Elucidating copper deposition additive structure and its effect on the mechanisms of deposition and the characteristics of the deposit

Bandas-Rivera, Christopher D.

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https://hdl.handle.net/2142/115646 Copy

Description

Title

Elucidating copper deposition additive structure and its effect on the mechanisms of deposition and the characteristics of the deposit

Author(s)

Bandas-Rivera, Christopher D.

Issue Date

2022-04-21

Director of Research (if dissertation) or Advisor (if thesis)

Gewirth, Andrew A

Doctoral Committee Chair(s)

Gewirth, Andrew A

Committee Member(s)

• Murphy, Catherine J
• Rodriguez-Lopez, Joaquin
• Su, Xiao

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Copper Electrodeposition
• Electroless Deposition of Copper
• Surface Enhanced Raman Spectroscopy

Abstract

An understanding of the interactions of copper deposition bath components is needed to further develop the field of copper metallization. The advancement of this field is critical to the success and improvement of interconnect technologies, which are an essential component of electronic devices. In this dissertation, vibrational spectroscopies are combined with electrochemical analysis to probe the interactions of organic deposition bath components during ongoing electrolytic and electroless depositions. Of particular merit is surface-enhanced Raman spectroscopy (SERS), which reports on the behavior of surface-confined species and is used in this work to clarify the effects observed from electrochemical analyses for these systems. These investigations reveal the interactions of additives correlate with their conformational structure which can be manipulated by altering the concentration of supplementary bath additives. Copper electrodeposition for the metallization of damascene and advanced packaging interconnects must achieve uniform deposition in recessed, high aspect ratio features. To this end, electrodeposition solutions are comprised of a combination of additives that interact to control the rates of deposition at different regions of the feature during its filling. In the first chapter of this dissertation, we investigate the effect of amine-based additives, known as levelers, on the catalytic function of the accelerator additives at the Cu-electrolyte interface. In the presence of the bis-(sodium sulfopropyl)-disulfide (SPS) accelerator, chronopotentiometric measurements show the potential changes from inhibition of the levelers increased with molecular weight and were greater to those of glycol-based suppressors. In situ surface-enhanced Raman spectroscopy (SERS) revealed significant conformational changes of the surface-adsorbed SPS in the presence of the amine-based levelers. This leveler-induced conformational perturbation of SPS diminishes the activity of SPS. SERS also revealed decreased coverages of surface-adsorbed SPS in the presence of the high molecular weight amine-based levelers at negative potentials, indicating that the leveler limits direct contact of SPS with the surface. Decreased coverages were also found for adsorbed chloride in the presence of all levelers considered, likely contributing to the deactivation of the accelerative effect of SPS. Secondary-ion mass spectrometry (SIMS) analysis of Cu electrodeposited from solutions comprised of a linear polyethyleneimine (PEI), SPS, and Cl– show increased S, Cl, and C content in the deposit relative to solutions absent PEI, indicating the presence of PEI results in co-incorporation of these additives. This leveler-assisted incorporation of SPS and Cl– also serves to mitigate SPS acceleration. Challenging copper electrodeposition processes for semiconductor applications require in depth understanding of the mode of operation of the organic leveling additives. In the second chapter of this dissertation, we investigate polyethylene imine (PEI) as a prototypical leveler additive using simulations, including PEI adsorption at the interface between copper as well as chloride-covered copper and water. Conformational analysis of the dihedral angles along the polymer chain allows insights into structural changes upon adsorption of the molecules in comparison with the bulk electrolyte. Distribution of the respective atoms of the polymeric molecules sorted by elements along the surface normal further provides information about the orientation. Both conformational changes and orientation depend on the degree of protonation, i.e., the pH value or acid concentration of the electrolyte. The results are compared with electrochemical and spectroelectrochemical data to confirm the accuracy of the simulations and to allow correlation to the performance in the actual deposition process. Solutions used for the electroless deposition of Cu typically consist of Ni(II) to increase deposit ductility and 2-mercaptobenzothiazole (MBT) to diminish the reduction of Cu nuclei in the solution. In the fourth chapter of this dissertation, the effects of these additives on plating rates are investigated. Linear sweep voltammetry (LSV) shows the deposition of Ni leads to inhibition of the electrolytic reduction of Cu in an alkaline solution. Similarly, LSV shows Cu deposition is inhibited yet more in the presence of MBT alone. Hysteretic voltammetry observed for solutions consisting of both Ni(II) and MBT marks a breakdown in the inhibitory effects of MBT coincident with the deposition of Ni. SERS revealed the origin of this breakdown results from significant depletion of MBT from the surface associated with the reduction of Ni. This Ni-assisted depletion of surface-adsorbed MBT results in increased plating rates of Cu.

Graduation Semester

2022-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Christopher Bandas-Rivera

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