Showing papers by "Karl Opsomer published in 2019"

Composition Optimization and Device Understanding of Si-Ge-As-Te Ovonic Threshold Switch Selector with Excellent Endurance

Abstract: In this work we explore the composition space of the Ovonic Threshold Switch (OTS) selector device based on Si-Ge-As-Te material system. Physical Vapor Deposition (PVD) co-sputtering capabilities enabled the tuning of the As/Te ratio, Ge and Si content to increase the crystallization temperature TX>450°C. Guided by ab initio calculations, we optimize the composition and achieve stable endurance characteristics of more than 1011 cycles on 65nm devices fabricated on 300mm wafers. Finally, we propose a switching model that can predict the statistical distribution of the threshold voltage (VTH), explaining V TH drift and time-dependent instabilities.

Selective electroless deposition of cobalt using amino-terminated SAMs

Abstract: The continuation of CMOS scaling leads to the necessity of replacing Cu as an interconnect material with a metal with lower resistivity and better reliability performance. At the same time, significant technological improvements are required to mitigate the pattern overlay requirements when forming multilevel structures with a half-pitch below 10 nm. Area-selective deposition (ASD) offers an elegant way to enable self-alignment of multilevel structures. However, defectivity is a typical bottleneck of ASD integration. This work explores the selective electroless deposition (ELD) of Co as a replacement of Cu as an interconnect metal. The selective metallization process is promoted by the selective placement of an amino-terminated organic layer in combination with confined grafting of a Pd catalyst. Co films thicker than 40 nm can be formed on amino-terminated surfaces, while the surfaces with no amino functionality remain completely free of Pd and Co according to EDS chemical analysis and SEM inspection. This article offers a detailed study of selective Co growth on blanket and patterned structures and investigation of the ELD Co film properties, such as low-temperature recrystallization at 420 °C, grain structure, chemical composition and segregation of impurities. It is demonstrated that the resistivity of the ELD Co films exhibits lower thickness dependence when compared to that of PVD Co, which can be attributed to the ELD Co grain size exceeding the Co film thickness. In addition, it is shown that the underlying organic layer prevents the silicidation of the annealed Co film on the Si substrate while promoting interface adhesion values as high as 8.2 J m−2 ± 0.7 J m−2 for a 50-nm thick Co film.

Assessing stability of metal tellurides as alternative photomask materials for extreme ultraviolet lithography

Abstract: Tellurium (Te) is one of the elements with highest extinction coefficient κ at the 13.5 nm extreme-ultraviolet (EUV) wavelength. It is being considered as an alternative absorber material for binary photomasks in EUV lithography. The absorber material is required to remain chemically stable during EUV exposure, at elevated temperatures up to 150 °C, during mask cleaning, and in the low hydrogen pressure environment that is present in the EUV scanner. However, Te is known to react with oxygen and hydrogen, forming less EUV absorbing TeO2 and more volatile H2Te, respectively. Since the melting temperature of Te is only 449.5 °C at normal pressure, alloying Te with a more stable metal might result in a high κ material that will remain thermally and chemically stable over a wider range of operating conditions. In this paper, the authors report on the stability assessment of metal telluride (M-Te) alloys for the EUV absorber material. They combined Te with high κ metals, noble metals, and etchable metals. High κ and noble M-Te materials are both thermally more stable than etchable M-Te, but they cannot be patterned easily for use in an EUV photomask. High κ M-Te exhibits polycrystal morphology at room temperature compared to quasiamorphous noble M-Te though both can crystallize at a higher temperature. Hydrogen stability and cleaning solution stability of M-Te materials are improved considerably compared to Te, but their higher surface reactivity cannot be completely mitigated without the addition of an inert capping layer. Furthermore, etchable M-Te alloys are easily oxidized during deposition, resulting in lower electron density and hence lower κ. Nevertheless, M-Te alloys may be a way to stabilize Te for usage as the EUV absorber material.