Detector modeling: The quality of the inspection system must be quantified at different positions within the optical system to make simulation results of different optical arrangements comparable. In most cases just a few of the effects are dominant and the other effects might be neglected without noticeable loss of simulation accuracy.ģ. However not all of the above mentioned effects must be included for all components. During the light propagation through the components, different physical effects like diffraction, refraction, reflection and polarization changes must be included. Propagation of light through the inspection system from the source to the detector plane: The light emitted by the source must be traced through the entire system consisting of a sequence of m = 1, 2, …, M different optical components with different homogeneous or inhomogeneous refractive index distributions n m and interface structures Γ m. For wafer inspection systems typically the spatial and temporal coherence of the light source, the spatial light distribution as well as the polarization state have significant influence on the image quality.Ģ. All properties of the source, which are relevant for the detector result or which have influence on the light propagation, must be included. Source modeling: A proper model for the light source has to be found. Here especially the following problems are crucial:ġ. Reasons for these insufficiencies are the complexity and size of the wafer inspection system and the involved physical-optics effects taking place within the system. However the analysis of modern optical wafer inspection systems is either not accurate enough or numerically inefficient, if common simulation techniques like ray-tracing, ABCD-matrix approaches 2 or rigorous Maxwell solver (e.g. The basis of any optical design or optimization algorithm is a fast, flexible and accurate system simulation. In these R&D cycles, optical system designers can profit from computer-aided design, optimization and tolerancing tools, which are essential to improve the resolution and throughput rates of inspection systems further. 1 The rapid miniaturization of ICs in the recent and upcoming years leads to an acceleration of development cycles of optical wafer inspection systems. For this purpose IC manufacturer employ these systems to detect defects and sources of problems during the IC fabrication process. Nowadays high-quality optical wafer inspection systems make an important contribution to maintain and improve the quality of the manufacturing process of integrated circuit (IC) chips. Image contrast of a simple wafer inspection system are shown. As an example different tilt tolerance effects on the polarization state and Numerically efficient algorithm for the coordinate transformation of electromagnetic fields, field tracing enables Propagation through macroscopic lenses, a rigorous Fourier Modal Method (FMM) for the modeling of lightĭiffraction at the wafer microstructure and different free-space diffraction integrals. These techniques are mainly geometrical optics for the light Wafer inspection system are discussed in detail. In this work the different modeling techniques for the analysis of an exemplary Per subdomain a different approximative or rigorous solution of Maxwell’s equations isĪpplied to propagate the light. The main idea is the decomposition of the complex optical setup in a We show that all of these effects can be included in a system simulation by field tracing, whichĬombines physical and geometrical optics.

Due to this variety of scale plenty of different physical effects like refraction,ĭiffraction, interference and polarization have to be taken into account for a realistic analysis of such inspection Macroscopic lens systems and on the other hand light is diffracted at microscopic structures with features in the On the one hand light is propagated through The different feature sizes, which are involved in these systems.

The simulation, design and tolerancing of optical systems for wafer inspection is a challenging task due to

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