CMP Fundamentals and Challenges
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ABSTRACT Chemical Mechanical Polishing (CMP) as a semiconductor polishing technology has grown dramatically during the past decade. It has been a key enabling technology, facilitating the development of high density multilevel interconnects. Its widespread application has exceeded the growth of the scientific understanding. Models for silicon dioxide polishing mechanisms have built upon the work originally done for glass polishing. Recent work has augmented our insight, but our understanding is far from complete. A quantitative picture of the basic interaction mechanisms for silicon dioxide polishing does not yet exist. The models for metal polishing are now an active area of investigation. Recent work has demonstrated that more work is need to adequate explain the CMP of metals. The metal CMP mechanisms appear to be substantially more complex than originally assumed. The challenges for CMP have been to improve the performance of the technology, and increasingly this needs a foundation of scientific understanding to achieve the needed gains. We can expect that, as the scientific foundation grows, it will contribute significantly to manufacturing improvements as has been the case in other areas of semiconductor technology.
INTRODUCTION Chemical Mechanical Polishing (CMP) has emerged over the last decade as an enabling technology within the semiconductor industry. It has allowed the widespread application of high density multilevel interconnects, and has also found use in applications such as shallow trench isolation (STI). There will soon be almost 2000 polishing machines being used for CMP world wide. The technology itself has advanced tremendously as substantial improvements in capability have led to greatly improved performance with increasingly tight process control. Many semiconductor processes used in manufacturing now have over ten CMP steps within them; this revolution in semiconductor technology has occurred because of demand pull. CMP based processes can be more powerful than those processes without CMP. This advance of CMP technology has naturally been directed toward application to the semiconductor industry. The large majority of the "research and development" effort has focussed on near term process improvements, in hardware, consumables and in the CMP process itself In all of these areas the current processes in use are markedly different from those in use 810 years ago. Currently, the effort focussed on further advances in all three areas is larger than it ever has been. The basic physical and chemical mechanisms of CMP are, however, poorly understood. The polishing process as used in semiconductor applications is the sum of a very large number of polishing interactions, with a range of conditions determined by the tools used. The sum of these individual interactions creates the polished surface. The specific conditions of these individual interactions are not well understood and it is quite difficult to set up experiments and measure local interactions which correspond meaningfully to those used in
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