Micro Feature Pad Development and Its Performance in Chemical Mechanical Planarization
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Micro Feature Pad Development and Its Performance in Chemical Mechanical Planarization Sunghoon Lee and David A. Dornfeld Laboratory for Manufacturing Automation Department of Mechanical Engineering University of California at Berkeley Berkeley, CA 94720-1742 ABSTRACT There are many elements affecting CMP performance such as the slurry, pad, process parameters and pad conditioning. Among these, the pad is considered to be one of the most important parts because of its deterioration during polishing. However, specific pad design techniques have not yet been fully investigated. In this paper, conventional polyurethane pad characteristics are investigated. A pad design based on this analysis is suggested. Prototype pads are fabricated using micro molding and are used in an experiment for examining the pad deterioration mechanism.
INTRODUCTION Chemical mechanical planarization (CMP) has been considered to be one of the most capable IC fabrication technologies for achieving planar surfaces essential for very large scale integrated (VLSI) circuits. During the CMP process, a wafer is placed face side down on a pad with high pressure. The wafer and pad rotate simultaneously with slurry. High pressure, rotational speeds, and chemical-mechanical reactions enhanced by the slurry result in a planarized surface on a wafer [1]. Generally, a pad has a wavy surface profile consisting of peaks and valleys. Real contact between the wafer and pad occurs on the crests of the pad (i.e. contact region). Fresh slurry temporarily collects in the valleys (i.e. reservoir region) and is supplied to the active regions through the relative movement of the wafer and pad, traveling between the peaks and valleys (i.e. transition region). However, degradation in the pad is generated primarily by abrasion in the active region. As a result, the real contact area increases and the real contact pressure drops rapidly during the CMP process, causing the material removal rate (MRR) to decrease dramatically in the absence of a conditioning process [2]. The pad deterioration mechanism mentioned above causes many problems such as removal rate fluctuations (process repeatability), scratches from diamond conditioning grit (pad maintenance), erosion, dishing (chip-topography dependence), and so on. A novel set of design rules is suggested in this paper for pad fabrication and this design is based on analysis of a conventional pad. This new pad aims to satisfy the demands for a new pad with features such as constant real contact area, no-diamond conditioning, topography independence and end point detection functionality. Then, a micro molding technology is used to fabricate micro features on the pad which follows the designs rules.
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Pad degradation mechanism in contact area is experimentally investigated with these pads. Micro scale features on a pad make contact with the wafer and various types of geometries on the pad are fabricated to verify the pad deterioration mechanism.
PAD CHARACTERIZATION To provide design rules for pad fabrication,
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