Cover Story


Right:ZyALD Structure


Far right: Star-Ti Structure


dielectrics, memory makers are looking into doping of these films to further increase the dielectric constant. Various elements can be considered for such purposes, and no clear front runner has yet emerged. Needless to say, such doping would require appropriate precursors that can function within the process parameters.


These features combine to result in high process throughput, excellent uniformity and film quality. This precursor has now been widely adopted in high volume manufacturing by leading end users worldwide. As an incremental improvement to ZrO2


8


30-20 nm node: Range of choices for dielectric and electrode materials Noting that incremental improvements via doping of ZrO2


STO Efficient deposition of STO films is particularly complex because two materials (Sr & Ti based) must have perfectly matched deposition properties in order to allow the deposition of quality films at the desired conditions. However, all the ALD processes reported so far have limited manufacturability. To date, only solid strontium molecules have


shown promise, but they have undesirably high melting points and poor volatility (e.g. Sr(tmhd)2 which has MP of 210°C and VP of only ~0.1 Torr at 230°C), posing a challenge for manufacturing. With conventional Ti molecules, the main drawback has been the inability to deposit films in ALD mode at temperatures higher than 350°C.


will result in limited gains, there


is an obvious need to delve into the materials cook book for choices that provide a significantly high dielectric constant. Two choices are under serious consideration for the dielectric – one is titanium oxide (TiO2


) and the other is Strontium


Titanium Oxide (STO). Simultaneously, replacement of conventional TiN electrodes with alternative materials, such as Ruthenium based materials is required for effective performance of devices based on these stacks.


Air Liquide’s ALOHA product line has developed two novel products – Absolute-Sr and Star-Ti, which together can be used for efficient deposition of STO films. These two precursors were designed and developed to provide not only far superior physical properties (volatility, thermal stability), but also high growth rate of film deposition in ALD mode, versus any available precursors. The design process included an exhaustive screening of tens of newly synthesized molecules.


This new STO solution (Absolute-Sr + Star-Ti combination) has the following advantages:  They are easy to handle: high volatility liquid/low melting point solid


 They have higher reactivity than standard Sr & Ti molecules.


 Absolute-Sr, is derived from sterically bulky ligands which not only prevents dimerization, but also stabilizes coordination sphere around the central Sr ion, thus making it more volatile and reactive.


Vapor Pressure of ZyALD vs. TEMAZ


 Star-Ti is specially designed to provide very unique properties that enable a wider process window regime in ALD


www.euroasiasemiconductor.com  Issue IV 2010


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