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Essential techniques that allow W h e r scaling of trench DRAMs beyond 100 nm have been developed. (1) A1203 was implemented as high-k node dielectric in silicon-insulatorsilicon trench capacitors. A1203 films were deposited by ALD with excellent step coverage at aspect ratios of up to AR --60. Even.after thermal stressing at 1050 "C an effective oxide thickness ( = capacitance equivalent thickness) of to, = 3.6 nm and a leakage current of well below 1 fA/cell were obtained. (2) Both selective and non-selective HSG Si was formed inside high-aspect ratio straight and bottled trenches. On fully integrated 0.17 pm trench DRAMs, a storage capacitance of 45 fF/cell with acceptable leakage current was achieved. Both the aluminum oxide node dielectric and the HSG silicon have thus been proven to withstand the high thermal budget required for integration into trench DRAMs. (3) In addition, a silicon etch process was developed that allows trench aspect ratios of AR = 60 at critical dimensions of CD = 80 nm.

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