Cover Story
Precursors for advanced memory applications
Materials continue to play an ever increasing role in fabrication of semiconductor devices as geometrics shrink and conventional materials no longer meet the performance criteria. Ashutosh Misra, Jean-Marc Girard, Venkateswara Pallem and Julien Gatineau of Air Liquide Electronics discuss how their company is preparing with their latest enabling precursors for advanced memory applications.
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Anticipated Materials Evolution in DRAM devices
apid advancements in memory technologies necessitate the
integration of novel materials in the film stack in order to address challenges raised by continuing shrinkage and performance expectations of memory devices. There is constant quest for materials that can provide a breakthrough for fabrication of highly demanding consumer electronic devices, where higher memory capacity and lower power consumption is desirable. Films of these materials need to be deposited in Atomic Layer Deposition (ALD) mode because of stringent conformality and extremely high aspect ratio requirements. The development of ALD processes can not be made without innovating on the chemistry side, hence there is an ever growing need of engineered molecules (“precursors”) that can enable the deposition of these novel materials within challenging process constraints. Materials with high charge storage capacity (high-k) have been exhaustively studied in the last several decades, and widely employed in DRAM manufacturing. Starting with aluminum oxide based and progressing through hafnium oxide based dielectrics, the memory industry somewhat settled on zirconium oxide as the dielectric material of choice in ~ 2006. Through several technology nodes, titanium nitride (TiN) has
remained as the choice for electrode material. We use this as a reference point for our discussion on advancements in dielectrics and electrode materials in fabrication of memory devices.
TiN (electrode) TEMAZ (tetrakis ethylmethylamido zirconium) has been the industry standard precursor for deposition of ZrO2
50-40 nm node: ZrO2
/doped ZrO2 films. It offered a viable, cost
effective means for first order transition from Hafnium to Zirconium. However, there was a need to deposit such high-k films at temperatures in excess of 300°C, as it would bring multiple benefits, such as higher as- deposited k-value due to the predominant tetragonal phase of the oxide, as well as allowing faster chamber purge-out to avoid material build- up and particle excursions. TEMAZ was been found to yield self-limited ALD growth behavior up to ~ 275°C only, beyond which point parasitic CVD is obtained. Clearly, the need for an alternative precursor for high temperature processing existed, and Air Liquide’s ALOHA product line engineered ZyALD (Tris(dimethylamino)cyclopentadienyl
Zirconium; winner of Euro Asia’s Enabling Material Award in 2007), a precursor that enables the widening of the self limited growth ALD process window of high-k films. Additional key benefits of this compound are its high volatility and evaporation rate, thermal stability and similar growth per cycle to that of TEMAZ. Owing to its very high thermal stability, ZyALD exhibits perfect self limited ALD growth, with a saturated growth per cycle up to 1.28 Angstroms (with ozone as a co-reactant). Self limited growth can be obtained up to 350°C temperatures.
(dielectric) and
www.euroasiasemiconductor.com Issue IV 2010
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