Chemical-mechanical wear mechanism in polyurethane polishing pad materials

Keywords

Grinding and polishing, Polyurethanes

Abstract

In the highly competitive and lucrative industry of semiconductors, the effectiveness of the Chemical Mechanical Polishing (CMP) process is crucial for developing smaller device technologies. In this study, the structure of the two-layered stacked IClOOO/Suba IV pad and its individual layers (IC 1000, Suba IV), and their interactions with liquids (pH buffers, organic solvents, slurries) and under mechanical load were investigated. To probe the relative importance of liquid penetration and hydrogen bond disruption of the urethane bridge, various methods (absorption tests, Shore hardness, Dynamic Mechanical Analysis) were applied to monitor the modifications as a function of exposure. A model was proposed based on the interaction between liquid-borne chemical species and the polyurethane backbone of the pad. Solvent molecules must first wet and penetrate the polyurethane matrix and once inside, they interact with the urethane structure by breaking the cross-link through solvation and formation of new hydrogen bonds. The bond disruption effectively destabilizes the polymer network structure and causes the observed pad swelling. The stronger the electron donating strength of the chemical species, the greater the structural destabilization and hence, a shorter pad lifetime. Results indicated that the fibrous Suba IV sub-pad has a greater impact during the polishing process by retaining and thus, providing more time for the chemical species to

disrupt cross-links in the polyurethane matrix. In so doing, the bulk properties of the Suba IV are compromised and hence, the stacked pad as well. Dynamic Mechanical Analysis (DMA) illustrated the effects of aging behavior in the pads. During storage, the polyurethane-base pads undergo aging that over time can drastically affect pad performance. Depending on the chemical make-up of the pad, the physical properties are further modified to varying extents by environmental factors (heat, oxygen and moisture) that accelerate degradation. Thus, a fundamental understanding of how the classes of pad degrading species interact both chemically and mechanically, with the pad was elucidated from the work presented. Efficiency and lifetime of the polyurethane pads may be estimated by knowing such basic chemical properties as relative Lewis base properties of the bulk solvent, active oxidizers (hydroxide) and/or other additives, as well as the pH of the polishing media. Storage of the polishing pads following fabrication is another consideration that must be accounted for because depending on conditions, the shelf-life may either be shortened or extended. Fundamental knowledge of these complex pads is crucial in furthering the advances of the semiconductor industry.

Notes

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Graduation Date

2000

Advisor

Richardson, Kathleen

Degree

Master of Science (M.S.)

College

College of Arts and Sciences

Department

Chemistry

Format

PDF

Pages

140 p.

Language

English

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Identifier

DP0028710

Subjects

Arts and Sciences -- Dissertations, Academic; Dissertations, Academic -- Arts and Sciences

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