Comparison of high- and low-voltage x-ray mapping of an electronic device

In recent years, field-emission gun scanning electron microscopes, FEG-SEMs, with high-brightness electron guns and excellent performance at low electron beam energies (E-0 less than or equal to 5 keV) have become readily available. Concurrently the performance of solid-state x-ray detectors such as the Si-Li detector has improved significantly and with the addition of ultra-thin window materials these devices are easily capable of detecting characteristic x-rays with energies as low as 150 eV. In conventional x-ray mapping the energy of the electron beam is usually 15 keV-25 keV and the maps are acquired with the K, L, and M shell x-ray lines with energies from 1keV to 15 keV. At these electron beam energies, the lateral resolution of the x-ray maps is on the order of 1 mum -3 mum. Reducing the electron beam energy to 5 keV or below and utilizing the K, L, and M lines with energies from 400 eV to 4 keV should significantly improve the lateral resolution of the x-ray maps. In this study, x-ray maps were acquired for SI-K x-rays at 1.74 keV and O-K x-rays at 0.53 keV on a poly Si gate region of a CMOS device. The maps were acquired at a magnification of 70,000 diameters at beam energies of 15 keV and 5 keV. The 15 keV maps showed little or no variation in intensity corresponding to the device structure. In comparison, the intensity variation in the 5 keV maps correlated well with the Si and SiO2 features in the device. In addition the intensity profiles from the 5 keV maps were used to estimate the effective resolution of the Si and O maps at 16nm and 130 nm respectively.