Metal Gate Recessed Access Device (RAD) for DRAM Scaling
A functional DRAM with higher data retention characteristics than a planar access device has been demonstrated, using a metal gate recessed access device (RAD). Chemical vapor deposition (CVD) and atomic layer deposition (ALD) were used to deposit titanium nitride (TiN) and tantalum nitride (TaN), respectively. CVD TiN and ALD TaN-CVD TiN laminate gate stacks were integrated with a RAD module. ALD TaN-CVD TiN laminate gates showed enhanced drive current (IDS), higher transconductance (GM), higher mobility (¿EFF) and reduced off current (IOFF) characteristics compared to CVD TiN gates. Device characteristics and reliability data for both the planar devices and RADs are presented. The ALD TaN-CVD TiN laminate metal gate RAD showed much improved data retention characteristics compared to a conventional planar device with a poly silicon gate. The optimum thickness of ALD TaN in the laminate stack is discussed.
Atomic layer deposition of TaN and Ta3N5 using pentakis(dimethylamino)tantalum and either ammonia or monomethylhydrazine
Abstract TaN x thin films were grown at temperatures ranging from 200 to 375 °C using atomic layer deposition (ALD). Pentakis(dimethylamino)tantalum (PDMAT) was used as a tantalum source with either ammonia or monomethylhydrazine (MMH) as a nitrogen co-reactant. Self-limiting behaviour was observed for both ammonia and MMH processes, with growth rates of 0.6 and 0.4 A/cycle, respectively at 300 °C. Films deposited using ammonia were found to have a mono-nitride stoichiometry with resistivities as low as 70 mΩ cm. In contrast, films deposited using MMH were found to be nitrogen rich Ta 3 N 5 with high resistivities. A Quartz Crystal Microbalance (QCM) was used to measure mass gain and loss during the cyclic ALD processes and the data was used in combination with medium energy ion scattering (MEIS) to elucidate the PDMAT absorption mechanisms.
Electrical properties of Ru-based alloy gate electrodes for dual metal gate Si-CMOS
In this letter, low resistivity Ru and Ru-Ta alloy films, deposited via reactive sputtering, were evaluated as gate electrodes for p- and n-MOSFET devices, respectively. MOSFETs fabricated via a conventional process flow indicated that the work functions of Ru and Ru-Ta alloys were compatible with p- and n-MOSFET devices, respectively. Both of the metal gated devices eliminated gate depletion effects. Good MOSFET characteristics, such as I/sub DS/-V/sub GS/ and mobility, were obtained for both Ru-gated PMOSFETs and Ru-Ta gated NMOSFETs.