Oxygen incorporation and precipitation behavior in heavily boron-doped Czochralski silicon crystals

Abstract

To understand the effect of heavy boron-doping, p+-type (100) silicon crystals doped with boron in the order of 1 × 1019atoms cm−3 (0.006–0.01 Ω cm) and a p-type (100) silicon crystal doped with boron in the order of 1 × 1015atoms cm−3 (12–16 Ω cm) were grown in a Czochralski puller and studied. The oxygen contents in the p+-type crystals were determined by gas fusion analysis and shown to be on the average about 23% higher than those in a comparable p-type crystal. Etch pit features of oxide precipitates after a high-low-high annealing were generally different between the two types of silicon, and three distinct regimes of behavior about the critical boron and oxygen concentrations were identified. Those are: with resistivity ≳ 0.007 Ω cmor oxygen concentration ≲ 30 ppma (Old ASTM), the oxide precipitate density, in the order of 1010 cm−3, is basically unaffected by heavy boron-doping and dependent on oxygen concentration; with resistivity ≲ 0.007 Ω cmand oxygen concentration ≳ 37 ppma, however, large platelets, which are 10–15 μm in size and in the order of 107 cm−3 in density, are formed instead and completely gettered oxide precipitates. In a medium-oxygen range of about 28–30 ppma, both p- and p+-type (100) silicon wafers formed an ideal internal gettering structure, consisting of a well-defined precipitate-free zone (PFZ) to a depth of about 15 μm from the surface and dense bulk oxide precipitates in the order of 1010 cm−3 below the PFZ, after a high-low-high annealing.