Richard F. Reidy

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 vol %. 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.

Exploring the limits of N-type ultra-shallow junction formation.

Low resistivity, near-surface doping in silicon represents a formidable challenge for both the microelectronics industry and future quantum electronic devices. Here we employ an ultra-high vacuum strategy to create highly abrupt doping profiles in silicon, which we characterize in situ using a four point probe scanning tunnelling microscope. Using a small molecule gaseous dopant source (PH3) which densely packs on a reconstructed silicon surface, followed by encapsulation in epitaxial silicon, we form highly conductive dopant sheets with subnanometer control of the depth profiles. This approach allows us to test the limits of ultra-shallow junction formation, with room temperature resistivities of 780 Ω/□ at an encapsulation depth of 4.3 nm, increasing to 23 kΩ/□ at an encapsulation depth of only 0.5 nm. We show that this depth-dependent resistivity can be accounted for by a combination of dopant segregation and surface scattering.

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 450 °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.

Further studies of DAM-1 mesoporous silica preparations

Abstract A number of preparations for the synthesis of novel hexagonal mesoporous materials referred to as Dallas amorphous material-1 (DAM-1) have been developed using Vitamin E tocopheryl polyethylene glycol 1000 succinate (TPGS), a water-soluble form of the lipid soluble natural Vitamin E, as the structure directing agent. Depending upon the temperature and gel composition, highly ordered and hydrothermally stable 2-D hexagonal mesoporous DAM-1 with various morphologies could be achieved, including spheres, gyroids, discoids, hexagonal plates, and rods.

Supercritical CO2 Applications in BEOL Cleaning

Introduction As the semiconductor industry prepares for the 45 and 32 nm technology nodes, supercritical fluid methods offer flexible chemistries, rapid transport, and environmentally benign alternatives to wet and dry BEOL cleans processes. In addition, supercritical methods have been demonstrated to remove photoresist and post-ash residue,[1,2,3] deposit metal lines and low-k films,[4] extract lowk porogens,[5] and repair post-ash damage to porous low-k films.[6,7,8,9] Recent work by a number of groups have demonstrated the effective removal of 248 and 193nm photoresist layers using supercritical CO2 (SC-CO2) with co-solvents.[10,11,12] First patented by researchers at Los Alamos National Lab,[13] resist removal techniques employ swelling, interfacial attack, and dissolution mechanisms. Recently, researchers at Cornell[14] and Univ. of North Carolina[15] have reported novel photoresists that can be developed and removed using supercritical CO2. Other work has examined the use of co-solvents in SC-CO2 to dissolve photoresist [1,12] and thermal oxide layers.[16] However, without significant advantages over current processes of record, the large capital expenditures necessary to introduce high pressure fluids into manufacturing environments will delay the implementation of supercritical methods in the manufacture of semiconductor devices.

Modification of cement mortar with recycled ABS

Abstract Cement mortar was modified using recycled acrylonitrile butadiene styrene (ABS) in powder form. Mixtures with polymer–cement ratios of 8, 15, and 25 wt.% were investigated for changes in compressive properties and adhesion to steel rebar. Compressive tests indicated an increase in Youngs modulus for samples with 8% and 15% ABS. Adhesion strength to the steel rebar decreased on adding the ABS. However, when the ABS was treated with maleic anhydride, an increase in adhesion strength was obtained. The decrease in adhesion of the untreated ABS-modified cement to steel was attributed to the disruption of the interface between the cement mortar and steel rebar. Scanning electron microscopy (SEM) indicated changes in the cured cement with addition of ABS. Gas adsorption measurements of pore size distribution indicated an increase in pore volume of the 8 and 15 wt.%-containing cement mortar.

Small angle neutron scattering characterization of colloidal and fractal aerogels

Extreme length scales of aerogel structures limit the effectiveness of many characterization techniques. With the resolutions commensurate with the length scales found in these materials, small angle neutron scattering measurements were conducted and interpreted using several models developed for other ceramic systems (polydispersed hard-sphere, fractal, and maximum entropy models). Interference (polydispersed hard-sphere) and maximum entropy models indicate that tetraethoxysilane (TEOS) aerogel structure may be comprised of oblate nanoparticles within oblate mesoparticles. The fractal model was used to describe the structures of triethoxysilane (TES) and trimethoxysilane (TMS) aerogels and to quantify their fractal properties. TES aerogels appear to be networks of volume fractals while TMS aerogels contain both volume and surface fractal elements.

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.