by vacancies in growing crystals, the diffusivity D V was estimated to be around 2 × 10 −5 cm 2 s −1 at a typical void formation temperature, 1100 °C.…”

Influence of rapid thermal processing on carrier concentration in high resistivity silicon

“…Several models have been proposed to describe vacancy‐related defect profiles after various thermal treatments. Thus, oxygen precipitation profiles after RTA annealing at 1250 °C with different ramp down rates can be described by a simple vacancy and self interstitial diffusion and recombination , while changes in such defect profiles during the subsequent anneals at 1000 °C temperature range require an introduction of vacancy agglomeration , or most recently, the introduction of multiple vacancy species with different diffusivities . Most of the models agree that the vacancies bind to oxygen atoms and exist predominantly in the form of VO 2 complexes at room temperature.…”