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Ph.D. 1972, Harvard University
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| Current Research Interests |
| Fabricating advanced materials and structures has become an
important part of chemical engineering and is the main focus of our research.
The major application of our work is submicron patterning for semiconductor
manufacturing. Additionally, we are interested in the patterning of micro-electromechanical
systems (MEMS), and of other types of substrates. At present, the most manufacturing-relevant approach to submicron patterning utilizes a combination of optical lithography to provide a photoresist mask, followed by pattern transfer to the underlying semiconducting, conducting, or insulating film using plasma etching. In our work, we focus on the plasma etching step, in which the plasma creates chemically reactive species and energetic ions which interact synergistically to produce an anisotropic pattern transfer. The anisotropy preserves the characteristic small dimensions required for high-density semiconductor devices and their interconnections. In addition to anisotropy, the etching step must be selective with respect to other materials (e.g., the photoresist mask, underlying films), and must not introduce damage or contamination. The hallmark of the semiconductor industry has been the ability to shrink devices and circuits by a factor of four every three years. Such "shrink technology" has been the basis for the remarkable advances in and decreasing costs of computers, communication equipment, and consumer electronics. Continuation of shrink technology to the deep submicron regime poses formidable challenges for pattern transfer in general and plasma etching in particular. The main objective of our research program is the development of well characterized plasma reactors and associated processes that achieve the future manufacturing requirements for advanced semiconductors, while minimizing cost-of-ownership. This objective is facilitated by a better understanding of the fundamental chemical and physical processes, including the homogeneous plasma chemistry, and the heterogeneous chemical processes occurring at the plasma-wafer interface. In reactor development, we are focusing on low-pressure, high-density reactors that can achieve the high degree of directionality required for submicron pattern transfer. Types of reactors include inductive coupled plasmas, helicon wave-supported plasmas, and electron cyclotron resonance plasmas. One major issue is the control of the plasma chemistry in the low-pressure regime where wall reactions dominate. Another significant issue is maintaining etching uniformity across large wafers. We are developing and implementing plasma diagnostics for the low-pressure, high-density regime. Plasma diagnostics are essential for characterization of the plasma operation and correlation of the plasma parameters with etching or deposition characteristics. In addition, diagnostics afford an important means of process monitoring and realtime feedback control. Diagnostics of interest include microwave interferometry, Langmuir probes, ion energy analyzers, optical spectrometers, laser-induced fluorescence, and diode laser spectroscopy. MEMS technology is being utilized to fabricate an oxide charging monitor another micro-analyzers. Our research is done in close collaboration with semiconductor manufacturers, equipment manufacturers, and national laboratories. |
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