Atomic Layer Deposition of HfO2/ZrO2 Superlattices
Description
Student’s Name: Sarah Levine
Home Institution: Worcester Polytechnic Institute
NNCI Site: CNF @ Cornell University
REU Principal Investigator: Grace Huilli Xing - School of Electrical and Computer Engineering and the Department of Materials Science and Engineering, Cornell University
REU Mentor: Jeremy Clark - CNF, Cornell University
Abstract: Conventional HfO2-based high K dielectrics gate stacks cannot produce such a small effective oxide thickness and the consequent high capacitance without removing the interfacial SiO2, which negatively impacts electron transport and gate leakage current. The superlattice gate stacks offer much-reduced leakage current and zero mobility deterioration as they lack the need for this kind of scavenging. The gate stacks are used in GaN transistors for power and communication, the existing dielectric in these transistors causes significant leakage and damages the underlying material. Ultrathin ferroic HfO2-ZrO2 multilayers, stabilized with competing ferroelectric–antiferroelectric order, offer a new method for advanced gate oxide stacks in electronic devices beyond traditional HfO2-based high-dielectric-constant materials. The project is looking to develop a process to deposit the high-k HfO2/ZrO2 superlattices. Atomic Layer Deposition (ALD) is used to build up the superlattice, we use ALD because it provides uniform and precisely tuned thickness, then through various depositing methods such as sputtering and e-beam evaporation aluminum was deposited through a capacitor shadow mask and then annealed through rapid thermal processing. The fabricated devices were characterized on a DC probe station and graphed for current versus voltage, voltage over time, and Capacitance - Voltage (C-V), the latter of which solves for the dielectric constant and also examines other material parameters such as defect density. The project is working towards the smallest leakage at the smallest equivalent oxide thickness.
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