Paper MN+NC-MoA4
Fabrication of Nanopore and Nanochannel Structures through E-Beam Lithography and Atomic Layer Deposition Processes

Monday, October 20, 2008, 3:00 pm, Room 206

The reliable and reproducible fabrication of nanopore and nanochannel structures is essential for building nano-fluidic systems, such as a device to control bio-molecules or DNA. Here, we report on CMOS-compatible fabrication methods to generate electrode-embedded nanopore and nanochannel structures as small as 10 nm feature size. To fabricate a small size fluidic channel, we adopt a combined process of e-beam lithography and atomic layer deposition (ALD). E-beam lithography is used for generating few tens of nanometer sized hole and line structures and ALD is employed for further shrinking down the features less than 10 nm. In the case of a pore fabrication, we used a membrane of SiO₂ (100 nm)/Si₃N₄ (20 nm)/TiN (30 nm)/Si₃N₄ (20 nm) on Si wafer. PMMA (300 nm thickness) hole structures on top of the membrane were patterned by e-beam lithography, which were then transferred to the membrane layers through two-step RIE process, consisting of sequential CHF₃+O₂ and CH₄ steps to remove SiO₂ and Si₃N₄/TiN/Si₃N₄, respectively. This drilling process formed 50~80 nm diameter pore structures on membrane. In a parallel way, we fabricated trench structures by using a stack of Si₃N₄ (5 nm)/a-Si (20 nm)/SiO₂ (100 nm) films on a bulk Si substrate. PMMA (200 nm thickness) line patterns fabricated by e-beam lithography were transferred to the Si₃N₄, a-Si and SiO₂ layers through a multi-step RIE process, which generated ~50 nm width and ~60 nm depth trench structures. Then, a selective isotropic etching of SiO₂ by a dilute HF(1:500) induced a round-shaped etch profile along the trench line. Alternatively, the a-Si layer could be oxidized by furnace oxidation to partially close the trench. For both pore (70~80 nm diameter) and trench (~50 nm width) structures, we used an amorphous, conformal ALD TiO₂ film to reduce the pore or trench dimensions down to less than 10 nm. ALD film provided a self-limiting process by remaining void along the pore and the trench, which will serve as fluidic channels less than 10 nm.