In digital holography an object wave is numerically reconstructed from a recorded hologram. Using this technique it is
possible to detect the position and size of particles in a 3D domain. In this work, particular focus is placed on
quantification of particles with non-spherical morphologies. The in-line configuration is chosen due to the simplicity of
the optical setup and minimal distortions of in-plane morphologies. However, this geometry is also characterized by a
large depth-of-focus and high uncertainty in the detected depth. To quantify these uncertainties, this work begins with
the definition of a non-dimensional model of hologram recording and reconstruction applied to single spherical and nonspherical
particles. Typical CCD noise sources are included. Application of this model to two particle detection
methods reveals the relevant merits and limitations of each particle detection method. From the lessons learned, a new
hybrid particle detection method is proposed. Simulations indicate the hybrid method significantly improves upon the
accuracy of the measured depth and particle morphologies. Furthermore, the proposed method automatically determines
the optimum threshold for each particle, and, therefore, requires minimal user inputs. Finally, initial experimental results
for spherical particles confirm the accuracy of the proposed hybrid method.
A microchannel plate is demonstrated as both an optical low-pass filter and a heterodyning modulator. The frequency response function of the microchannel plate indicates it behaves as a low-pass filter. Antialiasing with the microchannel plate is demonstrated using a two-tone amplitude modulated laser beam, with the higher tone above the cutoff frequency being successfully suppressed while the frequency within the bandwidth of the filter is passed through. Selection of different commercially available phosphors controls the filtering and frequency response characteristics of the optical filter, effectively moving the cutoff frequency. By gating the microchannel plate at different frequencies, the microchannel plate can also be used analogously to a heterodyning spectrum analyzer, supplying all of the required functions of a local oscillator, mixer, and filter.
Long-term reliability testing of Micro-Electro-Mechanical Systems (MEMS) is important to the acceptance of these devices for critical and high-impact applications. In order to make predictions on aging mechanisms, these validation experiments must be performed in controlled environments. Additionally, because the aging acceleration factors are not understood, the experiments can last for months. This paper describes the design and implementation of a long-term MEMS reliability test bed for accelerated life testing. The system is comprised of a small environmental chamber mounted on an electrodynamic shaker with a laser Doppler vibrometer (LDV) and digital camera for data collection. The humidity and temperature controlled chamber has capacity for 16 MEMS components in a 4x4 array. The shaker is used to dynamically excite the devices using broadband noise, chirp or any other programmed signal via the control software. Driving amplitudes can be varied to maintain the actuation of the test units at the desired level. The actuation is monitored optically via the LDV which can report the displacement or velocity information of the surface. A springmass accelerated aging experiment was started using a controlled environment of 5000 ppmv humidity (roughly 13% at room temperature), temperature of 29 °C, and ±80μm maximum displacement of the mass. During the first phase of the experiment, the resonant frequency was measured every 2 hours. From 114.5 to 450 hours under stress, measurements were taken every 12 hours and after that every 24 hours. Resonant frequency tracking indicates no changes in the structures for 4200 hours of testing.
Image fidelity is one of the fundamental requirements in lithography and it is becoming more important as feature sizes shrink below 90 nm. Image distortion depends on the mask deformation caused by the intrinsic stress in the film-substrate system. To develop an understanding of stress generation and to control film quality, measuring film stress is essential. In recent years, research laboratories and industry have increasingly adopted indirect methods for determining film stress. All of these methods are based on the measurement of substrate deformation, and the film stress is calculated from the substrate curvature by the local application of Stoney’s equation. When the two principal stresses at each point in the film plane are not equal to each other and their distribution is not uniform, the local application of Stoney’s equation is invalid. Even though the accuracy of the measurement may be high, the stress determined may not be. An alternative technique based on numerical analysis has been developed. The limitations of using Stoney’s equation and the new stress measurement technique are discussed in this paper.
Minimizing mask-level distortions is critical to ensuring the success of electron projection lithography (EPL) in the sub-65-nm regime. Previous research has demonstrated the importance of controlling the stress in the patterned stencil membranes to minimize image placement distortions. Low-stress, 100-mm diameter EPL mask blanks have been patterned with a layout that simulates the effects of the cross-mask and intra-subfield pattern density gradients found in a realistic circuit design. Extensive IP measurements were made to illustrate how local subfield correction schemes can be used to reduce all mask-level distortions (regardless of pattern type) to less than 15 nm (3s). Combining membrane stress control with the use of repeatable and identical reticle chucking is expected to reduce EPL mask-level distortions to the values that will be needed for the 65-nm design node.
Electron Projection Lithography ( EPL) is a leading candidate for the sub-65 nm lithography regime (1),(2). The development of a low-distortion mask is critical to the success of EPL. EPL has traditionally used either a stencil format mask with a single scatterer layer having the pattern represented by voids in the membrane (3), or a continuous membrane format mask with a patterned scatterer layer supported by an unperforated membrane(4).
Minimizing mask-level distortions is critical to the success of electron projection lithography (EPL) in the sub-100-nm regime. A number of possibilities exist to reduce mask-fabrication and pattern-transfer distortion including subfield correction, "dummy" patterns, pattern splitting, and film stress control. Finite element modeling was used to illustrate the advantages and capabilities of these correction schemes for a 100-mm stencil mask with 1-mm×1-mm membrane windows. Static-random-access-memory-type circuit features, including both the interconnect and contact levels, were used, to simulate realistic circuit layouts with both cross-mask and intra-membrane pattern density gradients. With such correction techniques, it is possible to reduce the EPL mask-level distortions for "worst-case" mixed pattern types to less than 1.0 nm.
To meet the stringent image placement error budgets for the insertion of 157-nm lithography in the sub-65 nm regime, photomask-related distortions must be minimized, corrected, or possibly eliminated. Sources of distortions include the pellicle system, which has been previously identified as a potential cause of image placement error. To characterize the many aspects of static pellicle-induced distortions, experiments have been conducted, and comprehensive finite element simulations have been performed for hard pellicle systems. The results of these benchmarking studies showed the capabilities of modeling and simulation to accurately predict static pellicle-induced distortions. In addition, the dynamic response of hard pellicles during exposure scanning was determined, taking into account both inertia effects and fluid / structure interaction. This paper focuses on the vibratory response of modified fused silica (hard) pellicles due to acoustic / dynamic pressure loadings during exposure scanning, studied both experimentally and numerically. A modal analysis was performed, the structural damping of the pellicle system was assessed, and a harmonic study was conducted to characterize the effects of acoustic excitation. The results obtained facilitate the timely establishment of viable hard pellicle designs and related standards for 157-nm lithography.
Minimizing mask-level distortions is critical to the success of Electron Projection Lithography (EPL) in the sub-100 nm regime. A number of possibilities exist to reduce mask fabrication and pattern transfer distortion including subfield correction, 'dummy' patterns, pattern splitting and film stress control. Finite element modeling was used to illustrate the advantages and capabilities of these correction schemes for a 100-mm stencil mask with 1 mm X 1 mm membrane windows. SRAM-type circuit features including both the interconnect and contact levels were used to simulate realistic circuit layouts with both cross-mask and intra-membrane pattern density gradients. With such correction techniques, it is possible to reduce the EPL mask-level distortions for 'worst-case' mixed pattern types to less than 1.0 nm.
Potential transmission problems for polymeric pellicle membranes at 157 nm have led to alternative designs incorporating ultra-thin modified fused silica, i.e., so-called 'hard pellicles.' The mechanical characteristics of hard pellicles are unique. Forces can be generated between the pellicle frame and the patterned reticle during bonding because of misalignment and warpage. These forces create out-of-plane distortions of the reticle, which can subsequently induce in-plane distortions. Also, since the hard pellicle is an optical element, its deflection can be a source of error. In addition, because the reticle is rapidly repositioned during exposure, vibration of the pellicle could be excited by stage motion. It is important, therefore to understand the structural and modal response of the composite pellicle / reticle system. Experimental analyses were conducted to determine changes in the reticle and hard pellicle profiles (out-of-plane) due to bonding. Finite element modeling was used to support the experimental study, as well as identify the gravitational distortions of the pellicle. A modal analysis was also performed on the hard pellicle after bonding. The experimental measurements and finite element results were in excellent agreement, both for mode shapes and vibration frequencies.
To extend optical lithography technology to the sub-100 nm linewidth regime, all mask-related distortions must be eliminated or minimized. Thermal distortion during the exposure process can be a significant contribution to the total pattern placement error budget for advanced photomasks. Consequently, several finite element (FE) models were developed to predict the thermal and the mechanical response of the optical reticle during exposure. This paper presents the experimental verification of the FE thermal models. In particular, the results of the numerical simulation were compared with the experimental data and excellent agreement was found.
Masks for electron projection lithography require the use of thin membrane structures due tot he short scattering range of electrons in solid materials. The two leading mask formats for electron projection lithography are the continuous membrane scatterer mask and the stencil mask. The reduced mechanical stability of the membranes used for electron projection masks relative to conventional optical masks leads to increased levels of process induced image placement distortions. This paper evaluates the image placement distortions due to the pattern transfer processes on the continuous membrane mask format. Image placement was measured from both a cross-mask and intramembrane perspective to evaluate the effects of different patterns, pattern densities and density gradients on the observed image placement and the experimental results obtained were then compared to those predicted by finite element modeling.
The stringent requirements placed on sub-100 nm feature lithography require the development of a low distortion mask. The distortions due to the fabrication process of extreme ultraviolet lithography masks have been predicted using finite element methods. The investigation included the simulation of the mask blank fabrication, pattern transfer and mounting. Film stress gradient effects for the multilayer stack, absorber layer and resist layer were also evaluated, considering both in-plane and out-of-plane distortions. To assist in optimizing the final substrate and pattern dimensions, a number of different substrate formats and materials were considered. To determine the effects of pattern density, different types of patterns were modeled, including uniform coverage, a 'half-and-half' pattern and an orthotropic feature pattern. Reticle placement errors were less than 2 nm at the mask level (0.5 nm at the wafer level) for nearly all cases studied.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.