Three-dimensional atom mapping of dopants in Si nanostructures

Abstract

Atom-probe tomography has successfully mapped three-dimensional ͑3D͒ dopant atom distributions in nanoscale volumes of Si subjected to various processing procedures. The 3D evolution of dopants, specifically effects such as dopant clustering and grain-boundary segregation, were analyzed in implanted polycrystalline Si gate contacts and implanted shallow junctions. A cluster of dimensions 2 ϫ 7 ϫ 8 nm 3 and containing 264 B atoms, was identified at the intersection of three poly-Si grains, verifying that annealing highly overdoped thin poly-Si layers does not facilitate uniformly doped and highly conductive gate contact layers. The downsizing of Si devices continues to drive advances in the electronics industry. Next generation nanodevices require novel diagnostic techniques in order to monitor the effects of macroprocessing on the nanoscale microstructure, to correlate the discovery of new nanoscale phenomena to macrorecorded events, and to understand how local nonuniformities of atomic distributions relate to electrical performance. It is increasingly apparent that this requires a three-dimensional ͑3D͒ microscopy technique that provides the location and elemental identity of atoms within a nanostructure. A practical 3D atomic mapping instrument should accurately measure, analyze, and display the composition of volumes of semiconducting materials that range in scale from 1 to 100 nm.An area of specific interest is the mapping of dopant atoms in Si. Great strides have been made to meet these needs via transmission electron microscopy ͑TEM͒ ͑Refs. 1 and 2͒. While TEM provides critical information regarding the physical composition of nanostructures, the most advanced electron microscopes have difficulty providing the volumetric dopant mapping desired by the semiconductor community. Alternatively, nano-secondory-ion-mass spectorocopy͑sims͒ instruments using liquid metal ion sources may provide ϳ50 nm lateral resolution, but this is still too coarse for quantitative analysis of nanostructures. 3 A combination of recent innovations in instrumentation technology and specimen preparation-primarily enabled by the use of a "local electrode"-has transformed the traditional atom probe into a tool that provides such a capability. 4,5 Recent experiments demonstrate that atom probing with a local electrode provides a ϳ100 nm-diam field of view and collection rates of 1 nm/ min for a 100-nmdiam analysis region. This article describes several new experimental measurements that illustrate the powerful capabilities of this new nanoimaging technique in monitoring dopant distributions in shallow implanted wafers and in implanted poly-Si wafers which contain significant grain structure.Samples for analysis are formed into atom-probe specimens by etching an array of tall ͑Ͼ80 m͒ , ϳ 5 m-diam posts out of the Si surface, ͑Fig. 1͒. The posts are sharpened with a focused ion beam ͑FIB͒ to a radius of curvature at the apex of 50-100 nm Ref. 6. A capping material such as Pt, Au, or Ni is deposited on the specimen surface to protect it fr...

Atom probe tomography

“…95,99,100 Lift-out or coupon extraction methods 95 have been used for site-specific specimen preparation of features such as grain boundaries, 99 interphase interfaces, low volume fraction or inhomogeneously distributed phases, coarse precipitates, 101 as well as ionimplanted and subsurface regions. 102 In addition, the FIB may be used as a final step for electropolished specimens to correct electropolishing artifacts and ensure a circular cross section with a smooth taper angle. 103 Generally, the FIB-based methods require a two-stage process.…”

“…Pulsed-laser APT has been used to map one-, two-, and three-dimensional distributions of boron, arsenic, and phosphorus with high spatial and compositional resolution. Some examples include the observation of arsenic implant profiles in silicon, 102 boron segregated to grain boundaries in polysilicon, 102 and the lateral diffusion profile of boron in a transistor from a source/drain into the gate region.…”

“…With the recent resurgence of PLAP, more high resistivity materials have been examined. 102,143 However, much more work needs to be done to show that the correct compositions and quality 3D projections can be obtained. Progress is being made, and there are certainly many deserving materials characterization challenges in ceramics.…”

Three Dimensional Atom Probe Study of Ni-Base Alloy/Low Alloy Steel Dissimilar Metal Weld Interfaces

“…4 (d)) j. A tungsten needle is prepared in the same way as a conventional atom probe sample and an array of silicon micro tips [20,22]. k. The part of the detached sample is welded with the tungsten tip by platinum deposition.…”

A guide on FIB preparation of samples containing stress corrosion crack tips for TEM and atom-probe analysis

“…To date, no research of atom-probe examination of crack tips has been reported (with the exception of the one of the samples described in this paper in Cerezo et al (2007)), although there is a growing literature on the application of the FIB to the preparation of site-specific specimens (Thompson et al, 2005(Thompson et al, , 2007a. Additionally, only several TEM images of crack tips have appeared in the literature.…”