A Systematic Approach of Understanding and Retaining Pmos Compatible Work Function of Metal Electrodes On HfO 2 Gate Die
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0917-E04-05
A SYSTEMATIC APPROACH OF UNDERSTANDING AND RETAINING PMOS COMPATIBLE WORK FUNCTION OF METAL ELECTRODES ON HfO2 GATE DIELECTRICS Rashmi Jha1, Jiyoung Chung2, Bei Chen1, Robert Nemanich2, and Veena Misra1 1 Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC, 27695 2 Department of Physics, North Carolina State University, Raleigh, NC, 27695 ABSTRACT In this work we have performed Ultraviolet Photoelectron Spectroscopy (UPS) and XRay Photoelectron Spectroscopy (XPS) on: (i) 40Å of Ru deposited on 20Å of ALD-HfO2 (RuHfO2), (ii) 40Å of Re deposited on 20Å of ALD-HfO2 (Re-HfO2), and (iii) 40Å of W deposited on 20Å of ALD-HfO2 (W-HfO2) in as deposited as well as after 600˚C in-situ anneal exposure. The samples with Ru and Re indicated significant reduction in the oxygen content and shift in the Hf peaks towards higher binding energy after anneal as compared to the as deposited state. The loss of oxygen after anneal was associated with the reduction in the surface work function of Ru and Re measured by UPS. However, the sample with W showed a redistribution of oxygen after anneal leading to the formation of multiple oxides of W having a net higher surface work function. The spectroscopic measurements were correlated with the electrical measurements made on MOS capacitors with Ru metal gates on HfO2 gate dielectric. The results indicated that the oxygen content at metal/high-k interface plays an important role in governing the effective work function of Ru on HfO2 gate dielectric. INTRODUCTION Recently, much attention has been focused on studying HfO2 as gate dielectric for future generation CMOS devices. The polycrystalline silicon gates have been reported to suffer from Fermi level pinning on HfO2 which has necessitated the investigation of dual work function metal gate electrodes on HfO2 gate dielectric [1-2]. Recent reports have shown that the high work function metal gates suffer from a significant reduction in the effective work function on ultra-thin HfO2 after subsequent anneals, which poses a challenge for the development of candidate metal gates suitable for PMOS applications [3-4]. Furthermore, it has been demonstrated that the starting surface condition of HfO2 before the metal gate deposition and the oxygen content at metal/HfO2 interface play an important role in governing the effective work function (Φm,eff) of high work function metals [5]. In this work, we have performed extensive spectroscopic analysis to understand the origin of the instability in Φm,eff after subsequent anneals and proposed routes to retain the high Φm,eff. EXPERIMENTAL DETAILS High-k samples consisting of 20Å of ALD HfO2 on 10Å of interfacial SiON on p-type silicon substrates were obtained from Sematech. The as-received high-k samples were transferred to RF magnetron sputtering machine with a base pressure of 1x10-8 torr.
The spectroscopic samples were prepared by depositing 40Å of Ru (Ru-HfO2), 40Å of Re (ReHfO2), and 40Å of W (W-HfO2) using sputtering in Argon plasma. The sampl
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