Implanted boron distribution in p+n structures using scanning capacitance microscopy

Most of the past work on dopant profiling using scanning capacitance microscopy (SCM) deals mainly with either p + /p or n + /n samples. The presence of a pn junction poses an additional consideration to the use of SCM in the quantitative interpretation of dopant profiles. In this paper, the SCM technique was used to measure the two-dimensional (2D) boron dopant profile from cross sections of a high-energy boron-implanted pn junction and a laser annealed ultra-shallow p + n junction. Secondary ion mass spectrometry (SIMS) was employed for depth profiling of the one-dimensional (1D) boron distribution of the respective samples. The net dopant concentration at each depth determined by SIMS was used to calculate the respective theoretical capacitance-voltage (C-V) curve for a MOS system consisting of a cobalt (SCM tip)-oxide-semiconductor structure. Effects such as oxide and interface trapped charges were incorporated into the calculation of the theoretical C-V curves. The effect of a finite tip size was discussed. It was found that the calculated SCM profiles agree well with the SCM measurements provided the interface or surface charge density is high, which is reasonable as the very thin passivating oxide on the semiconductor sample is generally not a good-quality oxide. Fringing field effects due to the finite tip size affect the neighbouring regions, resulting in a spatial broadening in the measured SCM profile. In addition, it was observed that the electrical junction measured by SCM (indicated by the zero crossing in the measured SCM signal, or dC/dV) is a strong function of the dc bias and does not coincide exactly with the metallurgical junction obtained from SIMS. The discrepancy could be due to slight deviations from the flatband voltage that causes carriers from either side of the pn junction to flow into the depletion region, which could affect the position of the zero crossing in the SCM signal. In the second case study, the 2D boron dopant profile within a 100-nm depth of a laser annealed ultra-shallow abrupt p + n junction was studied. A very narrow region of zero SCM signal related to the space charge region of the abrupt junction was detected. It was found that in abrupt junctions, 2D dopant profiling becomes more difficult as the effect of the finite tip size and pn junction play an even significant role in the SCM results obtained.