Graduation Year

2008

Document Type

Thesis

Degree

M.Ch.E.

Degree Granting Department

Chemical Engineering

Major Professor

Vinay K. Gupta, Ph.D

Co-Major Professor

Ashok Kumar, Ph.D.

Committee Member

Andrew M. Hoff, Ph.D.

Committee Member

John T. Wolan, Ph.D.

Keywords

Chemical mechanical polishing, Conditioning, Pad wear, Contact area, Plasma synthesis

Abstract

Chemical Mechanical Planarization (CMP) has emerged as the central technology for polishing wafers in the semiconductor manufacturing industry to make integrated multi-level devices. As the name suggests, both chemical and mechanical processes work simultaneously to achieve local and global planarization. In spite of extensive work done to understand the various components and parameters affecting the performance of this process, many aspects of CMP remain poorly understood. Among these aspects of CMP is the role of abrasives in the processes of conditioning and polishing. These abrasives are present in the chemical slurry between the wafer and the pad for polishing and play an important role during the conditioning to regenerate the clogged polishing pads.

This thesis has focused on the study of abrasives, both in conditioning and polishing. The first part of the thesis concentrates on the effect of abrasive size for conditioning purposes. Diamond is being widely used as an abrasive for conditioning the polishing pad. Five different sizes of diamonds ranging from 0.25µm to 100µm were selected to condition the commercially available IC 1000 polishing pad. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) analysis were carried out on the pad to study the effect of the abrasive size on the pad morphology. In-situ 'coefficient of friction' was also monitored on the CETR bench top Tester. The final impact was seen in the form of surface defects on the polished copper wafers. As pad morphologies resulting from different conditioning affect contact areas, the second part of the thesis focuses on developing a simple method to quantify the area of contact between the wafer and pad using optical microscopy. Optical images that were obtained were analyzed for the change in contact area with the change in operating conditions. Finally, the third part of the thesis details the synthesis and characterization of nano-zirconia for potential slurry applications. Nano-zirconia was synthesized using the plasma route and then characterized using different analytical techniques like TEM and XRD. These nanoparticles were then used to make abrasive slurry for oxide CMP and the polished wafers were analyzed for surface defects.

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