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NIST may soon put the venerable photoresist etching lithography process to rest with some old-fashioned press power.

Lithography is now a ubiquitous term when it comes to integrated circuits. As lithography techniques have improved, ICs have become more densely packed with the all-important transistor. The latest processor cores from popular manufacturers AMD and Intel pack hundreds of millions of transistors into a few square centimeters.

Lithography allows chip manufacturers to etch patterns into silicon insulating material where nanoscale transistors and copper wire make up the bulk of an IC's work center. But both the physical limit of current lithography techniques as well the insulating properties of silicon are being stressed as the insulating channels grow smaller and the important transistors are squeezed even closer together.

Work with high-K metal logic gates has allowed further miniaturization, but these materials will soon be at their limits. Carbon nanotubes may replace the copper interconnects, but that won't boost the insulating properties of silicon or improve lithography further.

The National Institute of Standards and Technology has been working on a new form of lithography, called nanoimprint lithography (NIL). Rather than etching patterns into a material like most methods, NIL is, as the name implies, an embossing process. A die containing the necessary patterns is created and used to stamp the insulating material.

The actual material is important as well, as it must be malleable enough to accept the nanoscale imprint, but rigid enough to hold the shapes. Most NIL films are physically hardened after impression, using heat or ultraviolet radiation.

NIST has been using spin-on organosilicate glass (SOG) as the insulating film in their work. SOG starts as a fluid film, which is then hardened to glass using heat. SOG is also a superior insulator due to being laced with nanoscale pores. One of the reasons SOG is not presently used in ICs is that photoresist etching can damage the material, compromising its properties as an insulator. NIL on the other hand leaves the material unaffected.

Not only can NIST's NIL process successfully stamp SOG, the process itself actually makes the glass film a better insulator. Normally SOG is laced with large and small nanopores. While the small pores help increase insulation, the larger pores can interfere with it. The NIL process helps to eliminate large pores, creating the beneficial smaller ones. It also creates a dense protective skin on the surface of the film, further protecting it from external interference.

NIST's work looks promising and may provide chip manufacturers with better products involving less process and better materials than present manufacturing techniques. Combined with new interconnect materials and extremely small transistors, Moore's law might yet survive another two decades.





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