A research team led by University of Massachusetts chemical engineer James Watkins has developed a new method of depositing copper films within tiny channels etched in silicon wafers.
The technique is believed to be significant because it offers an efficient way to create the tiny circuitry demanded by the microelectronics industry. ‘This process really makes possible the fabrication of extremely small features that are necessary for future generations of integrated circuits,’ said Watkins.
Historically the processor speed of integrated circuits has doubled every 18 months and this requires making individual components smaller.
Current fabrication techniques are projected to reach their limit within the next few years and the current technology roadmap used by industry offers no solution to the problem after 2005.
‘When we build devices for microelectronics there are problems in placing the metal exactly where it is needed,’ said Watkins. ‘We just can’t do that in the very small features that will soon be required using current techniques in a way that would be practical for industry.’
The conventional fabrication methods deposit metals and other materials onto silicon from either a gas or from liquid solution.
Both approaches have their own advantages and disadvantages. Watkins and his group took a different view. ‘We reasoned that individually each of the methods is probably limited in a fundamental way, but if you could combine the most desirable attributes of the methods into a single process, then you could solve the problem. This is possible by depositing the materials from a supercritical fluid.’
A supercritical fluid is a substance that has some of the properties of a liquid and some of the properties of a gas.
‘If you heat and compress a gas like carbon dioxide, it can be used to dissolve a wide range of compounds,’ explained Watkins. ‘The solution, however, does not behave like a liquid but rather like a gas and therefore flows easily over complex surfaces and into narrow gaps.’
This combination of properties makes Watkins’s process, dubbed ‘chemical fluid deposition,’ ideal for the fabrication of tiny devices with complicated features.
The use of carbon dioxide has other benefits. It is non-flammable, non-toxic, and renewable and offers environmental advantages to current metal deposition techniques.
The generation of contaminated wastewater is a major concern for the metal plating industry but this new process is said to eliminate it entirely.