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Toshiba's New Fabrication Method of Gate Oxide for MOS Devices Will Improve Long -term Reliability of LSI

12 December, 2000


San Francisco--In an increasingly mobile world of go-anywhere, do-everything personal products, the semiconductor industry is locked into a search for technologies that support lower power consumption and enhanced reliability in highly integrated LSI. Toshiba Corporation today announced a major breakthrough that promises the most desirable combination of all: metal-oxide semiconductors--and end-products--offering faster processing, reduced power consumption and much greater reliability.

Data flows through semiconductors are controlled by gates that switch between open and closed states. Effective operation demands that the gates are isolated, the role undertaken by the gate oxide layer. Ideally, the best gate oxide layer is a thin one, allowing faster processing and lower power consumption. In practise, the thinner the gate oxide, the higher the stress-induced leakage current (SILC), leakage that occurs in the low gate voltage region after high-field stressing. SILC degrades performance and raises power dissipation, and has long stood as barrier to realizing thinner gate oxides and enhanced device performance.

Toshiba's breakthrough attacks the problem with a new fabrication process that uses deuterium in its gaseous state. While previous studies had confirmed the effectiveness of deuterium annealing in reducing interface-defect generation at the gate oxide-silicon substrate interface, Toshiba advanced the process to the level of suppressing SILC: and cut it by a highly significant 30%.

The new process burns deuterium in ambient oxygen during the gate oxidation process, introducing deuterium atoms into the gate oxide as growing SiO2 film. Tests confirm that the process achieves more stable chemical bonding of deuterium atoms than the annealing process. SILC suppression was rendered even more effective by replacing SiH4 gas with SiD4 gas during polycrystalline silicon deposition of the gate electrode. The number of deuterium atoms in the SiO2 film after polycrystalline silicon deposition by SiD4 gas was 10 times larger than achieved with deuterium oxidation alone.

The chief value of Toshiba's new oxidation process is its strong potential as a real-world solution compatible with the conventional oxidation process. Suppression of SILC can be achieved simply by changing from hydrogen gas, widely used for the gate oxidation process, to deuterium gas. The equipment required is essentially the same as that currently used in the fabrication process.

This new process can also be applied to realize higher reliability in thin-tunnel oxides for nonvolatile memories.

Details of the new gate oxide fabrication method of work on which was partly performed under the management of ASET (Association of Super-Advanced Electronics Technologies) in a MITI (Ministry of International Trade and Industry) R&D program supported by NEDO (New Energy and Industrial Technology Development Organization), were presented at the recent IEDM (International Electron Devices Meeting) in San Francisco.

Gate oxide is a silicon dioxide (microscopic glass) formed by oxidizing the IC's silicon substrate. It separates the polysilicon gate from the NMOS and PMOS channels beneath it. The quality and thickness of the oxide are key process parameters, and have a very strong, direct impact on the ultimate performance of devices.


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