Simultaneous IR material recognition and conductivity mapping by nanoscale near-field microscopy

摘要: Nanostructures are at the heart of ever-shrinking electronic and photonic devices. The engineering nanocomposite materials, building blocks, conduction properties necessitate advanced microscopy tools to assess critical dimensional, compositional, structural, for analysis quality control. Here we demonstrate with industrial bipolar metal-oxide-semiconductor (MOS) devices that mid-IR scattering-type near-field optical (s-SNOM) has potential probe all these parameters, thereby excels electron other scanning-probe microscopies. Within a single IR image, relevant components such as Al, Ti, TiN, Si, Si3N4, SiO2 positively identified by material-specific amplitude phase contrasts in addition local conductivity form mobile-carrier concentration, here over range 10–10 cm. We image cross sections routinely prepared failure 30 nm resolution, this limit could be pushed below 10 course future development. Resolution combined high specificity material makes s-SNOM promising tool beyond microelectronics field chemical nanotechnology, molecular electronics, photonics, bioanalytics. spectroscopy tremendous merit structural analyses materials assessment, but until now limited spatial resolution prevented its application Instead, scanning (SEM) is employed, which offers nanoscale sensitivity particularly when Auger, energy-dispersive X-ray (EDX), or wavelength-dispersive (WDX) spectroscopies. However, only qualitative doping information decoration-etched samples can obtained. Transmission (TEM) elemental combination EDX energy loss (EELS), it suffers from complicated time-consuming sample preparation. Moreover, feature sizes semiconductor structures have already been reduced minimum thickness TEM so details no longer imaged. Scanning (SPM) provides topography, extended versions capacitance (SCM) spreading resistance (SSRM), also poor sensitivity. introduce method choice, SNOM generally extends SPM interaction between tip sample, thus enables power spectroscopies, fluorescence, Raman, IR, exploited resolution. In particular, demonstrated composition, category, variation, electrical conduction. Our technique based on atomic force (AFM) described previously; imaging relies commercial, Pt-coated, cantilevered operating tapping mode (frequency X ≈ kHz) 20–30 radius curvature. illuminated focused CO2 laser beam wavelength k = 10.7 lm. backscattered light analyzed interferometrically record both phase. Pure contrast attained pseudoheterodyne interferometric detection harmonic frequency nX, n>1, yielding sn phase!n signals simultaneously. According point-dipole model, parameters relate complex dielectric value e= e1 + ie2. Thus, us distinguish different levels model. model E scattered approximated dipolar apex surface,