Distribution of trace impurities in microvolumes and analysis of concentration using laser sputtered neutral mass spectrometry

The performance of semiconductor devices has been improved by the miniaturization and the adoption of various materials. Together with this improvement, it has become difficult to measure the amount of injected impurities to control the electrical conductivity under the three-dimensional microstructure. As the volume decreases, the lower limit of the concentration that can be defined increases. In a 10-nm cubic region of silicon, there are approximately 64 000 atoms. One atom is approximately 16 ppm, and concentrations below that level cannot be defined. The limitation on the measurement accuracy of the PN junction position becomes unclear. Generally, the electrical characteristics of a semiconductor device are determined by the position of the PN junction and the concentrations in the P and N regions. In this paper, we elucidate the interface state of a minute PN junction. Based on the above, we will examine the lowest extent to which the concentration of impurities can be measured in a microvolume, with the current physical analysis technology, assuming ideal measurement conditions without any disturbance. Finally, we measure the sensitivity improvement of mass spectrometry using postionization technology with a femtosecond pulse infrared laser and demonstrate that it is possible to improve the performance of the impurity measurement.