Infrared Mapping of Oxygen and Correlation with Electrical Measurements on CZ Grown Wafers

Abstract

AbstractSpatial variation of interstitial oxygen concentrations ([Oi]) have been observed in wafers sliced from CZ grown ingots. Oxygen precipitation can occur with subsequent heat treatments causing non-uniform electrical device characteristics across a processed wafer. A new method is presented using infrared absorption measurements to map [Oi]in silicon wafers for correlation with wafer electrical measurements. The new infrared mapping method uses a spectrometer fitted with a software controllable wafer positioner. 100 m m diameter wafers were mapped to show the concentration variations and oxygen precipitation effects resulting from thermal heat treatments. Electrical measurements were made on nearly adjacent wafers from the same ingot and subjected to the same thermal cycling plus a diode-capacitor fabrication process. Two types of electrical measurements were used to map diode-capacitor arrays: reverse leakage current (Ir) and transient reverse recovery lifetime (τr. The measured values for each device tested were positionally correlated to the fourier transform infrared spectrometer (FT-IR) [Oi] data. Scatter plots were generated by plotting the electrical measurements as a function of the interpolated concentration data or differential concentration data parameterized at equivalent positions on the wafers. The scatter plots show that the electrical characteristics are strongly dependent on the precipitated oxygen (∆ [Oi]) for larger values of ∆[Oi], but nearly independent for lower ∆[Oi] values.