Successful Development of Capacitor Technology for Next Generation Memory

(Taipei News) Toshiba Semiconductor Company, Fujitsu Ltd. and Winbond Electronics Corporation today announced the successful joint development of Ru/Ta2O5/Ru cylinder capacitor technology. This technology is applicable to next generation of DRAM products below 0.1micron. 

Project Background 
For high density, high-speed operation, and implementation of DRAM (Dynamic Random Access Memory) technology embedded systems, LSIs are required. In order to fulfill these requirements, further miniaturization down to 0.13micron and 0.1micron is necessary. One of the most critical issues for developing this technology is how to fabricate storage capacitor in a minute memory cell. In this joint development effort, Toshiba, Fujitsu and Winbond succeeded in fabricating a MIM (Metal-Insulator-Metal) capacitor structure suitable for mass production of 0.1mm generation and below. In order to do so, a Ta2O5 (Tantalum Pentoxide) dielectric film was utilized, which yielded a higher dielectric constant than before, as well as a cylindrical-shape electrode structure made of Ru (Ruthenium).

Technology Overview
It is already known that Ta2O5 film deposited on a Ru electrode has higher dielectric constant than that on other electrode materials. This made the combination suitable for device miniaturization. In order to successfully develop a Ru/Ta2O5/Ru capacitor structure, however, there still remained some challenges including adhesion between Ru and conventional materials such as SiO2 and oxidation of the plug electrode surface during the Ta2O5 deposition process.

In order to solve the afore listed problems, the three Companies co-developed the following:

1. Improved adhesion utilizing a TiN (Titanium Nitride) liner

The Companies jointly utilized a Ru electrode employing TiN liner layer under the Ru bottom electrode in order to improve adhesion between Ru electrode and surrounding SiO2 film. By using this new electrode structure, the Companies were effectively able to prevent abnormal etching of SiO2 (void formation) and avoid collapse of the cylinder electrode.

2. Creation of an oxidation-tolerant plug formation by TiN layer as barrier material 

In order to prevent W (Tungsten) plug from oxidizing during the Ta2O5 deposition process, a electrode structure was developed in which a TiN barrier layer was inserted between Ru bottom electrode and underlying W plug. As a result, stable electrical contact between storage node and substrate was achieved.

3. Creation of cylinder capacitor formation technology for sufficient storage capacity

A cylinder-shape capacitor was created using a Ru electrode with TiN liner. Use of this structure created sufficient storage capacity in a minute memory cell area because both inner and outer surfaces of the cylinder as capacitor electrode were effectively utilized.

Use of the afore mentioned technologies enabled Toshiba, Fujitsu and Winbond to successfully fabricate a 0.13micron Ru/Ta2O5/Ru cylinder capacitor with good electrical characteristics such as storage capacitance and leakage current. A prototype 0.13micron DRAM was also successfully tested. Both Companies expect that the developed technologies will be applicable to designs below 0.1micron because Ta2O5 film's dielectric constant can be better leveraged in Ru/Ta2O5/Ru MIM capacitor when compared with conventional electrode materials.

The content of this technology will be presented at the International Electron Devices Meeting to be held on Dec. 13th, 2000, in San Francisco. The topic of the paper to be presented is entitled, "Liner- Supported-Cylinder (LSC) Technology for Ru/Ta2O5/Ru Capacitor in Future DRAMs".

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