Electrochemical Atomic Layer Deposition of Copper: A Lead-Free Process Mediated by Surface-Limited Redox Replacement of Underpotentially Deposited Zinc

Venkatraman, Kailash; Gusley, Ryan; Yu, Lu; Dordi, Yezdi; Akolkar, Rohan

doi:10.1149/2.0021612jes

Cited by 22 publications

(27 citation statements)

References 35 publications

(43 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…From the slope of this curve, an equivalent etch rate was computed to be 0.103 (10.3%) per etch cycle. Since the original un-etched electrode was prepared by depositing 10 atomic layers of Cu via e-ALD, 5 one expects ∼10 cycles of e-ALE to be required to etch this film completely which is consistent with the measured etch rate of ∼10% per e-ALE cycle. This suggests an etch rate of ∼1 Cu monolayer per e-ALE cycle.…”

Section: Resultssupporting

confidence: 69%

See 1 more Smart Citation

Communication—Electrochemical Atomic Layer Etching of Copper

Gong

Venkatraman

Akolkar

2018

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

A novel process for the electrochemical atomic layer etching (e-ALE) of copper (Cu) is presented. In this process, Cu first undergoes surface-limited sulfidization to form a monolayer of copper sulfide (Cu 2 S). The Cu 2 S layer is then selectively etched in hydrochloric acid without etching the underlying Cu. The steps of surface-limited sulfidization of Cu and selective etching of the resulting Cu 2 S are repeated sequentially to achieve a net etch rate of close to one Cu monolayer etched per e-ALE cycle. Surface-limited etching is shown to minimize roughness amplification thereby preserving the near-atomic flatness of the original Cu electrode. Atomic layer etching (ALE) processes are critically important for the precise tailoring of materials and structures in nano-electronics. 1For atomically precise etching of metals, plasma-based approaches are available which generate nonvolatile etch products thereby contaminating the metal surface. Hess and co-workers have developed a two-step process that etches copper (Cu) films with chlorine and hydrogen plasmas at low temperature (below 20• C). This process generates a volatile etch product that minimizes surface contamination. 2In most plasma-based approaches, the metal etching rate is higher than 1 nm per etch cycle. Such high etch rates do not provide the requisite atomic-scale control over etching required in ALE. While plasma-assisted ALE processes for oxides are mature, 1 ALE of metals is still in its infancy and numerous development efforts are currently underway. 3In this communication, we report on an electrochemical approach for the layer-by-layer etching of Cu with atom-scale control over the etching rate. The two-step approach consists of surface-limited electrochemical sulfidization of Cu followed by selective etching of the resulting copper sulfide (Cu 2 S) monolayer. Surface-limited sulfidization has been used previously for fabricating semiconductors. 4 Feasibility of the electrochemical ALE of Cu is demonstrated and process performance parameters (etch rate, surface roughness) are characterized. ExperimentalCyclic voltammetry and chronoamperometry.-Surface-limited sulfidization of Cu was studied using cyclic voltammetry (CV) performed using a three-electrode cell consisting of a sputter-deposited Cu substrate as the working electrode, a platinum (Pt) wire as the counter electrode, and a saturated Ag/AgCl reference electrode (Fisher Scientific). The electrolyte contained 0.1 M potassium hydroxide (KOH, Fisher Chemical) and 0.5 mM sodium sulfide (Na 2 S, SigmaAldrich) and was prepared using de-aerated DI water. A VersaSTAT 3 potentiostat was used for all electroanalytical measurements. All potentials reported below are referenced to the standard hydrogen electrode (SHE). The Cu substrate was rinsed first with ethanol and then with DI water before drying with N 2 . The cleaned substrate was immersed in 2 M sulfuric acid (H 2 SO 4 , Fisher Scientific) for 1 min to remove surface Cu oxides. A potential of -1.2 V vs. SHE was applied for 100 s to further ...

show abstract

Section: Resultssupporting

confidence: 69%

“…5 Cu e-ALD for 10 cycles was performed on a sputter-deposited Ru substrate to form a ∼2 nm Cu film with RMS surface roughness of ∼0.2 nm. Surface-limited sulfidization of Cu was performed at -0.75 V vs. SHE in an alkaline Na 2 S-containing electrolyte (composition reported above).…”

Section: Methodsmentioning

confidence: 99%

Communication—Electrochemical Atomic Layer Etching of Copper

Gong

Venkatraman

Akolkar

2018

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

show abstract

“…In recent development, R. Akolkar et al employed a one-cell SLRR approachfor the growth of Cu with Zn UPD as a sacrificial layer in alkaline media thus realizing a Pb-free Cu deposition routine [81]. Following this protocol each SLRR step provides a monolayer of Cu on the substrate surface.…”

Section: Cu Depositionmentioning

confidence: 99%

Recent Advances in the Growth of Metals, Alloys, and Multilayers by Surface Limited Redox Replacement (SLRR) Based Approaches

Dimitrov

2016

Electrochimica Acta

View full text Add to dashboard Cite

A B S T R A C TIn the realm of ever increasing importance of nanotechnology, the deposition of ultrathin metal/alloy layers with perfect structure and unique functionality becomes an objective of paramount importance. In the last decade many research groups have been working on the development and application of a new method for epitaxial thin film growth that employs a surface limited redox replacement (SLRR) as a building block reaction. The multiple repetition of this reaction enables the controlled deposition of a monolayer of metal or alloy per cycle. Work in the field has been done on the development of SLRR deposition protocols along with understanding and modelling of the SLRR reaction kinetics, on comparative studies of SLRR based routines, and on other deposition approaches. Most recently, the development of SLRR was extended to the application of all-electroless approaches for carrying out the SLRR (ESLRR). In this paper an overview of all SLRR, ESLRR and related approaches is presented. The description of the background and reaction formalism introduces the method with emphasis on its general applicability and limitations. The discussion then continues with the description of experimental approaches for carrying out a deposition process by SLRR. In this section specific consideration is given to the deposition by shuttling of the working electrode, the flow-cell configuration, the one-cell configuration, and the all-electroless approaches for realizing the repetitive application of a single-cycle SLRR reaction. Next, the ability of these approaches to produce epitaxial, flat and uniform deposits will be discussed through results of electrochemical, in-situ scanning tunneling microscopy, X-ray Photoelectron Spectroscopy and other characterization experiments showing advantages and limitations of SLRR growth in a variety of systems classified into three categories. In the first of these categories Cu, Ag, and Au are used as model systems to introduce the deposition by SLRR. In the second category Pd and Ru deposition by SLRR has been discussed. In the third category all studies concerning a variety of scenarios for Pt deposition by SLRR are presented and in the last part of that section deposition of alloys and multilayers is critically discussed. The paper then continues with a section presenting and discussing modelling approaches of studying the kinetics of a single-cycle SLRR reaction and concludes with the presentation of the extension of modelling to a system where multi-cycle SLRR deposition processes have been investigated. The analysis in this part focuses on the kinetic parameters of the replacement reaction like rate constant, order of the reaction, type of adsorption behavior of the sacrificial metal etc. Finally, this section concludes with a discussion of the mechanistic aspects of the SLRR reaction and more specifically on the factors impacting the deposition process and in turn the resulting structure, morphology, uniformity and continuity of the accordingly grown thin films. The paper a...

show abstract

“…Voltammetry studies of Zn upd on Co and Ru substrates.-Zn is known to exhibit underpotential deposition on Cu, 42,44,45 Ni, 46 Pt, 47,48 and Au. 48 In our work, LSV measurements of Zn upd were performed on PVD-Ru and PVD-Co substrates.…”

Section: Resultsmentioning

confidence: 99%

“…The growth protocol for e-ALD Co consisted of STEP-1 and STEP-2 repeated cyclically: The relatively large Co 2+ concentration employed in STEP-2, i.e., 100 mM, accelerated the SLRR kinetics compared to previously reported SLRR kinetics. 42 Thus, the SLRR process was terminated after just 60 s which allowed the redox replacement reaction to proceed to near completion.…”

mentioning

confidence: 99%

Electrochemical Atomic Layer Deposition of Cobalt Enabled by the Surface-Limited Redox Replacement of Underpotentially Deposited Zinc

Venkatraman

Dordi

Akolkar

2017

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

Electrochemical atomic layer deposition (e-ALD) process for fabricating cobalt (Co) nano-films is reported. The e-ALD process employs a two-step approach in which underpotential deposition (UPD) is first used to form a sacrificial adlayer of zinc (Zn) on a ruthenium (Ru) substrate. The sacrificial Zn adlayer then undergoes spontaneous surface-limited redox replacement (SLRR) by nobler Co. This provides an atomic layer of Co on the substrate surface. The two-step process is repeated cyclically to build multilayers of Co. The unique feature of the e-ALD approach presented herein is that it utilizes Zn as the sacrificial adlayer instead of Pb or Cu used conventionally in the e-ALD sequence of noble metals. The use of sacrificial Zn uniquely renders its redox replacement by Co to be thermodynamically favorable, thereby enabling Co e-ALD. In the present report, we discuss the electrochemical characteristics of the UPD and SLRR process steps, the e-ALD deposition rate and the deposit surface roughness. The Co deposits formed via e-ALD do not exhibit roughness amplification during the first 10 cycles of e-ALD, which is indicative of atomic-scale layer-by-layer growth of Co on the underlying Ru substrate. High-performance integrated circuits utilize nano-scale, currentcarrying copper (Cu) interconnects. In accordance with the Moore's law, 1 miniaturized interconnects are required in modern devices to obtain superior device performance. The continued shrinkage in the size (cross-sectional area) of each interconnect leads to an increase in its electrical resistance. This detrimentally impacts the electrical performance of the integrated circuit.2 Furthermore, aggressive interconnect size scaling below the 10 nm node poses challenges to void-free interconnect fabrication. State-of-the-art interconnects are fabricated of Cu metal due to its low electrical resistivity and superior electromigration resistance.3 The interconnect signal delay (τ) is given by τ = RC, where R is the interconnect resistance and C is the capacitance of the surrounding inter-layer dielectric. The interconnect resistance R increases dramatically for Cu interconnect dimensions below 40 nm due to the substantial increase in the electrical resistivity of Cu at such narrow dimensions. The resistivity increase is typically attributed to electron scattering processes at grain boundaries and at interfaces within the Cu interconnect structure. Such scattering processes become dominant when the interconnect dimension approaches the electron mean free path (EMFP = 39 nm at room temperature) in Cu.4,5 As a consequence, the interconnect signal delay increases. To overcome this critical issue, an interconnect material which exhibits lower electrical resistivity at narrow (sub 10 nm) dimensions is required. Cobalt (Co) is considered as a promising alternative interconnect material to replace the conventionally used Cu.6,7 At narrow dimensions, i.e., below 10 nm, Co exhibits comparable or lower electrical resistivity compared to Cu, largely attributed to the lower ...

show abstract

Electrochemical Atomic Layer Deposition of Copper: A Lead-Free Process Mediated by Surface-Limited Redox Replacement of Underpotentially Deposited Zinc

Cited by 22 publications

References 35 publications

Communication—Electrochemical Atomic Layer Etching of Copper

Communication—Electrochemical Atomic Layer Etching of Copper

Recent Advances in the Growth of Metals, Alloys, and Multilayers by Surface Limited Redox Replacement (SLRR) Based Approaches

Electrochemical Atomic Layer Deposition of Cobalt Enabled by the Surface-Limited Redox Replacement of Underpotentially Deposited Zinc

Contact Info

Product

Resources

About