RETHINKING THE IMPOSSIBLE: Most microprocessors today measure 90 nanometers as the shortest distance between gates. But 45–nanometer distances are now becoming available and minute distances of 32 and 22 nanometers, once thought to be out of reach, are on the horizon. Image: Courtesy of ASM America, Inc.
Microprocessors are the engines performing the logic functions that make computers, cell phones and countless other indispensable electronic gadgets run. Improvements in microprocessor speed and power allow us to use sophisticated software on our cell phones and process loads of multimedia data on our laptops that just a few years ago would have seemed impossible. To continue to meet our growing technological demands—such as using a cell phone like a secure credit card or to download and watch an entire movie—processors must become ever more powerful even as they shrink.
Not an easy task for chipmakers, given that the recipe for faster microprocessors thus far has been to pack more transistors closer together in smaller spaces, which creates more complexity and requires some way of dissipating all of the heat generated by these electrical components before it damages the circuitry that runs our expensive toys. Relief may be on the way, though, as computer scientists seek to build tomorrow's microprocessors using new materials, processes and microscopic components.
Within a microprocessor, electrical current in a transistor flows from a power source through a gate to a power drain. Most microprocessors today measure 90 nanometers as the shortest distance between gates. But 45–nanometer distances are now becoming available and minute distances of 32 and 22 nanometers, once thought to be out of reach, are on the horizon. To give some perspective on just how tiny we're talking: one nanometer is the size of a few atoms, DNA molecules measure around two nanometers in size and a human hair is about 50,000 nanometers in diameter.
To achieve 45-nanometer gate–length distances and make 32- and 22-nanometer gaps a reality, ASM International, NV, a Netherlands-based semiconductor equipment maker, says it can construct materials on chips, atom by atom, using its atomic layer deposition technology. "The technology we have been developing over the past 10 years is to deposit a very thin layer of a very good insulator—hafnium oxide—making it easier to control the transistor," says Ivo Raaijmakers, ASM's chief technology officer. "This is a major shift; the whole industry has been making [complementary metal-oxide semiconductor] CMOS transistors with silicon oxide for the past 30 or 40 years."
ASM America, Inc., a subsidiary of ASM International, Monday announced that its technology and processes for making 45-nanometer chips in large volumes are now in production, a move expected to make manufacturing these chips much more efficient. "With a 45-nanometer chip, the insulation layer would be one nanometer, or four atoms, thick," Raaijmakers says. "Sooner or later, it's no longer possible to make a reasonable insulator with that thin layer of atoms." As microprocessors shrink below 45 nanometers, conventional insulating materials such as silicon dioxide become too thin to operate effectively. Hafnium—also used to make the control rods for nuclear reactors—provides an alternative to help prevent leakage and improve the control of the current through the transistor.
Hafnium oxide turns out to be the best replacement for silicon oxide in such thin layers because hafnium has a "high-k dielectric," which means that it lowers the transistor gate's resistance, allowing more current to pass through as well as reducing the amount of power loss. For 45- and 32-nanometer microprocessors, ASM has also developed a process to use its deposition technology to deposit a one-nanometer layer of lanthanum oxide between the hafnium oxide and the actual metal gate on each transistor. Lanthanum, a silvery white metallic element, helps control the interface between the metal gate and hafnium dielectric.