IN the fast-paced semiconductor industry, staying ahead means optimizing and controlling the manufacturing processes down to the atomic level wherever possible. At stake is the $44-billion market in integrated circuits that power computers, communication devices, and consumer electronics.|
INDUCT95, a unique simulation code developed by Livermore physicist Peter Vitello (Figure 1), may give the U.S. a leg up in the race. INDUCT95 helps designers of plasma-aided semiconductor manufacturing to optimize the process and equipment. Such tools are also used in the aerospace, automotive, steel, and biomedical industries.
Plasmas--gases containing ions and electrons--are widely used to fabricate microelectronic devices. Out of the nearly 800 steps to create today's intricate integrated circuits, nearly one-third use plasmas.
The increasing use of plasmas for etching, deposition, and other processes reflects the advantages of this technique. First, the plasma breaks down the gas molecules into chemicals that etch materials very rapidly. Second, the plasma ionizes chemicals, giving them an electrical charge that renders them maneuverable. Finally--and of key interest to chip manufacturers--plasma etching produces nearly perfect vertical etching profiles. Getting exact profiles of uniform depth is extremely important: uniform, sharp features in the final product mean that each chip can yield more usable circuits.
However, controlling a plasma--particularly at sub-micrometer levels--is not easy. The plasma gases used in semiconductor manufacturing are usually highly reactive ones such as chlorine and oxygen. The interactions between these gases and the surface of the chamber walls, as well as the material being etched, are complex and not entirely understood. For the manufacturing process to be most efficient, the ion energy of the plasma must be carefully controlled, and the flux of plasma ions onto surfaces must be uniform.
Until now, designing plasma-aided manufacturing tools has been done mostly by trial and error. But as integrated circuits began to incorporate smaller and smaller features--some now approach the nanometer scale--a more rigorous process for designing tools was needed.
Designing the Best Plasma Tools Possible
Designing Plasma Electrodes for High Voltages|
Accurately modeling high voltages is important to the design of the electrodes that apply these voltages to the plasma. This voltage controls two critical aspects of the plasma: shaping the plasma's density in space and accelerating the ions onto the etching surfaces.
Manufacturers want a semiconductor device that is etched uniformly or that has a uniform deposit across the surface. To achieve this, the shape, position, frequency, and voltage of each electrode must be finely controlled.
"For example," said Vitello, "the use of multiple electrodes with wildly differing properties may lead to great variations in the plasma behavior, which can degrade the final product. These conditions are very difficult to accurately follow in semiconductor processing. INDUCT95 is the only software capable of modeling this environment."
Modeling Electronegative Plasmas
Other Ventures for Plasma Modeling
Key Words: computer-aided design, INDUCT95, plasma, plasma simulation, semiconductor.
For further information contact Peter Vitello (925) 422-0079 (firstname.lastname@example.org).