Materials Synthesis and Processing Laboratory


	Materials Synthesis and Processing Laboratory


*people*	*research*	*equipment*	*recent publications*

Our focus: the development and characterization of aerogels, xerogels, and other novel ceramics for semiconductor, dielectric, energy, and sensor applications.

Current research interests:
Supercritical processing of semiconductor materials- development of supercritical methods to repair plasma-damaged porous low-k, drying of porous low-k films, and removal of photoresist and BARC layers from damascene structures.

Ultra-low K xerogel films- synthesis and characterization of silica xerogel films with enhanced mechanical properties and compatibility with semiconductor device structures and processes (Appl. Phys. Lett. 79 (2001) 4010)

cross-sectional TEM of triethoxyfluorsilane xerogel film
exhibiting highly cross-linked microstructure


cross-sectional TEM of triethoxyfluorsilane xerogel film exhibiting highly cross-linked microstructure

silica aerogel structures and synthesis kinetics- use of Si(29) NMR, FTIR, SANS, gas adsorption, and electron microscopy to describe aerogel structures and gel formation mechanisms

TEM of triethoxysilane aerogel showing fractal structure
antibacterial coatings- use of dopants in silica films to create anti-bacterial substrates


TEM of triethoxysilane aerogel showing fractal structure

biomaterial growth templates- growth of artifical tooth enamel onto silica xerogel substrates

The people who make up our group



Rick Reidy		Pawan Nerusu Graduate Student Supercritical Silylation of Porous Low-k Films

Mingming Du Graduate Student Synthesis and characterization of Low-k films	Casey Smith Graduate Student Pore sealing and reliablity of Low-k films	Allison Hendley Undergraduate (TAMS) Student Development of porous silica substrates as antibacterial delivery platforms

Rosie and Rick at the Metroplex Research Consortium for Electronic Devices and Materials (MRCEDM) Poster Session April 2003		Rick appears to be telling a colleague, "Seriously, we are not making this up..."
	Former Students

Dr. Hanjiang Dong (Graduated 2003) Characterization of methyltrimethoxysilane sol-gel polymerization and the resulting aerogels current position: Postdoctoral Fellow McMaster Univeristy	Dr. Aman Zhang (Graduated 2004) *Hydrophobic, fluorinated silica xerogels for low-k applications* current position: Materials Scientist and Process Engineer, Ferro Corp., Penn Yan, NY	Dr. Rosie Orozco-Teran (Graduated 2005) *Synthesis and characterization of Low-k films and Supercritical silylation reactions of low-k films* current position: Process Engineer, Silicon Technology and Development, Texas Instruments, Dallas TX

RESEARCH EQUIPMENT (or what we play with):

Nicolet Nexus 470 FTIR with thin film grazing angle, ATR, liquid cell, variable angle, variable temperature capabilities
Supercritical FTIR (transmission) cell
Supercritical reactor capable for 200mm Si wafers
Supercritical Driers capable of several samples sizes and solvents
Headway Research photoresist spinners
Capacitance-Voltage/Current-Voltage Micromanipulator system with variable temperature, Agilent 4294A Impedance Analyzer, Agilent 4156B Parameter Analyzer
Quantachrome NOVA 2200 Gas Adsorption Analyzer
JA Woollam Infrared Variable Angle Spectroscopic Ellipsometer
Single angle ellipsometer
Brookfield DV-II+ Programmable Viscometer
Rame-Hart Contact Angle measurement apparatus
Two nitrogen atmosphere glove boxes

SELECTED RECENT PUBLICATIONS:


2001
*Small Angle Neutron Scattering Characterization of Colloidal and Fractal Aerogels,* Richard F. Reidy, Andrew J. Allen, and Susan Krueger (J. Non-Crys. Sol. 285 (2001) 181) Abstract 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 maybe 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.
*High strength, low dielectric constant fluorinated silica xerogel films* B. P. Gorman, Rosa A. Orozco-Teran, Jodi A. Roepsch, Hanjiang Dong, Richard F. Reidy, D.W. Mueller (App. Phys. Lett. 79 (2001) 410-412) Abstract 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.
*Processing-Mechanical Property Relationships In Ultra-Low K Xerogel Films* Richard F. Reidy, B.P. Gorman, Rosa A. Orozco-Teran, Jodi A. Roepsch, Hanjiang Dong, D.W. Mueller (Proceeding of the Advanced Metallization Conference 2001 p. 319-323) Abstract Novel ultra low-k fluorinated silica xerogels have been produced using a one step spin-on process. These materials exhibit improved mechanical properties and unusual microstructures. In this work we report additional improvements to the mechanical properties, characterize the structure of these films using cross-sectional SEM, TEM and FTIR, detail the effects of processing on film properties, and discuss the effects of microstructure and chemistry on the concomitant mechanical and dielectric properties.
2002
*Further studies of DAM-1 mesoporous silica preparations* Decio Coutinho ,Rosa A.Orozio-Tevan, Richard F.Reidy, Kenneth J.Balkus Jr. (Micropor. Mesopor. Mater. 54 (2002) 229–248) Abstract A number of preparations for the synthesis of novel hexagonal mesoporous materials referred to as Dallas amor- phous 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,highlyordered and hydrothermallystable 2-D hexagonal mesoporous DAM-1 with various morphologies could be achieved,including spheres,gyroids,discoids,hexagonal plates,and rods.
*Effects Of Supercritical Processing On Ultra Low-K Films (pdf file)* R.F. Reidy , B.P. Gorman, R.A. Orozco-Teran, Zhengping Zhang, Shelley Chang, D.W. Mueller, Advanced Metallization Conference, ed. B.M. Melnick, T.S. Cale, S. Zaima, T. Ohta, 2002. p. 602-606. Abstract Supercritical processing offers a potentially attractive means to functionalize porous low-k films. Potential applications include the replacement of hydrophillic surface species and repair of ash-damaged films. In both liquid and supercritical states, the density of CO2 is greatly affected by pressure, and impacts its solubilization and wetting of other materials. FTIR and contact angle measurements have been used to determine the extent of functionalization and relative reaction rates. This work compares silylation reactions under ambient, and liquid and supercritical CO2 conditions.
*Processing of Ultra-Low K Xerogel Composite Films* B.P. Gorman, Shelley Chang, D.W. Mueller, R.F. Reidy, Advanced Metallization Conference, ed. B.M. Melnick, T.S. Cale, S. Zaima, T. Ohta, 2002. p. 607-612. Abstract In response to ITRS future ILD dielectric constant requirements (K=2.2 initially and 1.3 within five years), we are developing ultra low-k (ULK) composite thin films with mechanical, dielectric and microstructural properties commensurate with IC integration. By controlling processing and compositional variables in fluorine-functionalized silica xerogels (TEFS) doped with colloidal diamond particles, a range of mechanical properties and microstructures have been attained.
2003
*Investigation of polymerization and cyclization of dimethyldiethoxysilane by 29 Si NMR and FTIR* Zhengping Zhang, B. P. Gorman, Hanjiang Dong, Rosa A. Orozco-Teran, D.W. Mueller, R.F. Reidy Journal of Sol-Gel Science and Technology 28 (2003) 159-165. Abstract 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=1:4:4:2.22*10 -3 in molar ratio) was investigated by high resolution liquid 29 Si 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 equilibrium very quickly. 3-membered rings ((CH3)2SiO)3 appears about half later and 4-membered rings ((CH3)2SiO)4 an hour later, which continues to form past 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.
*Methyltrimethoxysilane sol-gel polymerization in acidic ethanol solutions studied by 29 Si NMR spectroscopy (* Hanjiang Dong, Manho Lee, Ruthanne D. Thomas, Zhengping Zhang, Richard F, Reidy, and Dennis W. Mueller, Journal of Sol-Gel Science and Technology 28 (2003) 5-14, Abstract 29 Si solution NMR has been used to study the acid-catalyzed polymerization of methyltrimethoxysilane (MTMS) in ethanol. The complex reaction pathways have been analyzed, and the general trends described. New interpretations are given to the rate constants of condensation reactions. The steric effects and inductive effects are found to work in coordination to reduce the reactivity of the silicon sites with the increasing connectivity. The extensive cyclization is attributed to the low steric effects of a tetramer ring closure compared to other end/end species condensations.
*Gaussian Random Field Models of Aerogels* J. Quintanilla, R.F Reidy , B.P. Gorman and D.W. Mueller, Journal of Applied Physics 93 (2003) 4584-9 Abstract This paper describes a model capable of predicting pore characteristics and rendering representative images of porous materials. 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 (SANS) 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.
*Sol-gel polycondensation of Methyltrimethoxysilane in ethanol studied by 29 Si NMR spectroscopy using a two-step acid/base procedure* Hanjiang Dong , Man-Ho Lee, Ruthanne D. Thomas, Zhengping Zhang, Richard F. Reidy, and Dennis W. Mueller (submitted to Chemistry of Materials) Abstract 29 Si NMR spectroscopy is used to investigate the structural evolution of Methtrimethoxysilane (MTMS) polymerization in a two-step acid/base catalyzed system (B2). Study of the maximum concentration of intermediate silicon species show nearly random condensation reactions in the basic step, which are justified by conflicting inductive and steric effects. Both condensation-controlled cluster-cluster growth and the reaction pathway to form 4-membered rings are postulated to different between using acid catalysis and B2 catalysis. Moreover, the concentration of ring species is much lower under B2 conditions than under acid conditions. The empirical degree of condensation at the gel point is determined to 0.88. The effects of cyclization and phase separation on MTMS gelation are discussed.
*Synthesis And Characterization Of Hydrophobic Fluorinated Silica Xerogel Films (pdf file)* Zhengping Zhang, Hanjiang Dong, B.P. Gorman, Chun Yao, D.W. Mueller, R.F. Reidy ("Copper Interconnects, New Contact Metallurgies and Low-K Interlevel Dielectrics"(ed. G.S. Mathad) The Electrochemical Society, PV 2002, p.170, 2003.) Abstact Hydrophobic fluorinated silica films were successfully fabricated by sol gel methods. After a specific time of hydrolysis, dimethyldiethoxysilane (DMDES) was introduced to triethoxyfluorosilane (TEFS). Fourier transform infrared spectra show that methyl groups from DMDES and fluorine from TEFS at 60% atomic percent of DMDES have an optimized combination. To improve hydrophobicity, DMDES was reacted before introduction to the TEFS. Optimized films were characterized by C-V and I-V methods.
*Drying and Functionalization of Triethoxyfluorosilane-based Low-k Dielectrics in CO2(pdf file)* B.P. Gorman, D. W. Mueller, R. F. Reidy, Electrochemical Society Letters 6 (2003) F40-41, 2003 Abstract In order 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. In this letter, we report a new method of drying and chemical surface modification of triethoxyfluorosilane (TEFS) based low-k dielectrics using liquid and supercritical (SC) CO2 as a solvent. CO2 is an environmentally friendly, recyclable solvent, and the use of SC-CO2 allows for full surface modification in less than 5 minutes with hydrophobic chemical reagent volumes one thousandth those previously used in bulk chemical modifications.
*Effects of Supercritical CO2 Drying and Photoresist Strip on Low-k Films (pdf file)* R.F. Reidy, Zhengping Zhang, R.A. Orozco-Teran, B.P. Gorman, D.W. Mueller, accepted by MRS Symposium on Materials, Technology, and Reliability for Advanced Interconnects and Low-k Dielectrics, 2003 Abstract Future interlayer dielectric (ILD) requirements necessitate reductions in dielectric constant to 2.1 within four years. Due to gaseous-like transport properties and near liquid-like densities, supercritical methods have been developed to dry and strip resist from these highly porous materials. Although a non-polar molecule, the solvating capability of supercritical CO2 (SC-CO2) can be tailored by varying pressure, temperature, and co-solvents. This flexibility has been employed to remove photoresist and moisture from porous low-k films. The results of these experiments have been characterized using FTIR, ellipsometry, and SEM.
*Supercritical Carbon Dioxide-based Fluids Used as a Recovery Tool for Low-k Materials (pdf file)* Rosa A. Orozco-Teran, Brian P. Gorman, Zhengping Zhang, Dennis W. Mueller, Richard F. Reidy, accepted by MRS Symposium on Materials, Technology, and Reliability for Advanced Interconnects and Low-k Dielectrics, 2003 Abstract Conventional ash strippers can easily damage most porous low-k materials, causing increased dielectric constants and decreased film thicknesses. This effect is more prominent in carbon containing porous low-k materials such as methylsilsesquioxane (MSQ). Ashed MSQ films exhibit increased water adsorption and dielectric constants due to the removal of methyl groups and structural damage caused by interaction with plasma species. Supercritical carbon dioxide (SC-CO2), has attracted considerable attention due its low cost, low critical point temperatures and pressures, and environmentally benign nature. This work describes the effects of SC-CO2 in combination with silylating agents on O2 ash-damaged MSQ films. FTIR, sessile-drop goniometric contact angle measurements, and SEM were used to monitor changes in the films’ chemical bonding, composition, and microstructure.
2004
*Dielectric Behavior Of Triethoxyfluorosilane Aerogels* J.A. Roepsch, B.P. Gorman, D.W. Mueller, R.F. Reidy Journal of Non-Crystalline Solids 336 (2004) 53-58 Abstract Low dielectric constant aerogels are being considered by the semiconductor industry as interlayer dielectrics to overcome capacitance problems which limit device feature sizes. Using sol-gel methods and CO2 supercritical drying, a triethoxyfluorosilane (TEFS) precursor has been used to prepare bulk aerogels. Effects of pH and water to precursor ratio were studied with respect to aerogel dielectric and chemical properties. Methods of analysis for this study include FTIR-ATR and dielectric constant determination by impedance. Si-F bonds were determined to be present in both acid- and base-catalyzed TEFS. Dielectric constants were determined to increase slightly with increasing water to precursor ratios
Synthesis of DAM-1 molecular sieves containing single walled carbon Nanotubes, E. Munoz, D. Coutinho, R.F. Reidy, A. Zakhidov, W.L. Zhou, K.J. Balkus, Microporous And Mesoporous Materials 67 (2004) 61-65 Abstract The mesoporous silica DAM-1 (Dallas Amorphous Material) has been synthesized in the presence of single walled carbon nanotubes (SWNT) using vitamin E TPGS as the template. It is proposed that this water soluble version of vitamin E wraps and partially debundles the SWNTs en route to partial encapsulation within the DAM-1 particles. XRD, adsorption, SEM and TEM provide evidence for occlusion of the nanotubes.
*Effect Of Silylation On TEFS Xerogel Films By Means Of Atmospheric Pressure Drying* R.A. Orozco-Teran, B.P. Gorman, D.W. Mueller, M.R. Baklanov, R.F. Reidy, 471 (2004) 145-153 Abstract Fluorinated silica xerogel films formed from triethoxyfluorosilane (TEFS) have been reacted with silylation agents and characterized. TEFS has been employed because it forms a robust silica network, and the presence of fluorine lowers the films dielectric constant. However, a drawback of using this precursor is the moisture absorption that it presents. Employing silylation reactions enhances film hydrophobicity and permits possible introduction of this film as an interlayer dielectric material. FTIR was used to verify the presence of methyl groups and extent of silylation in the silica films. Thicknesses and refractive index of the subject films were determined by ellipsometry studies, and porosity was determined by the refractive index. Hydrophobicity of the silica films was measured by the sessile-drop goniometric contact angle technique.
*Rapid Repair of Plasma Ash Damage in Low-k Dielectrics Using Supercritical CO2* B.P. Gorman, R.A. Orozco-Teran, Z. Zhang, P.D. Matz, D.W. Mueller, and R.F. Reidy, Journal of Vacuum Science and Technology B 22, 3 (2004) 1210-1212 Abstract 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 letter, 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 minute 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 volume%. Further, this process is also shown to reduce material loss during subsequent wet etch processes. Film thickness measured by SEM before and after treatment illustrates a difference of approximately 0.1mm after etching in a dilute HF solution for 30 seconds.
*Copper Ion Behavior in Silica Xerogels* Zhengping Zhang, Hanjiang Dong, B.P. Gorman, D.W. Mueller, and R. F. Reidy, Journal of Non-Crystalline Solids, 341 (2004) 157-161 Abstract Various concentrations of copper were introduced into tetraethoxyorthosilicate (Si(OC2H5)4) based xerogels by CuSO4 solutions.After ambient drying and different thermal treatments, samples were characterized by gas adsorption, atomic adsorption spectroscopy (AAS), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The behavior of Cu cations during aging and subsequent heating was deduced. Based on the experimental data, no direct metal–oxygen–silicon bonds were found in Cu concentrations up to 2000 ppm. After heating at 600 C for 3 h, copper was observed as dispersed Cu ions and Cu polycrystals.
Drying Methods for Low-? Films and their Effects on Dielectric Constants P.M. Capani, B.P. Gorman, R.F. Reidy, D.W. Mueller, E.R. Walter, P. D. Matz, J.T. Rhoad, E.L. Busch, Advanced Metallization Conference 2004 (accepted) Abstract Plasma ash processes damage low-? methylsilsesquioxane (MSQ) ILD films resulting in loss of methyl species, and consequently, increased water adsorption and dielectric permittivities. In this work, we report that subcritical carbon dioxide as well as supercritical carbon dioxide (SC-CO₂) effectively removes water from hydrogen ash-damaged MSQ as shown by in-situ Fourier transform infrared spectroscopy (FTIR). After water extraction, the MSQ film was repaired with hexamethyldisilazane (HMDS) in SC-CO₂. Contact angle measurements as a function of the volume percent of HMDS show functionalization and repair of the MSQ is achieved with only 1 volume percent HMDS in SC-CO₂. Finally, capacitance-voltage (C-V) measurements show that the dielectric constant of the hydrogen ash-damaged MSQ was restored to 2.23.
*Supercritical Pore Sealing of Porous MSQ* R.F. Reidy, P.K. Nerusu, E.C. Chaung, R.A. Orozco-Teran, P.P. Kadam, P.D. Matz, J.T. Rhoad, E.L. Busch, D.W. Mueller, Advanced Metallization Conference 2004 (accepted) Abstract To successfully integrate porous low-k films into the 45nm technology node, an effective means of preventing metal intrusion into film pores must be developed. Supercritical fluids can provide an efficient means of functionalizing low-k surfaces with bulky organic groups and effectively thwart the intrusion of CVD organometallic precursors. In this effort, a series of silylating agents (R₃-Si-Cl) with R= CH₃, C₂H₅, C₃H₇, and C₆H₅ have been used to examine their relative abilities to react with surface hydroxyls and prevent organometallic precursor intrusion. As measured by contact angle, hydrophobicity was affected by the size of the alkyl or aromatic group. Tetrakis (dimethylamido) titanium (TDMAT) (diameter ~ 10Å), a TiN CVD precursor, was chosen as a penetrant test molecule. As the average pore size of MSQ is approximately 30-40Å, the alkyl groups chosen are large enough in affect TDMAT penetration. Cross-sectional SEM and electrical measurements were conducted to determine the extent of TDMAT penetration and its impact on device performance.