Electrochemical Behavior of Citric Acid and Its Influence on Cu Electrodeposition for Damascene Metallization

Abstract

The electrolyte for Cu superfilling generally consists of copper sulfate, sulfuric acid, a chloride ion, an accelerator, and a suppressor. In this study, the characteristics of citric acid-based electrolytes and the interaction between citrate species and accelerators are investigated, with the ultimate goal being the replacement of both sulfuric acid and the suppressor with citric acid. Electrochemical impedance measurements were adopted to measure the changes in solution and charge transfer resistances with respect to citric acid and accelerator concentrations. In addition to a decrease in solution resistance resulting from the addition of citric acid, charge transfer inhibition was observed during Cu electrodeposition, which is likely the result of adsorption of citrate species onto Cu surface. A competitive adsorption between the citrate species and the accelerator was also observed and the new additive system was applied to the feature filling in the absence of the conventional polyethylene glycol suppressor. Using this new copper sulfate, citric acid, chloride ion, and accelerator system, trenches were successfully bottom-up filled, resulting in no internal defects.

Graphite-Polyimide Sensor

“…The presence of the two distinct operating frequency ranges for the resistance values of citric acid can be ascribed to the presence of four single-bond hydroxyl ions (OH) in its structure (Electrical Conductivity of Aqueous Solutions). The increase in the resistive values at higher frequencies can be ascribed to the presence of solution resistance (Rs) (Kim et al 2015). The change in the reactance values for citric acid can be ascribed to the adsorption capacitance (Cad) of the solution and the presence of the double-layer capacitance (Cdl) at the electrodeelectrolyte interface.…”

Study of anode processes during development of the new complex thiocarbamide­citrate copper plating electrolyte

“…Anode current output is close to 100 %. This is explained by the fact that copper forms with thiocarbamide and citric acid stable complex compounds [10][11][12] The evidence of stability of anodic process is the chronopotentiograms acquired on copper in the current density range of 2-8 mА•cm -2 [13]. There are no abrupt changes in potential on dependences, indicating copper dissolution with a uniform etching of boundaries and the volume of grain.…”

Effects of Acetic Acid, Tartaric Acid and Pb UPD on Cu Electrodeposition in Sub-Micron Trenches

“…Even though a measurable Pb content was not detected by EDS in the films grown by UPD mediation, we suspect that these films likely contain small quantities of Pb (∼1 at% or less) since previous studies using the same technique showed that some Pb was incorporated into Cu films. 23 While the use of Pb is undesirable for environmental and health related reasons, other metals that demonstrate UPD behavior on Cu might be suitable for UPD mediated deposition for IC applications. Zn has recently been demonstrated as a mediator for 2D Cu deposition by deposition schemes employing galvanic displacement of UPD deposited Zn with Cu.…”

“…[18][19][20][21][22][23] Replacing traditionally used acid-based electrolytes with weak organic acid based electrolytes has recently been studied for copper deposition in through-holes on printed circuit boards. 24,25 These studies showed that replacement of H 2 SO 4 with acetic acid improved film quality.…”