Identification of metal impurities in crystalline silicon wafers

Injection dependent lifetime spectroscopy (IDLS) was performed to identify the type and concentration of the defects associated with metal impurities in crystalline silicon wafers. Minority carrier lifetimes in intentionally contaminated silicon wafers using various metal concentrations were measured by a transformer-coupled, radio frequency-based photo conductance measurement tool, GLM™ 2000. Lifetimes in the bulk of the silicon wafers were measured at low injection level using a square pulse cycle of light with half period > 10 milliseconds to ensure steady state photoconductance was reached. Analysis of the data using Shockley-Read-Hall theory demonstrates the ratio of capture cross-section of electrically active defect level associated with molybdenum (Mo) and copper (Cu). Concentrations (N
t
) of electrically active defect states associated with Mo and Cu impurity are determined from measured bulk lifetime at low level injection, using Shockley-Read-Hall carrier concentrations (n
1
and p
1
), and known activation energy levels (E
t
) of the identified metal from the literature.