D.W. Mueller

Rapid repair of plasma ash damage in low-k dielectrics using supercritical CO2

Plasma damage to methylsilsequioxane (MSQ) based low-k dielectrics degrades the material’s resistance to subsequent wet etch processes. In addition, the loss of methyl species during plasma exposure increases their susceptibility to water absorption leading to increased dielectric permittivities. In this article, we introduce a process in which silylating agents dissolved in supercritical CO2 are used to functionalize ash-damaged surfaces. This silylation process greatly decreases the time necessary to induce hydrophobicity (less than 1 min as determined by a change in contact angle from 18° to 90°). The process also reduces the concentration of reactive silylation agents needed for full hydrophobicity to less than 1 volu200a%. Further, this process is also shown to reduce material loss during subsequent wet etch processes. Film thickness measured by scanning electron microscopy before and after treatment illustrates a difference of approximately 0.1 μm after etching in a dilute HF solution for 30 s.

Forward angle scattering effects in the measurement of total cross sections for positron scattering

Measurements of total scattering by positron impact have typically excluded a significant portion of the forward scattering angles of the differential cross section. This paper demonstrates the effect that this can have on measurements of the total cross section. We show that much of the apparent disagreement between experimental measurements of positron scattering from atoms and molecules may be explained by this excluded angular range. It is shown that this same effect may also lead to an anomalous energy dependence of some cross sections.

High strength, low dielectric constant fluorinated silica xerogel films

The mechanical, electrical, and microstructural properties of low-k fluorinated silica xerogels produced using a one step spin-on process are reported. Derived from a fluorinated silane monomer, these films are easily processed and exhibit very low dielectric constants (2.1 as processed and 2.3 after heat treating at 450u200a°C in air). Structural determination by Fourier transform infrared spectrophotometry indicates a fluorinated silica structure with shortened Si–O bonds; however, some of the fluorine is lost during annealing. Nanoindentation studies show high elastic moduli (12 GPa) and hardness (1 GPa). Microstructural analyses by transmission and scanning electron microscopy indicate an unusual morphology with highly linked features and pore sizes in the 20–30 nm range. We believe the low dielectric constants and robust mechanical properties are due to the unusual microstructure of these films.

Investigation of Polymerization and Cyclization of Dimethyldiethoxysilane by 29Si NMR and FTIR

Dimethyldiethoxysilane (DMDES) appears to be a very promising modifier to introduce functional groups to a silicate network. The polymerization and cyclization of DMDES under acid-catalyzed conditions (DMDES : Ethanol : water : HCl = 1:4:4:3.68 × 10−4 in molar ratio) were investigated by high resolution liquid 29Si nuclear magnetic resonance (NMR) and Fourier transform infrared spectrometry (FTIR). Time-dependent NMR and FTIR data illustrate that monomers of (CH3)2Si(OC2H5)2, (CH3)2Si(OC2H5)(OH), and (CH3)2Si(OH)2 reach meta-equilibrium in less than 4 minutes. 3-membered rings ((CH3)2SiO)3 appear about half an hour later and 4-membered rings ((CH3)2SiO)4 an hour later, which continue to be formed over 24 hours. The relative concentrations of monomers, linear structures and cyclic structures suggest a modified model for the kinetics of cyclization, where 4-membered rings are formed by dimer-dimer interactions, as opposed to monomer-trimer interactions previously proposed.

Low-energy positron interactions with xenon

Low-energy interactions of positrons with xenon have been studied both experimentally and theoretically. The experimental measurements were carried out using a trap-based positron beam with an energy resolution of ?80?meV, while the theoretical calculations were carried out using the convergent close-coupling method and the relativistic optical potential approach. Absolute values of the grand total, positronium formation and grand total minus positronium formation cross sections are presented over the energy range of 1?60?eV. Elastic differential cross sections (DCS), for selected energies, are also presented both below and above the positronium formation threshold. Fine energy-step measurements of the positronium formation cross section over the energy range of 4.4?8.4?eV, and measurements of the elastic DCS at the energies of 5.33 and 6.64?eV, have been carried out to investigate the ionization threshold regions corresponding to the 2P3/2 and 2P1/2 states of the Xe+ ion. The present results are compared with both experimental and theoretical values from the literature where available.

Drying and Functionalization of Triethoxyfluorosilane-Based Low-k Dielectrics in CO 2

To minimize the deleterious effects of water on the electrical properties of porous low-k dielectrics in integrated circuits, these materials are chemically treated to create a hydrophobic surface group. Typically, this process is slow and involves a large concentration of organic solvents and silylation agents. We report a method of drying and chemical surface modification of triethoxyfluorosilane-based low-k dielectrics using liquid and supercritical (SC) CO 2 as a solvent. CO 2 is an environmentally friendly, recyclable solvent, and the use of SC-CO 2 allows for full surface modification in less than 5 min with hydrophobic chemical reagent volumes one-thousandth those previously used in bulk chemical modifications.

Gaussian random field models of aerogels

A model capable of predicting pore characteristics and rendering representative images of porous materials is described. A long-term goal is to discriminate between open and closed porosities. Aerogels are modeled by intersecting excursion sets of two independent Gaussian random fields. The parameters of these fields are obtained by matching small-angle neutron scattering data with the scattering function for the model. The chord-length probability density functions are then computed for the model, which contain partial clustering information for the aerogels. Visualizations of this model are performed and compared to electron microscopy images and gas adsorption pore size distributions.

Application of Deuterium Exchange to Analyze Moisture Uptake Characteristics of Porous Low-Dielectric-Constant SiOCH Films

In this work, deuterium exchange was used as a chemical marker to monitor moisture uptake in ash-damaged, low-k spin-on and chemical vapor deposited SiOCH films. Fourier transform infrared spectroscopy was performed to detect differences in deuterium adsorption. A broad-band in the 2550-3050 cm -1 range and peaks at approximately 1350 and 1460 cm -1 were found after D 2 O adsorption. The spectral distribution of the deuterium species giving rise to the detected bands is investigated as a function of plasma treatment and surface topography. These results demonstrate the utility of the deuterium exchange as a potentially useful technique for characterization of the moisture uptake properties of low-k materials.

Fully differential molecular-frame electron impact ionization measurements

(e,2e) measurements in the molecular frame using a new spectrometer are described. This work requires a triple coincidence experiment in which (e,2e+ion) events are detected. Preliminary results are presented for a nitrogen target, which illustrate the performance of the apparatus. The nitrogen data clearly shows that the (e,2e) cross section depends sensitively on the orientation of the molecule relative to the incident direction.

A high energy resolution modulated GaAs photoelectron source

Abstract A photoelectron source that produces an electron current of as high as 200 × 10−6 A with an effective electron brightness as high as between 107A/cm2 sr has been developed. This electron source has been shown to have an energy width as low as 0.036 eV FWHM.