Simultaneous IR Material Recognition and Conductivity Mapping by Nanoscale Near‐Field Microscopy

Abstract

Nanostructures are at the heart of ever-shrinking electronic and photonic devices. The engineering of nanocomposite materials, building blocks, [1,2] and conduction properties [3,4] necessitate advanced microscopy tools to assess critical dimensional, compositional, structural, and conduction properties for analysis and quality control. [5] Here we demonstrate with industrial bipolar and metal-oxide-semiconductor (MOS) devices that mid-IR scattering-type near-field optical microscopy (s-SNOM) [6,7] has the potential to probe all of these parameters, and thereby excels electron and other scanning-probe microscopies. . We image cross sections of the devices routinely prepared for failure analysis at 30 nm resolution, and this limit could be pushed below 10 nm in the course of future development. Resolution combined with high specificity to material and conductivity properties makes IR s-SNOM a promising tool beyond the microelectronics field for chemical nanotechnology, molecular electronics, photonics, and bioanalytics.IR spectroscopy has tremendous merit in the chemical and structural analyses of materials and in conduction assessment, but until now the limited spatial resolution has prevented its application in industrial failure analysis and quality control. Instead, scanning electron microscopy (SEM) is employed, which offers nanoscale resolution and sensitivity to materials, particularly when combined with Auger, energy-dispersive X-ray (EDX), or wavelength-dispersive X-ray (WDX) spectroscopies. However, only qualitative doping information with decoration-etched samples can be obtained. Transmission electron microscopy (TEM) offers elemental sensitivity [8,9] in combination with EDX or electron energy loss spectroscopy (EELS), but it suffers from complicated and time-consuming sample preparation. Moreover, the feature sizes of semiconductor structures have already been reduced below the minimum thickness of TEM samples so that details can no longer be imaged.[10] Scanning probe microscopy (SPM) provides topography, and in the extended versions of scanning capacitance microscopy (SCM) [11] and scanning spreading resistance microscopy (SSRM), also doping [12] but poor material sensitivity. We introduce IR s-SNOM as a method of choice, as SNOM generally extends SPM by the optical near-field interaction between tip and sample, and it thus enables the power of optical spectroscopies, such as fluorescence, [13] Raman, [14,15] or IR, [6,[16][17][18][19][20][21][22][23] to be exploited with nanoscale spatial resolution.In particular, IR s-SNOM has a demonstrated specificity to chemical composition, [22,24] material category, [7] structural variation, [25,26] and electrical conduction. [17,27,28] Our IR s-SNOM technique is based on atomic force microscopy (AFM) as described previously; [6,29] imaging relies on a commercial, Pt-coated, cantilevered tip operating in tapping mode (frequency X ≈ 30 kHz) with a 20-30 nm radius of curvature. The tip is illuminated by a focused CO 2 laser beam at a wavelength k = 10.7 lm. Th...

Review of Near-Field Terahertz Measurement Methods and Their Applications

“…Following their work done in the near-infrared regime [50], Keilmann's group at the Max Planck Institute of München developed its own approach: they collect the scattered field in the back-scattered direction placing a cantilevered W tip, used in tapping AFM mode, at the focus of a paraboloid mirror as shown in Fig. 9c [51].…”

Nanoscale Conductivity Contrast by Scattering-Type Near-Field Optical Microscopy in the Visible, Infrared and THz Domains

“…As already mentioned, a doping gradient can be determined from just a single near-field image [34]. The extraction of the scattering contrast along the gradient results in resonance curves akin to those in Fig.…”

“…Further work with mid-infrared s-SNOM has confirmed that the local conductivity contrast can indeed be quantified along a doping gradient, by imaging a series of real-world nanostructured device samples produced by microelectronics industry [34]. For this a sample containing transistor elements was prepared by polishing, and SEM was used to visualize the position of the different elements of the nanocircuit.…”

“…5 Mid-infrared near-field microscopy of highly-doped semiconductors Much of the advancement of s-SNOM has been attained using the CO 2 and CO lasers, in the 9-11µm and 5-6µm wavelength regions, respectively [5,6,8,10,11,20,21,24,[27][28][29][30][31][32][33][34][35][36][37]. This came first of all because mid-infrared can be used to exploit chemical fingerprints for recognizing chemical composition, now at nanometric resolution [8,31,33,37,38], but furthermore for technical reasons.…”

High-Resolution Near-Field Optical Microscopy: A Sub-10 Nanometer Probe for Surface Electromagnetic Field and Local Dielectric Trait

“…Specifically, the scattering radiation can be induced upon the presence of certain surface electromagnetic field. Surface plasmon wave (SPW) exemplifies such surface electromagnetic field, by which the evanescent wave propagates on the metal-dielectric or metal-vacuum interface [29,43,50]. In this section, the near-field characteristics of the SPW emanating from single hole or hole arrays of nanometer size made by focused ion beam on metal film are present.…”