Search

ABSTRACT In this work, the etching characteristics of InGaZnO4 (IGZO) thin films were systemically investigated in inductively coupled CH4/Ar plasmas with various gas ratios, bias voltages, and surface temperatures. The ion flux in the CH4/Ar plasmas was analyzed using bias power and voltage, whereas the relative densities of CH and H radicals were quantified through optical actinometry. The change in CH3 radical density was also estimated based on plasma kinetics analysis. The correlations between the plasma properties and IGZO etch rate were investigated. In CH4/Ar plasmas with CH4 ratios below 80%, the IGZO etch rate increases with a higher CH4 proportion, aligning with the ascending trend of CH3 radical density, which suggests that CH3 radical density acts as a limiting factor (radical‐limited regime). However, the IGZO etch rate decreases when the CH4 ratio exceeds 80%, corresponding to the reduction in ion flux, which indicates that ion flux becomes a limiting factor in this ion‐limited regime. The IGZO etch rate shows a linear relationship with bias voltage and follows the Arrhenius equation with varying surface temperature in plasmas without bias voltage. A spontaneous etch model was proposed based on these relationships. In this model, the IGZO etch rate depends on CH3 radical density and IGZO surface reactivity, where ion bombardment contributes more significantly to surface reactivity than high surface temperature. IGZO thin film was deposited on SiO2 during the fabrication of a 3D stacked ferroelectric field‐effect transistor (FeFET) memory device. The interaction between IGZO and SiO2 during CH4/Ar plasma processing was investigated using time‐of‐flight secondary ion mass spectrometry. The efficacy of removing IGZO atoms that had diffused into the SiO2 network was enhanced when subjected to plasma with a bias voltage, compared to the process without a bias voltage. However, exposure to CH4/Ar plasma resulted in a deeper diffusion of IGZO atoms into the SiO2 network, primarily attributed to ion bombardment rather than elevated surface temperature. A significant improvement in surface smoothness was achieved after IGZO and SiO2 etch by introducing BCl3 into the SiO2 etching chemistry. [ABSTRACT FROM AUTHOR]

Herein, the operation of a GeSe ovonic threshold switch (OTS) is studied as a self‐selecting memory cell based on the polarity effect. From the observed operating current (Iop) dependence and area scaling behavior, the critical role of Joule heating in ensuring exceptionally large memory window in this material is confirmed. The underlying mechanism is further investigated by means of chemical analysis and is confirmed to be caused by polarity‐dependent atomic migration under high‐Iop regime, consistent with elemental segregation due to electronegativity contrast. More specifically, selective diffusion of Ge atoms through the TiN layer into negatively biased top electrode stack is observed. At the same time, there is no sign of a similar process for Se atoms under opposite voltage polarity. Based on these observations, a novel memory concept utilizing a selective diffusion barrier is proposed. Furthermore, under low‐Iop regime, no major composition change is observed, leaving room for alternative interpretation of the polarity effect under such conditions. Finally, it is demonstrated that functional GeSe OTS‐only memory is fabricated with atomic layer deposition, making it suitable for vertical 3D integration to enable low‐cost applications. [ABSTRACT FROM AUTHOR]

Cross-point memory architecture involves high-density, fast yet cost-effective storage class memories (SCM). As a result, ovonic threshold switches (OTS) are extensively researched as they are needed in series with the SCM-based memory element for its precise functioning. In addition, these OTS-based devices exhibit the potential to be self-selecting memories too. Hence, its integration-friendly patterning becomes pivotal for large-scale manufacturing. Chalcogenide-based alloys are often the desired candidate for OTS. Here, we study the patterning of one of the widely investigated chalcogenide alloysSiGeAsTe. While the elements of the alloy generate highly volatile halogenated etch by-products, this material is also prone to severe etch-induced lateral undercuts and material damage. Thus, its high-density patterning is challenging. A conventional method to minimize this undercut damage is to increase the hydrocarbon passivation during the etch process to prevent the exposure of the chalcogenide's sidewalls (SWs) to any type of etchant. Inherently, this leads to the tapering of the OTS-based pillars, consequently becoming an impediment to their scaling at tighter pitches. Here, we clearly establish that OTS-based devices with well-preserved chemical and morphological properties can be fabricated using lower hydrocarbon passivation by tuning the ion energies during etching. Higher ion energies ensure better etch directionality. Concurrently, a well-controlled high energy ion bombardment is likely to enhance deposition of the passivating hydrocarbon from the etch front on to the chalcogenide's SWs. This is achieved without any unwanted redeposition from underlying layers in the OTS-based stack. We successfully demonstrate high-density nanopatterning of chalcogenide-based OTS devices of diameter ∼65 nm at 200 nm wide pitch. This is also effectively reproduced on 300 mm semiconductor wafers. The electrically measured devices exhibit low leakage and high endurance. This distinctive yet uncomplicated etch tailoring is also discussed to be scalable for pitches <200 nm and for other chalcogenide compositions. [ABSTRACT FROM AUTHOR]

Shallow embedding of C+ ions (<2nm) into commercial CoCrPt-based magnetic media using the filtered cathodic vacuum arc technique improves its anti-oxidation and anti-wear properties which are comparable to the conventionally used thicker carbon overcoats of ~3 nm. The next generation L10 FePt media subjected to low energy embedment of C+ ions have the potential to provide reduced magnetic spacing along with smaller and thermally stable grains, which is pivotal for achieving areal densities beyond 1 Tb/in.² However, the impact of low energy C+ ions embedding on the magnetics of FePt media is not known. Here, the magnetic properties of L10 FePt, post-shallow C+ ion embedment at 350 eV, were investigated. It was observed that bombardment of C+ ions in the 5nm thick FePt films produced a monumental reduction of ~86% in the out-of-plane coercivity value. Increasing the FePt film thickness did not significantly suppress the impact of these C+ ions on the media. Structural and elemental analyses attributed this alteration caused in the magnetic properties of the well-ordered FePt films to the penetration of >2 nm by the C+ ions into the FePt film. The media's crystallography with respect to the size and direction of the incoming ions has emerged to be accountable for the deeper distribution of the C+ ions and the associated widespread cascade damages within the magnetic layer. The consequences of low energy C+ ions embedding to attain high storage densities using high anisotropy L10 FePt media are discussed. [ABSTRACT FROM AUTHOR]

Density functional theory simulations are used to identify the structural factors that define the material properties of ovonic threshold switches (OTS). They show that the nature of mobility‐gap trap states in amorphous Ge‐rich Ge50Se50 is related to GeGe bonds, whereas in Se‐rich Ge30Se70 the Ge valence‐alternating‐pairs and Se lone‐pairs dominate. To obtain a faithful description of the electronic structure and delocalization of states, it is required to combine hybrid exchange–correlation functionals with large unit‐cell models. The extent of localization of electronic states depends on the applied external electric field. Hence, OTS materials undergo structural changes during electrical cycling of the device, with a decrease in the population of less exothermic GeGe bonds in favor of more exothermic GeSe. This reduces the amount of charge traps, which translates into coordination changes, an increase in mobility‐gap, and subsequently changes in the selector‐device electrical parameters. The threshold voltage drift process can be explained by natural evolution of the nonpreferred GeGe bonds (or "chains"/clusters thereof) in Ge‐rich GexSe1–x. The effect of extrinsic doping is shown for Si and N, which introduce strong covalent bonds into the system, increase both mobility‐gap and crystallization temperature, and decrease the leakage current. [ABSTRACT FROM AUTHOR]

A novel scheme of pre-surface modification of media using mixed argon-nitrogen plasma is proposed to improve the protection performance of 1.5 nm carbon overcoats (COC) on media produced by a facile pulsed DC sputtering technique. We observe stable and lower friction, higher wear resistance, higher oxidation resistance, and lower surface polarity for the media sample modified in 70%Ar + 30%N2 plasma and possessing 1.5 nm COC as compared to samples prepared using gaseous compositions of 100%Ar and 50%Ar + 50%N2 with 1.5 nm COC. Raman and X-ray photoelectron spectroscopy results suggest that the surface modification process does not affect the microstructure of the grown COC. Instead, the improved tribological, corrosion-resistant and oxidation-resistant characteristics after 70%Ar + 30%N2 plasma-assisted modification can be attributed to, firstly, the enrichment in surface and interfacial bonding, leading to interfacial strength, and secondly, more effective removal of ambient oxygen from the media surface, leading to stronger adhesion of the COC with media, reduction of media corrosion and oxidation, and surface polarity. Moreover, the tribological, corrosion and surface properties of mixed Ar + N2 plasma treated media with 1.5 nm COCs are found to be comparable or better than ~2.7 nm thick conventional COC in commercial media. [ABSTRACT FROM AUTHOR]