Control of shallow p-n junctions with low-power focused ion beam

The junction depths and electrical properties of shallow p-n junctions fabricated with 20 keV focused ion beam (FIB) on crystalline silicon substrates are investigated. The n-type silicon substrates are implanted with Ga⁺ both on-axis and 7-degree-tilted at dose of 1×10¹⁴/cm². The stain method is utilized to measure the junction depths before and after 800°C, 30 minutes furnace annealing. The junction depth after annealing is 560 nm for on-axis implantation and 410 nm for 7-degree-tilted implantation. These results are found to be larger than what are projected by the LSS theory. On the other hand, the junction depth is not measurable with stain method in the samples before annealing. Therefore the distribution profile of dopants before annealing in the sample with on-axis implantation is further investigated with SIMS technique. The profile has a long tail deep into the substrates, which indicates strong channeling effect. Therefore the larger than expected p-n junction depth is considered to be the result of channeling effect. The Van der Pauw method is also applied to measure the resistivity and the Hall effect properties of the implanted layer. The results show that the p⁺ layer is properly created with the resistivity of 0.16 Ω-cm and the carriers concentration of 2.9×10¹⁷/cm³ . The I-V characteristics measurement of the p-n junction is performed and the result shows well-formed p-n junctions.