Vlad Temchenko

Selective inverse lithography methodology

Selective Inverse Lithography (ILT) approach recently introduced by authors [1] has proven to be advantageous for extending life-span of lower-NA 193nm exposure tools to achieve satisfactory 65nm contact layer patterning. We intend to find an alternative solution without the need for higher NA tools and advanced light source optimization. In this paper we explore possible region selection criteria for ILT application based on pitch for a full chip optical proximity correction (OPC). Through studying the impact of a given selection criteria on runtime, resolution, and the process window we recommend an optimal combination. With a justified choice of an ILT selection criteria, we construct a hybrid OPC flow comprising a recursive sequence of direct assist features generation, selective ILT application, layout repair, model OPC and hot spots screening.

Manufacturability of ILT patterns in low-NA 193nm environment

With escalating costs of higher-NA exposure tools, lithography engineers are forced to evaluate life-span extension of currently available lower-NA exposure tools. In addition to common resolution enhancement techniques such as off-axis illumination, edge movement, or applying sub-resolution assist features, Inverse Lithography Technology (ILT) tools available commercially at this moment offer means of extending current in-house tool resolution and enlarging process window for random as well as periodic mask patterns. In this paper we explore ILT pattern simplification procedures and model calibration for a range of illumination conditions. We study random pattern fidelity and critical dimension stability across process window for 65nm contact layer, and compare silicon results for both conventional optical proximity correction and inverse lithography techniques.

Consideration of VT5 etch-based OPC modeling

Including etch-based empirical data during OPC model calibration is a desired yet controversial decision for OPC modeling, especially for process with a large litho to etch biasing. While many OPC software tools are capable of providing this functionality nowadays; yet few were implemented in manufacturing due to various risks considerations such as compromises in resist and optical effects prediction, etch model accuracy or even runtime concern. Conventional method of applying rule-based alongside resist model is popular but requires a lot of lengthy code generation to provide a leaner OPC input. This work discusses risk factors and their considerations, together with introduction of techniques used within Mentor Calibre VT5 etch-based modeling at sub 90nm technology node. Various strategies are discussed with the aim of better handling of large etch bias offset without adding complexity into final OPC package. Finally, results were presented to assess the advantages and limitations of the final method chosen.

Source and mask optimization applications in manufacturing

Among available lithography resolution enhancement techniques the Selective Inverse Lithography (SILT) approach recently introduced by authors [1] has been shown to provide the largest process window on lower-NA exposure tools for 65nm contact layer patterning. In present paper we attempt to harness the benefits of source mask optimization (SMO) approach as part of our hybrid RET. The application of source mask optimization techniques further extends the life-span of lower-NA 193nm exposure-tools in high volume manufacturing. By including SMO step in OPC flow, we show that model-based SRAF solution can be improved to approach SILT process variation (PV) band performance. Additionally to OPC, the complexity of embedded flash designs requires a high degree of exposure tool matching and a lithography process optimized for topographically different logic and flash areas. We present a method how SMO can be applied to scanner matching and topography-related optimization.

Coupled-dipole modelling for 3D mask simulation

The growing importance of mask simulation in a low-k1 realm is matched by an increasing need for numerical methods capable of handling complex 3D configurations. Various approximations applied to physical parameters or boundary conditions allowed a few methods to achieve reasonable run-times. In this work the theoretical foundation and simulation results of an alternative 3D mask modeling method suitable for OPC simulations are presented. We have established the throughput and accuracy of the Coupled-Dipole Simulation Method and have compared results to the rigorous FDTD approach using a test pattern. We will discuss in detail possible approximations needed in order to accelerate the methods performance.

Process influence study on optical model generation during model based OPC development

Optical & process model are used in conjunction with Mentors Calibre OPC tool to predict the behavior of a lithography process. Resist models rely exclusively on empirical measurement data, while optical models are calibrated based on the users knowledge of tool settings, but also fitting unknown parameters to empirical measurements. The final OPC model is a combination of optical & process behaviors prediction which includes resist & other process influence to meet the ever increasing demand of advanced lithography technology nodes like 90nm & below on model accuracy. Reliance of optical model creation on empirical measurement data is undoubtedly raising suspicion of how well the derived diffraction model is able to provide an accurate description of how light energy is distributed inside the resist. Various work & effort had been conducted in the past to cover defocus phenomenal on final model outcome & methodology introduced on better prediction from defocus to achieve better simulation quality, investigation has been carried out to study in further detail of existing strategy of resist & optical decoupling methodology in this work.