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Abstract
A new method to map the thermal donor concentration in silicon wafers using carrier density imaging is presented. A map of the thermal donor concentration is extracted with high resolution from free carrier density images of a silicon wafer before and after growth of thermal donors. For comparison, free carrier density mapping is also performed using the resistivity method together with linear interpolation. Both methods reveal the same distribution of thermal donors indicating that the carrier density imaging technique can be used to map thermal donor concentration. The interstitial oxygen concentration can also be extracted using the new method in combination with Wijaranakula's model. As part of this work, the lifetime at medium injection level is correlated to the concentration of thermal donors in the as-grown silicon wafer. The recombination rate is found to depend strongly on the thermal donor concentration except in the P-band region.
Highlights
Cz silicon is generally enriched with interstitial oxygen (Oi) and thermal donors (TDs) form during the cooling process mainly in the temperature range of 400–500◦C.1 TDs are believed to be clusters of oxygen atoms forming during the early stages of oxygen aggregation.[2]
As the TD concentration was calculated from the emission signal that is unrelated to the free carrier mobility, the effect of TDs on the majority mobility doesn’t have to be taken into account in the carrier density imaging (CDI) method
CDI has been used to map the concentration of TDs and Oi in n-type Cz silicon wafer
Summary
Cz silicon is generally enriched with interstitial oxygen (Oi) and thermal donors (TDs) form during the cooling process mainly in the temperature range of 400–500◦C.1 TDs are believed to be clusters of oxygen atoms forming during the early stages of oxygen aggregation.[2]. CDI is a lifetime measurement technique based on IR absorption or emission of free carriers in silicon wafers.[12,13] It can work in two different modes, absorption mode or emission mode, depending on the set-up of the equipment.[12] In our experimental setup, the sample is placed on an temperature-controlled mirror which can be heated to 100◦C. This mirror is coated with aluminum giving a high reflectivity of IR radiation. The Oi concentration was estimated from the TD concentration based on the model of Wijaranakula.[9,14] As the TD concentration was calculated from the emission signal that is unrelated to the free carrier mobility, the effect of TDs on the majority mobility doesn’t have to be taken into account in the CDI method
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