Empirical Analysis of Electron Beam Lithography Optimization Models from a Pragmatic Perspective

Electron Beam (EB) lithography is a process of focussing electron beams on silicon wafers to design different integrated circuits (ICs). It uses an electron gun, a blanking electrode, multiple electron lenses, a deflection electrode, and control circuits for each of these components. But the lithography process causes critical dimension overshoots, which reduces quality of the underlying ICs. This is caused due to increase in beam currents, frequent electron flashes, and reducing re-exposure of chip areas. Thus, to overcome these issues, researchers have proposed a wide variety of optimization models, each of which vary in terms of their qualitative & quantitative performance. These models also vary in terms of their internal operating characteristics, which causes ambiguity in identification of optimum models for application-specific use cases. To reduce this ambiguity, a discussion about application-specific nuances, functional advantages, deployment-specific limitations, and contextual future research scopes is discussed in this text. Based on this discussion, it was observed that bioinspired models outperform linear modelling techniques, which makes them highly useful for real-time deployments. These models aim at stochastically evaluation of optimum electron beam configurations, which improves wafer’s quality & speed of imprinting when compared with other models. To further facilitate selection of these models, this text compares them in terms of their accuracy, throughput, critical dimensions, deployment cost & computational complexity metrics. Based on this discussion, researchers will be able to identify optimum models for their performance-specific use cases. This text also proposes evaluation of a novel EB Lithography Optimization Metric (EBLOM), which combines multiple performance parameters for estimation of true model performance under real-time scenarios. Based on this metric, researchers will be able to identify models that can perform optimally with higher performance under performance-specific constraints

Combined Electron Beam Lithography

Tato práce se zabývá reliéfní elektronovou litografií a přípravou difrakčních optických elementů. Řešena jsou tři témata. Prvním tématem je reliéfní kombinovaná elektronová litografie, kde je cílem zkombinovat expozice dvou systémů s rozdílnou energií elektronů primárního svazku. Kombinovaná technika vede k efektivnějšímu využití jednotlivých systémů, kdy se různé struktury lépe připravují jinými energiemi elektronů v primárním svazku. Dalším tématem je optimalizace hranic objektů exponovaných struktur, které jsou definovány obrazovými vstupy. Zkoumá se vliv této optimalizace na rychlost přípravy expozičních dat, na dobu expozice a na optickou odezvu testovaných struktur. Třetím tématem je zkoumání možností přípravy hlubokých víceúrovňových difrakčních optických elementů do bloků plexiskla, jako náhrada soustavy rezist/substrát. S tím se pojí nový způsob zápisu, který minimalizuje teplotní zátěž na plexisklo během expozice elektronovým svazkem a zároveň zvyšuje homogenitu výsledného motivu. V této části byla dále navržena metoda výpočtu expozičních dávek specifických víceúrovňových struktur vycházející z existujících modelů pro výpočet korekcí jevu blízkosti, která minimalizuje čas výpočtu expozičních dávek.This thesis deals with grayscale e-beam lithography and diffractive optical elements fabrication. Three topics are addressed. The first topic is combined grayscale e-beam lithography. The goal of this task is combining exposures performed by two systems with various beam energies. This combined technique leads to a better usage of both systems because various structures can be more easily prepared by one electron beam energy than by the other. The next topic is the optimization of shape borders of exposing structures that are defined by image input. The influence of such optimization on exposure data preparation is evaluated, as well as the exposure time and the change of optical properties of testing structures. The possibility of deep multilevel diffractive optical element fabrication in plexiglass blocks is researched as the third topic. Plexiglass can replace the system of a resist and a substrate. A new approach to writing down the structures by electron beam is presented, minimizing thermal stress on the plexiglass block during the exposure. The writing method also improves the homogeneity of exposed motifs. A method for computing the exposure dose for specific multilevel structures was designed. This method is based on the existing model of proximity effect computation and it minimizes the computing time necessary to obtain the exposure doses.