Quantification of dopant species using atom probe tomography for semiconductor application

Doping of semiconductors serve various purposes in metal-oxide-semiconductor (CMOS) technology, eg, increase carrier concentration and modify electric field distribution. With the scaling down of device and the introduction of three-dimensional fin field-effect transistors (FinFET), precise and reliable dopant quantification of concentration at the nano-scale is critical. Laser-assisted atom probe tomography (APT) provides a unique approach to characterize and quantify the dopant in three dimensions at sub-nanometer resolution. Nevertheless, quantification accuracy of APT is strongly influenced by the experimental conditions. Although B quantification has been widely studied, the correlation of B signal loss to B concentration is not yet established. In addition, no phosphorous quantification study has been reported. In this work, we found that, due to B multi-hit effect in APT, high B dose sample has larger B loading compared with low B dose sample. For standard calibration with minimized impact from multi-hit effect, we recommend B dose in the range of 1e14 atoms/cm². Despite the fact that B loading is dose dependent, APT quantification of B achieves precision within 2% to 6% relative standard deviation (RSD), which demonstrates that APT has good accuracy. On the other hand, P quantification suffers from mass interference of ³¹P⁺ and ³¹P₂²⁺ at 31 Da resulting in a large loading between APT and secondary ion mass spectrometry (SIMS). Nevertheless, we recommend that 31 Da to be labeled as ³¹P⁺ for smaller P variation for the APT analysis.