Date of Award

Fall 2017

Project Type

Dissertation

Program or Major

Chemical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Dale P Barkey

Second Advisor

Russell T Carr

Third Advisor

Nivedita Gupta

Abstract

The fabrication of on-chip interconnects in the semi-conductor industry employs electrodeposition of copper for fabrication of lines and vertical interconnects (vias) on scales as small as a few tens of nanometers. A significant challenge is to control the distribution of current to assure void-free bottom up filling of these features, a process commonly referred to as superfilling. The presence of a combination of additives on the copper surface regulates the copper deposition rate, and in the proper concentrations produce a high deposition rate at the bottom of features and a reduced deposition rate on the planar wafer surface and upper side-walls of the features. It is known that the adsorption of the additives results in superfilling. However, there are few direct measurements of the coverage of the respective adsorbates and limited information is available for the surface chemistry of additives at various concentrations. The present study is built on the competitive adsorption model in which adsorbed benzyl viologen (BV) or polyethylene glycol (PEG) are displaced progressively from the interface by 3-mercapto-1-propane sulfonic acid (MPS) adsorption during copper electrodeposition. Adsorption of BV and interactions between BV and MPS as well as PEG and MPS were explored by chronoamperometry.

During copper electrodeposition with simultaneous BV adsorption, the fractional surface coverage of BV was shown to be potential and temperature dependent. By fitting the data to the Langmuir model, it was shown the adsorption of BV on the copper electrode surface is a spontaneous exothermic process.

During copper electrodeposition with displacement of BV by MPS, increased MPS concentration in the electrolyte increases the driving force for MPS adsorption and BV desorption. This potential and temperature dependent displacement was shown to be a spontaneous endothermic process.

During copper electrodeposition with displacement of PEG by MPS, more negative potential, higher MPS concentration and higher temperature promotes MPS adsorption and desorption of PEG. Displacement of PEG by MPS was shown to be a spontaneous endothermic process.

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