Mechanistic insight into competing precipitation behaviors of phosphorus and oxygen in heavily phosphorus-doped Czochralski silicon

Abstract

Heavily phosphorus-doped Czochralski (HP-Cz) silicon is a critical substrate material for power electronic devices. Its supersaturated phosphorus and oxygen impurities can precipitate during the device thermal processing, degrading the carrier concentration stability. This work systematically investigates the thermodynamics and kinetics of phosphorus precipitation and oxygen precipitation in HP-Cz silicon (∼1 mΩ ⋅ cm) annealed at 850–1050 °C. Thermodynamic analyses reveal that phosphorus precipitation dominates initially at each temperature due to its smaller critical nucleation radius and higher nucleation rate, experimentally verified by the decrease in carrier concentration due to silicon phosphide (SiP) precipitate formation. However, oxygen precipitation becomes increasingly significant with the prolonged annealing time, triggering the dissolution of pre-formed SiP precipitates via two distinct density functional theory-validated mechanisms: oxidative dissolution by the interstitial oxygen impurities and decomposition mediated by the silicon interstitials generated by oxygen precipitation. The SiP precipitate dissolution leads to the gradual recovery of carrier concentration, reaching nearly complete recovery after 128 h at 950 °C or 16 h at 1050 °C, but remaining incomplete after 128 h at 850 °C due to phosphorus trapping within the oxide precipitates. Transmission electron microscopy (TEM) provides direct evidence of oxygen precipitation heterogeneously nucleating on the pre-existing SiP precipitates at 850 and 950 °C. Furthermore, systematic TEM characterization reveals a temperature-dependent morphological evolution of oxide precipitates: from hexagonal platelets (850 °C) to quadrangular platelets (950 °C) and finally to octahedral/truncated octahedral geometries (1050 °C), consistent with the energy-minimization principles. Collectively, this work elucidates the competing thermodynamics and kinetics governing phosphorus and oxygen precipitation, providing a fundamental understanding of impurity interactions and carrier concentration evolution critical for optimizing the processes of devices using HP-Cz silicon.