January 23, 2012 – JCN Newswire — Tanaka Kikinzoku Kogyo K.K., a company of Tanaka Precious Metals, developed a ruthenium material able to form a film up to 6x the normal depth for capacitor electrodes used in dynamic random access memory (DRAM) semiconductors, working with Professor Seiji Ogo of the Graduate School of Engineering Department of Applied Chemistry at Kyushu University.
The ruthenium material is a metal organic chemical vapor deposition (MOCVD) precursor for 20nm and below, next-generation DRAM devices. It forms a uniform ruthenium film inside fine pores with a 40:1 aspect ratio. This enables the manufacture of capacitor electrodes with six times the normal depth. Tanaka expects to commercialize the material in 2012.
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| Figure a) SEM observation image of the ruthenium film formed inside a pore with a depth of 10um and an aperture diameter of 250nm (40:1 aspect ratio. b) Enlarged images of the top of a pore, c) middle of a pore, and d) bottom of a pore. |
New semiconductor memory manufacturing techniques increase capacity by deeply carving memory cells using MOCVD, giving capacitor electrodes a 3D structure. The ruthenium precursor from Tanaka Kikinzoku Kogyo is a metallo-organic complex made up of organic compounds (Cyclooctatetraene and Carbonyl) and a metallic element (Ruthenium). Because it has properties of high vapor pressure (tendency to evaporate when forming a film) and easy precipitation of metal by heating, it is possible to form a ruthenium film with a coverage factor of 70% within pores with the high aspect ratio of 40:1 at 165C.
High vapor pressure and easy vaporization supplies the necessary precursor gas on the base material when forming a film, creating a uniform film to the pore edges. The low processing temperature (165C) can reduce the damage to the base material caused by heat when forming a film. The ruthenium precursor developed here has a low melting point, and is a liquid at room temperature.
Normally, a reaction accelerator (reaction gas) such as oxygen is used to promote the thermal decomposition of the precursor to form a pure metal film when forming a film. Oxygen is a highly reactive gas that facilitates the formation of metal film, but it also has adverse effects such as oxidation of the base material. A gas such as hydrogen causes little damage to the base material, but hydrogen has low reactivity and difficulty in forming metal film. This ruthenium material is able to form a pure metal film even in a hydrogen atmosphere.
As memory elements become smaller, the metallic film used as electrodes needs to be smoother. Rough film with irregularities causes variability in electrical properties, and can also cause problems such as shorts and disconnections. Ruthenium films formed using the material successfully developed here show high smoothness with asperity of 1.1 nanometers or less (RMS value obtained from AFM observation with a film thickness of 12nm).
It has been indicated that MOCVD presents a danger of film becoming contaminated due to precursor resolvent (organic components, etc.) becoming mixed into the metallic film. The ruthenium material can form a ruthenium film with high purity and little film contamination (confirmed through XPS measurement).
The results of development of this ruthenium precursor are scheduled to be published in Dalton Transactions published by the United Kingdom’s Royal Society of Chemistry.
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