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To: Ian@SI who wrote (1593)	6/13/2002 11:38:15 AM
From: Ian@SI	Read Replies (1) \| Respond to of 2006

TI to roll out ALD processes during the next couple years... siliconstrategies.com TI takes high-k plunge to stem gate leakage By David Lammers EE Times (06/11/02 18:44 p.m. EST) HONOLULU ? While the rest of the industry ponders various high-k gate materials, Texas Instruments Inc. has fixed its sights on a gate oxide that will be introduced to the company's process flow over the next couple of years. TI has selected a quaternary (four-part) hafnium silicate material, created by introducing the metal hafnium (Hf) to a mixture of oxygen, nitrogen and silicon. The HfSiON gate oxide was described at the 2002 Symposium on VLSI Technology here Tuesday (June 11). The search for a replacement for silicon dioxide is critical to the semiconductor industry, which faces a looming crisis in terms of controlling power consumption. As silicon dioxide has been thinned to less than 15 angstroms at the gate insulation layer, electrons increasingly are able to burrow through the SiO2. Leakage through the gate has come to rival the other major source of wasted power, i.e., current dissipation through the source and drain regions. Bob Doering, TI's technology strategy manager and the co-chairman of the International Technology Roadmap for Semiconductor (ITRS), said the leakage issue is particularly important for chips that need a relatively high level of performance but which operate on batteries, requiring a minimum of both active and standby power consumption. TI's DSPs are a prime example, as they are widely used in what has become the largest power-aware market: the baseband processors of cellular phones. The HfSiON material has a dielectric constant of 12 to 14, which the head of TI's gate oxide development team, TI fellow Luigi Colombo, described as "medium-k." Compared with the oxynitride gate insulator currently used by TI, which has a k-value of 4.5, the new material boosts the k-value by a factor of three. It has an equivalent oxide thickness of 1.3 nanometers. The chip industry is searching for a gate insulator with a low equivalent oxide thickness that mimics the electrical properties of very thin SiO2, while providing a thicker physical blanket over the gate to prevent quantum-mechanical tunneling: oxides burrowing through the gate to cause leakage and, in the worst case, disfunctions. However good the high-k materials are at preventing tunneling, all of them have unwanted properties, including a slowdown in mobility as electrons and holes move through the channel. Less leakage Colombo said test chips fabricated with the HfSiON material thus far have exhibited about 80 percent of the mobility of comparable devices with the tried-and-true SiO2 insulator. Colombo called the 80 percent mobility figure "the best in the industry," with the major benefit that leakage is "significantly" reduced. Doering said TI's goal is to be able to move from the 130-nm (0.13-micron) process node to the node at 90 nm while keeping power consumption for a chip at about the same level. TI's 90-nm process, which uses the oxynitride gate insulator, will deliver a 25 percent performance boost and a doubling in transistor density, while keeping switching power to 5.25 microwatts per gigahertz per gate ? roughly half the per-gate active power consumption of the 130-nm node. TI director of silicon technology Hans Stork said that TI would like to introduce the HfSiON insulator in the second generation of its 65-nm process, a technology half-node that TI will implement to manufacture the Sparc microprocessors from Sun Microsystems. Prototypes will be made in 2005, said Stork. Introducing the hafnium silicate in the second generation of the 65-nm node would position TI to use the HfSiON material throughout the 45-nm process. Work ahead For TI to achieve Stork's goal, Colombo's group "will need to work through the manufacturing process issues with the new material," Doering said. Colombo declined to comment on when the HfSiON material will be introduced to manufacturing, but said it brings "the minimal amount of change" compared with the oxynitride material now used at company's fabrication facilities. "As much as we feel comfortable with this material, there is a lot of work left to be done. There are fixed charge issues to be dealt with, and we want to further improve on the mobility," Colombo said. By adding silicon and nitrogen to the mix, HfSiON remains an amorphous, glass-like material similar to oxynitride, even at 1,100°C. Other high-k gate materials crystallize as they go through the brief high-temperature annealing steps needed for dopant activation. Also, "the success of any high-k gate material depends on the ability to engineer the interface" with silicon, Colombo said. The introduction of nitrogen and oxygen helps create a good interfacial layer, and nitrogen prevents excessive boron penetration through the gate, another problem with some other high-k candidates with higher k-values. This year's VLSI Technology meeting has seen a sharp increase in the number of papers considering new gate oxide materials. Of the 15 gate oxide papers presented this year, about half are on some form of hafnium oxide, which is now considered the leading candidate at the 65-nm node.