The atomic layer deposition (ALD) of copper oxide films from [(ⁿBu₃P)₂Cu(acac)] and wet oxygen on SiO₂ and TaN has been studied in detail by spectroscopic ellipsometry and atomic force microscopy. The results suggest island growth on SiO₂, along with a strong variation of the optical properties of the films in the early stages of the growth and signs of quantum confinement, typical for nanocrystals. In addition, differences both in growth behavior and film properties appear on dry and wet thermal SiO₂. Electron diffraction together with transmission electron microscopy shows that nanocrystalline Cu₂O with crystallites < 5 nm is formed, while upon prolonged electron irradiation the films decompose and metallic copper crystallites of approximately 10 nm precipitate. On TaN, the films grow in a linear, layer-by-layer manner, reproducing the initial substrate roughness. Saturated growth obtained at 120&deg;C on TaN as well as dry and wet SiO₂ indicates well-established ALD growth regimes. <br> &copy; 2009 The Electrochemical Society. All rights reserved.

This article has been published online on 21st May 2014, in Journal of Vacuum Science & Technology A: Vac (Vol.32, Issue 4): http://scitation.aip.org/content/avs/journal/jvsta/32/4/10.1116/1.4878815?aemail=author DOI: 10.1116/1.4878815 This article may be accessed via the issue's table of contents at this link: http://scitation.aip.org/content/avs/journal/jvsta/32/4?aemail=author The surface chemistry of the bis(tri-n-butylphosphane) copper(I) acetylacetonate, [(nBu3P)2Cu(acac)], and the thermal atomic layer deposition (ALD) of Cu2O using this Cu precursor as reactant and wet oxygen as co-reactant on SiO2 substrates are studied by in-situ X-ray photoelectron spectroscopy (XPS). The Cu precursor was evaporated and exposed to the substrates kept at temperatures between 22 °C and 300 °C. The measured phosphorus and carbon concentration on the substrates indicated that most of the [nBu3P] ligands were released either in the gas phase or during adsorption. No disproportionation was observed for the Cu precursor in the temperature range between 22 °C and 145 °C. However, disproportionation of the Cu precursor was observed at 200 °C, since C/Cu concentration ratio decreased and substantial amounts of metallic Cu were present on the substrate. The amount of metallic Cu increased, when the substrate was kept at 300 °C, indicating stronger disproportionation of the Cu precursor. Hence, the upper limit for the ALD of Cu2O from this precursor lies in the temperature range between 145 °C and 200 °C, as the precursor must not alter its chemical and physical state after chemisorption on the substrate. 500 ALD cycles with the probed Cu precursor and wet O2 as co reactant were carried out on SiO2 at 145 °C. After ALD, in situ XPS analysis confirmed the presence of Cu2O on the substrate. Ex-situ spectroscopic ellipsometry indicated an average film thickness of 2.5 nm of Cu2O deposited with a growth per cycle of 0.05 Å/cycle. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) investigations depicted a homogeneous, fine, and granular morphology of the Cu2O ALD film on SiO2. AFM investigations suggest that the deposited Cu2O film is continuous on the SiO2 substrate.

Copper films with a thickness in the nanometer range are required as seed layers for the electrochemical Cu deposition to form multilevel interconnects in ultralarge-scale integrated (ULSI) electronic devices. Continuously shrinking device dimensions and increasing aspect ratios of the dual-damascene structures in the copper-based metallization schemes put ever more stringent requirements on the films with respect to their conformality in nanostructures and thickness homogeneity across large wafers. Due to its intrinsic self-limiting film growth characteristic, atomic layer deposition (ALD) appears appropriate for homogeneously coating complex substrates and to replace conventional physical vapor deposition (PVD) methods beyond the 32 nm technology node. To overcome issues of direct Cu ALD, such as film agglomeration at higher temperatures or reduced step coverage in plasma-based processes, an ALD copper oxide film may be grown under mild processing conditions, while a subsequent reduction step converts it to metallic copper. In this poster, which was presented at the AVS 9th International Conference on Atomic Layer Deposition (ALD 2009), held in Monterey, California from 19 to 22 July 2009, we report detailed film growth studies of ALD copper oxide in the self-limiting regime on SiO2, TaN and Ru. Applications in subsequent electrochemical deposition processes are discussed, comparing Cu plating results on as-deposited PVD Ru as well as with PVD and reduced ALD Cu seed layer.

Copper-based multi-level metallization systems in today’s ultralarge-scale integrated electronic circuits require the fabrication of diffusion barriers and conductive seed layers for the electrochemical metal deposition. Such films of only several nanometers in thickness have to be deposited void-free and conformal in patterned dielectrics. The envisaged further reduction of the geometric dimensions of the interconnect system calls for coating techniques that circumvent the drawbacks of the well-established physical vapor deposition. The atomic layer deposition method (ALD) allows depositing films on the nanometer scale conformally both on three-dimensional objects as well as on large-area substrates. The present work therefore is concerned with the development of an ALD process to grow copper oxide films based on the metal-organic precursor bis(tri-n-butylphosphane)copper(I)acetylacetonate [(nBu3P)2Cu(acac)]. This liquid, non-fluorinated β-diketonate is brought to react with a mixture of water vapor and oxygen at temperatures from 100 to 160°C. Typical ALD-like growth behavior arises between 100 and 130°C, depending on the respective substrate used. On tantalum nitride and silicon dioxide substrates, smooth films and self-saturating film growth, typical for ALD, are obtained. On ruthenium substrates, positive deposition results are obtained as well. However, a considerable intermixing of the ALD copper oxide with the underlying films takes place. Tantalum substrates lead to a fast self-decomposition of the copper precursor. As a consequence, isolated nuclei or larger particles are always obtained together with continuous films. The copper oxide films grown by ALD can be reduced to copper by vapor-phase processes. If formic acid is used as the reducing agent, these processes can already be carried out at similar temperatures as the ALD, so that agglomeration of the films is largely avoided. Also for an integration with subsequent electrochemical copper deposition, the combination of ALD copper and ruthenium proves advantageous, especially with respect to the quality of the electroplated films and their filling behavior in interconnect structures. Furthermore, the ALD process developed also bears potential for an integration with carbon nanotubes. / Kupferbasierte Mehrlagenmetallisierungssysteme in heutigen hochintegrierten elektronischen Schaltkreisen erfordern die Herstellung von Diffusionsbarrieren und leitfähigen Keimschichten für die galvanische Metallabscheidung. Diese Schichten von nur wenigen Nanometern Dicke müssen konform und fehlerfrei in strukturierten Dielektrika abgeschieden werden. Die sich abzeichnende weitere Verkleinerung der geometrischen Dimensionen des Leitbahnsystems erfordert Beschichtungstechnologien, die vorhandene Nachteile der bisher etablierten Physikalischen Dampfphasenabscheidung beheben. Die Methode der Atomlagenabscheidung (ALD) ermöglicht es, Schichten im Nanometerbereich sowohl auf dreidimensional strukturierten Objekten als auch auf großflächigen Substraten gleichmäßig herzustellen. Die vorliegende Arbeit befasst sich daher mit der Entwicklung eines ALD-Prozesses zur Abscheidung von Kupferoxidschichten, ausgehend von der metallorganischen Vorstufe Bis(tri-n-butylphosphan)kupfer(I)acetylacetonat [(nBu3P)2Cu(acac)]. Dieses flüssige, nichtfluorierte β-Diketonat wird bei Temperaturen zwischen 100 und 160°C mit einer Mischung aus Wasserdampf und Sauerstoff zur Reaktion gebracht. ALD-typisches Schichtwachstum stellt sich in Abhängigkeit des gewählten Substrats zwischen 100 und 130°C ein. Auf Tantalnitrid- und Siliziumdioxidsubstraten werden dabei sehr glatte Schichten bei gesättigtem Wachstumsverhalten erhalten. Auch auf Rutheniumsubstraten werden gute Abscheideergebnisse erzielt, jedoch kommt es hier zu einer merklichen Durchmischung des ALD-Kupferoxids mit dem Untergrund. Tantalsubstrate führen zu einer schnellen Selbstzersetzung des Kupferprecursors, in dessen Folge neben geschlossenen Schichten während der ALD auch immer isolierte Keime oder größere Partikel erhalten werden. Die mittels ALD gewachsenen Kupferoxidschichten können in Gasphasenprozessen zu Kupfer reduziert werden. Wird Ameisensäure als Reduktionsmittel genutzt, können diese Prozesse bereits bei ähnlichen Temperaturen wie die ALD durchgeführt werden, so dass Agglomeration der Schichten weitgehend verhindert wird. Als besonders vorteilhaft für die Ameisensäure-Reduktion erweisen sich Rutheniumsubstrate. Auch für eine Integration mit nachfolgenden Galvanikprozessen zur Abscheidung von Kupfer zeigen sich Vorteile der Kombination ALD-Kupfer/Ruthenium, insbesondere hinsichtlich der Qualität der erhaltenen galvanischen Schichten und deren Füllverhalten in Leitbahnstrukturen. Der entwickelte ALD-Prozess besitzt darüber hinaus Potential zur Integration mit Kohlenstoffnanoröhren.

Four cluster models for a copper(I)oxide (111) surface have been designed, of which three were studied with respect to their applicability in density functional calculations in the general gradient approximation. Formic acid adsorption on these systems was modelled and yielded four different adsorption structures, of which two were found to have a high adsorption energy. The energetically most favourable adsorption structure was further investigated with respect to its decomposition and a few reactions with adsorbed H and OH species using synchronous transit methods to estimate reaction barriers and single point energy calculations for the reaction energy.

Atomic layer deposition (ALD) of copper films is getting enormous interest. Ultrathin Cu films are applied as the seed layer for electrochemical deposition (ECD) of copper in interconnect circuits and as the non-magnetic material for the realization of giant magnetoresistance (GMR) sensors. Particularly, Co/Cu multi-layered structures require sub 4.0 nm copper film thickness for obtaining strong GMR effects. The physical vapor deposition process for the deposition of the copper seed layers are prone to non-conformal coating and poor step coverage on side-walls and bottoms of trenches and vias, and presence of overhanging structures. This may cause failure of interconnections due to formation of voids after copper ECD. ALD is the most suitable technology for the deposition of conformal seed layers for the subsequent ECD in very high aspect ratio structures, also for the technology nodes below 20 nm. Surface chemistry during the ALD of oxides is quite well studied. However, surface chemistry during the ALD of pure metal is rather immature. This knowledge is necessary to optimize the process parameters, synthesize better precursors systems, and enhance the knowledge of existing metal ALD processes. The major goal of this work is to understand the surface chemistry of the used precursor and study the growth of ultrathin copper films using in-situ X-ray photoelectron spectroscopy (XPS). Copper films are deposited by ALD using the precursor mixture consisting of 99 mol% [(nBu3P)2Cu(acac)], as copper precursor and 1 mol% of Ru(η5 C7H11)(η5 C5H4SiMe3), as ruthenium precursor. The purpose in having catalytic amount of ruthenium precursor is to obtain the Ru doped Cu2O layers for subsequent reduction with formic acid at temperatures below 150 °C on arbitrary substrates. Two different approaches for the growth of ultrathin copper films have been studied in this dissertation. In the first approach, direct thermal ALD of copper has been studied by using H2 as co-reactant on Co as catalytic substrate. In the second approach, Ru-doped Cu2O is deposited by ALD using wet-O2 as co-reactant on SiO2 as non-catalytic substrate. The Ru-doped Cu2O is successfully reduced by using either formic acid or carbon-monoxide on SiO2. / Atomlagenabscheidung (ALD) von Kupfer steht im Fokus der ALD Gemeinschaft. Ultradünne Kupferschichten können als Keimschicht für die elektrochemische Abscheidung (ECD) von Kupfer in der Verbindungstechnologie eingesetzt werden. Sie können ebenfalls für Sensoren, welche auf den Effekt des Riesenmagnetowiderstandes (GMR) basieren, als nicht-ferromagnetische Zwischenschicht verwendet werden. Insbesondere Multischichtstrukturen aus ferromagnetische Kobalt und Kupfer erfordern Schichtdicken von weniger als 4,0 nm, um einen starken GMR-Effekt zu gewährleisten. Das derzeit verwendete physikalische Dampfabscheidungsverfahren für ultradünne Kupferschichten, ist besonders anfällig für eine nicht-konforme Abscheidung an den Seitenwänden und Böden von Strukturen mit hohem Aspektverhältnis. Des Weiteren kann es zur Bildung von Löchern und überhängenden Strukturen kommen, welche bei der anschließenden Kupfer ECD zu Kontaktlücken (Voids) führen können. Für die Abscheidung einer Kupfer-Keimschicht ist die ALD besonders gut geeignet, da sie es ermöglicht, ultradünne konforme Schichten auf strukturierten Oberflächen mit hohem Aspektverhältnis abzuscheiden. Dies macht sie zu einer der Schlüsseltechnologien für Struckturgrößen unter 20 nm. Im Gegensatz zur Oberflächenchemie rein metallischer ALD sind die Oberflächenreaktionen für oxidische ALD Schichten sehr gut untersucht. Die Kenntnis der Oberflächenchemie während eines ALD Prozesses ist essenziel für die Bestimmung von wichtigen Prozessparametern als auch für die Verbesserung der Präkursorsynthese ansich. Diese Arbeit beschäftigt sich mit der Untersuchung der Oberflächenchemie und Charakterisierung des Wachstums von ultradünnen Metall-Cu-Schichten mittels In-situ XPS, welche eines indirekten (Oxid) bzw. direkten Metall-ALD Prozesses abgeschieden werden, wobei die Kupfer-Oxidschichten im Anschluss einem Reduktionsprozess unterworfen werden. Hierfür wird eine Präkursormischung bestehend aus 99 mol% [(nBu3P)2Cu(acac)] und 1 mol% [Ru(η5 C7H11)(η5-C5H4SiMe3)] verwendet. Die katalytische Menge an Ru, welche in der entstehenden Cu2O Schicht verbleibt, erhöht den Effekt der Reduktion der Cu2O Schicht auf beliebigen Substraten mit Ameinsäure bei Wafertemperaturen unter 150 °C. In einem ersten Schritt wird ein direkter thermisches Kupfer ALD-Prozess, unter Verwendung von molekularem Wasserstoff als Coreaktant, auf einem Kobalt-Substrat untersucht. In einem zweiten Schritt wird ein indirekter thermischer Cu2O-ALD-Prozess, unter gleichzeitiger Verwendung von Sauerstoff und Wasserdampf als Coreaktant, mit anschließender Reduktion durch Ameinsäure oder Kohlenstoffmonoxid zu Kupfer auf den gleichen Substraten betrachtet. Die vorliegende Arbeit beschreibt das Wachstum von ultradünnen und kontinuierlichen Kupfer-Schichten mittels thermischer ALD auf inerten- SiO2 und reaktiven Kobalt-Substraten.

Copper films with a thickness in the nanometer range are required as seed layers for the electrochemical Cu deposition to form multilevel interconnects in ultralarge-scale integrated (ULSI) electronic devices. Continuously shrinking device dimensions and increasing aspect ratios of the dual-damascene structures in the copper-based metallization schemes put ever more stringent requirements on the films with respect to their conformality in nanostructures and thickness homogeneity across large wafers. Due to its intrinsic self-limiting film growth characteristic, atomic layer deposition (ALD) appears appropriate for homogeneously coating complex substrates and to replace conventional physical vapor deposition (PVD) methods beyond the 32 nm technology node. To overcome issues of direct Cu ALD, such as film agglomeration at higher temperatures or reduced step coverage in plasma-based processes, an ALD copper oxide film may be grown under mild processing conditions, while a subsequent reduction step converts it to metallic copper. In this poster, which was presented at the AVS 9th International Conference on Atomic Layer Deposition (ALD 2009), held in Monterey, California from 19 to 22 July 2009, we report detailed film growth studies of ALD copper oxide in the self-limiting regime on SiO2, TaN and Ru. Applications in subsequent electrochemical deposition processes are discussed, comparing Cu plating results on as-deposited PVD Ru as well as with PVD and reduced ALD Cu seed layer.

The atomic layer deposition (ALD) of copper oxide films from [(ⁿBu₃P)₂Cu(acac)] and wet oxygen on SiO₂ and TaN has been studied in detail by spectroscopic ellipsometry and atomic force microscopy. The results suggest island growth on SiO₂, along with a strong variation of the optical properties of the films in the early stages of the growth and signs of quantum confinement, typical for nanocrystals. In addition, differences both in growth behavior and film properties appear on dry and wet thermal SiO₂. Electron diffraction together with transmission electron microscopy shows that nanocrystalline Cu₂O with crystallites < 5 nm is formed, while upon prolonged electron irradiation the films decompose and metallic copper crystallites of approximately 10 nm precipitate. On TaN, the films grow in a linear, layer-by-layer manner, reproducing the initial substrate roughness. Saturated growth obtained at 120&deg;C on TaN as well as dry and wet SiO₂ indicates well-established ALD growth regimes. <br> &copy; 2009 The Electrochemical Society. All rights reserved.

Copper-based multi-level metallization systems in today’s ultralarge-scale integrated electronic circuits require the fabrication of diffusion barriers and conductive seed layers for the electrochemical metal deposition. Such films of only several nanometers in thickness have to be deposited void-free and conformal in patterned dielectrics. The envisaged further reduction of the geometric dimensions of the interconnect system calls for coating techniques that circumvent the drawbacks of the well-established physical vapor deposition. The atomic layer deposition method (ALD) allows depositing films on the nanometer scale conformally both on three-dimensional objects as well as on large-area substrates. The present work therefore is concerned with the development of an ALD process to grow copper oxide films based on the metal-organic precursor bis(tri-n-butylphosphane)copper(I)acetylacetonate [(nBu3P)2Cu(acac)]. This liquid, non-fluorinated β-diketonate is brought to react with a mixture of water vapor and oxygen at temperatures from 100 to 160°C. Typical ALD-like growth behavior arises between 100 and 130°C, depending on the respective substrate used. On tantalum nitride and silicon dioxide substrates, smooth films and self-saturating film growth, typical for ALD, are obtained. On ruthenium substrates, positive deposition results are obtained as well. However, a considerable intermixing of the ALD copper oxide with the underlying films takes place. Tantalum substrates lead to a fast self-decomposition of the copper precursor. As a consequence, isolated nuclei or larger particles are always obtained together with continuous films. The copper oxide films grown by ALD can be reduced to copper by vapor-phase processes. If formic acid is used as the reducing agent, these processes can already be carried out at similar temperatures as the ALD, so that agglomeration of the films is largely avoided. Also for an integration with subsequent electrochemical copper deposition, the combination of ALD copper and ruthenium proves advantageous, especially with respect to the quality of the electroplated films and their filling behavior in interconnect structures. Furthermore, the ALD process developed also bears potential for an integration with carbon nanotubes. / Kupferbasierte Mehrlagenmetallisierungssysteme in heutigen hochintegrierten elektronischen Schaltkreisen erfordern die Herstellung von Diffusionsbarrieren und leitfähigen Keimschichten für die galvanische Metallabscheidung. Diese Schichten von nur wenigen Nanometern Dicke müssen konform und fehlerfrei in strukturierten Dielektrika abgeschieden werden. Die sich abzeichnende weitere Verkleinerung der geometrischen Dimensionen des Leitbahnsystems erfordert Beschichtungstechnologien, die vorhandene Nachteile der bisher etablierten Physikalischen Dampfphasenabscheidung beheben. Die Methode der Atomlagenabscheidung (ALD) ermöglicht es, Schichten im Nanometerbereich sowohl auf dreidimensional strukturierten Objekten als auch auf großflächigen Substraten gleichmäßig herzustellen. Die vorliegende Arbeit befasst sich daher mit der Entwicklung eines ALD-Prozesses zur Abscheidung von Kupferoxidschichten, ausgehend von der metallorganischen Vorstufe Bis(tri-n-butylphosphan)kupfer(I)acetylacetonat [(nBu3P)2Cu(acac)]. Dieses flüssige, nichtfluorierte β-Diketonat wird bei Temperaturen zwischen 100 und 160°C mit einer Mischung aus Wasserdampf und Sauerstoff zur Reaktion gebracht. ALD-typisches Schichtwachstum stellt sich in Abhängigkeit des gewählten Substrats zwischen 100 und 130°C ein. Auf Tantalnitrid- und Siliziumdioxidsubstraten werden dabei sehr glatte Schichten bei gesättigtem Wachstumsverhalten erhalten. Auch auf Rutheniumsubstraten werden gute Abscheideergebnisse erzielt, jedoch kommt es hier zu einer merklichen Durchmischung des ALD-Kupferoxids mit dem Untergrund. Tantalsubstrate führen zu einer schnellen Selbstzersetzung des Kupferprecursors, in dessen Folge neben geschlossenen Schichten während der ALD auch immer isolierte Keime oder größere Partikel erhalten werden. Die mittels ALD gewachsenen Kupferoxidschichten können in Gasphasenprozessen zu Kupfer reduziert werden. Wird Ameisensäure als Reduktionsmittel genutzt, können diese Prozesse bereits bei ähnlichen Temperaturen wie die ALD durchgeführt werden, so dass Agglomeration der Schichten weitgehend verhindert wird. Als besonders vorteilhaft für die Ameisensäure-Reduktion erweisen sich Rutheniumsubstrate. Auch für eine Integration mit nachfolgenden Galvanikprozessen zur Abscheidung von Kupfer zeigen sich Vorteile der Kombination ALD-Kupfer/Ruthenium, insbesondere hinsichtlich der Qualität der erhaltenen galvanischen Schichten und deren Füllverhalten in Leitbahnstrukturen. Der entwickelte ALD-Prozess besitzt darüber hinaus Potential zur Integration mit Kohlenstoffnanoröhren.

Four cluster models for a copper(I)oxide (111) surface have been designed, of which three were studied with respect to their applicability in density functional calculations in the general gradient approximation. Formic acid adsorption on these systems was modelled and yielded four different adsorption structures, of which two were found to have a high adsorption energy. The energetically most favourable adsorption structure was further investigated with respect to its decomposition and a few reactions with adsorbed H and OH species using synchronous transit methods to estimate reaction barriers and single point energy calculations for the reaction energy.:1 Introduction 1.1 Preliminary Work 1.2 Known Reactions and Issues 1.3 Overview of Reactions and Species involved in Formic Acid Decomposition 2 Theoretical Background 2.1 The Schrödinger-Equation 2.2 Density Functional Theory 2.3 Exchange-Correlation Functionals 2.4 The Self-Consistent-Field Procedure 2.5 Geometry Optimization and Transition State Searches 2.6 Kinetics 3 Computational Details 3.1 Synchronous Transit Schemes 3.2 Transition State Searches using Eigenvector Following 4 Model System 5 Results and Discussion 5.1 Geometry of the Cu2O cluster structures 5.2 Adsorption of formic acid 5.3 Decomposition and Reaction Paths 5.3.1 Vibrational Analysis of the adsorbed Formic Acid Molecule 5.3.2 Reaction Modelling using Linear Synchronous Transit 5.3.3 Transition State Searches using Eigenvector Following 6 Summary and Outlook