Ebo Croffie

An accurate ILT-enabling full-chip mask 3D model for all-angle patterns

As the technology node keeps shrinking down to sub-28 nm, mask topography (Mask3D) effect is one of the most influential factors to draw intensive research lately. To build a successful Mask3D compact model, the runtime efficiency, accuracy and the flexibility to handle various geometry patterns are the three most important criterion to fulfill. Different approaches have been tried to resolve the difficulties in the full-chip modeling, but so far none of the existing Mask3D modeling methods have succeeded in meeting all the three criterion at the same time. It is often seen that an existing Mask3D model to succeed in one or two criteria, but fails in the rest. In this paper, we propose our innovative full chip Mask3D modeling method to successfully handle the above criterion at the same time. To our best of knowledge, it is the first ever Mask3D modeling in literature that is be able to achieve this goal. In our modeling flow, we first analyze the Mask3D effect by using rigorous simulation as the reference and generate edge-based kernels to mimic the Mask3D effect near the feature boundaries. The flexibility of handling the kernel helps us enable the support for all-angle patterns and be extendable for edge coupling effect and off-axis illumination. Our experimental results show that with only less than 30% runtime overhead compared to the conventional Mask2D model, we are able to achieve less than 0.8 nm CD RMS on the flexible feature patterns. An ILT-based OPC and simulation result is provided to validate the capability of all-angle support of our proposed model.

Efficient full-chip mask 3D model for off-axis illumination

Mask topography (Mask3D) effect is one of the most influential factors in sub-28 nm technology node. To build a successful Mask3D compact model, the runtime efficiency, accuracy and the flexibility to handle various geometry patterns are the three most important criterion to fulfill. In the meanwhile, Mask3D modeling must be able to handle the off-axis illumination (OAI) condition accurately. In this paper, we propose our full chip Mask3D modeling method which is an extension to the edge-based Mask3D model. In our modeling flow, we first review the edge-based Mask3D model and then analyze the impact from the off-axis source. We propose a parameter-based extension to characterize the off-axis impact efficiently. We further introduce two methods to calibrate the OAI-aware parameters by using rigorous or wafer data as the reference. Our experimental results show the great calibration accuracy throughout the defocus range with OAI sources, and validate the accuracy of our two parameter calibration approach.

Process window modeling using focus balancing technique

In this work, we present a methodology for process window capable optical proximity correction (OPC) compact model building which requires only one nominal process condition empirical data for model calibration, and enables full and predictable extrapolation to any process condition within focus-exposure matrix. In order to ensure modeling success, a focus and dose balancing techniques are used during model calibration. The model optimization method is based on a stepwise fitting methodology where staged optimization of the OPC model components is used. Model components are added during the OPC model calibration starting with more physical components, such as mask and optics, followed by resist components. In each optimization stage, a component is optimized using global regression methods. The optimized parameters regressed in a small range about their optimal values during subsequent model component optimization. The effectiveness of this approach in terms of accurate correction, process window interpol...

Resist development modeling for OPC accuracy improvement

A precise lithographic model has always been a critical component for the technique of Optical Proximity Correction (OPC) since it was introduced a decade ago [1]. As semiconductor manufacturing moves to 32nm and 22nm technology nodes with 193nm wafer immersion lithography, the demand for more accurate models is unprecedented to predict complex imaging phenomena at high numerical aperture (NA) with aggressive illumination conditions necessary for these nodes. An OPC model may comprise all the physical processing components from mask e-beam writing steps to final CDSEM measurement of the feature dimensions. In order to provide a precise model, it is desired that every component involved in the processing physics be accurately modeled using minimum metrology data. In the past years, much attention has been paid to studying mask 3-D effects, mask writing limitations, laser spectrum profile, lens pupil polarization/apodization, source shape characterization, stage vibration, and so on. However, relatively fewer studies have been devoted to modeling of the development process of resist film though it is an essential processing step that cannot be neglected. Instead, threshold models are commonly used to approximate resist development behavior. While resist models capable of simulating development path are widely used in many commercial lithography simulators, the lack of this component in current OPC modeling lies in the fact that direct adoption of those development models into OPC modeling compromises its capability of full chip simulation. In this work, we have successfully incorporated a photoresist development model into production OPC modeling software without sacrificing its full chip capability. The resist film development behavior is simulated in the model to incorporate observed complex resist phenomena such as surface inhibition, developer mass transport, HMDS poisoning, development contrast, etc. The necessary parameters are calibrated using metrology data in the same way that current model calibration is done. The method is validated with a rigorous lithography process simulation tool which is based on physical models to simulate and predict effects during the resist PEB and development process. Furthermore, an experimental lithographic process was modeled using this new methodology, showing significant improvement in modeling accuracy in compassion to a traditional model. Layout correction test has shown that the new model form is equivalent to traditional model forms in terms of correction convergence and speed.

A pattern- and optics-independent compact model of Mask3D under off-axis illumination with significant efficiency and accuracy improvements

As the critical dimension keeps shrinking, mask topography effect (Mask3D) becomes considerable to impact the lithography modeling accuracy and the quality of full-chip OPC. Among many challenges in Mask3D modeling, it is critical and particularly demanding to treat off-axis illumination (OAI) properly. In this paper, we present a novel Mask3D model that is completely test pattern- and optics- independent. Such model property enables greatly improved performance in terms of accuracy and consistency on various pattern types (1D/2D) and through a wide range of focus conditions, while no runtime overhead is incurred. The novel model and formulation will be able to save significant modeling time and greatly improve the model reliability, predictability and ease of use. Experimental results validate the claims and demonstrate the superiority to the current state-of-the-art Mask3D modeling method. This is a new generation Mask3D modeling process.

Generation of isofocal target patterns using process modeling during optical proximity correction

Isofocal patterns produce the most ideal manufacturing conditions on a reticle, however, most semiconductor designs contain few isofocal features. A new way of looking at defocus conditions based on the change in intensity with respect to nominal focus [L. S. Melvin III et al., J. Vac. Sci. Technol. B 23, 2631 (2005)]—referred to as IΔ—can be used to resize the target pattern to isofocal dimensions. The pattern is quantitatively analyzed using IΔ to find modified pattern shapes that give isofocal target patterns for optical proximity correction and/or resolution enhancement techniques. The target pattern is then made isofocal by resizing the pattern to the modified shape prior to the use of optical proximity correction and/or resolution enhancement techniques. Results of this concept demonstrate excellent improvement in the feature robustness of different features at various defocus conditions. The proposed isofocal targeting method can be applied to layers where trade-offs between pattern shape and final...