Growth of Organic Films on Semiconductor Surfaces: Fundamental Reactivity Studies and Molecular Layer Deposition Involving Isocyanates and Isothiocyanates

Paul Loscutoff
Abstract & Cover

The continued pursuit of smaller device dimensions by the semiconductor industry has led to an increased interest in functional organic films. Organics have great potential as advanced materials, owing to the versatility of organic moieties and vast knowledge base of organic reactivity. In order to implement organic films into semiconductor devices, the inorganic/organic hybrid interfaces must be investigated, so that the reactivity at these pivotal features is well-known. In this work organic films are studied in two environments: the Ge(100)-2xl surface and the SiC>2 surface. The reconstructed Ge(100)-2xl surface offers a well-defined substrate, ideal for fundamental reactivity studies. Organic reactants are deposited under ultrahigh vacuum conditions, allowing reactions between gas-phase organic molecules and the surface to be isolated and analyzed by in situ spectroscopic techniques. By use of infrared (IR) spectroscopy, x-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) modeling, we investigate the reactivity of phenyl and tert-butyl isocyanate and isothiocyanante at the Ge(100)-2xl surface. The isocyanate and isothiocyanate moieties are both highly reactive groups consisting of a cumulated double bond containing two heteroatoms, allowing for many potential products with the Ge surface. We find that dative bonding through the heteroatoms plays an important role in the surface reactions, functioning as either reaction intermediates or final products depending on the adsorbate. Various cycloaddition products are also observed at the surface, with prominent reactivity trends resulting from the differences in oxygen and sulfur reactivity. In order to study the practical implementation of organic films, molecular layer deposition (MLD) reactions are studied on the hydroxlyated Si02 surface. MLD is a layer-by-layer technique, where films are deposited one molecular unit at a time, allowing for film tailorability and composition control down to single molecule specificity. Coupling reactions between isocyanate and isothiocyanate moieties with amines to form polyurea and polythiourea films, respectively, are studied. The MLD films are analyzed by ex situ ellipsometry, IR spectroscopy, XPS, and DFT. A constant growth rate and monomer dose saturation is observed for both the urea and thiourea coupling chemistry, and chemical composition of the films agrees well with theoretical models. The ability to precisely control film composition is demonstrated through the deposition of polyurea blends, with a homogenous composition throughout the film, and polyurea laminates, with layers of distinct composition within the film. Organic films have shown promise as copper diffusion barrier layers, and the effectiveness of the MLD films as copper barrier layers is investigated through thermal stability, adhesion, and copper penetration measurements. The films demonstrate potential in this application, but further modification of the films is necessary to meet all the requirements necessary for barrier layer implementation. The thesis concludes with some perspectives on the future of organic films on semiconductors.

Source of Information
Stanford Libraries
Stanford University
(Stanford, USA)
External Link
Read Thesis
linkedin invite