Fabrication of the Si<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> phase change cell structure for PCRAM by using UV nanoimprint lithography

Abstract

Phase-change random access memory (PCRAM) is emerging as one of the most promising non-volatile memories for the next generation media due to its fast write/read speed, wide dynamic range, high degree of cycling endurance, excellent data retention, simple structure, low operating voltage, good compatibility with CMOS technologies, and easy applicability. The PCRAM utilizes a reversible phase change phenomena between crystalline and amorphous states of chalcogenide materials by electrical resistive joule heating. A resistance of the crystalline phase (set) is much lower than that of the amorphous phase (reset).Being able to pattern and etch phase change memory in nanometer scale is essential for low power consuming operation of PCRAM device. In particular, high-density electronic memory, uniform, consistent and smooth sidewall storage unit structure for the electrical properties of memory is essential.UV nanoimprinting lithography (UV-NIL) is a new emerging lithographic technique in which patterns as small as sub-100 nm can be easily replicated onto a resin layer from surface protrusions of a stamp with a potential for high throughput at low cost, and a promising as one of the next generation lithography. This study uses the UV-NIL for patterning the PCRAM device. Si wafers coated with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were used as. substrates. Titanium bottom electrode, TiN contact layer, and Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (SST) were deposited by sputtering method. The thicknesses of Titanium, TiN and SST layer is about 100, 40, and 200 nm, respectively. Patterns of UV imprinting resin were formed using UV-NIL on the surface of SST films, and that were etched using SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma in a RoTH&RAU MS-350 reactive ion etching (RIE) etcher. The experimental results show that by using UV-NIL processing uniformly consistent, high-quality edge smooth sidewall structure for PCRAM devices is obtained. The operation behaviors of the fabricated devices were characterized by using electrical measurement system, SST material possesses lower threshold current with a resistance ratio of 65 has been achieved.