In optical lithography, aberrations induced by lens heating effects of a projection lens lead to degradation of imaging quality. In order to compensate for thermal aberrations, it is crucial to apply an accurate method for thermal aberration prediction. An effective and accurate method for thermal aberration prediction is proposed. A double exponential model is modified in respect of the timing of exposure tools, and a particle filter is used to adjust the double exponential model. Parameters of the model are updated recursively pursuant to the aberration data measured during the exchange of wafers. The updated model is used to predict thermal aberrations during the following exposure of wafers. The performance of the algorithm is evaluated by the simulation of a projection lens for argon fluoride lithography. Simulation results show that predictive errors of primary defocus and astigmatism are significantly reduced, and the mean value of wavefront error in the whole field of view is reduced by about 30% in a vertical line/space pattern. The proposed method is easily adaptable to different types of aberration measurement error.
In optical lithography tools, thermal aberration of a projection lens, which is caused by lens heating effect, leads to degradation of imaging quality. In addition to in-line feedforward compensation technology, thermal aberration can be reduced by optimizing optical design of a projector. Thermal aberration analysis of a projection lens benefits the optimization of optical design. A model of lens heating effect for a lithographic projector is introduced, which is capable of evaluating the synthetical thermal aberration of a projector as well as analyzing the contribution of an individual optical element. Simulation results by the introduced model show that not only the deformation of lens surface, the variance of refractive index but also the change of optical path, which depends on optical design, should be considered in thermal aberration analysis. The contributions of optical elements at different locations of the projector are also analyzed. Based on the model and the simulation results, an optimization method is proposed. A projector for i-line lithography is optimized by the proposed method. Main aberrations Z5, Z9, and Z17 are reduced by about 40%. The image quality of the lithographic projector in steady state is also improved.
In optical lithography, lens heating induced aberrations of a projection lens lead to degradation of imaging quality. In order to accurately compensate for thermal aberrations by integrated manipulators in projection lens, it is crucial to apply an accurate method for thermal aberration prediction. In this paper, an effective and accurate method for thermal aberration prediction is proposed. Double exponential model is simplified in respect of the timing of exposure tools, and particle filter is used to adjust the parameters of the double exponential model. Parameters of the simplified model are updated recursively pursuant to the aberration data measured during the exchange of wafers. The updated model is used to predict thermal aberrations of the lens during the following exposure of wafer. The performance of the algorithm is evaluated by simulation of a projection lens for ArF lithography. Maximum root mean square (RMS) value of perdition error of thermal aberration under annular illumination and dipolar illumination are reduced by 68.3% and 76.1%, respectively. The proposed method is also of well adaptability to different types of aberration measurement error.
In optical lithography tools, thermal aberration of a projection lens, which is caused by lens heating, leads to degradation of imaging quality. In addition to in-line feedforward compensation technology [1], the thermal aberration can be reduced by optimizing projection lens design. Thermal aberration analysis of a projection lens benefits the optimization of projection lens design. In this paper, thermal aberration analysis methods using physical model and simplified model are compared. Physical model of lens heating provides accurate thermal aberration analysis, but it is unable to analyze the contribution of an element of the lens to thermal aberration which is significant for thermal optimization[2]. Simplified model supports thermal analysis of an element of a lens[3]. However, only the deformation of lens surface and the variance of refractive index are considered in the simplified model. The thermal aberration analysis, in this paper, shows not only the deformation of lens surface, the variance of refractive index but also the change of optical path should be considered in thermal aberration analysis. On the basis of the analysis, a strategy for optimizing projection lens design is proposed and used to optimize thermal behavior of a lithography projection lens. The RMS value of thermal aberration is reduced by 31.8% in steady state.
To enhance the performance of the Insulated Gate Bipolar Transistor (IGBT), sub-microsecond laser annealing (LA) is propitious to achieve maximal dopant activation with minimal diffusion. In this work, two different lasers are used as annealing resource: a continuous 808 nm laser with larger spot is applied to preheat the wafer and another sub-microsecond pulsed 527 nm laser is responsible to activate the dopant. To optimize the system’s performance, a physical model is presented to predict the thermal effect of two laser fields interacting on wafer. Using the Finite-Element method (FEM), we numerically investigate the temperature field induced by lasers in detail. The process window corresponding to the lasers is also acquired which can satisfy the requirements of the IGBT’s annealing.
With decreasing of critical dimension (CD), the availability of depth of focus (DOF) goes down from technology node to technology node. Monitoring and controling of scanner focus on product wafers will be necessary. A technique entitled Iso-Dense Focus Monitor(IDFM) is developed to measure the focus errors of scanner systems. This IDFM method uses double side chrome mask and iso-dense binary overlay mark. The accuracy of this IDFM technique using binary mark may equal to the conventional PGFM method, and the IDFM technique only expose the wafer one time comparing with Z-SPIN which may expose two times. This method was simulated and also implemented on a litho tool of SMEE SSA600/10.
KEYWORDS: Overlay metrology, Semiconducting wafers, Metrology, Optical alignment, Source mask optimization, Data modeling, Control systems, Software development, Time metrology, Process control
Based on the in-line metrology sampling and modeling, the Advanced Process Control (APC) system has been widely
used to control the combined effects of process errors. With the shrinking of overlay budgets, the automated optimized
overlay management system has already been necessary. To further improve the overlay performance of SMEE
SSA600/10A exposure system, the overlay manager system (OMS) is introduced. The Unilith software package
developed by SMEE included in the OMS is used for the decomposition and analysis of sampled data. Several kinds of
correction methods integrated in the OMS have been designed and have demonstrated effective results in automated
overlay control. To balance the overlay performance and the metrology time, the exponential weighting method for
sampling is also considered.
With reduction of design rules, a number of corresponding new technologies, such as i-HOPC, HOWA and DBO
have been proposed and applied to eliminate overlay error. When these technologies are in use, any high-order error
distribution needs to be clearly distinguished in order to remove the underlying causes. Lens aberrations are normally
thought to mainly impact the Matching Machine Overlay (MMO). However, when using Image-Based overlay (IBO)
measurement tools, aberrations become the dominant influence on single machine overlay (SMO) and even on stage
repeatability performance. In this paper, several measurements of the error distributions of the lens of SMEE SSB600/10
prototype exposure tool are presented. Models that characterize the primary influence from lens magnification, high
order distortion, coma aberration and telecentricity are shown. The contribution to stage repeatability (as measured with
IBO tools) from the above errors was predicted with simulator and compared to experiments. Finally, the drift of every
lens distortion that impact to SMO over several days was monitored and matched with the result of measurements.
A new company in the lithography world, SMEE has developed and produced a prototype wafer exposure tool, with an
ArF laser light source. This tool, SMEE SSA600/10, adopted step and scan technology to obtain a large exposure filed
and to average optical aberrations for a scanned image to improve CD uniformity and reduce distortion. The maximum
numerical aperture is 0.75 and the maximum coherence factor of illumination system is 0.88. The illuminator provides
continuously variable conventional and off-axis illumination modes to improve resolution. In this paper, the
configuration of the exposure tool is presented and design concepts of the scanner are introduced. We show actual test
data such as synchronization accuracy, focus and leveling repeatability, dynamic imaging performance (resolution, depth
of focus) and overlay.
The recent observation of enhanced optical transmission through a periodic array of subwavelength apertures in a metal film has elicited significant interest both because it represents a novel phenomenon and because it raises the prospect of a series of new applications. Recently, an ~104 increase in conversion efficiency of second harmonic generation (SHG) from a periodically nanostructured silver film structure consisting of a single subwavelength aperture surrounded by a set of concentric surface grooves was reported. Although the phase-matching condition for extraordinary transmission has been discussed by many researchers, the phase-matching conditions of SHG process was neglected in former experiments. In this paper, we design a silver film with two different sets of periods on a quartz substrate with the silver thickness of 20nm in order to excite long-range surface plasma wave that could transmit millimeter-order distance in the metal surface, which greatly contribution to the improvement of the conversion efficiency of SHG for about 102 times. The fundamental light is perpendicularly coupled into the metal film with about 29 percent coupling efficiency, and the direction of the transmitted SH light is also perpendicular to the metal surface. Furthermore, this new type of structure could contribute to high conversion efficiency of SHG for the virtues of low losses, extremely compact structure and easily fabrication process.
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