Dependence of crystal nature on the gettering efficiency of iron and nickel in a Czochralski silicon wafer
The gettering efficiency of both iron and nickel in a Czochralski silicon wafer strongly depends on the crystal nature, i.e. an interstitial silicon dominant crystal or a vacancy dominant crystal. After heat treatment of dynamic random access memory, iron is mainly precipitated in the vacancy dominant crystal region rather than the interstitial silicon dominant crystal region, since the density of silicon oxide precipitate in the vacancy dominant crystal region is approximately two orders higher than that in the interstitial silicon dominant crystal region. This indicates that the mechanism of iron gettering is associated with relaxation gettering by silicon oxide precipitates. Otherwise, nickel silicides at the wafer surface are dominantly produced in the interstitial silicon crystal region, while nickel is chiefly precipitated at silicon oxide precipitates in the vacancy dominant crystal region. Also, this result demonstrates that the mechanism of nickel gettering is associated with relaxation gettering by silicon oxide precipitates, since silicon oxide precipitates are virtually not produced in the interstitial silicon dominant crystal region. A super silicon wafer designed for proximity gettering by silicon oxide precipitates shows a superior gettering efficiency for iron and nickel via the elimination of the memorized crystal nature.
gettering efficiency iron nickel czochralski silicon wafers