Oxygen Precipitation Behavior in 300 mm Polished Czorchralski Silicon Wafers

Abstract

The oxygen precipitation behavior in large diameter (300 mm) Czochralski silicon polished wafers with initial oxygen concentrations between 25-36 parts per million atomic and low carbon content, has been studied following two step heat-treatments (lowhigh annealing). It was found that an oxygen precipitation retardation and recovery phenomena occurred. Transmission electron microscopy observations showed that extended defect formation is drastically changed from punched-out dislocations in precipitate retardation samples, to stacking faults in precipitation recovery samples. The precipitation retardation phenomenon is consistent with a previous model on smaller diameter wafers; however, the current experimental results for 300 mm wafers indicate platelet precipitate growth during the first low temperature annealing plays a key role in the oxygen precipitation recovery phenomenon.

Crack Propagation in Large Diameter PV Silicon

“…aggregates of self-interstials, vacancies and OP clusters) are commonly observed in CZ grown silicon crystal (5). The formation of OP clusters is controlled by a complex interplay of the diffusion of vacancies (V), oxygen interstials (O i ), and ejection of silicon self-interstials (I) under specific temperature gradient conditions (5,7,15). Large diameter CZ ingot production at faster growth rates containing substantial thermal gradients, favors oxygen clustering and precipitation producing large residual stresses (16) at the included SiO x precipitate / Si matrix boundary.…”

“…Due to competing cost pressures, PV crystal growers been experimenting with employing new scenarios using faster growth rates (above critical v/G ratios, where v= growth velocity, G= thermal gradient) (5), larger diameter ingots (>200 mm) (6,7) and thinner wafer sawing processes (<150 µm) (8). The combination of enhanced ingot thermal gradients and associated point defect clustering can develop conditions of large wafer warpage and residual stresses (>100 MPa) (9,10).…”

Oxygen Precipitation Related Stress-Modified Crack Propagation in High Growth Rate Czochralski Silicon Wafers

“…The formation of OP clusters is controlled by a complex interplay of the diffusion of vacancies (V), oxygen interstials (O i ), and ejection of silicon self-interstials (I) under specific temperature gradient conditions. 5,7,31 Expanding our FTIR analysis at Location 1 and 4, micro-FTIR maps have been generated in the Fig. 5.…”

“…1 An experimental evidence and analysis of the dynamic stress release process at the crack-tip in a thin PV silicon lattice is crucial to fundamentally understand the wafer breakage, where the simplistic atomic bond breaking approach using Griffith's thermodynamic energy criterion 2 does not account for defect associated lattice trapping, velocity gaps, crack instabilities and hyperelasticity. 3,4 Due to competing cost pressures, the recent PV crystal growth experiments employ new scenarios of faster growth rates (above critical v/G ratios, where v = growth velocity, G = thermal gradient at meltsolid interface), 5 larger diameter ingots (≥200 mm) 6,7 and thinner wafer sawing processes (<140 μm), 8 where the combination of enhanced ingot thermal gradients and associated point defect clustering induce large wafer warpage and local residual stresses (>50 MPa). 9,10 At the critical v/G ratio, the driving force for oxygen precipitation is significantly changed due to transition from solidification of interstialrich silicon to vacancy-rich silicon.…”

(Invited) Modeling of Oxygen Precipitation in Silicon

“…Oxygen is known to enhance the mechanical strength of silicon substrates and, in precipitated form, serves as a getter for metal contaminants, which can sharply degrade yield if located near the active regions of devices. Oxygen precipitation also leads to the formation of dislocation loops (2)(3)(4), which act as gettering sites but can also cause slip and warpage (5). In recent years, there has been strong interest among solar cell manufacturers in understanding and controlling the impact of oxygen on carrier lifetime.…”