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On the Potential of Tungsten as Next-generation Semiconductor Interconnects
최두호,Katayun Barmak 대한금속·재료학회 2017 ELECTRONIC MATERIALS LETTERS Vol.13 No.5
The continuous scaling of copper (Cu) interconnects produced two majorshortcomings – a severe resistivity size effect and material reliability issues. Tungsten (W), with the expected reduction in resistivity size effect due to itsshorter electron mean free path and improved reliability due to its highactivation energy for diffusion, is a worthwhile candidate to replace Cu. Inthis article, the potential of W for future interconnects is critically discussedby reviewing the current status of W technology, including various Wprocessing methods and the resulting phases, resistivity and microstructure. The compatibility of W with the back-end-of-line processes in CMOSdevices is also discussed. The resistivity of W and Cu wires at similar nanoscaleis compared based on the Fuchs-Sondheimer surface scattering modeland Mayadas-Shatzkes grain boundary scattering model using the reportedscattering parameters (p = 0.11 and R = 0.42 for W, and p = 0.52 andR = 0.43 for Cu), which shows that the resistivity of W wires is predicted toexhibit lower resistivity than that of Cu wires at line-widths below ~15 nm. Finally, anisotropy in the resistivity size effect in W wires is discussed, witha suggested method to reduce wire resistivity.
최두호 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.8
Severe resistivity size effect in Cu interconnects is attributed to the relatively long bulk electron mean free path (39 nm at 298 K), which is inherently determined by phonon scattering. In this regard, Ru and Co have been recently considered as attractive alternatives for next-generation interconnect materials because the significantly shorter electron mean free paths for Ru (6.6 nm) and Co (11.8 nm) have been predicted to lead to a dramatically reduced resistivity size effect, which may allow lower resistivity of these materials than Cu at sufficiently reduced interconnect dimensions despite their relatively high bulk resistivies. In this study, the impact of surface and grain boundary scattering for Ru and Co was assessed based on the Fuchs-Sondheimer surface scattering model and the Mayadas-Shatzkes grain boundary scattering model, first by fitting these models to the resistivity data reported in the literature and second by artificially varying the scattering parameters in the models. The results predict that the wire resistivities of Ru and Co will cross below that of Cu at wire-widths of 10-15 nm.
Variation-tolerant Non-volatile Ternary Content Addressable Memory with Magnetic Tunnel Junction
최두호,김경민,유창식 대한전자공학회 2017 Journal of semiconductor technology and science Vol.17 No.3
A magnetic tunnel junction (MTJ) based ternary content addressable memory (TCAM) is proposed which provides non-volatility. A unit cell of the TCAM has two MTJ’s and 4.875 transistors, which allows the realization of TCAM in a small area. The equivalent resistance of parallel connected multiple unit cells is compared with the equivalent resistance of parallel connected multiple reference resistance, which provides the averaging effect of the variations of device characteristics. This averaging effect renders the proposed TCAM to be variation-tolerant. Using 65-nm CMOS model parameters, the operation of the proposed TCAM has been evaluated including the Monte-Carlo simulated variations of the device characteristics, the supply voltage variation, and the temperature variation. With the tunneling magnetoresistance ratio (TMR) of 1.5 and all the variations being included, the error probability of the search operation is found to be smaller than 0.033-%.
기판 바이어스와 스퍼터 압력 조절을 통한 저저항 알루미늄 박막 형성 연구
최두호 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.10
In this study, the critical role of substrate bias during the sputter deposition of Al thin films is discussed. Two sets of Al thin films having a nominal thickness of 300 nm were deposited at sputtering pressures of 4.1 and 1.5 mTorr, respectively, with an applied negative substrate bias in the range of 0-200 V. It was found that the microstructure, surface roughness, film resistivity and grain size were greatly altered by the combination of bias magnitudes and sputtering pressures. The sputtering pressure of 4.1 mTorr resulted in greater changes in the film properties with the application of substrate bias, and a lesser but still significant degree was observed for the films deposited at 1.5 mTorr. The resistivity values for the films deposited at 1.5 mTorr were found to be significantly lower, with the lowest resistivity value of 3.1 μΩcm achieved at a substrate bias of 50 V. Based on grain size measured by the line intercept method and Mayadas- Shatzkes grain boundary scattering model, the resistivity contribution of grain boundary scattering for the lowest-resistivity film was found to be 0.37 μΩcm, which indicates that the film resistivity in the optimized condition is close to the known bulk resistivity of 2.65 μΩcm.