Dopant and Thin Film Analysis at Sub-Å Equivalent Thickness

March 28, 2024 3 min read

Dopant and Thin Film Analysis at Sub-Å Equivalent Thickness



Within the semiconductor and nanotechnology research community, one of the main capabilities sought is the capacity to quickly, non-destructively, and quantitatively analyze the composition of trace level dopants and nanostructures. Modern 3D finFET transistors, which are non-planar and generally use single-digit nanometer high-K dielectric insulators in place of SiO2 gate oxides, are an example of the technological advancements in electronics and materials that have created the necessity for this kind of learning.


Current Approaches: SIMS and TEM

Secondary Ion Mass (SIMS) spectrometry has been the workhorse analytical technique, in which a focused ion beam sputters the surface of a specimen, forming secondary ions that are analyzed for composition. However, the advent of new devices and materials can introduce substantial challenges in its use, including quantification inaccuracies because of sputtering rate variations, which can be due to factors such as non-planar structures and impurities in high-k gate hafnium dielectrics. In addition, the acquisition times required for accurate analysis is a bottleneck, typically taking ~30 minutes per test pad point.

To address these problems, Transmission electron microscopy (TEM) is used. TEM measures the transmission of electrons through a sample, and as a result, requires the preparation of an ultrathin lamella of <100 nm for a region-of-interest. TEM is labor-intensive and very low throughput, and the sample preparation and region-of-interest can remove or destroy features of interest.



Figure 1: Current approaches to measure thin films are SIMS or TEM sectioning, both which are low-throughput and destructive. Shown above is a TEM image of a 16-nm finFET. D James, “Moore’s Law Continues into the 1x-nm Era.” 21st Itnl Conference on Ion Implanation Technology 2016.



Sigray AttoMap Patented MicroXRF System Sigray, through patented breakthroughs in x-ray source and x-ray optic technologies, has developed the AttoMap microXRF system with sub-femtogram sensitivities. The MicroXRF system is non-destructive, with a high spatial resolution of 10 µm, making it ideal as a complementary upstream technique to SIMS and TEM for identifying regions of interest for follow-on characterization.



The AttoMap was used on third party prepared samples of thin films on Si substrates to validate its capabilities and to measure its lower limit of detection (LLD). Its multi-target x-ray source enabled the selection of different x-ray targets to optimize the x-ray fluorescence signal for different thin films of interest.



Figure 2: Lower Limits of Detection with 3-sigma Confidence at 400s: LDLs of well below sub-angstrom can be obtained with Sigray’s AttoMap non-destructively. Moreover, as can be seen from the Co thin film rows, choice of x-ray source target matters: Cu has a ~10X better LDL than a Mo target. This is why AttoMap uses a patented multi-target x-ray source



Sigray’s AttoMap provides a non-destructive, ultrahigh sensitivity approach for quantifying thin film thicknesses and dopant concentrations. Its patented high brightness x-ray source and x-ray optics enable excellent throughput and sensitivity, and moreover, due to its multi-target x-ray source design, has optimal performance for most elements-of-interest. The system can be used for single layers (as discussed) or even multiple elements and multi-layers (microXRF provides simultaneous detection of all elements).

Because of its high spatial resolution, the AttoMap can provide rapid (seconds to minutes) region-of-interest identification for follow-on analysis with complementary approaches such as SIMS and TEM.