After-develop inspection (ADI) and photo-cell monitoring (PM) are part of a comprehensive lithography process
monitoring strategy. Capturing defects of interest (DOI) in the lithography cell rather than at later process steps shortens
the cycle time and allows for wafer re-work, reducing overall cost and improving yield. Low contrast DOI and multiple
noise sources make litho inspection challenging. Broadband brightfield inspectors provide the highest sensitivity to litho
DOI and are traditionally used for ADI and PM. However, a darkfield imaging inspector has shown sufficient sensitivity
to litho DOI, providing a high-throughput option for litho defect monitoring. On the darkfield imaging inspector, a very
high sensitivity inspection is used in conjunction with advanced defect binning to detect pattern issues and other DOI
and minimize nuisance defects. For ADI, this darkfield inspection methodology enables the separation and tracking of
'color variation' defects that correlate directly to CD variations allowing a high-sampling monitor for focus excursions,
thereby reducing scanner re-qualification time. For PM, the darkfield imaging inspector provides sensitivity to critical
immersion litho defects at a lower cost-of-ownership. This paper describes litho monitoring methodologies developed
and implemented for flash devices for 65nm production and 45nm development using the darkfield imaging inspector.
This paper describes a methodology for after-develop inspection (ADI) using a broadband DUV/UV/visible brightfield inspector with a unique optical mode. The VIB (Varied Illumination Brightfield) optical mode enables capture of unique killer defects at low nuisance rate on certain 45nm and 32nm ADI layers, significantly improving litho inspection sensitivity.
By implementing this inspection, defect engineers were able to detect critical excursions at ADI rather than at later process steps. This shortened process development time and allowed for re-work, significantly reducing wafer cost.
The temperature dependent thermal difference reflectance (TDR) spectra of thin film samples of Tl2Ba2Ca2Cu3O10, (BiPb)2Sr2Ca2Cu3O10, Tl2Ba2CaCu2O8 and YBa2Cu3O7 have been measured for photon energies between 0.3 and 4.5 eV at temperatures above and below each material's superconducting critical temperature. The amplitude of the characteristic optical structure near the screened plasma frequency of each sample in the normal state TDR spectrum varies approximately linearly with temperature, T, indicating that the temperature dependent optical scattering rate in these materials scales with temperature as T2. From the TDR spectra collected above and below the critical temperature of each sample, the superconducting to normal state reflectance ratio, Rs/RN, has been obtained. In these materials, a feature exists in the experimental Rs/RN spectrum at energies between 1.5 and 2.0 eV which can be accounted for by treating the superconductivity in an Eliashberg model with a coupling function that includes both an electron-phonon interaction and a high energy electron-boson interaction located between 1.6 and 2.1 eV. Good agreement is obtained between theory and experiment based upon this description of the superconducting state.
We have previously measured the temperature dependent thermal difference reflectance (TDR) spectra of several high-temperature superconducting thin films. From the TDR spectra collected above and below the critical temperature of each sample, the superconducting to normal state reflectance ratio, RSRN, has been obtained. We observe significant deviations from unity in this reflectance ratio at photon energies on the order of 2.0 eV. Both the temperature dependence and location of this structure in the RS/RN spectra may be described by solving the Eliashberg integral equations with an electron-boson coupling function that includes both an electron-phonon interaction and an interaction located at approximately the energies of known charge transfer excitations in these materials (approximately 2.0 eV). We found remarkably good agreement between the experimental data and the results of our calculations based upon this description of the superconducting state. We also use the technique of TDR spectroscopy to probe the superconducting proximity effect. By measuring the TDR spectra of the silver layer in a Ag-(BiPb)2Sr2Ca2Cu3O10 bi-layer junction or the indium layer in a In-Ag-(BiPb)2Sr2Ca2Cu3O10 tri-layer junction, at temperatures above and below the critical temperature of the high temperature superconductor, we hope to observe structure due to a proximity induced gap function in the normal metal.
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