Gold Superfill in Sub-Micrometer Trenches

Wheeler

2006

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Bottom-up deposition of gold in fine trenches, also called "superfill," was recently demonstrated using a submonolayer coverage of preadsorbed, deposition-rate-accelerating lead followed by gold electrodeposition. The present study has used experiments on planar substrates to quantify the effect of Pb adsorption on the Au deposition rate and the rate at which the adsorbed Pb was consumed during the Au deposition process. The values obtained have been incorporated into the curvature enhanced accelerator coverage mechanism of superfill where they were used to quantitatively predict the nonconformal, bottom-up deposition observed during filling of the patterned features. The results indicate the potential of the process for damascene interconnect fabrication in GaAs, GaN, and related technologies.The bottom-up "superfill" process for fabrication of copper interconnects 1 is now the standard for state-of-the-art interconnect fabrication within the silicon-based semiconductor industry. However, gold is used to form a variety of ohmic and Schottky contacts for semiconductor technologies based on, for example, gallium arsenide 2 and gallium nitride 3 as well as for chip-level wire bonding; hence, an interest exists in a process for fabricating gold interconnects. A bottom-up, "superfill" process for Au that would be appropriate for fabricating interconnects in damascene processing was recently demonstrated for Au superfill in fine trenches, 4 as was an alternative process. 5 The present paper uses measurement techniques and models first developed to understand the related copper superfill process in order to elucidate the relevant kinetics of the new Au superfill process. The kinetics obtained are then used to quantitatively predict the Au superfill process.While several mechanisms have been proposed to underlie the superfill process during electrochemical deposition ͑ECD͒ of copper, 6-9 the curvature-enhanced accelerator coverage ͑CEAC͒ mechanism 8,9 has been demonstrated to quantitatively predict superfill during electrodeposition of copper 8-12 and silver 13-16 and chemical vapor deposition of copper. 17 The CEAC mechanism predicts that an electrolyte-additive system can yield superfill when two requirements are met: ͑i͒ the additive adsorbs on the deposit surface and accelerates the local deposition rate and ͑ii͒ the adsorbed additive remains on the surface of the deposit during deposition. Under these circumstances, the CEAC predicts that the decreasing area of the metal surface at the bottoms of filling features will lead to locally increasing coverage of the adsorbed accelerator, which will lead to increased local deposition rate and bottom-up superfill. Predictive models based on the CEAC mechanism use kinetics obtained from studies on planar substrates; no additional parameters are needed for simulating feature filling or more general interface evolution. Because superfill processes based on the CEAC mechanism derive from surface segregation of adsorbates, they not only eliminate void and seam formation but mig...

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confidence: 96%

Gold Superfill in Submicrometer Trenches: Experiment and Prediction

Wheeler

2006

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“…21,41 For example, adsorption of anions or dilute metal ion additives, via under potential deposition (upd), enables fabrication of structures such as Au nanospikes of moderate aspect ratio using a Pb additive 42,43 and highly faceted, moderately elongated dendrite-like grains using Tl as an additive 44 on unpatterned substrates. This work, part of a broader study of the impact of Pb 2+ and Tl + additives on the morphology of Au electrodeposits on planar and patterned substrates, [32][33][34] demonstrates the use of dilute Tl + for controlled growth of single crystal nanowires of much higher aspect ratio on unpatterned surfaces. The additive selection is based on its surfactant quality, derived from the absence of Tl-Au intermetallic phases electrolyte at pH 9.…”

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confidence: 99%

Morphological Transitions during Au Electrodeposition: From Porous Films to Compact Films and Nanowires

Levin

2015

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Gold electrodeposition was studied in a sulfite electrolyte to which micromolar concentrations of Tl 2 SO 4 were added. Hysteresis and a regime of negative differential resistance (NDR) evident in electroanalytical measurements are correlated with deposit morphology and interpreted through measurements of thallium underpotential deposition (upd). Deposit morphologies range from specular surfaces to highly faceted dendrite-like grains of moderate aspect ratio and, for potentials within the NDR region, sub-50 nm diameter, high aspect ratio 110 oriented single crystal nanowires. The nanowires exhibit an epitaxial relationship to the substrate that permits one step fabrication of surfaces densely covered with high aspect ratio nanowires having controlled orientations. The NDR and nanowires are a consequence of the non-monotonic relationship between Tl coverage and growth velocity; at low coverage Tl accelerates Au deposition while at higher coverage it inhibits deposition. Immiscibility of the Tl and Au supports on-going surface segregation during area expansion that accompanies nanowire growth leading to greater dilution of the additive coverage and more rapid growth at the nanowire tips, while the sidewalls remain passivated by a saturated Tl coverage. Interest in nanostructures is driven by the unique properties associated with high surface area to volume materials that express quantum or mesoscale phenomena of importance to diverse subjects ranging from biology and medicine 1-3 to optics and energy conversion. [4][5][6][7] Of particular interest is the substantial literature on solution or vapor processing to yield a wide variety of nanostructures including high aspect ratio nanowires. 4,8,9 Solution-based, chemical reduction processes are attractive because they are inexpensive and scalable.9-18 Subsequent processing involving particle packing and/or substrate interactions can lead to higher order organization and colloidal crystals.19 Alternatively, nanostructures can be grown on or in surfaces that have been shaped by lithography or other means to obtain control of orientation and/or placement.8 Electrochemical processing may involve throughmask plating in patterned templates 20,21 or superconformal electrodeposition of metals and alloys [22][23][24][25][26][27][28][29][30][31] including gold 32-34 in high aspect ratio features. However, these processes require nanoscale patterned topography to create such structures and the associated patterning often comes with increased processing complexity.Controlled anisotropic growth and orientation, if not position, is possible through vapor-liquid-solid (VLS) growth processes. Fabrication of semiconductor and oxide nanowires typically uses dewetting of a low melting point metal catalyst where the resulting clusters set the feature size while epitaxy to the underlying substrate can control the growth orientation. 5,[35][36][37] More recently, an electrochemical electrolyte-liquid-solid analog has been demonstrated for growth of Ge nanowires. [38][39][40] In another ap...

“…5 When this acceleration is combined with mass conservation of the surfactant in the presence of electrode area change, superconformal Au void-free feature filling occurs in accord with the CEAC model. 6,7 Practically speaking, two short-comings of the system are electrolyte toxicity and the aggressive nature of the alkaline media towards photoresist materials. 3,4 In order to address these challenges a sulfite-based Au electrolyte was evaluated by Hu and Ritzdorf.…”

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confidence: 99%

Superfilling Damascene Trenches with Gold in a Sulfite Electrolyte

2013

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Superconformal Au deposition is demonstrated in a Na 3 Au(SO 3 ) 2 -Na 2 SO 3 based electrolyte using underpotential deposited (upd) Pb to catalyze the reduction of Au(SO 3 ) 2 3− . Micromolar additions of Pb 2+ to the electrolyte give rise to acceleration of the Au deposition rate as evidenced by hysteretic voltammetry and rising chronoamperometric transients that convolve the diffusion, adsorption kinetics and coverage isotherm of the upd Pb catalyst. The catalytic activity on the Au deposition reaction may be quenched, or reset, by stepping the potential to more positive values to deactivate or strip the Pb catalyst. Void-free Damascene trench superfilling at various fixed potentials and Pb 2+ concentrations is demonstrated and shown to be congruent with the curvature enhanced accelerator model (CEAC) of superconformal growth. This includes enhanced deposition due to catalyst enrichment on concave surface segments at the bottom corners of the trenches, followed by rapid bottom-up growth and, for certain conditions, bump formation above the filled trenches.Superconformal film growth by additive-based electrodeposition underlies the successful implementation of Cu in state-of-the-art multilevel interconnect metallization for the silicon based semiconductor industry. 1,2 In contrast, electrodeposited Au remains the metallization of choice for interconnects and contacts in compound semiconductors and related optoelectronics applications as detailed in recent reviews. 3,4 To date the majority of these applications have involved through-mask-electrodeposition. However, increasing circuit densification demands a move to three-dimensional metallization to enable the fabrication of interconnect networks of arbitrary design and complex architectures. 1 Implementation of the Damascene process calls for a Au electroplating chemistry that can provide void-free filling of recessed surface features. Previously two different Au electrolytes have been examined and shown to be capable of void-free feature filling. The first derives from the original observation of McIntryre and Peck that underpotential deposited (upd) Pb catalyzes Au deposition from KAu(CN) 2 -based electrolytes. 5 When this acceleration is combined with mass conservation of the surfactant in the presence of electrode area change, superconformal Au void-free feature filling occurs in accord with the CEAC model. 6,7 Practically speaking, two short-comings of the system are electrolyte toxicity and the aggressive nature of the alkaline media towards photoresist materials. 3,4 In order to address these challenges a sulfite-based Au electrolyte was evaluated by Hu and Ritzdorf. 8 The addition of mercaptopropane sulfonic acid (MPS) to a commercial electrolyte comprised of Na 3 Au(SO 3 ) 2 , Na 2 SO 3 , a pH buffer and Tl + as a "grain refiner" enabled void-free superconformal deposition. Electroanalytical measurements indicate that MPS serves as an inhibitor that facilitates feature filling in line with traditional leveling concepts 9 although no quantitative modeli...