Myoung-kwan Cho

S-RCAT (sphere-shaped-recess-channel-array transistor) technology for 70nm DRAM feature size and beyond

For the first time, S-RCAT (sphere-shaped-recess-channel-array transistor) technology has been successfully developed in a 2Gb density DRAM with 70nm feature size. It is a modified structure of the RCAT (recess-channel-array transistor) and shows an excellent scalability of recessed-channel structure to sub-50nm feature size. The S-RCAT demonstrated superior characteristics in DIBL, subthreshold swing (SW), body effect, junction leakage current and data retention time, comparing to the RCAT structure, in this paper, S-RCAT is proved to be the most promising DRAM array transistor suitable for sub-50nm and mobile applications.

A mechanically enhanced storage node for virtually unlimited height (MESH) capacitor aiming at sub 70nm DRAMs

Fully reliable lean-free stacked capacitor, with the meshes of the supporter made of Si/sub 3/N/sub 4/, has been successfully developed on 80nm COB DRAM application. This novel process terminates persistent problems caused by mechanical instability of storage node with high aspect ratio. With Mechanically Enhanced Storage node for virtually unlimited Height (MESH), the cell capacitance over 30fF/cell has been obtained by using conventional MIS dielectric with an equivalent 2.3nm oxide thickness. This inherently lean-free capacitor makes it possible extending the existing MIS dielectric technology to sub-70nm OCS (one cylindrical storage node) DRAMs.

High-density low-power-operating DRAM device adopting 6F/sup 2/ cell scheme with novel S-RCAT structure on 80nm feature size and beyond

For the first time, the DRAM device composed of 6F/sup 2/ open-bit-line memory cell with 80nm feature size is developed. Adopting 6F/sup 2/ scheme instead of customary 8F/sup 2/ scheme made it possible to reduce chip size by up to nearly 20%. However, converting the cell scheme to 6F/sup 2/ accompanies some difficulties such as decrease of the cell capacitance, and more compact core layout. To overcome this strict obstacles which are originally stemming from the conversion of cell scheme to 6F/sup 2/, TIT structure with AHO (AfO/AlO/AfO) is adopted for higher cell capacitance, and bar-type contact is adopted for adjusting to compact core layout. Moreover, to lower cell V/sub th/ so far as suitable for characteristic of low power operation, the novel concept, S-RCAT (sphere-shaped-recess-channel-array transistor) is introduced. It is the improved scheme of RCAT used in 8F/sup 2/ scheme. By adopting S-RCAT, V/sub th/ can be lowered, SW, DIBL are improved. Additionally, data retention time characteristic can be improved.

An outstanding and highly manufacturable 80nm DRAM technology

For the first time, fully working 512 Mb DRAMS have been developed successfully using an 80 nm DRAM technology, which is the smallest feature size in DRAM technology ever reported. With an ArF lithography, recess-channel-array-transistors (RCAT), low-temperature MIS capacitor technologies and a newly developed top spacer storage node contact (TSC), we have realized these 512 Mb DRAMS. Also, we have reduced process steps, including the layer requiring ArF lithography, by using the TSC process.

Gate oxide integrity (GOI) of MOS transistors with W/TiN stacked gate

With W/TiN stack gate deposited at high temperature, excellent time-dependent dielectric breakdown (TDDB) characteristics of the gate oxide were obtained in MOS capacitors. In the case of negative gate bias where thin oxide reliability becomes critical, the TiN gate provides a much longer time to breakdown than that of n/sup +/-poly gate due to a larger barrier height and less F-N tunneling current. In spite of skipping the conventional reoxidation process, a breakdown field larger than 10 MV/cm could be obtained in MOS transistors by undercutting TiN with boiling H/sub 2/SO/sub 4/. With a double spacer and undercutting scheme, the short channel effect of NMOS and PMOS transistors could be suppressed up to L/sub gate//spl sim/0.3 /spl mu/m.

Novel robust cell capacitor (Leaning Exterminated Ring type Insulator) and new storage node contact (Top Spacer Contract) for 70nm DRAM technology and beyond

For the first time, novel robust capacitor (Leaning exterminated Ring type Insulator - LERI) and new storage node (SN) contact process (Top Spacer Contact - TSC) are successfully developed with 82nm feature size. These novel processes drastically improved electrical characteristics such as cell capacitance, parasitic bit line capacitance and cell contact resistance, compared to a conventional process. The most pronounced effect using the LERI in COB structure is to greatly improve cell capacitance without twin bit failure. In addition, the TSC technology has an ability to remove a critical ArF lithography. By using the LERI and TSC processes in 82nm 512M DDR DRAM, the cell capacitance of 32fF/cell is achieved with Toxeq of 2.3nm and the parasitic bit line capacitance is reduced by 20%, resulted in great improvement of tRCD (1.5ns).

Analysis of Thermal Variation of DRAM Retention Time

Variation of DRAM retention time induced by thermal stress was investigated. Thermal activation energies (Ea) of sub-threshold leakage, junction leakage and GIDL (Gate Induced Drain Leakage) current of a DRAM cell were measured using the test vehicles. The values were compared with Ea of 1/tREF for the DRAM cell of which the retention time had been varied after a thermal stress. Ea of 1/tREF for the thermally degraded DRAM cell was in the range of that for GIDL current, while Ea for the normal DRAM cells with high retention time was in the range of Ea for junction leakage. It is insisted that the thermal degradation of retention time is induced by increase in GIDL current. The contributions of gate oxide/substrate interface states to the GIDL current are discussed

A novel robust TiN/AHO/TiN capacitor and CoSi/sub 2/ cell pad structure for 70nm stand-alone and embedded DRAM technology and beyond

For the first time, a novel robust (square-shape cylinder type) TiN/AHO (Al/sub 2/O/sub 3/-HfO/sub 2/)/TiN capacitor with Co-silicide on landing cell pad suitable for both stand-alone and embedded DRAMs are successfully developed with 88nm (pitch 176nm) feature size, which is the smallest feature size ever reported in DRAM technology, using ArF lithography for aiming 70nm stand-alone and embedded DRAM technology. The capacitor with Toxeq of 1.5nm and leakage current of less than 1 fA/cell is achieved. The cell contact resistance is greatly improved by using Co-silicidation on landing cell pad and metal storage node contact plug, which results in high performance.

Highly manufacturable 90 nm NOR flash technology with 0.081 /spl mu/m/sup 2/ cell size

A manufacturable 90 nm NOR Flash technology has been developed with extremely small cell size of 0.081/spl mu/m/sup 2/, which is the smallest cell size of NOR cell, for high density code storage memory featuring with low voltage operation. The small cell size of 0.081/spl mu/m/sup 2/ is successfully achieved with three key main technologies such as an advanced KrF lithography with off-axis illumination system, appropriate dielectric thin film and junction scaling and optimized oxidation encroachment of inter-poly oxide nitride oxide (ONO) and tunnel oxide.