Gold Superfill in Submicrometer Trenches: Experiment and Prediction

Abstract

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...

Superconformal Electrodeposition for 3‐Dimensional Interconnects

“…[6] In a similar fashion, sub-monolayer concentrations of Pb are known to accelerate Au deposition. [7,32] Bottom-up feature filling with gold by the two-step derivatization and plate process is in excellent agreement with shape change simulation, as shown in Figure 13. [7] The CEAC superfilling process has also been shown to apply to dry chemically-mediated deposition processes.…”

“…[7,32] Bottom-up feature filling with gold by the two-step derivatization and plate process is in excellent agreement with shape change simulation, as shown in Figure 13. [7] The CEAC superfilling process has also been shown to apply to dry chemically-mediated deposition processes. [33] The catalytic behavior of an iodine surfactant layer towards a Cu-CVD reaction on planar surfaces was first reported in 2001.…”

“…[29] Gold was also examined, since it is the metallization of choice for many compound semiconductors. [7] Figure 11. One-to-one correlation between acceleration of the Ag deposition rate from a KAg(CN) 2 electrolyte and accumulation of SeCN -catalyst on the surface as measured by LMM Se Auger transition in XPS.…”

“…The predictive power of the curvature enhanced accelerator coverage (CEAC) model [5] is shown for Cu deposition, while its generality is demonstrated by its successful extension to describe the deposition of the other Group IB conductors, Ag [6] and Au. [7] 2. The Damascene Process…”

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

“…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.…”