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research and optoelectronics have also produced a new range of compound semiconductor-based devices with complex thin layer structures. CERAM has developed a range of analytical
protocols using SIMS and other techniques to provide those in the semiconductor and related industries with solutions to problems in product development, process improvement, reverse engineering and failure analysis.
Depth Profiling of Dopants in Silicon Dopant elements are deliberately added to semiconductor materials in order to provide the correct electrical characteristics for performance. The concentrations of dopants are typically in the low atomic % levels, to below parts per million (ppm). Dopant concentrations are usually expressed in atoms cm-3, i.e. the typical concentration range is 1e21atoms cm-3 to > 1e15atoms cm-3.
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The key p-type and n-type dopants in silicon are boron, arsenic and phosphorus. SIMS depth profiling can be used to determine dopant profile shapes, e.g. diffusion studies, implant dosimetry, and dosage comparisons between wafers and specific wafer areas. The usual analysis area sizes vary in a range from ~500µm x 500µm to 50µm x 50µm. The SIMS depth profile (Fig. 2) shows a super-imposition of
Fig. 3 – ULE-SIMS depth profile of a delta-doped B in Si structure
boron, arsenic and phosphorous profiles from ion-implanted reference materials, illustrating the typical dynamic range of the technique and detection sensitivity.
Delta-Doped B in Si
The scaling of ultra-shallow semiconductor materials to thinner layers and dopant profiles presents a continuing analytical challenge. The development of analytical protocols for shallow SIMS depth profiling with high depth resolution Ultra Low Energy-SIMS (ULE-SIMS) requires the use of delta-doped structures to provide an objective measurement of the effects of ion beam mixing and ion-induced topography as a function of depth. The ULE-SIMS profile (Fig. 3) of a boron delta-doped layer structure using 500eV O2+ ions shows the near-surface layers (5nm separation) resolved with good peak-valley resolution. The high depth resolution is maintained throughout the profile.
Fig. 2 – Low level detection of B, As and P in silicon
Low Energy Boron Implants in Silicon These implant materials are fundamental to the increased performance of the emerging generation of devices.
Accurate determination of junction depth
www.euroasiasemiconductor.com Issue IV 2010
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