In the present work, the plasma repair for damaged ultra-low-k (ULK) materials, newly developed at the Fraunhofer ENAS, is studied with density functional theory (DFT) and molecular dynamic (MD) methods to obtain new insights into this repair mechanism. The ULK materials owe their low dielectric constant (k-value) to the insertion of k-value lowering methyl groups. During the manufacturing process, the ULK materials are damaged and their k-values increase due to the adsorbtion of hydroxyl groups (OH-damage) and hydrogen atoms (H-damage) that replaced themethyl groups. The first investigation point is the creation of repair fragments. For this purpose the silylation molecules bis(dimethylamino)-dimethylsilane (DMADMS) and octamethylcyclotetrasiloxane (OMCTS) are fragmented. Here, only fragmentation reactions that lead to repair fragments that contain one silicon atom and at least one methyl group were considered. It is shown that the repair fragments that contain three methyl groups are preferred, especially in a methyl rich atmosphere. The effectivity of the obtained repair fragments to cure an OH- and H-damage are investigated with two model systems. The first system consists of an assortment of small ULK-fragments, which is used to scan through the wide array of possible repair reactions. The second system is a silicon oxide cluster that investigates whether the presence of a cluster influences the reaction energies. In both model systems, repair fragments that contain three methyl groups or two oxygen atoms are found to be most effective. Finally, the quantum chemical results are compared to experimental findings to get deeper insight into the repair process.

Nanoporous low-k dielectrics are used for integrated circuit interconnects to reduce the propagation delays, and cross talk noise between metal wires as an alternative material for SiO2. These materials, typically organosilicate glass (OSG) films, are exposed to oxygen plasmas during photoresist stripping and related processes which substantially damage the film by abstracting carbon, incorporating O and OH, eventually leading to significantly increased k values. Systematic studies have been performed to understand the oxygen plasma-induced damage mechanisms on different low-k OSG films of various porosity and pore interconnectedness. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and atomic force microscopy are used to understand the damage kinetics of O radicals, ultraviolet photons and charged species, and possible ways to control the carbon loss from the film. FTIR results demonstrate that O radical present in the plasma is primarily responsible for carbon abstraction and this is governed by diffusion mechanism involving interconnected film nanopores. The loss of carbon from the film can be controlled by closing the pore interconnections, He plasma pretreatment is an effective way to control the damage at longer exposure by closing the connections between the pores.

Ce travail de thèse s'inscrit dans la problématique de la préparation et l'intégration des matériaux diélectriques poreux à très faible permittivité (ULK) dans les interconnexions des puces microélectroniques. Cette étude porte sur le développement de couches minces hydrophobes ULK à porosité organisée et isolée, préparées par voies sol-gel et PECVD. Elle vise une amélioration des propriétés mécaniques et une diminution de la diffusion de polluants au coeur des films. Des matériaux hydrophobes mésostructurés et ULK (k < 2,2) ont ainsi été obtenus par voie sol-gel, après retrait d'un porogène par traitement thermique, ou pour la première fois, par traitement thermique sous UV. Les caractéristiques mésostructurales et microstructurales des couches ont été reliées aux caractéristiques de porosité et aux propriétés mécaniques. Les mesures électriques et de perméation de gaz de ces matériaux sont également discutées en vue de leurs applications en tant que matériaux ULK ou comme membranes de séparation de gaz. En PECVD, des matériaux polymère plasma à base de styrène ont été synthétisés et également caractérisés en termes de propriétés mécaniques et de séparation de gaz.

In the present work, the plasma repair for damaged ultra-low-k (ULK) materials, newly developed at the Fraunhofer ENAS, is studied with density functional theory (DFT) and molecular dynamic (MD) methods to obtain new insights into this repair mechanism. The ULK materials owe their low dielectric constant (k-value) to the insertion of k-value lowering methyl groups. During the manufacturing process, the ULK materials are damaged and their k-values increase due to the adsorbtion of hydroxyl groups (OH-damage) and hydrogen atoms (H-damage) that replaced themethyl groups. The first investigation point is the creation of repair fragments. For this purpose the silylation molecules bis(dimethylamino)-dimethylsilane (DMADMS) and octamethylcyclotetrasiloxane (OMCTS) are fragmented. Here, only fragmentation reactions that lead to repair fragments that contain one silicon atom and at least one methyl group were considered. It is shown that the repair fragments that contain three methyl groups are preferred, especially in a methyl rich atmosphere. The effectivity of the obtained repair fragments to cure an OH- and H-damage are investigated with two model systems. The first system consists of an assortment of small ULK-fragments, which is used to scan through the wide array of possible repair reactions. The second system is a silicon oxide cluster that investigates whether the presence of a cluster influences the reaction energies. In both model systems, repair fragments that contain three methyl groups or two oxygen atoms are found to be most effective. Finally, the quantum chemical results are compared to experimental findings to get deeper insight into the repair process.:1. Introduction 2. Theoretical Background 2.1. Ultra-low-k Materials 2.1.1. Definition, Usage and Challenges 2.1.2. k-Restore 2.2. Reaction Theory 2.2.1. Reaction Process 2.2.2. Thermal Influence 3. Computational Methods 3.1. Overview 3.2. Density Functional Theory 3.2.1. Theoretical Background 3.2.1.1. The Schrödinger Equation and the Variational Principle 3.2.1.2. From the Electron Density to the Kohn-Sham Approach 3.2.1.3. Exchange-Correlation Functionals and Basis Sets 3.2.2. Used Program Packages 3.3. ReaxFF 3.3.1. Theoretical Background 3.3.2. Used Program Packages 4. Model System 4.1. Damaged ULK Materials 4.1.1. ULK-Fragments 4.1.2. Silicon Oxide Cluster 4.2. Repair Fragments 4.2.1. Overview 4.2.2. Fragmentation of DMADMS 4.2.3. Fragmentation of OMCTS 4.2.4. Continuing Reactions 5. Results and Discussion 5.1. Reactions between Repair Fragments and ULK-Fragments 5.1.1. Repair of OH-damages 5.1.2. Repair of H-damages 5.1.3. Selected Repair Reactions with Gaussian 5.2. Reactions Between Repair Fragments and Silicon Oxide Cluster 5.2.1. Comparison Between ULK-Fragments and Silicon Oxide Cluster 5.2.2. Comparability of DFT and MD Results 5.3. Comparison with Experimental Results 6. Summary and Outlook A. Appendix A.1. Temperature Influence . A.1.1. Temperature Influence on the DMADMS Fragmentation in Dmol3 A.1.2. Temperature Influence on the OMCTS Fragmentation in Dmol3 . A.2. Tests A.2.1. DMADMS Fragmentation with Gaussian A.2.2. G2 Test Set A.2.3. Calculation Time of the Silicon Oxide Cluster in Dmol3 A.3. Error Analysis A.3.1. Basis Set Superposition Error in Dmol3 A.3.2. Dispersion Correction A.4. Illustration of Defects A.5. Bookmark