CMP Active Diamond Characterization and Conditioner Wear
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CMP Active Diamond Characterization and Conditioner Wear Leonard Borucki1, Rumin Zhuang2, Yun Zhuang1,2, Ara Philipossian1,2, and Naoki Rikita3 1 Araca Incorporated, Tucson, AZ, 85720 2 Chemical and Environmental Engineering, The University of Arizona, Tucson, AZ, 85721 3 Mitsubishi Materials Corporation, Omiya, Japan ABSTRACT Using a pad substitute material, we measure the number of active or working diamonds on a conditioner and find that it is generally a small fraction of the total number on the disc. The number of active diamonds also increases with the applied load and varies somewhat with sliding direction. However, even among the active diamonds, most do relatively little cutting. A few diamonds on a disc do most of the deep bulk cutting, a larger fraction skim the higher areas of the pad surface and most of the diamonds on the disc apparently merely help to support the load. While all of the diamonds that make contact, cutting or otherwise, may show evidence some of mechanical wear, wear of the small number of deep bulk cutting diamonds may be responsible for declining cut rates and for surprisingly low observed conditioner lifetimes.
INTRODUCTION Pad conditioning is necessary for maintaining polish rate stability on most types of polishing pads. Pad conditioners that employ artificial industrial diamonds are constructed by bonding, plating, sintering or brazing crystals of a selected grit size, morphology and quality to a metal or ceramic substrate. Diamond is preferred because it is a very hard, wear-resistant material that is immune to chemical attack in the environments normally present in polishing tools. Nevertheless, the useful life of a polyurethane pad conditioner in most chemicalmechanical planarization processes is measured in tens of hours at best. Short lifetimes occur even though the nominal pressure on the conditioner working face may be relatively light - often less than 1 psi - and the face may contain thousands of diamonds that could plausibly be participating in cutting the pad. For example, polyurethane pad surfaces that have a total height variation of 60 µm could theoretically contact most of the diamonds on a conditioner constructed to have a mean protrusion from the substrate of 50 µm. Individual diamonds that do contact the pad would of course differ in their quantitative contribution to load balance and cutting. The details would depend on the geometry of the diamond and that of the immediately surrounding grit. Due to the large population statistics involved, however, this scenario implies that the average cut rate produced by conditioners of a fixed, carefully controlled design under given kinematic conditions should fall into an extremely tight range. This, however, is paradoxically often not the case. One of the basic facts about conditioners that may shed light on conditioner lifetimes and other characteristics concerns the actual proportion of working grit, or active diamonds, that participate in cutting the pad. Many conditioner suppliers understandably claim a
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