CHAMPAIGN, Ill. - A new chemical process for the deposition of titanium
disilicide -- a crucial component of silicon-based semiconductors -- shows
promise as a method of fabricating smaller, faster microelectronic devices,
a University of Illinois researcher says.
The process, which has been patented, can deposit a thin layer of titanium disilicide on submicron-scale device structures in a fashion compatible with current manufacturing methods -- a goal that has eluded researchers for years.
"Titanium disilicide is widely used for making contacts to transistors in integrated circuits," said Edmund Seebauer, a professor of chemical engineering. "The current technology used to make this material involves reacting metallic titanium with the underlaying silicon substrate at high temperature. Because of problems associated with substrate consumption, dopant diffusion and film agglomeration, this technique cannot be scaled to smaller, next-generation devices."
To avoid these problems, the microelectronics industry turned to an alternate fabrication technique -- chemical vapor deposition (CVD). Despite a decade of trial-and-error work on a replacement CVD process, no satisfactory results were achieved.
Recently, Seebauer and graduate students Mike Mendicino and Robert Southwell took a different approach. First, they devised a series of experiments under carefully controlled conditions and at low pressures that permitted precise measurements of the various reaction rates involved with the CVD process. Then, based on the measured reaction rates, a mathematical model was created to predict what should occur at the much higher pressures required for practical applications. Finally, they compared the deposition of titanium disilicide produced under actual operating conditions with what their model had predicted. The results matched nearly perfectly.
"By injecting the reactants in a gas phase at lower temperature, the CVD process avoids problems with substrate consumption, phase transformation and high-temperature agglomeration," Seebauer said. "Therefore, this chemical process can be used on much smaller device structures.
"We have developed a kinetic methodology for fully modeling the chemical vapor deposition of titanium disilicide," Seebauer said. "This work represents to our knowledge the first time such kinetic models have successfully guided the a priori development of a practical process governed by surface reactions in which optimization has not already been accomplished by enlightened trial and error."
Currently, the new chip chemistry is being scaled up to accommodate the large wafer sizes used in the commercial production of integrated circuits.
"In a general sense, this work also can serve as a template for the difficult and heretofore largely unsuccessful business of a priori optimization of other practical surface reactions," Seebauer said.