Technologies Of The Year -- IBM Corp.'s Nanotechnology For Semiconductor Processing

Polymer molecules that self-assemble will enable smaller, more powerful semiconductor devices for the future.

While the first computers occupied the space of a large room, today, computing capability thousands of times greater can be held in the palm of your hand. One reason for this compacting of power is the ability to form smaller and smaller electronically functional structures on the silicon chips that are integrated circuits. But the current technology that helps accomplish the shrinkage, photo-resist lithography, is approaching its limits, being able to form features down to about 100 nanometers in size (a human hair is about 10,000 nanometers in diameter). Recently, IBM Corp. made a quantum leap in miniaturization capability with a science-fiction-sounding technology called polymer self-assembly. Now able to form functional structures of 20 nanometers and less, polymer self-assembly has moved from a research curiosity to application in real-world challenges of semiconductor manufacture. It promises significantly reduced feature size, higher component density, improved performance and lower voltage requirements for microelectronic devices. In addition, polymer self-assembly can be applied without extraordinary changes in current semiconductor manufacturing practices because the materials and processes used are very similar to those employed today in photo-resist lithography. IBM first demonstrated this exciting technology in a working device in December 2003 at its T.J. Watson Research Center, Yorktown Heights, N.Y. Since then, the company has created a semiconductor memory device that can be shrunken to smaller sizes while maintaining performance, can survive 10 times more read/write cycles and operates at half the voltage of current similar units. In 2004 IBM made a decoupling capacitor that occupies one-fourth the space these devices occupy on today's microprocessors. Another breakthrough occurred in March, when IBM researchers learned to harness polymer self-assembly in a way to create more ordered structures allowing construction of far more complex electronics such as memory arrays and microprocessors. As with photo-resist lithography, self-assembling polymers generate "masks" that act like stencils in creating the nooks and crannies on silicon wafers that house the active portions of electronic micro-devices. Because it operates at the molecular level, however, this technology creates much finer stencils. While the term self-assembly implies some molecular consciousness, it is actually a common natural phenomenon, as evidenced by the star-like pattern of snowflakes, geese flying in formation and rain forming a droplet. To create polymers that self assemble, IBM researchers connect two different long-chain polymers together to form a copolymer. The individual polymers, like long pieces of spaghetti, are selected because they won't mix with each other, like oil and water. When the copolymer is applied to a surface, the two different kinds of spaghetti try to minimize the area where they are touching. But like two chained prisoners, they can only have so much privacy. The compromise, depending on polymer ratio, film thickness and environmental conditions, results in films with various ordered patterns. In one, the co-polymer form honeycombs, with one polymer defining the hexagonal pattern structure and the other occupying the center "holes." The hole polymer can be selectively removed by chemical means, leaving an incredibly fine honeycomb lattice that can act as a mask in semiconductor manufacturing operations. The mask is applied to a silicon wafer coated with silicon dioxide. The dioxide is etched away under the holes in the mask, leaving spots of silicon wafer exposed and the manufacturing process is begun. Self-assembling polymers also can create lines and spaces, useful in the manufacture of transistors and "wires" connecting circuitry. As described, self-assembly creates ordered patterns suitable for the internal workings of individual devices. However, it was not until the March breakthrough that IBM could control the position and orientation of the patterns. Integrated circuits are made up of layers of devices and structures that need to be precisely positioned relative to each other. IBM researchers found that self-assembling polymers line up on edges of "steps," which can be created with lithography, directing the molecules into place to generate structure suitable for microchip fabrication processes.

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