Query: Superfilling and the Curvature Enhanced Accelerator Coverage Mechanism

Candidate papers:

abstract: The Electrochemical Society Interface Winter 2004 tate of the art manufacturing of semiconductor devices involves the electrodeposition of copper for on chip wiring of integrated circuits. In the Damascene process, interconnects are fabricated by first patterning trenches and vias in a dielectric medium and then filling by metal electrodeposition over the entire wafer surface. This is followed by a planarization step that leaves an array of wires and interlevel vias embedded in the dielectric matrix. The metallization process, pioneered by IBM, depends on the use of electrolyte additives that affect the local metal deposition rate, thereby resulting in superfilling, or bottom up void free filling of trenches and vias.1,2 An example of this remarkable deposition behavior is given in Fig. 1 where growth as a function of electrodeposition time and feature aspect ratio reveals preferential metal deposition at the bottom of the trenches followed by bump formation above the filled trench.3 In the early years of copper Damascene technology an understanding of the superfilling process lagged behind its implementation due to a combination of factors. The first generation of electrolytes contained numerous components and general knowledge of both the chemistry and processing conditions was significantly constrained by proprietary concerns. As a result, early modeling studies focused on traditional leveling theory where the location dependent growth rate derived from diffusion limited accumulation and consumption of an inhibiting species on the metal surface.2,4,5 In these studies it was necessary to empirically modify the area blockage leveling theory to describe feature filling.2,4 Despite these modifications, detailed studies of shape evolution and the observation of bump formation above the filled trenches made it clear that superfilling could not be rationalized by traditional transport limited leveling Superfilling and the Curvature Enhanced Accelerator Coverage Mechanism
author_names: Thomas P Moffat

Daniel Wheeler

Daniel Josell
title: Superfilling and the curvature enhanced accelerator coverage mechanism
year: 2004

abstract: Abstract Superconformal electrodeposition is explained by the curvature enhanced adsorbate coverage (CEAC) mechanism. A CEAC model is used to quantitatively explain shape evolution during bottom up "superfill" of trenches and vias. The bottom up filling dynamic is seen to be a consequence of competitive adsorption between a rate suppressing polyethylene glycol chloride layer (PEG Cl) and a depassivating or rate accelerating species comprised of sulfonate terminated propane thiol/disulfide and chloride (SPS Cl) The SPS is the stronger surfactant and it adsorbs concurrently with displacement of the more rapidly formed PEG Cl layer; growth on non planar geometries thus leads to enrichment of SPS on advancing concave surfaces and dilution on convex sections. Because the metal deposition rate rises monotonically with the local accelerator (SPS Cl) surface coverage, this yields positive feedback that naturally gives rise to desirable bottom up superfilling. As the accelerating action of SPS can also be quenched by the addition of a cationic surfactant (LEV) additive concentrations can be optimized to allow SPS derived bottom up superfilling followed by LEV induced SPS deactivation. The LEV addition can thus be used to inhibit overshoot that otherwise would result in undesirable bump formation above the features. This paper presents a summary of electroanalytical experiments and simulations designed to determine the mechanism and rate constants of the adsorbate interactions during copper deposition in the PEG Cl SPS LEV system as well as predictions of feature filling using the CEAC shape change model.
author_names: Thomas P Moffat

Daniel Wheeler

Soo-Kil Kim

Daniel Josell
title: Curvature enhanced adsorbate coverage mechanism for bottom up superfilling and bump control in damascene processing
year: 2007

abstract: The influence of a catalyst deactivating leveling additive in electrodeposition is explored in the context of the previously developed curvature enhanced accelerator coverage model of superconformal film growth. Competitive adsorption between a rapidly adsorbed suppressor, rate accelerating catalyst, and catalyst deactivating leveler is examined. Rate equations are formulated where the leveling agent is capable of deactivating the adsorbed catalyst by either direct adsorption from the electrolyte or by deactivation/displacement during surface area reduction that accompanies advancing concave surfaces. The influence of a prototypical cationic surfactant leveler on electrochemical kinetics and feature filling is examined for copper electrodeposition from an electrolyte containing polyethylene glycol chloride bis(3 sulfopropyl)disulfide (PEG Cl SPS)
author_names: Thomas P Moffat

Daniel Wheeler

Soo Kyum Kim

Daniel Josell
title: Curvature Enhanced Adsorbate Coverage Model for Electrodeposition
year: 2006

abstract: Bottom up superconformal feature filling during electrodeposition, called "superfilling," that is used for industrial processing of damascene copper interconnects has also been demonstrated during electrodeposition of silver and gold. The curvature enhanced accelerator coverage (CEAC) mechanism has been proposed to underlie all three processes and has been used to quantitatively predict observed filling of patterned features. The key feature of the CEAC mechanism is redistribution of adsorbed additives through changes of local surface area as dictated by mass conservation and the relative strengths of adsorption. Previous studies of CEAC mediated superfilling have neglected adsorbate diffusion along the surface that might arise during deposition due to the CEAC induced gradients in surface coverage. This paper extends the CEAC model to include such diffusion, applying the resulting formulation to understand differences in the geometries of experimental superfilling systems.
author_names: Daniel Josell

Thomas P Moffat

Daniel Wheeler
title: Superfilling When Adsorbed Accelerators Are Mobile
year: 2007

abstract: Interesting phenomena were observed during an investigation on the accelerating effects of 3 mercapto 1 propane sulfonic acid (MPSA) i.e. different aging times of MPSA result in different filling profiles. When MPSA wasadded to the electrolyte immediately before electrodeposition, subconformal deposits appeared, whereas MPSA aged over 12 h enabled superfilling. From UV visible analysis, over 99% MPSA was converted to bis(3 sulfopropyl)disulfide (SPS) within 12 h through the reaction with Cu 2 which means that SPS was, in terms of "visible" superfilling, the real accelerator. This arose from the fact that SPS experienced adsorption first, while MPSA underwent Cu 2 reduction first at the trench entrance.
author_names: Soo-Kil Kim

Jae Jeong Kim
title: Superfilling Evolution in Cu Electrodeposition Dependence on the Aging Time of the Accelerator
year: 2004

abstract: The effects of plating process on the surface coverage of the accelerator were investigated in terms of Cu superfilling for device metallization. When a substrate having 500 nm wide trench patterns on it was immersed in an electrolyte containing poly (ethylene glycol) (PEG) chloride ion bis(3 sulfopropyl) disulfide (SPS) additives without applying deposition potential for such a time of about 100s, voids were generated inside of the electrodeposit. In time evolved electrochemical analyses, it was observed that the process (immersion without applying potential) in the electrolyte led to the build up of high initial coverage of SPS Cl on the surface, resulting in the fast saturation of the coverage. Repeated experiments suggested that the fast saturation of SPS Cl failed in superfilling while a gradual increase in the SPS Cl coverage through competition with initially adsorbed PEG Cl enabled it. Consequently, superfilling was achievable only in the case of applying the plating potential as soon as the substrate is dipped in an electrolyte to prevent rapid accumulation of SPS Cl on the surface.
author_names: Sung-Ki Cho

Myung Jun Kim

Hyo-Chol Koo

Soo-Kil Kim

Jae Jeong Kim
title: An Empirical Relation between the Plating Process and Accelerator Coverage in Cu Superfilling
year: 2012

abstract: Electroanalytical measurements and feature filling experiments have been conducted to study the effect of dodecyltrimethylammonium chloride (DTAC) a quaternary ammonium cationic surfactant, on Cu deposition in the presence of various combinations of superfilling additives. A variety of other surfactants, cetyltrimethylammonium chloride, cetyltrimethylammonium hydrogen sulfate, and sodium dodecyl sulfate were examined to reveal the significance of head group charge, counterion, and chain length for the adsorption and interaction of levelers with the accelerator bis(3 sulfopropyl) disulfide (SPS) Dodecyltrimethylammonium chloride (DTAC) saturated surfaces yield substantial inhibition of Cu deposition that is similar in magnitude to that provided by polyethylene glycol (PEG) Cl. This suggests that such layers operate by physically limiting access of Cu 2+ to the Cu surface. However, the addition of DTAC and related cationic surfactants quench the characteristic voltammetric hysteresis of the PEG Cl SPS system. This is attributed to ion pairing between the cationic head group of the surfactants and the anionic tail group of SPS, resulting in the deactivation of SPS. Deactivation may occur either by DTAC accumulation from the electrolyte or by lateral interaction during area reduction that occurs on advancing concave surfaces in accordance with the curvature enhanced adsorbate coverage mechanism. The combined process may be optimized to enable the superfilling dynamic to be sustained while overfill bump is effectively attenuated.
author_names: Soo Kyum Kim

Daniel Josell

Thomas P Moffat
title: Cationic Surfactants for the Control of Overfill Bumps in Cu Superfilling
year: 2006

abstract: To avoid complications brought about by employing organic additives, microcontact printing using a flat stamp was used in forming trench selective Cu superfilling on damascene structure. Self assembled monolayers of 1 decanethiol transferred on top surface of the trench could withstand the H 2 SO 4 electrolyte and were used as a barrier for current transfer below a certain potential that was not yet dominated by the tunneling current. Subsequent electrodeposition on the printing area was successfully inhibited. The resulting filling profile was a defect free superfilling with bumps on top. This is comparable to the three additive system consisting of accelerator and two component suppressor.
author_names: Soo-Kil Kim

Jae Jeong Kim
title: Additive Free Superfilling in Damascene Cu Electrodeposition Using Microcontact Printing
year: 2004

abstract: Accelerator dominant bottom up copper superfilling of TSVs was demonstrated. Because of the 100 times large dimensions compared to on chip interconnections, strong inhibition on the top surface is needed and the superfilling of TSVs are generally achieved by addition of levelers in the plating bath. Recently, we reported that accelerator can be deactivated by reverse pulses and the deactivation needs solution agitation. It was expected that reverse pulses deactivate the acceleration selectively on the top surface and the acceleration around via bottoms was preserved and obvious bottom up superfilling was demonstrated by three step plating process. Some levelers, such as PEI (Polyethyleneimin) is known to suppress the deposition strongly. We verified that PEI deactivated the accelerator and explored the use of PEI to deactivate the accelerator. In this study, we demonstrated that the bottom up superfilling by the modified three step process in which a PEI bath was used instead of the reverse pulse proposed in our previous study.
author_names: Masanori Hayase

Naoki Mizukoshi

Masayuki Nagao
title: Copper deep via superfilling by selective accelerator deactivation
venue: 2011 IEEE International 3D Systems Integration Conference (3DIC) 2011 IEEE International
year: 2012

abstract: The impact of branched polyethyleneimine (PEI) on Cu electrodeposition from an acidified cupric sulfate electtrolyte containing a combination of superfilling additives, specifically polyethylene glycol, bis(3 sulfopropyl)disulfide, and chloride (PEG Cl SPS) is examined. Electroanalytical measurements reveal that adsorption of cationic PEI leads to inhibition of the metal deposition reaction to an extent similar to that provided by PEG Cl adsorption. However, unlike the PEG Cl suppressor, PEI is shown to deactivate adsorbed SPS accelerator. As a result, addition of PEI quenches the hysteretic voltammetric response that is a signature of competitive adsorption in the PEG Cl SPS additive system. Trench filling experiments in a PEI PEG Cl SPS electrolyte demonstrate that the deactivating interaction between PEI adsorption and adsorbed SPS can be optimized to prevent overfill bump formation without substantial detrimental impact on bottom up, void free feature filling.
author_names: Soo Kyum Kim

Daniel Josell

Thomas P Moffat
title: Electrodeposition of Cu in the PEI PEG Cl SPS Additive System Reduction of Overfill Bump Formation During Superfilling
year: 2006