Jaya Parulekar, Illinois Institute of Technology Sathees Selvaraj, University of Illinois at Chicago Christos Takoudis, University of Illinois at Chicago NSF REU: UIC August 1 st, Selective Atomic Layer Deposition of Zirconium Oxide on Copper Patterned Silicon Substrates

Motivation 2 Applications in microelectronics and nanoelectronics  Semiconductors, transistors, memory and fuel cells Challenges  Need for transistor gates made with high dielectric constant materials  Need to achieve a precise level of thickness for gate dielectric layers to prevent problems, such as leakage  Need to selectively deposit layers on to specific surfaces

Atomic Layer Deposition (ALD) 3 Process by which thin films are deposited on surface of substrates at the Ångström level Precursors are injected one at a time in a sequential and self-limiting manner

Schematic of ALD design 4 Ethanol Nitrogen Metal Precursor Silicon wafer Reactor Activated switching valve Vacuum pump LN2 cold trap Substrate loading port Quartz tube Furnace

ALD Reactor 5

Selective atomic layer deposition (SALD) 6 Selectively depositing films on patterned substrates Molecular masking and self-assembled monolayers are techniques for SALD, but are inefficient More efficient and practical method: SALD based on surface physics and chemistry of different materials

Work from previous studies 7 Growth of HfO 2 was observed on silicon immediately Not observed on copper after 25 cycles Growth on copper after 50, but not to the extent of silicon Figure from Q. Tao, C. Takoudis, and G. Jursich, Appl. Phys. Lett. 96, (2010)

Work from previous studies 8 Increased amounts of Hf and O and decreased amounts of Si from 0 to 50 ALD cycles indicate HfO 2 film growth HfO 2 deposition for copper is not observed until after more than 25 ALD cycles Table from Q. Tao, C. Takoudis, and G. Jursich, Appl. Phys. Lett. 96, (2010)

Reduction of copper oxide to metallic copper 9 Method to achieve purely SALD As the number of cycles increases, the copper surface undergoes oxidation and deposition is observed. Challenge: selecting a reducing agent powerful and practical enough to ensure deposition of metal oxide Reducing Agent selected: Ethanol

Accomplishments and Open Challenges 10 Adding a reactant line to supply ethanol to the ALD reactor E-beam deposition of 200 nm metallic copper on silicon substrate Chose zirconium precursor, (Tris(dimethylamino)cyclopentadienyl zirconium).

Accomplishments and Open Challenges 11 Difficulty in measuring film thickness on copper with ellipsometer  Four point probe to measure sheet resistance

Accomplishments and Open Challenges 12 Ran trials on silicon wafers at 10, 15, 20, 25, 50, 75, 100, 150, and 200 cycles XPS on silicon wafers treated with ethanol and zirconium precursor Determined H 2 O oxidant line is unnecessary

Results Obtained 13 Linearity is observed, indicating ALD has occurred on silicon substrate *Carried out at 200 °C and base pressure of 500 mTorr

Results Obtained 14 Zr 4p Zr 3d Zr 3p Zr 3s O 1s O KVV C 1s Si 2p

Future Work 15 XPS for copper patterned wafers Four point probe analysis Submitting for potential publication in reference journal

Acknowledgements 16 The National Science Foundation: REU program  EEC-NSF Grant # Additional National Science Foundation support  CBET-NSF Grant # Air Liquide for supply of precursor Professor Christos Takoudis and Dr. Gregory Jursich Sathees Selvaraj, Graduate Student The Advanced Materials Research lab Fellow REU participants

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