| AVS 61st International Symposium & Exhibition | |
| Electronic Materials and Processing | Wednesday Sessions |
| Session EM2-WeM |
| Session: | High-K Dielectrics from Non-Classical Channels |
| Presenter: | Tyler Klarr, Oregon State University |
| Authors: | T. Klarr, Oregon State University L. Wei, National Institute of Standards and Technology (NIST) N.V. Nguyen, National Institute of Standards and Technology (NIST) O.A. Kirillov, National Institute of Standards and Technology (NIST) J. McGlone, Oregon State University J. Wager, Oregon State University J.F. Conley, Oregon State University |
| Correspondent: | Click to Email |
As scaling of Si based devices approaches fundamental limits, thin film metal-insulator-metal (MIM) tunnel diodes are attracting interest due to their potential for high speed operation. Because operation of these devices is based on tunneling, electrode / interfacial roughness is critical. Recently, we showed that combining ultra-smooth bottom electrodes with insulators deposited via atomic layer deposition (ALD) enabled reproducible fabrication of MIM diodes with stable I-V behavior.1 Key performance parameters of MIM diodes include high I-V asymmetry and low turn-on voltage. The standard way to achieve asymmetry relies on the use of non-equivalent workfunction metal electrodes to induce a built-in field that creates polarity dependent electron tunneling barrier.2 Assessment of metal-insulator barrier heights is therefore critical for predicting diode performance.
In this work, we report the first use of internal photoemission spectroscopy (IPE) to measure barrier heights between an amorphous ZrCuAlNi (ZCAN) metal bottom electrode and several high-k dielectrics. MIM stacks were fabricated on Si substrates capped with 100nm of thermally grown SiO2 and a 150nm thick ZCAN amorphous metal bottom electrode deposited via DC magnetron sputtering. Al2O3 and HfO2 were deposited via thermal ALD at 250ºC using H2O and TMA or TEMA-Hf, respectively. SiO2 was deposited using plasma-enhanced ALD (PEALD) at 200ºC using O2 and bis-diethylaminosilane (BDEAS). For IPE measurements, semitransparent top electrodes were formed by electron beam evaporation of Al (0.04mm2) and patterned by a multistep photolithography process. In IPE, the conduction band offset between two materials is characterized by measuring the additional current created by photo-excitation of carriers under an applied bias (Vapp). Devices were tested in a custom built IPE system in which incident photon energy (Eph) from a broadband 150W xenon lamp source was swept from 1.5 to 5eV while the increase in current (photoemission yield) was monitored. The Vapp polarity was such that photoemission occurs at the ZCAN/insulator interface. The photoemission yield1/2 was plotted vs. Eph to determine the spectral threshold at each Vapp. Finally, a Schottky plot of spectral threshold vs. Vapp1/2 was used to estimate the zero field barrier heights from the y-axis intercept. Initial analysis indicates barriers of 3.4, 3.2, and 2.7 eV for SiO2, Al2O3, and HfO2, respectively. Additional dielectrics and metals are under investigation. IPE results will be compared to electrical methods of barrier extraction.
1. N. Alimardani et al, JVSTA 30, 01A113 (2012).
2. J.G. Simmons, JAP 34, 2581 (1963); JAP 34, 1793 (1963).