Chemical and mechanical analysis on CMP polyurethane pads

Keywords

Grinding and polishing, Polyurethanes

Abstract

Chemical Mechanical Polishing (CMP) is a critical process for integrated circuit (IC) fabrication. Polishing pads play an important role in chemical mechanical polishing which has recently been recognized as the most effective method to achieve global planarization in very large-scale integrated circuit multi-level interconnects. In one model, the polishing process involves intimate contact between high points on the wafer surface and the pad material in the presence of slurry. In this study, structural, chemical and mechanical property changes of polyurethane polishing pad during CMP were studied. The polyurethane pads analyzed were a laminate structure consisting of an IC lOOO and a Suba IV pad which were pre-stacked. The top IClOOO layer contains randomly distributed pores, or voids. The CMP polishing removal rate is sensitive to pad surface structure and chemistry. White light interferometer (WLI) was used to understand the roughness of pad surface. A surface-sensitive chemical technique - Attenuated Total Reflectance Fourier Transform Infrared (ATR/Ff-IR) spectroscopy was used for the nondestructive analysis of the polymer pads. Chemical and structural changes to the pad surface were seen after polishing, though changes were restricted only to surface not in the bulk of pads.

In order to understand the structural and mechanical behaviors of new (unused) and spent (end of use) pads, various thermal techniques were employed. Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermo­gravimetric analysis (TGA) were used to qualitatively and quantitatively probe pad structural modifications with use. These thermal and dynamic studies show that the mechanical behavior of polyurethane pads was modified after CMP process. In contrast, it was found that the chemical modification reacting with use has less effect on the structural of pad materials. This thesis presents comprehensive interpretation that the mechanical factors rather than the chemical factors have the largest impact on modifying pad's elastic property and accelerating the degradation. Using this information, pads that minimize the need for conditioning would be highly desirable, since the improvement in pad life and tool throughput would significantly reduce process cost.

Notes

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Graduation Date

2001

Advisor

Richardson, Kathleen

Degree

Master of Science (M.S.)

College

College of Arts and Sciences

Department

Chemistry

Format

PDF

Pages

139 p.

Language

English

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Identifier

DP0028718

Subjects

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

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