Reactions of thiophenes and thiols with supported molybdenum oxides: A model for hydrodesulfurization reactions
Organometallic precursors were used to prepare silica-supported molybdenum oxides as isolated spe... more Organometallic precursors were used to prepare silica-supported molybdenum oxides as isolated species, pairs or dimers with oxidation states ranging from 1+ to 4+. Our goal is to understand the role of oxidation state and structure on the hydrodesulfurization of thiophenes, compounds typically found in fossil fuels, and thiols. We used gas chromatography and mass spectroscopy to study the reactions of thiophenes and thiols with supported molybdenum oxide systems.
This report vuas.prepared as an account of work sponsored by an agency of the United States Gover... more This report vuas.prepared as an account of work sponsored by an agency of the United States Government.
ChemInform Abstract: Growth of Epitaxial (100) GaAs Films Using the Single-Source Precursor (Me2Ga(μ-tBu2As))2
ChemInform, Aug 22, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Industrial & Engineering Chemistry Research, Mar 1, 1990
An experimental protocol and model for predicting the viscosity rise with reaction time of a solu... more An experimental protocol and model for predicting the viscosity rise with reaction time of a solution that contains anionically polymerizing styrene in styrene are presented. The solution simulates that to be used in a reaction injection molding (RIM) process for encapsulating microchips. The model prediction of viscosity is based on the use of material balances to relate the separately determined influences of polymer concentration, polymer molecular weight, temperature, shear rate, and chemical kinetics. The model is found to predict the induction period for viscosity rise to within about 25% relative error. T h e primary source of error is found to be the rate constant for polymerization. Modification of the rate constant leads to predictions of induction times that agree to within 10% relative error.
Journal of vacuum science & technology, Nov 1, 2009
Metal insulator semiconductor structures were fabricated from n-Si͑100͒ and n-Ge͑100͒ wafers pass... more Metal insulator semiconductor structures were fabricated from n-Si͑100͒ and n-Ge͑100͒ wafers passivated with thin ͑4.5-5 nm͒ films of N-rich BC x N y ͑0.09Յ x Յ 0.15, 0.38Յ y Յ 0.52͒ and with atomic layer deposition HfO 2 ͑10 nm͒ as the gate dielectric. C-V and I-V characteristics of devices with BC x N y films grown at 275-400°C by chemical vapor deposition showed that lower deposition temperatures resulted in improved electrical characteristics, including decreased hysteresis, lower V FB shift, lower leakage current, and less C-V stretch out. The electrical improvement is attributed to decreased bulk and interfacial defects in lower temperature deposited BC x N y films, which also had a higher optical bandgap ͓E g = 3.55 eV at 275°C on Ge͑100͔͒, lower subbandgap absorption, lower index of refraction ͓n͑633 nm͒ = 1.84 at 275°C on Ge͑100͔͒, reduced O uptake during ambient exposure, and increased percentage of B. Even for the lowest growth temperature studied ͑275°C͒, BC x N y-passivated Ge͑100͒ devices had considerable hysteresis ͑1.05 V͒, and electrical characteristics worsened after a postmetallization anneal. BC x N y-passivated Si͑100͒ devices outperformed similar Ge͑100͒ devices likely due to the higher interface state densities at the BC x N y-Ge͑100͒ interface associated with the higher relative inertness of Ge͑100͒ to thermal nitridation. C-rich BC 0.61 N 0.08 films were also investigated but large amounts of hysteresis and fixed negative charge motivated the abandonment of these films.
CVD Boron Carbo-Nitride as Pore Sealant for Ultra Low-K Interlayer Dielectrics
MRS Proceedings, 2005
Blanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent ... more Blanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent to seal the pores and prevent penetration of a metallic precursor during barrier deposition. The blanket pMSQ films studied were approximately 220 nm thick and had been etched and ashed. When tantalum pentafluoride (TaF5) is exposed to an unsealed pMSQ sample, X-ray photoelectron spectroscopy (XPS) depth profiling and secondary ion mass spectroscopy (SIMS) depth profiling reveal penetration of Ta into the pores all the way to the pMSQ / Si interface. Boron carbo-nitride films were grown by thermal chemical vapor deposition (CVD) using dimethylamine borane (DMAB) precursor with Ar carrier gas and C2H4 coreactant. These films had a stoichiometry of BC0.9N0.07 and have been shown in a previous study to have a k value as low as 3.8. BC0.9N0.07 films ranging from 1.8 to 40.6 nm were deposited on pMSQ and then exposed to TaF5 gas to determine the extent of Ta penetration into the pMSQ. Ta penetration was determined by XPS depth profiling and sometimes SIMS depth profiling. XPS depth profiling of a TaF5 / 6.3 nm BC0.9N0.07 / pMSQ / Si film stack indicates the attenuation of the Ta signal to < 2 at. % throughout the pMSQ. Backside SIMS of this sample suggests that trace amounts of Ta (< 2 at. %) are due to knock-in by Ar ions used for sputtering. An identical film stack containing 3.9 nm BC0.9N0.07 was also successful at inhibiting Ta penetration even with a 370°C post-TaF5 exposure anneal, suggesting the stability of BC0.9N0.07 to thermal diffusion of Ta. All BC0.9N0.07 films thicker than and including 3.9 nm prevented Ta from penetrating into the pMSQ.
Isosynthesis reactions of CO/H/sub 2/ over zirconium dioxide
Journal of Catalysis, Feb 1, 1988
The reaction of an equimolar mixture of H/sub 2/ and CO was studied over ZrO/sub 2/ at 350 to 450... more The reaction of an equimolar mixture of H/sub 2/ and CO was studied over ZrO/sub 2/ at 350 to 450/sup 0/C, 35 atm total pressure, and varying residence times. The isosynthesis reaction mechanisms were studied by monitoring the incorporation of oxygenated compounds into the isosynthesis products. Propionaldehyde and (/sup 13/C)acetone, (/sup 13/C)isopropanol, and (/sup 13/C)methanol were added to the CO/H/sub 2/ reactant stream. Their effect on the isosynthesis product distributions and on the isotopic distribution of the products was monitored as a function of oxygenate feed rate. Propionaldehyde, acetone, and methanol were found to incorporate into the isosynthesis products. The isotopic distribution of the products was used to support an isosynthesis reaction scheme that involves CO insertion into a bound aldehyde or ketone as the major chain growth step and a second chain growth step that involves condensation between methoxide and a surface bound enolate. 32 references.
AlxTi I-xN film growth has been studied by a organometallic chemical vapor deposition and in-situ... more AlxTi I-xN film growth has been studied by a organometallic chemical vapor deposition and in-situ X-ray photoelectron spectroscopy. Terakis(dimethylamido)titanium (TDMAT) and dimethyl aluminum hydride (DMAH) were used as the Ti, N and Al precursors. AlTiN film growth was observed on SiO2/Si(100) with substrate temperatures between 200 and 400 *C. The Al content in the film is controlled by the ratio of partial pressures of the two precursors in the gas phase. The metal to C to N ratio is approximately constant at 1:1:1 for most conditions studied. The chemical states of Ti, C, and N in AlxTilxN and titanium-carbo-nitride (TiCN) films are identical, while the Al chemical state is nitride at low, but increasingly carbidic at high Al concentration. The initial growth rate on SiO2 was significantly suppressed by the presence of DMAH. At lower growth temperatures, the DMAH effect is more severe. Good step coverage was observed for AlxTil-xN on 0.3 gtm vias with a 3:1 aspect ratio.
<title>New directions in surface spectroscopy enabled by ultrafast lasers</title>
Proceedings of SPIE, Apr 30, 1998
ABSTRACT Si(001) interfaces are among the most technologically important, yet their weak interfac... more ABSTRACT Si(001) interfaces are among the most technologically important, yet their weak interfacial second order nonlinear susceptibility Chi((2)) has strongly inhibited quantitative interface specific Second Harmonic (SH) spectroscopy and related nonlinear optical process control applications. The advent of widely tunable, unamplified femtosecond (fs) solid-state lasers has overcome this barrier by enabling unprecedented SH generation efficiency (similar to 10(6) photons/sec) with minimal surface heating (&lt;20 K).(1) We have exploited this capability to characterize the micro-roughness(2), band-bending(3), strain(4), interface oxidation states(5) and contamination(6) of buried Si(001)/SiO2 interfaces by SH spectroscopy. The sensitivity of SHG to H-coverage(7) of the Si(001), Ge(001) and Si1-xGex(001) growth surfaces has been applied to the real-time monitoring of Chemical Vapor Depostion (CVD) surface kinetics.(8) Amplification of fs Ti:Sapphire lasers has enabled the observation of Fourth Harmonic Generation (FHG) below the damage threshold of Si(001) and GaAs(001) surfaces. Unique properties of the fourth order nonlinear susceptibility Chi((4)) create a superior surface specificity compared to SHG.(9,10) Finally, Ti:Sapphire lasers with pulse durations &lt;20 fs have spectral bandwidths large enough to cover features such as the E-1 critical point in Si1-xGex thus allowing the real-time acquisition of SH spectra.
Germanium nanoparticle growth on SiO 2 proceeds via defect-mediated nucleation and particle densi... more Germanium nanoparticle growth on SiO 2 proceeds via defect-mediated nucleation and particle density can be enhanced by chemically treating the SiO 2 with SiH x. The influence of SiH x fragments on SiO 2 surface sites is studied using a fluorescent probe-based technique to understand the chemical nature of the inherent defect trapping sites and the chemical nature of the additional trapping sites formed by SiH x. Oxygen-vacancy sites on SiO 2 are the inherent sites for defectmediated nucleation. SiH x fragments, generated by cracking disilane on a hot tungsten filament, are shown to react with strained siloxane sites, leading to a conversion of these strained siloxane sites into a different low density defect site that is shown to display reactive characteristics similar to the oxygen-vacancy defect sites. Previous work demonstrating an increased density of Ge nuclei on SiO 2 surfaces with increasing SiH x exposure is interpreted in the context of the current experimental results.
Characterization of Boron Carbo-Nitride Films Deposited By Low Temperature Chemical Vapor Deposition
MRS Proceedings, 2003
This study reports low temperature chemical vapor deposition of amorphous boron carbonitride film... more This study reports low temperature chemical vapor deposition of amorphous boron carbonitride films on SiO2 using a dimethylamine borane complex at temperatures ranging from 360 to 500°C and with varying NH3 flow at 360°C. The dielectric constant, k, of the films ranged from 4.11 to 4.83, and increased with temperature while the addition of nitrogen using NH3 decreased k. The index of refraction changed correspondingly with k, ranging from 1.826 to 2.226. Higher substrate temperature caused nitrogen and carbon content to increase with additional bonding to boron. The addition of ammonia increased the N:B ratio to as high as 0.64 and reduced k to 4.11. The higher nitrogen incorporation displaced both boron and carbon in the film, leaving boron bonded primarily to nitrogen and other boron atoms. These films were amorphous with smooth surfaces of RMS roughness ranging from 0.30 nm to 0.53 nm.
Vacuum ultraviolet enhanced atomic layer etching of ruthenium films
Journal of vacuum science & technology, Dec 24, 2020
Vacuum ultraviolet (VUV) enhanced atomic layer etching (ALE) of thin (∼8 nm) Ru films is demonstr... more Vacuum ultraviolet (VUV) enhanced atomic layer etching (ALE) of thin (∼8 nm) Ru films is demonstrated. Oxidation half-cycles of 2–5 min VUV/O2 co-exposure are used to oxidize near-surface Ru to RuO2 at 1 Torr O2 and 100–150 °C. In situ x-ray photoelectron spectroscopy measurements indicate that RuO2 formation saturates after ∼5 min of VUV/O2 exposure at 100 and 150 °C. The depth of Ru oxidation is limited by the rate of oxidation and can be controlled with substrate temperature and exposure time. Etching half-cycles are performed by exposing the oxidized Ru film to HCOOH vapor at 0.50 Torr for 30 s isothermally, which results in the removal of the oxidized Ru layer. The amount of Ru removed per ALE cycle is determined by comparing ex situ x-ray reflectivity (XRR) measurements of the film before and after etching. When using 2 min VUV/O2 co-exposure, approximately 0.8 and 0.9 Å of Ru is etched per cycle at 100 and 150 °C, respectively. XRR and atomic force microscopy measurements indicate that the as-deposited and sputtered Ru film surface becomes smoother as ALE is performed. The etch rate decreases with ALE cycles and corresponds to a slowing oxidation rate, which is likely associated with the decrease in surface roughness. Density functional theory is used to study the adsorption of oxidants in a model Ru system, and nudged elastic band (NEB) calculations describe O diffusion into the Ru substrate by following an O “probe” atom as it moves between Ru(002) atomic planes with 0.50 monolayer (ML) O on the surface. NEB results reveal an approximate energetic barrier to diffusion, Ea, of 5.10 eV for O to move through the second and third atomic Ru layers when O, which can form an RuOx species, is subsurface. This Ea is in excess of the energetic gain of 4.23 eV in adsorbing an O atom to Ru(002) with 0.50 ML O. The difference in Ea and the adsorption energy likely contributes to the self-limiting nature of the oxidation and explains the observation that VUV/O2 co-exposure time must be increased to allow additional time for O diffusing into the subsurface as it overcomes the barrier to subsurface O diffusion. The self-limiting oxidation of Ru arising from VUV/O2 at low temperatures, in turn, enables an ALE process for Ru.
Investigations into the kinetics and mechanism of the thermal decomposition of the novel organome... more Investigations into the kinetics and mechanism of the thermal decomposition of the novel organometallic precursor 1,3-di-tert-butyl-1,3,2-diazagarmolidin-2-ylidine are reported. On the basis of these results, thin films of surprisingly pure amorphous germanium were deposited at temperatures between about 140 and 440°C. A high selectivity of the deposition on a Si surface as compared with SiO 2 was obtained.
Reactions of thiophenes and thiols with supported molybdenum oxides: A model for hydrodesulfurization reactions
Organometallic precursors were used to prepare silica-supported molybdenum oxides as isolated spe... more Organometallic precursors were used to prepare silica-supported molybdenum oxides as isolated species, pairs or dimers with oxidation states ranging from 1+ to 4+. Our goal is to understand the role of oxidation state and structure on the hydrodesulfurization of thiophenes, compounds typically found in fossil fuels, and thiols. We used gas chromatography and mass spectroscopy to study the reactions of thiophenes and thiols with supported molybdenum oxide systems.
This report vuas.prepared as an account of work sponsored by an agency of the United States Gover... more This report vuas.prepared as an account of work sponsored by an agency of the United States Government.
ChemInform Abstract: Growth of Epitaxial (100) GaAs Films Using the Single-Source Precursor (Me2Ga(μ-tBu2As))2
ChemInform, Aug 22, 2010
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Industrial & Engineering Chemistry Research, Mar 1, 1990
An experimental protocol and model for predicting the viscosity rise with reaction time of a solu... more An experimental protocol and model for predicting the viscosity rise with reaction time of a solution that contains anionically polymerizing styrene in styrene are presented. The solution simulates that to be used in a reaction injection molding (RIM) process for encapsulating microchips. The model prediction of viscosity is based on the use of material balances to relate the separately determined influences of polymer concentration, polymer molecular weight, temperature, shear rate, and chemical kinetics. The model is found to predict the induction period for viscosity rise to within about 25% relative error. T h e primary source of error is found to be the rate constant for polymerization. Modification of the rate constant leads to predictions of induction times that agree to within 10% relative error.
Journal of vacuum science & technology, Nov 1, 2009
Metal insulator semiconductor structures were fabricated from n-Si͑100͒ and n-Ge͑100͒ wafers pass... more Metal insulator semiconductor structures were fabricated from n-Si͑100͒ and n-Ge͑100͒ wafers passivated with thin ͑4.5-5 nm͒ films of N-rich BC x N y ͑0.09Յ x Յ 0.15, 0.38Յ y Յ 0.52͒ and with atomic layer deposition HfO 2 ͑10 nm͒ as the gate dielectric. C-V and I-V characteristics of devices with BC x N y films grown at 275-400°C by chemical vapor deposition showed that lower deposition temperatures resulted in improved electrical characteristics, including decreased hysteresis, lower V FB shift, lower leakage current, and less C-V stretch out. The electrical improvement is attributed to decreased bulk and interfacial defects in lower temperature deposited BC x N y films, which also had a higher optical bandgap ͓E g = 3.55 eV at 275°C on Ge͑100͔͒, lower subbandgap absorption, lower index of refraction ͓n͑633 nm͒ = 1.84 at 275°C on Ge͑100͔͒, reduced O uptake during ambient exposure, and increased percentage of B. Even for the lowest growth temperature studied ͑275°C͒, BC x N y-passivated Ge͑100͒ devices had considerable hysteresis ͑1.05 V͒, and electrical characteristics worsened after a postmetallization anneal. BC x N y-passivated Si͑100͒ devices outperformed similar Ge͑100͒ devices likely due to the higher interface state densities at the BC x N y-Ge͑100͒ interface associated with the higher relative inertness of Ge͑100͒ to thermal nitridation. C-rich BC 0.61 N 0.08 films were also investigated but large amounts of hysteresis and fixed negative charge motivated the abandonment of these films.
CVD Boron Carbo-Nitride as Pore Sealant for Ultra Low-K Interlayer Dielectrics
MRS Proceedings, 2005
Blanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent ... more Blanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent to seal the pores and prevent penetration of a metallic precursor during barrier deposition. The blanket pMSQ films studied were approximately 220 nm thick and had been etched and ashed. When tantalum pentafluoride (TaF5) is exposed to an unsealed pMSQ sample, X-ray photoelectron spectroscopy (XPS) depth profiling and secondary ion mass spectroscopy (SIMS) depth profiling reveal penetration of Ta into the pores all the way to the pMSQ / Si interface. Boron carbo-nitride films were grown by thermal chemical vapor deposition (CVD) using dimethylamine borane (DMAB) precursor with Ar carrier gas and C2H4 coreactant. These films had a stoichiometry of BC0.9N0.07 and have been shown in a previous study to have a k value as low as 3.8. BC0.9N0.07 films ranging from 1.8 to 40.6 nm were deposited on pMSQ and then exposed to TaF5 gas to determine the extent of Ta penetration into the pMSQ. Ta penetration was determined by XPS depth profiling and sometimes SIMS depth profiling. XPS depth profiling of a TaF5 / 6.3 nm BC0.9N0.07 / pMSQ / Si film stack indicates the attenuation of the Ta signal to &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 2 at. % throughout the pMSQ. Backside SIMS of this sample suggests that trace amounts of Ta (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 2 at. %) are due to knock-in by Ar ions used for sputtering. An identical film stack containing 3.9 nm BC0.9N0.07 was also successful at inhibiting Ta penetration even with a 370°C post-TaF5 exposure anneal, suggesting the stability of BC0.9N0.07 to thermal diffusion of Ta. All BC0.9N0.07 films thicker than and including 3.9 nm prevented Ta from penetrating into the pMSQ.
Isosynthesis reactions of CO/H/sub 2/ over zirconium dioxide
Journal of Catalysis, Feb 1, 1988
The reaction of an equimolar mixture of H/sub 2/ and CO was studied over ZrO/sub 2/ at 350 to 450... more The reaction of an equimolar mixture of H/sub 2/ and CO was studied over ZrO/sub 2/ at 350 to 450/sup 0/C, 35 atm total pressure, and varying residence times. The isosynthesis reaction mechanisms were studied by monitoring the incorporation of oxygenated compounds into the isosynthesis products. Propionaldehyde and (/sup 13/C)acetone, (/sup 13/C)isopropanol, and (/sup 13/C)methanol were added to the CO/H/sub 2/ reactant stream. Their effect on the isosynthesis product distributions and on the isotopic distribution of the products was monitored as a function of oxygenate feed rate. Propionaldehyde, acetone, and methanol were found to incorporate into the isosynthesis products. The isotopic distribution of the products was used to support an isosynthesis reaction scheme that involves CO insertion into a bound aldehyde or ketone as the major chain growth step and a second chain growth step that involves condensation between methoxide and a surface bound enolate. 32 references.
AlxTi I-xN film growth has been studied by a organometallic chemical vapor deposition and in-situ... more AlxTi I-xN film growth has been studied by a organometallic chemical vapor deposition and in-situ X-ray photoelectron spectroscopy. Terakis(dimethylamido)titanium (TDMAT) and dimethyl aluminum hydride (DMAH) were used as the Ti, N and Al precursors. AlTiN film growth was observed on SiO2/Si(100) with substrate temperatures between 200 and 400 *C. The Al content in the film is controlled by the ratio of partial pressures of the two precursors in the gas phase. The metal to C to N ratio is approximately constant at 1:1:1 for most conditions studied. The chemical states of Ti, C, and N in AlxTilxN and titanium-carbo-nitride (TiCN) films are identical, while the Al chemical state is nitride at low, but increasingly carbidic at high Al concentration. The initial growth rate on SiO2 was significantly suppressed by the presence of DMAH. At lower growth temperatures, the DMAH effect is more severe. Good step coverage was observed for AlxTil-xN on 0.3 gtm vias with a 3:1 aspect ratio.
<title>New directions in surface spectroscopy enabled by ultrafast lasers</title>
Proceedings of SPIE, Apr 30, 1998
ABSTRACT Si(001) interfaces are among the most technologically important, yet their weak interfac... more ABSTRACT Si(001) interfaces are among the most technologically important, yet their weak interfacial second order nonlinear susceptibility Chi((2)) has strongly inhibited quantitative interface specific Second Harmonic (SH) spectroscopy and related nonlinear optical process control applications. The advent of widely tunable, unamplified femtosecond (fs) solid-state lasers has overcome this barrier by enabling unprecedented SH generation efficiency (similar to 10(6) photons/sec) with minimal surface heating (&lt;20 K).(1) We have exploited this capability to characterize the micro-roughness(2), band-bending(3), strain(4), interface oxidation states(5) and contamination(6) of buried Si(001)/SiO2 interfaces by SH spectroscopy. The sensitivity of SHG to H-coverage(7) of the Si(001), Ge(001) and Si1-xGex(001) growth surfaces has been applied to the real-time monitoring of Chemical Vapor Depostion (CVD) surface kinetics.(8) Amplification of fs Ti:Sapphire lasers has enabled the observation of Fourth Harmonic Generation (FHG) below the damage threshold of Si(001) and GaAs(001) surfaces. Unique properties of the fourth order nonlinear susceptibility Chi((4)) create a superior surface specificity compared to SHG.(9,10) Finally, Ti:Sapphire lasers with pulse durations &lt;20 fs have spectral bandwidths large enough to cover features such as the E-1 critical point in Si1-xGex thus allowing the real-time acquisition of SH spectra.
Germanium nanoparticle growth on SiO 2 proceeds via defect-mediated nucleation and particle densi... more Germanium nanoparticle growth on SiO 2 proceeds via defect-mediated nucleation and particle density can be enhanced by chemically treating the SiO 2 with SiH x. The influence of SiH x fragments on SiO 2 surface sites is studied using a fluorescent probe-based technique to understand the chemical nature of the inherent defect trapping sites and the chemical nature of the additional trapping sites formed by SiH x. Oxygen-vacancy sites on SiO 2 are the inherent sites for defectmediated nucleation. SiH x fragments, generated by cracking disilane on a hot tungsten filament, are shown to react with strained siloxane sites, leading to a conversion of these strained siloxane sites into a different low density defect site that is shown to display reactive characteristics similar to the oxygen-vacancy defect sites. Previous work demonstrating an increased density of Ge nuclei on SiO 2 surfaces with increasing SiH x exposure is interpreted in the context of the current experimental results.
Characterization of Boron Carbo-Nitride Films Deposited By Low Temperature Chemical Vapor Deposition
MRS Proceedings, 2003
This study reports low temperature chemical vapor deposition of amorphous boron carbonitride film... more This study reports low temperature chemical vapor deposition of amorphous boron carbonitride films on SiO2 using a dimethylamine borane complex at temperatures ranging from 360 to 500°C and with varying NH3 flow at 360°C. The dielectric constant, k, of the films ranged from 4.11 to 4.83, and increased with temperature while the addition of nitrogen using NH3 decreased k. The index of refraction changed correspondingly with k, ranging from 1.826 to 2.226. Higher substrate temperature caused nitrogen and carbon content to increase with additional bonding to boron. The addition of ammonia increased the N:B ratio to as high as 0.64 and reduced k to 4.11. The higher nitrogen incorporation displaced both boron and carbon in the film, leaving boron bonded primarily to nitrogen and other boron atoms. These films were amorphous with smooth surfaces of RMS roughness ranging from 0.30 nm to 0.53 nm.
Vacuum ultraviolet enhanced atomic layer etching of ruthenium films
Journal of vacuum science & technology, Dec 24, 2020
Vacuum ultraviolet (VUV) enhanced atomic layer etching (ALE) of thin (∼8 nm) Ru films is demonstr... more Vacuum ultraviolet (VUV) enhanced atomic layer etching (ALE) of thin (∼8 nm) Ru films is demonstrated. Oxidation half-cycles of 2–5 min VUV/O2 co-exposure are used to oxidize near-surface Ru to RuO2 at 1 Torr O2 and 100–150 °C. In situ x-ray photoelectron spectroscopy measurements indicate that RuO2 formation saturates after ∼5 min of VUV/O2 exposure at 100 and 150 °C. The depth of Ru oxidation is limited by the rate of oxidation and can be controlled with substrate temperature and exposure time. Etching half-cycles are performed by exposing the oxidized Ru film to HCOOH vapor at 0.50 Torr for 30 s isothermally, which results in the removal of the oxidized Ru layer. The amount of Ru removed per ALE cycle is determined by comparing ex situ x-ray reflectivity (XRR) measurements of the film before and after etching. When using 2 min VUV/O2 co-exposure, approximately 0.8 and 0.9 Å of Ru is etched per cycle at 100 and 150 °C, respectively. XRR and atomic force microscopy measurements indicate that the as-deposited and sputtered Ru film surface becomes smoother as ALE is performed. The etch rate decreases with ALE cycles and corresponds to a slowing oxidation rate, which is likely associated with the decrease in surface roughness. Density functional theory is used to study the adsorption of oxidants in a model Ru system, and nudged elastic band (NEB) calculations describe O diffusion into the Ru substrate by following an O “probe” atom as it moves between Ru(002) atomic planes with 0.50 monolayer (ML) O on the surface. NEB results reveal an approximate energetic barrier to diffusion, Ea, of 5.10 eV for O to move through the second and third atomic Ru layers when O, which can form an RuOx species, is subsurface. This Ea is in excess of the energetic gain of 4.23 eV in adsorbing an O atom to Ru(002) with 0.50 ML O. The difference in Ea and the adsorption energy likely contributes to the self-limiting nature of the oxidation and explains the observation that VUV/O2 co-exposure time must be increased to allow additional time for O diffusing into the subsurface as it overcomes the barrier to subsurface O diffusion. The self-limiting oxidation of Ru arising from VUV/O2 at low temperatures, in turn, enables an ALE process for Ru.
Investigations into the kinetics and mechanism of the thermal decomposition of the novel organome... more Investigations into the kinetics and mechanism of the thermal decomposition of the novel organometallic precursor 1,3-di-tert-butyl-1,3,2-diazagarmolidin-2-ylidine are reported. On the basis of these results, thin films of surprisingly pure amorphous germanium were deposited at temperatures between about 140 and 440°C. A high selectivity of the deposition on a Si surface as compared with SiO 2 was obtained.
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