Hae-Jeong Lee

Structural characterization of porous low-k thin films prepared by different techniques using x-ray porosimetry

Three different types of porous low-k dielectric films, with similar dielectric constants, are characterized using x-ray porosimetry (XRP). XRP is used to extract critical structural information, such as the average density, wall density, porosity, and pore size distribution. The materials include a plasma-enhanced-chemical-vapor-deposited carbon-doped oxide film composed of Si, C, O, and H (SiCOH) and two spin cast silsesquioxane type films—methylsilsesquioxane with a polymeric porogen (porous MSQ) and hydrogensilsesquioxane with a high boiling point solvent (porous HSQ). The porous SiCOH film displays the smallest pore sizes, while porous HSQ film has both the highest density wall material and porosity. The porous MSQ film exhibits a broad range of pores with the largest average pore size. We demonstrate that the average pore size obtained by the well-established method of neutron scattering and x-ray reflectivity is in good agreement with the XRP results.

Robust conductive mesoporous carbon–silica composite films with highly ordered and oriented orthorhombic structures from triblock-copolymer template co-assembly

In this work, we describe a facile approach to improve the robustness of conductive mesoporous carbon-based thin films by the addition of silica to the matrix through the triconstituent organic–inorganic–organic co-assembly of resol (carbon precursor) and tetraethylorthosilicate (silica precursor) with triblock-copolymer Pluronic F127. The pyrolysis of the resol–silica–pluronic F127 film yields a porous composite thin film with well-defined mesostructure. X-Ray diffraction (XRD), grazing incidence small angle X-ray scattering (GISAXS), and electron microscopy measurements indicate that the obtained carbon-based thin films have a highly ordered orthorhombic mesostructure (Fmmm) with uniform large pore size (∼3 nm). The orthorhombic mesostructure is oriented and the (010) plane is parallel to the silicon wafer substrate. The addition of silica to the matrix impacts the pore size, surface area, porosity, modulus and conductivity. For composite films with approximately 40 wt% silica, the conductivity is decreased by approximately an order of magnitude in comparison to a pure carbon mesoporous film, but the conductivity is comparable to typical printed carbon inks used in electrochemical sensing, ∼10 S cm−1. The mechanical properties of these mesoporous silica–carbon hybrid films are similar to the pure carbon analogs with a Youngs modulus between 10 GPa and 15 GPa, but the material is significantly more porous. Moreover, the addition of silica to the matrix appears to improve the adhesion of the mesoporous film to a silicon wafer. These mesoporous silica–carbon composite films have appropriate characteristics for use in sensing applications.

Effect of initial resist thickness on residual layer thickness of nanoimprinted structures

Quantification and control of the residual layer thickness is a critical challenge facing nanoimprint lithography. This thickness must be known to within a few nanometers, yet there are very few nondestructive measurement techniques capable of extracting such information. Here we describe a specular x-ray reflectivity technique that can be used to not only quantify the thickness of the residual layer with sub-nm resolution, but also to extract the pattern height, the line-to-space ratio, and relative linewidth variations as a function of the pattern height. This is illustrated through a series of imprints where the initial film thickness is varied. For films with sufficient resist material to fill the mold, complete pattern filling is observed and the residual layer thickness is directly proportional to the initial film thickness. When there is insufficient resist material in the film to completely fill the patterns in the mold, a finite residual layer thickness of approximately 50–100A is still observed.

X-ray and neutron reflectivity measurements of moisture transport through model multilayered barrier films for flexible displays

One encapsulation approach to extend the lifetime of flexible organic light-emitting diode (OLED) devices uses inorganic Al2O3-polymer multilayer barrier films. However, a recent theoretical examination of multilayer barriers indicated that the barriers should not be effective for OLED applications, despite empirical evidence of success. It was suggested that a long-lived transient process in the transport of water molecules through multilayer films is responsible for its practical success, but has not been directly observed experimentally. X-ray reflectivity (XR) and neutron reflectivity measurements are used to measure permeation rates and structural changes in model barrier films upon exposure to water vapor. A film consisting of a stack of an undercured organic and the typical inorganic phases was found to barely swell [(7±5)A] after an 11-d exposure to moisture [60 °C, 100% relative humidity (RH)]. Current measurements of ultralow moisture permeation assume that 10 d is sufficient for the equilibrium...

Nanoimprint pattern transfer quality from specular x-ray reflectivity

Specular x-ray reflectivity is used for high precision measurements of the pattern height, residual layer thickness, and the line-to-space ratio for parallel line and space patterns fabricated with nanoimprint lithography. The line-to-space ratio is profiled vertically to reveal relative linewidth variations as a function of the feature height. These relative linewidth variations are quantified through an external measure of the average pitch to fully define the line shape profile or cross section. An excellent fidelity of the nanoimprint pattern transfer process is quantified by comparing the line shape profiles of the mold to the imprinted pattern.

Evidence for internal stresses induced by nanoimprint lithography

The thermal embossing form of nanoimprint lithography is used to pattern arrays of nanostructures into three different polymer films. The shape of the imprinted patterns is characterized with nanometer precision using both x-ray scattering and reflectivity techniques. The time dependent response of the pattern shape at temperatures near the glass transition temperature reveals large levels of residual stress induced by the imprinting process. During the imprint, large shear fields are generated as the viscous polymer flows into the mold. If these shear distortions do not have time to relax during the imprinting, internal stresses are frozen into the final pattern. At elevated temperatures in the freestanding structures (once the mold has been separated from the imprint), there is an accelerated reduction in pattern height in the reverse direction from which the material originally flowed into the mold. Factors that influence this residual stress include the relative molecular mass or viscosity of the resi...

Characterization of chemical-vapor-deposited low-k thin films using x-ray porosimetry

Trimethylsilane-based carbon-doped silica films prepared with varying chemical-vapor-deposition process conditions were characterized using x-ray reflectivity and porosimetry to measure the film thickness, average film density, density depth profile, wall density, and porosity. Samples deposited under single or dual frequency conditions with either N2O or O2 as an oxidant were compared. The structural parameters were correlated with the chemical bond structure measured by Fourier transform infrared spectroscopy. The density profiles of the porous films were uniform with a slight densification at the film surface. The distribution of pores was also uniform through the film. Films prepared under a single frequency and/or N2O atmosphere had the lowest film density, wall density, and dielectric constant. The porosities of the films were similar and the pore sizes were less than 10 A.

Nonuniform structural degradation in porous organosilicate films exposed to plasma, etching, and ashing as characterized by x-ray porosimetry

X-ray porosimetry is used to characterize the porosity, the average film density, and the density of the wall material between the pores in ultralow-k films as a function of film thickness. These measurements are performed on films that have been plasma treated as well as plasma etched and an ashed to evaluate how these integration processes affect the pore characteristics of the interlayer dielectric. The damage, a decrease of porosity and an increase in the wall density, is strongly localized to the exposed surface of the film. The plasma etching and ashing tend to induce more surface damage than the plasma alone.

Structural characteristics of methylsilsesquioxane based porous low-k thin films fabricated with increasing cross-linked particle porogen loading

Methylsilsesquioxane (MSQ) based porous low-k dielectric films are characterized by x-ray porosimetry (XRP) to determine their pore size distribution, average density, wall density, and porosity. By varying the porogen content from 1% to 30% by mass, the porosity changes from 12% to 34% by volume, indicating that the base MSQ matrix material contains approximately 10% by volume inherent microporosity. The wall density of this matrix material is measured to be 1.33–1.35g∕cm3, independent of porosity. The average pore radii determined from the XRP adsorption isotherms increase from 6to27A with increased porogen loadings. Small angle neutron scattering measurements confirm these XRP average pore radii for the films with porogen loading higher than 10% by mass.

Direct observation of interfacial C60 cluster formation in polystyrene-C60 nanocomposite films.

Large interfacial C(60) clusters were directly imaged at the supporting film-substrate interface in physically detached polystyrene-C(60) nanocomposite films by atomic force microscopy, confirming the stabilizing mechanism previously hypothesized for thin polymer films. Additionally, we found that the C(60) additive influences basic thermodynamic film properties such as the interfacial energy and the film thermal expansion coefficient.