Finite difference time domain simulation of the electromagnetic coupling in millisecond radiation heating is used to explore how the energy couples, where it goes in the device structure, and wavelength dependencies. Millisecond annealing is advantageous for improving IC device characteristics; however, the application of short time scale annealing requires very careful control over the localized heating that can be pattern, device structure, and material dependent. The presence of metal gate structure introduces extra complexity. This paper considers the case of tungsten gates on poly-silicon pedestals with or without silicon nitride caps. Rigorous finite difference time domain techniques are used to compute the fields throughout the device structure as a function of polarization, angle of incidence, wavelength, CD, and pitch. One of the dominant effects is that a grating formed by a metal gate array acts like a polarizer. Thus the coupling changes with grating orientation. The coupling is the strongest when the incident plane is perpendicular to the gate and the electric field is p-polarized. In the case of laser light with a 10 μm wavelength incident near silicon’s Brewster angle, the absorptivity approaches 100% just as if the tungsten metal gates do not exist. Data from similar studies at shorter wavelengths is also presented as well as a comparison with experimental measurements.

Metal nanostructures that support surface plasmons are compelling as plasmonic circuit elements and as the building blocks for metamaterials. We demonstrate here the spontaneous self-assembly of shaped silver nanoparticles into three-dimensional plasmonic crystals that display a frequency-selective response in the visible wavelengths. Extensive long-range order mediated by exceptional colloid monodispersity gives rise to optical passbands that can be tuned by particle volume fraction. These metallic supercrystals present a new paradigm for the fabrication of plasmonic materials, delivering a functional, tunable, completely bottom-up optical element that can be constructed on a massively parallel scale without lithography.

The loss of through focus process latitude due to the interaction of electromagnetic fields that are at 90 degree phase with the intended 0 o and 180 o at mask edges and line-ends is characterized for 45 nm imaging using thick-mask and image simulation. TEMPEST and Panoramic Technologies simulators are used to determine near fields and images of chromeless, MoSi and Ta-SiO2 line ends. These fields are then analyzed in both space and plane wave spectra to determine rules of thumb for the effective narrowing (real) and leakage (quadrature) contributions in boundary layers to improve the accuracy of thin-mask models. Typical values for ATT-PSM are 0.05 to 0.1 λ/NA per edge. These values varied only slowly out to angles of incidence on the mask of 20 o suggesting an angle independent boundary layer parameter would be moderately accurate. For chromeless the values are larger and can be over 0.2 λ/NA per edge for the quadrature component. The through focus imaging for lines and line ends is then made using the full set of near fields, producing a tile of the Bossung curve through focus that is 18 nm for line-end shortening. The Ta-SiO2 mask stack showed more irregular behavior compared to the other masks.

Surface plasmon grating couplers are optimized by separately characterizing the collection efficiency, rescattering, and transmission effects of isolated grating elements with finite difference time domain methods and then using signal flow graph methods to assess the performance of arrays of N identical elements. Small bars, ridges, and trenches on silver at a wavelength of 700 nm are shown to have different coupling patterns and efficiencies from near zero to the physical width of the element. The overall efficiency requires a suitable trade-off of coupling and surface wave transmission and an example structure exhibiting an equivalent 100% capture length over ten wavelengths is shown.

An experimental technique for quantitatively characterizing edge effect contributions in transmission through thick photomasks is described and evaluated through electromagnetic simulation. The technique consists of comparing the 0(th) order transmission for various duty cycles to the expected experimental behavior from a thin mask model. The real electric field component from the edges is proportional to the shift in the position of the minimum energy in the 0(th) order field away from the expected thin mask location. The square root of the minimum 0(th) order diffraction energy normalized to a clear mask gives the imaginary edge contribution. The results indicate that Alternating Phase Shifting Masks (ALT-PSM) and Attenuating Phase Shifting Masks (ATT-PSM) technologies have significant edge effects on the order of 0.1 lambda to 0.2 lambda per edge respectively, as well as polarization dependence. For periods of 2 wavelengths and larger these edge contribution values are nearly independent of pitch. The existence of an imaginary (or quadrature) phase component is shown to result in an additive linear variation of line edge shortening through focus. This tilt can be interpreted as a focus shift of the normal parabolic behavior and is about 0.5 Rayleigh units (RU). This focus shift depends to some extent on the surrounding layout as well as the feature itself.

Numerical simulation is a useful tool for evaluating new technologies. In order to analyze new plasmonic and photonic band-gap devices we have re-written and extended our finite-difference time-domain (FDTD) simulator, TEMPEST, into a guided-wave analysis system. We illustrate our new simulation capabilities with investigations into two devices: 1) a sub-wavelength grating mirror, and 2) plasmon-enhanced Daguerreotype photographs.

Contact holes represent one of the biggest critical dimension (CD) mask metrology challenges for 45nm technology mask development. The challenge is a consequence of both wafer and mask sensitivities. Large mask error factors and the small process windows found when contact holes are imaged on wafers impose very tight mask specifications for CD uniformity. The resultant CD error budget leaves little room for mask metrology. Current advanced mask metrology deploys a CD-SEM to characterize the mask contact hole CD uniformity. Measuring a contact hole is complex since it is inherently two-dimensional and is not always well-characterized by one-dimensional x- and y-axis measurements. This paper will investigate contact metrics such as line edge roughness (LER), region of interest (ROI) size, area, and CD sampling methods. The relative merits of each will be explored. Ultimately, an understanding of the connection between what is physically measured on the mask and what impacts wafer imaging must be understood. Simulations will be presented to explore the printability of a contact hole's physical attributes. The results will be summarized into a discussion of optimal contact hole metrology for 45nm technology node masks.

Stray-light sources from pupil plane masks that may limit Terrestrial Planet Finder Coronagraph (TPF-C) performance are characterized1,2 and mitigation strategies are discussed to provide a guide for future development. Rigorous vector simulation with the Finite-Difference Time-Domain (FDTD) method is used to characterize waveguiding effects in narrow openings, sidewall interactions, manufacturing tool-marks, manufacturing roughness, mask tilt, and cross-wavelength performance of thick Silicon mask structures. These effects cause stray-light that is not accounted for in scalar thin-mask diffraction theory, the most important of which are sidewall interactions, waveguiding effects in narrow openings, and tilt. These results have been used to improve the scalar thin-mask theory used to simulate the TPF-C with the Integrated Telescope Model.3 Of particular interest are simulations of 100m thick vertical sidewall openings that model features typically found on Ripple masks4 fabricated by Reactive Ion Etching (RIE) processes.5 This paper contributes fundamental data for systematically modeling these effects in end-to-end system simulation. Leakage straight through the mask material varies greatly with wavelength, especially in Silicon (an attractive mask material due to the precision manufacturing techniques developed by the IC industry). Coating Silicon with 200nm of Chrome effectively mitigates the leakage without causing additional scattering. Thick-mask diffraction differs from the predictions of scalar thin-mask theory because diffraction spreading is confined by the mask's sidewalls. This confinement can make a mask opening look electro-magnetically larger or smaller than designed, by up to 3λ per vertical sidewall on a 50μm thick mask yet this can be reduced an order of magnitude by undercutting the sidewalls 20°. These confinement effects are sensitive to mask tilt (if light reaches the sidewalls) which can lead to an imbalance in stray-light sources and an extra wavelength of effective opening change on the illuminated sidewall.

Direct imaging and characterization of exo-solar terrestrial planets require coronagraphic instruments capable of suppressing star light to 10(-10). Pupil shaping masks have been proposed and designed(1) at Princeton University to accomplish such a goal. Based on Princeton designs, free standing (without a substrate) silicon masks have been fabricated with lithographic and deep etching techniques. In this paper, we discuss the fabrication of such masks and present their physical and optical characteristics in relevance to their performance over the visible to near IR bandwidth.

The edge generated stray-light from corner boundary conditions, interactions with the lower mask structure, and surface plasmon polaritons that may limit Terrestrial Planet Finder Coronagraph performance are characterized. Previously a number of stray light sources, unaccounted for by the ideal thin mask theory used to design the pupil-plane masks, were identified. In this paper we illustrate and quantify the most important outstanding stray-light sources in the near-field in order to improve the model of pupil-plane mask transmission used by the Integrated Telescope Model. Corner spikes, caused by the need to bring the ideal top-hat field into compliance with the boundary conditions set forth by Maxwell's equations, form the strongest source of stray-light, accounting for up to a 1λ shift in the effective opening width per edge. Undercutting mask edges by 20° reduces this source of stray-light by more than a factor of five. Interactions between light and the lower mask structure, a secondary effect, account for only a few percent of the stray-light in the TE polarization but account for up to 50% of the stray-light in the TM polarization due to surface plasmon polaritons. Surface plasmon polaritons, surface waves that run for tens of microns and radiate at corners, form the final stray-light source. On thin masks they may account for up to a 1λ shift in the effective opening width; however, their effects can be easily mitigated by choosing a poor surface plasmon material, such as Chrome. The results presented here are being used to facilitate end-to-end system modeling through the Integrated Telescope Model.

Rigorous finite-difference time-domain electromagnetic simulation is used to simulate the scattering from proto-typical pupil mask cross-section geometries and to quantify the differences from the normally assumed ideal on-off behavior. Shaped pupil plane masks are a promising technology for the TPF coronagraph mission. However the stringent requirements placed on the optics require that the detailed behavior of the edge-effects of these masks be examined carefully. End-to-end optical system simulation is essential and an important aspect is the polarization and cross-section dependent edge-effects which are the subject of this paper. Pupil plane masks are similar in many respects to photomasks used in the integrated circuit industry. Simulation capabilities such as the FDTD simulator, TEMPEST, developed for analyzing polarization and intensity imbalance effects in nonplanar phase-shifting photomasks, offer a leg-up in analyzing coronagraph masks. However, the accuracy in magnitude and phase required for modeling a chronograph system is extremely demanding and previously inconsequential errors may be of the same order of magnitude as the physical phenomena under study. In this paper, effects of thick masks, finite conductivity metals, and various cross-section geometries on the transmission of pupil-plane masks are illustrated. Undercutting the edge shape of Cr masks improves the effective opening width to within λ/5 of the actual opening but TE and TM polarizations require opposite compensations. The deviation from ideal is examined at the reference plane of the mask opening. Numerical errors in TEMPEST, such as numerical dispersion, perfectly matched layer reflections, and source haze are also discussed along with techniques for mitigating their impacts.

The TPF mission to search for exo-solar planets is extremely challenging both technically and from a performance modeling perspective. For the visible light coronagraph approach, the requirements for 1e10 rejection of star light to planet signal has not yet been achieved in laboratory testing and full-scale testing on the ground has many more obstacles and may not be possible. Therefore, end-to-end performance modeling will be relied upon to fully predict performance. One of the key technologies developed for achieving the rejection ratios uses shaped pupil masks to selectively cancel starlight in planet search regions by taking advantage of diffraction. Modeling results published to date have been based upon scalar wavefront propagation theory to compute the residual star and planet images. This ignores the 3D structure of the mask and the interaction of light with matter.In this paper we discuss previous work with a system model of the TPF coronagraph and propose an approach for coupling in a vector propagation model using the Finite Difference Time Domain (FDTD) method. This method, implemented in a software package called TEMPEST, allows us to propagate wavefronts through a mask structure to an integrated system model to explore the vector propagation aspects of the problem. We can then do rigorous mask scatter modeling to understand the effects of real physical mask structures on the magnitude, phase, polarization, and wavelength dependence of the transmitted light near edges. Shaped mask technology is reviewed, and computational aspects and interface issues to a TPF integrated system model are also discussed.

The Shaped Pupil Coronagraph (SPC) is a high-contrast imaging system pioneered at Princeton and designed for the TPF-C telescope. In this document, we summarize the work done to date on the SPC to date and evaluate its current and projected performance. What makes the SPC attractive for TPF is that it is very simple to make and set up, and it is inherently broadband. Owing to the simplicity of the SPC, it is quickly becoming a relatively mature technology with theoretical and experimental validations of its performance. Many shaped pupils have been designed to various specifications and tools are in place to quickly turn out more. Full vector-field simulations show that realistic shaped pupils can already achieve 1010 contrast in the absence of aberrations. A manufacturing process has been developed to make shaped pupils for as little as a few thousand dollars, at JPL and NIST. Shaped pupils have also been shown to be very insensitive to aberrations, and especially low order aberrations such as tilt and defocus. The SPC is undergoing extensive studies in the lab, and so far a suppression of 4 × 10-8 has been achieved in 10% broadband light (averaged across a region between 4 and 9 λ/D), after speckle-nulling-based wavefront correction. The limiting factor is now believed to be well-understood and is primarily the inability of the speckle nulling algorithm to correct for manufacturing errors in the mask. It was shown that this limitation can be overcome by using a more sophisticated estimation algorithm called peak-a- boo, or by using a shaped pupil design that is insensitive to manufacturing defects. The SPC lends itself well to many wavefront estimation and correction schemes. Simulations show that realistic shaped pupil manufacturing errors and realistic wavefront error can be corrected with a single DM at one wavelength, and 2 or 3 DMs in broadband. The main disadvantages of the SPC is throughput, sharpness, and working angle, but the throughput disadvantage may be counterbalanced to an extent by the fact that SPC requires very few optical components and the fact that the light blocked by the mask may still be used to sense aberrations.