Scatterometry is one of the advanced optical metrology techniques has been implemented in semiconductor
manufacturing for monitoring and controlling critical dimensions, sidewall angle and grating heights as well
as thicknesses of underlying films, due to its non-destructive nature, high measurement precision and speed.
In traditional scatterometry approach, the optical properties (<i>n&k</i>'s) of film stack have been used as fixed
inputs in a scatterometry model, therefore, the process engineers have to assume that there is no significant
impact on measurement results by small deviation from pre-extracted <i>n&k</i>'s. However, <i>n&k</i>'s of actual
production wafers will always vary from the fixed values used in the model. The magnitude of the variations
and its impact on the accuracy of scatterometry measurements has not been well-characterized yet.
In this study, a low-k dielectric stack with noticeable <i>n&k</i>'s variations was generated. The low-k dielectric
stack has the refractive index (<i>n</i>) variation around 0.01 @ 633nm within a wafer, and is under two layers of
patterned PR and BARC. Different scatterometry models with fixed and floated <i>n&k</i>'s have been analyzed.
Although comparable repeatability was obtained with either fixed or floated <i>n&k</i>'s model, the correlation
(R<sup>2</sup>) to CD-SEM result has been improved by floating <i>n&k</i> in the model in comparison to that of fixed <i>n&k</i>
model. In this paper, we also discuss some differences in applying various optical models (i.e, EMA and
Cauchy) in scatterometry measurements.
In this paper, one of the major contributions to the OCD metrology error, resulting from
within-wafer variation of the refractive index/extinction coefficient (n/k) of the substrate, is
identified and quantified. To meet the required metrology accuracy for the 65-nm node and beyond,
it is suggested that n/k should be floating when performing the regression for OCD modeling. A
feasible way of performing such regression is proposed and verified. As shown in the presented
example, the measured CDU (3σ) with n/k fixed and n/k floating is 1.94 nm and 1.42 nm,
respectively. That is, the metrology error of CDU committed by assuming n/k fixed is more than
35% of the total CDU.
In this paper, we study the linear and nonlinear responses of 1-D photonic bandgap (PBG) structures. We show that, the nonlinear interaction can be greatly enhanced by the use of Kerr defect modes in a 1D dielectric photonic crystal structure, such as low-intensity bistability and multistability, and by optimizing the design of the layer sequence. 1-D PBG structure can also be promising candidate as low-intensity nonlinear phase shifter. Nonlinear z-scan measurements of a 3-cavity thin-film PBG sample show that the nonlinearity is enhanced over the native material by a factor over 30, while maintaining a bandwidth greater than 1T Hz, which is great for all-optical switching.
A major challenge in many biosensing applications is the real-time detection of a multitude of analytes from a small sample volume. Achieving these goals would perhaps eliminate the need for an intermediate molecular amplification step. Our approach to this challenge involves the investigation of high sensitivity and scalable integrated optical transduction and scalable microfluidic sample delivery. The microfluidic architecture has small cross-section and allows the sample to visit each sensing zone, where a biospecific monolayer performs molecular recognition. Signal transduction occurs via a resonant optical microcavity, which has the dramatically increased signal to noise ratio in fluorescence detection necessary to detect small molecular numbers. Important performance issues in this architecture are sample flow rates, sensing zone size, and the use of passive mixing structures. In addition, microfabrication issues such as optical and microfluidic design, materials, and monolayer patterning are discussed.
The artificial resonance of optical ring resonators can be used to enhance the nonlinear phase shift resulting from a third-order material response. This enhancement results form the interaction of two effects: the internal intensity build up within the resonator which introduces a single pass nonlinear phase shift, and the resulting detuning of the resonance which causes a change in phase at the outputs. Devices consisting of multiple resonators in series can provide additional improvements in terms of allowing a large phase shift of the output. As compared to same material in bulk, devices consisting of single and multiple ring resonators constructed from an absorbing material can provide a much greater nonlinear phase shift, in some case by many orders of magnitude. In addition, these phase shifts exceed the maximum value allowed by absorption in bulk materials.
Optical microcavities can be used to enhance the detection sensitivity of evanescent-wave fluorescence biosensors to the binding of a labeled analyte to a biospecific monolayer. The enhancement results form the buildup of intensity within the microcavity on resonance, which thereby increases fluorescence output from species specifically bound on the surface of the microcavity. Target studies are directed at nucleic acid hybridization, and initial results using high-Q dielectric microspheres have been obtained.
The artificial resonances of dielectric optical microcavities can be used to enhance the detection sensitivity of evanescent-wave optical fluorescence biosensors to the binding of a labeled analyte to a biospecific monolayer. Microcavity sensors offer the high sensitivity of a slab waveguide evanescent fluorescence sensor of much larger sensing surface area. Alternatively, when compared to a slab waveguide of the same area, microcavity based sensors offer much improved sensitivity. In either case, the required number of bound analytes is dramatically reduced. These scaling relations are highly conducive to achieving large sensing arrays with small sample volumes.