candidates for database development support, it is certainly true that other applications are important and deserve support as well.
- The integrated circuit manufacturing industry remains in its historical pattern of rapid technological change, coupled with impressive rates of growth. This pattern has begun to seriously challenge plasma equipment suppliers to continue the trend toward ever higher performance/cost ratios. Rapidly changing plasma process requirements, increasingly stringent process control requirements, and pressure to decrease the time to market for both new semiconductor products and new plasma equipment all contribute to the demand for a more effective approach to plasma process engineering. Meeting these more stringent requirements will make the U.S. semiconductor manufacturing industry more competitive and responsive to both civilian and defense markets.
- Plasma processing tools are, in most cases, designed and optimized empirically. Real-time control of plasma processes is limited to individual subsystem loops for variables such as flow or pressure. Feedback control of important process parameters such as etching rate, uniformity, and selectivity has not been adopted by the industry. Further improvements in performance by means of empirical adjustments will soon reach a point of diminishing returns, if they have not already.
- Control of processes in plasma reactors must occur on length scales that range from tens of angstroms to tens of centimeters and time scales that range from seconds to tens of hours. Loss of control at any point in this spectrum of length and time scales can result in reduced yields of components and therefore significant economic losses. For example, precise control of transistor gate and metal wiring levels across the entire chip is necessary to manufacture microprocessors at the highest speeds. Loss of this control over etching precision produces slower microprocessors and a loss of hundreds of dollars per chip. Obviously, across-wafer control is equally important to maintain high yields and therefore high profitability.
- Plasma modeling and simulation can develop into a powerful scientific and engineering tool, but a number of obstacles are limiting the pace of progress. It is generally agreed that the primary obstacle is a lack of a suitable database for the many physical and chemical processes that make up a plasma process. This includes not only data characterizing individual collisional processes, but also the selection of the key chemical species, and the reaction pathways for these species.
- The most promising applications on which to focus for developing or improving the database are poly-Si etching, SiO2 etching, and SiO2 deposition. These applications are currently important and appear likely to remain important for the next 3 to 5 years at least.
The remainder of this report is intended to sharpen the focus on the existing state of the art in plasma modeling and simulation, and the database that supports it. While the treatment is not exhaustive, each subsequent chapter aims to summarize the most important current issues and to point the way to the most fruitful directions for improvement.
1. Semiconductor International, May 1996, p. 83.
2. A. Ghanbari, Workshop on Database Needs in Plasma Processing, Washington, D.C., April 1-2, 1995.
4. Semiconductor Industry Association, The National Technology Roadmap for Semiconductors (SEMATECH, Austin, Tex., 1994).
5. P Singer, "New Frontiers in Plasma Etching," Semiconductor International 19(8):152 (July 1996).
7. A. Voshchenkov, Workshop on Database Needs in Plasma Processing, Washington, D.C., April 1-2, 1995.