Metal Gate Recessed Access Device (RAD) for DRAM Scaling

Abstract

A functional DRAM with higher data retention and NH3. CVD TiN was deposited using TiCl4 and NH3. IOOA characteristics than a planar access device has been demonstrated, blanket films were characterized by x-ray reflectivity (XRR) using a metal gate recessed access device (RAD). Chemical vapor and x-ray diffraction (XRD). As observed from the XRD deposition (CVD) and atomic layer deposition (ALD) were used to patterns ( Fig.3 and 4), CVD TiN films are crystalline with deposit titanium nitride (TiN) and tantalum nitride (TaN), colu respectively. CVD TiN and ALD TaN-CVD TiN laminate gate columnar grains, and grain growth post heat treatment is stacks were integrated with a RAD module. ALD TaN-CVD TiN minimal. ALD TaN films are nanocrystalline as deposited and laminate gates showed enhanced drive current (IDs), higher exhibit non-uniform crystallinity post heat treatment. Blanket transconductance (GM), higher mobility (PEFF) and reduced off stress variation of TiN film versus thickness is shown in Fig.5. current (IOFF) characteristics compared to CVD TiN gates. Device Density (extracted from XRR) variation due to heat treatment is characteristics and reliability data for both the planar devices and RADs are presented. The ALD TaN-CVD TiN laminate metal gate plotted in Flg.6 for TaN and TiN. TEM images (Fig 7) of 0ouA RAD showed much improved data retention characteistics TaN flm post heat treatment show crystallites in an amorphous compared to a conventional planar device with a poly silicon gate. matrix. Post heat treatment, the interface of TaN/SiON was The optimum thickness of ALD TaN in the laminate stack is smoother and more distinct compared to the rough TiN/SiON discussed.

Atomic layer deposition of TaN and Ta3N5 using pentakis(dimethylamino)tantalum and either ammonia or monomethylhydrazine

“…The deposition method employed must produce high quality, uniform, pinhole free films with the desired stoichiometry and thickness. The films must often be conformal over high aspect ratio features, such as the trench structures in dynamic random access memory (DRAM) cells [26]. The thermal budget of the deposition process may also be an important consideration when temperature sensitive parts of the device have been formed prior to deposition [27].…”