Low resistivity tungsten for contact metallization

A new pulsed nucleation tungsten process, called ''PNL low-R"s W'', has been developed that results in near-bulk resistivity even in ultra-thin tungsten films. This solution greatly diminishes the need to develop alternative films for contact fill, probably for several generations. The process is done in a conventional, commercially available 300mm tool with standard hardware and operating conditions. Tungsten films deposited with this technique exhibit significantly larger grain size and a smoother surface compared with conventional PNL and ALD techniques. The larger grains account for lower resistivity due to less grain boundary electron scattering. The process results in higher fluorine content in the liner/barrier, but does not have an adverse effect on contact performance. A comparison of 6:1 aspect ratio contacts showed no difference in fill properties between the PNL low-R"s W and conventional PNL and ALD processes. This new film has been characterized and demonstrated on 65nm technology node product on contacts to nickel silicide, and on 90nm technology node product on eDRAM high aspect ratio contacts.