Figure 4.1

Schematic outline of a process simulator used in conjunction with statistical optimization and diagnostics to  develop plasma etching and deposition processes. Given a reactor design and initial operating parameters— which could come from computer-aided design and expert system tools—the simulator makes use of basic  cross-section and rate coefficient data to predict wafer attributes. Diagnostics of the plasma and surface are  used to limit the process model and provide feedback as to its accuracy. Fine-tuning of the process is  accomplished using statistical design methods.

These contributions have come from relatively small groups of researchers working in industrial, national, and university laboratories in the United States. However, the efforts have been almost totally uncoordinated. For example, diagnostic measurements are made on one material system and reactor design while simulations are performed on a different material system and reactor design. Furthermore, production reactors represent yet another technology. As a result, basic science studies have contributed greatly to our collective intuition but little to our ability to quantitatively simulate processes or design reactors.

The synergism of scientific intuition and the empirical method has been successful for the fabrication of the relatively simple and modest-density microelectronic devices of the 1980s. However, the empirical relationships that are used today to relate wafer attributes (film thickness, anisotropy, uniformity, damage, residues, and so on) to process variables (e.g., power, gas composition, flow rates, pressure) are equipment and process specific and cannot be applied to the new equipment and processes needed for future generations of devices. The recalibration and reoptimization of manufacturing process steps by empirical means alone is inefficient and costly.

Unfortunately, the complexity of plasma processes and the lack of fundamental understanding make detailed, quantitative process simulation based on first principles seem unlikely in the near future. However, scaling laws based on fundamental plasma science could readily be used in transferring processes from reactor to reactor or from one processing regime



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