High-Density Patterning of InGaZnO by CH4: a Comparative Study of RIE and Pulsed Plasma ALE.

InGaZnO (IGZO)-based thin-film transistors and selector diodes are increasingly investigated for a broad range of applications such as high-resolution displays, high-density memories, and high-speed computing. However, its potential to be a key material for next-generation devices is strongly contingent on developing patterning processes with minimal damage at nanoscale dimensions. IGZO can be etched using CH4-based plasma. Although the etched by-products are volatile, there remains a concern that passivation─an associated effect arising from the use of a hydrocarbon etchant─may inhibit the patterning process. However, there has been limited discussion on the CH4-based etching of IGZO and the subsequent patterning challenges arising with pitch scaling (<200 nm). In this work, we systematically investigate dry chemical etching schemes to pattern an IGZO film into densely packed nanostructures using CH4. Straight IGZO lines, ∼45 nm in width at a pitch of ∼135 nm, are produced by employing the traditional reactive ion etching method. While the passivating effect of CH4 does not impede the etching process, any further shrinkage of feature and pitch dimensions amplifies reactive ion etching-induced damage in the form of profile distortion and residue redeposition. We show that this is efficiently addressed via atomic layer etching (ALE) of IGZO with CH4 using a pulsed plasma. The unique combination of ALE and plasma pulsing enables controlled reduction of ion-assisted sputtering and redeposition of residues on the patterned IGZO features. This approach is highly scalable and is successfully applied here to achieve well-separated IGZO lines, with critical dimensions down to ∼20 nm at a dense pitch of ∼36 nm. These lines exhibit steep profiles (∼80°) and no undesirable change in IGZO composition post-patterning. Finally, ALE of IGZO under pulsed plasma, reproduced on 300 mm wafers, highlights its suitability in large-scale manufacturing for the intended applications.

Key material parameters driving CBRAM device performances.

This study is focused on Conductive Bridging Random Access Memory (CBRAM) devices based on chalcogenide electrolyte and Cu-supply materials, and aims at identifying the key material parameters controlling memory properties. The CBRAM devices investigated are integrated on CMOS select transistors, and are constituted by either Ge-Se or Ge-Te electrolyte layers of various compositions combined with a Cu2GeTe3 active chalcogenide electrode. By means of extensive physical and electrical characterization, we show for a given electrolyte system that slower write is obtained for a denser electrolyte layer, which is directly correlated with a lower atomic percentage of the chalcogen element in the layer. We also evidence that the use of Ge-Se electrolyte results in larger write energy (voltage and time), however with improved state retention properties than for Ge-Te electrolyte materials. We associate these results with the stronger chemical bonding of Cu with Se, resulting both in a stabilized Cu filament and a slower Cu cation motion. More robust processing thermal stability is also observed for Ge-Se compared to Ge-Te compounds, allowing more flexibility in the integration flow design.

Understanding the role of nitrogen in plasma-assisted surface modification of magnetic recording media with and without ultrathin carbon overcoats.

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.

Probing the role of carbon microstructure on the thermal stability and performance of ultrathin (<2 nm) overcoats on L10 FePt media for heat-assisted magnetic recording.

An understanding of the factors influencing the thermal stability of ultrathin carbon overcoats (COCs) is crucial for their application in heat-assisted magnetic recording (HAMR) at densities ≥ 1 Tb/in(2). Two types of non-hydrogenated ultrathin (∼1.5 nm) COCs were investigated after being subjected to laser-induced localized heating (at temperatures > 700 K) as envisaged in HAMR. Filtered cathodic vacuum arc (FCVA)-processed carbon with tuned C(+) ion energies of 350 eV followed by 90 eV provides significantly higher sp(3) C-C hybridization than magnetron sputter deposition even at very low thicknesses of ∼1.5 nm. As a result, the FCVA-deposited ultrathin carbon overcoats displayed excellent thermal stability along with improved wear and corrosion resistance. On the other hand, the sputtered carbon exhibited carbon loss and topographical and structural changes after laser irradiation owing to lower sp(3) hybridization. Therefore, this study highlights the pivotal role of carbon microstructure, primarily sp(3) hybridization, in non-hydrogenated carbon overcoats to maintain excellent thermal stability during the recurring high-temperature cycles in a HAMR process.

Enhanced tribological, corrosion, and microstructural properties of an ultrathin (<2 nm) silicon nitride/carbon bilayer overcoat for high density magnetic storage.

An ultrathin bilayer overcoat of silicon nitride and carbon (SiNx/C) providing low friction, high wear resistance, and high corrosion resistance is proposed for future generation hard disk media. The 16 Å thick SiNx/C overcoat consists of an atomically thin SiNx underlayer (4 Å) and a carbon layer (12 Å), fabricated by reactive magnetron sputtering and filtered cathodic vacuum arc (FCVA), respectively. When compared with monolithic overcoats of FCVA-deposited carbon (16 Å) and sputtered SiNx (16 Å), the SiNx/C bilayer overcoat demonstrated the best tribological performance with a coefficient of friction < 0.2. Despite showing marginally less electrochemical corrosion protection than monolithic SiNx, its ability to protect the magnetic media from corrosion/oxidation was better than that of an ∼27 Å thick commercial hard disk overcoat and 16 Å thick monolithic FCVA-deposited carbon. From X-ray photoelectron spectroscopy and Raman spectroscopy analyses, it was found that the introduction of the 4 Å SiNx underlayer facilitated higher sp(3) hybridization within the carbon layer by acting as a barrier and promoted the formation of strong bonds at the SiNx/C and the SiNx/media interfaces by acting as an adhesion layer. The higher sp(3) carbon content is expected to improve the thermal stability of the overcoat, which is extremely important for future hard disk drives employing heat assisted magnetic recording (HAMR).

Effect of angstrom-scale surface roughness on the self-assembly of polystyrene-polydimethylsiloxane block copolymer.

Self-assembly of block copolymers has been identified as a potential candidate for high density fabrication of nanostructures. However, the factors affecting its reliability and reproducibility as a patterning technique on various kinds of surfaces are not well-established. Studies pertaining to block copolymer self-assembly have been confined to ultra-flat substrates without taking into consideration the effect of surface roughness. Here, we show that a slight change in the angstrom-scale roughness arising from the surface of a material creates a profound effect on the self-assembly of polystyrene-polydimethylsiloxane block copolymer. Its self-assembly was found to be dependent on both the root mean square roughness (R(rms)) of the surface and the type of solvent annealing system used. It was observed that surface with R(rms)< 5.0 Å showed self-assembly. Above this value, the kinetic hindrance posed by the surface roughness on the block copolymer leads to its conforming to the surface without observable phase separation.