Ion Beam Etch for Patterning of Resistive RAM (ReRAM) Devices
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Ion Beam Etch for Patterning of Resistive RAM (ReRAM) Devices Narasimhan Srinivasan1, Katrina Rook1, Ivan Berry2, Binyamin Rubin1 and Frank Cerio1 1 Advanced Deposition and Etch, Veeco Instruments, 1 Terminal Drive, Plainview, NY 11803 2 Etch Product Group, Lam Research Corporation, 4400 Cushing Parkway, Fremont, CA 95438 ABSTRACT We investigate the feasibility of inert ion beam etch (IBE) for subtractive patterning of ReRAM-type structures. We report on the role of the angle-dependent ion beam etch rates in device area control and the minimization of sidewall re-deposition. The etch rates of key ReRAM materials are presented versus incidence angle and ion beam energy. As the ion beam voltage is increased, we demonstrate a significant enhancement in the relative etch rate at glancing incidence (for example, by a factor of 2 for HfO2). Since the feature sidewall is typically exposed to glancing incidence, this energy-dependence plays a role in optimization of the feature shape and in sidewall re-deposition removal. We present results of SRIM simulations to estimate depth of ion-bombardment damage to the TMO sidewall. Damage is minimized by minimizing ion energy; its depth can be reduced by roughly a factor of 5 over typical IBE energy ranges. For example, ion energies of less than ~250 eV are indicated to maintain damage below ~1nm. Multi-angle and multi-energy etch schemes are proposed to maximize sidewall angle and minimize damage, while eliminating redeposition across the TMO. We utilize 2-D geometry/3-D etch model to simulate IBE patterning of tight-pitched ReRAM features, and generate etched feature shapes. INTRODUCTION Resistive RAM (ReRAM or RRAM) is a new non-volatile memory technology that holds promise as a replacement for flash memory. ReRAM operates via the generation of defects within a thin transition metal oxide (TMO), forming a conducting filament through the dielectric under sufficient applied voltage. Two mechanisms are used: conductive bridge (CBRAM) where metal from the top electrode diffuses to generate the filament; and ‘OxRAM’ where oxygen vacancies generate the filament. The active stack of a ReRAM device consists of the TMO layer (e.g., HfOx, TaOx, TiOx) sandwiched between conducting electrodes.[1][2] For CBRAM, the top electrode is typically a low melting point noble metal such as Cu or Ag, and the bottom electrode is a high melting point noble, such as Pt or Ir. For OxRAM, the electrodes tend to be more typical electrode metals such as Ti, W or Ta. Precise control of stoichiometry, microstructure and interfaces is critical for device performance. Ion beam etch (IBE) is the process-of-record for patterning magnetic tunnel junctions (MTJs) in magnetic read heads that have similar M-I-M (metal-insulator-metal) geometry as ReRAM devices. IBE has several advantages for the patterning of multilayer devices of this type: an inert chemical environment for avoidance of chemical damage or residue; tight control of ion energy; independent control of the incident angle of the etching ions for re-deposi
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