Nano-boyutta kimyasal modifiye edilmiş ince filmlerin kimyasal-mekanik düzleştirme uygulamaları için karakterizasyonu

The aim of the microelectronics industry has historically been achieving increasing functionality through decreasing the device sizes while simultaneously reducing the unit manufacturing costs. This objective has been achieved by the implementation of multilevel metallization (MLM) based on the development of advanced photolithography processes and the chemical mechanical planarization (CMP) process that enabled the successful patterning through photolithography by planarization of the wafer surfaces. The projected targets of the Integrated Circuit (IC) manufacturing are facing some physical barriers with the current and forthcoming needs of the semiconductor industry to develop future metal oxide semiconductor field effect transistors (MOSFET). These challenges entail the introduction of new and more difficult materials to achieve better device performance such as use of Germanium due to its higher electron mobility to build faster microprocessors, as well as the use of III-V semiconductors such as GaN, GaAs or InAs which are being tested for high power device applications. Furthermore, new ideas such as reduced power consumption and ability of energy harvesting introduced ferroelectric and magnetic memories, as well as piezoelectric transducers which involve variety of materials harder to integrate to conventional semiconductor manufacturing. Chemical Mechanical Planarization process is one of the key enablers for the integration of the new materials into the current semiconductor fabrication processes. CMP functions on the principle of chemically modifying the surface to be polished while this surface is continuously abraded mechanically by the Nano-particles homogeneously suspended in the slurry environment. Development of new CMP processes require a robust slurry formulation that can provide high material removal rates (MRR) to promote high volume manufacturing throughput with low dissolution rates (DR) to achieve topographic selectivity and global planarity, in addition to creating minimum surface defectivity surface roughness values. Hence, it is important to understand the chemical and mechanical nature of the CMP process to better control the process and design future processes for the new generation materials. This dissertation focuses on the characterization of the chemically modified thin films which form during the CMP applications through the exposure of the surface to be polished to the slurry chemicals to optimize the process performance at a Nano-scale. The overall study is presented in two main sections the first part focusing on the findings on the chemically formed metal oxide thin films on metal CMP applications and the second part focusing on the chemically modified thin film characterization on the nonmetal CMP applications. On metal CMP applications, chemically modified thin films are required to be protective oxides to achieve topographic selectivity. Therefore, the chemically modified thin films of the metal (tungsten) substrates were characterized for thickness and composition as well as their protective nature by calculating their Pilling-Bethworth (P-B) ratio comparing the volume of oxide to the volume of the metal underneath. The analyses have shown a layered oxide film formation with the very top oxide film was detected to be a hydroxyl compound of the tungsten followed by W/WOx combination in the lower layers until a pure W substrate is reached. Furthermore, it has also been demonstrated that the surface topography of the tungsten wafers tend to change as a function of the oxidizer concentration. The observed changes in the surface topography were also found to affect the wettability and the total surface energy. Hence, it is obvious that the protective nature, as well as the surface nano-topography of the metal oxide thin films need to be studied to assess the metal CMP performance at a nano-scale. Changes in the surface roughness and topography with the oxidizer concentration were also studied through a mathematical modeling approach using Cahn-Hilliard Equation (CHE) approximation. CHE explains the formation of surface nano-structures in terms of reverse diffusion principal and expected to shed light to understanding the changes in the material removal rate mechanisms as a function of the CMP process variables. In the second half of the dissertation, slurry formulations are evaluated to characterize the chemically modified thin films to enhance selectivity for germanium/silica (Ge/SiO2) CMP systems. The chemically modified thin films are mainly the hydroxyl layers formed by the dissolution of the materials such as silicon, silica or germanium in front end applications of the CMP. To evaluate the impact of chemically modified thin films of the Ge/SiO2 system, it is necessary to modify these chemically modified films with oxidizers and surface active agents (surfactants) since the function of the chemically modified layers in these applications is to achieve optimal removal rate selectivity. Therefore, initially selectivity analyses were conducted by wear rate responses measured at a single particle-surface interaction level through Atomic Force Microscopy (AFM) with and without the use of surfactants. Both anionic (sodium dodecyl sulfate-SDS) and cationic (cetyl trimethyl ammonium bromide-C12TAB) surfactants were evaluated at their sub-micelle and above critical micelle concentrations (CMC) as a function of pH and oxidizer concentrations. CMP performances of Ge and SiO2 wafers were evaluated in terms of material removal rates, selectivity and surface quality. This dissertation is composed of seven chapters. The first chapter discusses the importance of nano-scale chemically modified thin films for chemical mechanical planarization process by an introduction to CMP process. Chapter 2 reviews the main components of the CMP process, its integration at the front end, middle section and back end of the line applications, as well as the importance of the characterization of the chemically modified thin films in CMP development. Chapter 3 discusses metal oxide protective thin film characterization for metal CMP applications by focusing on the growth and protective nature of the metal oxide thin films on CVD deposited tungsten wafers pre and post polishing in the presence of an oxidizer. In Chapter 4, CMP performance of the tungsten wafers are evaluated based on the material removal rate and surface quality analyses as a function of the changes in the slurry solids loading and H2O2 concentration as an oxidizer. Chapter 5 focuses on germanium/silica CMP through wear rate testing as a preliminary predictive approach as well as through standard CMP MRR evaluations to define a suitable slurry formulation with sufficient selectivity and removal rate performance. Chapter 6 extends the current knowledge base on the use of surfactant systems from standard shallow trench isolation (STI) CMP to Ge- based STI CMP. CMP results are reported with slurries made of silica particles with 3 wt % solids loading and 200-300 nm particle size in the presence of surfactants and 0.1 M H2O2 as an oxidizer. The optimal conditions for slurry formulations are presented as a function of pH and oxidizer concentration on Ge/SiO2 selectivity statistically through design of experiments (DOE). Finally, Chapter 7 provides a summary of the reported findings of this dissertation, and the suggested future work.