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In this study, pulsed CF3I/C4F8/Ar/O2 inductively coupled plasmas have been studied for low-k etching, and the effects of CF3I addition to C4F8/Ar/O2 on the plasma characteristics and etch characteristics of low-k materials were investigated. The increased ratio of CF3I/(CF3I+C4F8) in the gas mixture increased CF3 radicals while decreasing CF2 radicals in the plasma, and which are related to the etching and polymerization, respectively. Therefore, the etch rates of SiCOH increased with increasing the CF3I ratio. However, the etch selectivity over an amorphous carbon layer and photoresist was the highest at the ratio of 0.5 because the CF2/F flux ratio from the plasma and the C/F ratio on the polymer layer were the highest at the CF3I ratio of 0.5. The SiCOH damage was decreased with increasing CF3I ratio and the SiCOH damage appeared to be very low, particularly when the CF3I ratio was ≥0.5 by showing low Si–CH3 bond loss, low F penetration, and a low surface roughness. Therefore, it is believed that, as opposed to the C4F8/Ar/O2 gas mixture only, mixing 50% CF3I into the C4F8/Ar/O2 gas mixtures resulted in not only a high etch selectivity over mask materials, but also a potentially reduced etch damage.

The ultra-thin tin doped crystalline indium oxide (ITO) films (≤50 nm) were successfully deposited by a 3-dimensionally confined magnetron sputtering source (L-3DMS) at the temperature lower than 100 °C. The resistivity and the mobility of the ultra-thin ITO films deposited at a low processing temperature were about ~5 × 10−4 Ω · cm and >30 cm2/Vs, respectively, for the thickness of 30 nm. The high quality of the ultra-thin ITO films deposited by L-3DMS is believed to be related to the improved crystallinity with oxygen vacancies of the ITO films by high density plasma and low discharge voltage of the L-3DMS which enables the formation of a crystalline structure a low processing temperature.

Remote epitaxy has drawn attention as it offers epitaxy of functional materials that can be released from the substrates with atomic precision, thus enabling production and heterointegration of flexible, transferrable, and stackable freestanding single-crystalline membranes. In addition, the remote interaction of atoms and adatoms through two-dimensional (2D) materials in remote epitaxy allows investigation and utilization of electrical/chemical/physical coupling of bulk (3D) materials via 2D materials (3D-2D-3D coupling). Here, we unveil the respective roles and impacts of the substrate material, graphene, substrate-graphene interface, and epitaxial material for electrostatic coupling of these materials, which governs cohesive ordering and can lead to single-crystal epitaxy in the overlying film. We show that simply coating a graphene layer on wafers does not guarantee successful implementation of remote epitaxy, since atomically precise control of the graphene-coated interface is required, and provides key considerations for maximizing the remote electrostatic interaction between the substrate and adatoms. This was enabled by exploring various material systems and processing conditions, and we demonstrate that the rules of remote epitaxy vary significantly depending on the ionicity of material systems as well as the graphene-substrate interface and the epitaxy environment. The general rule of thumb discovered here enables expanding 3D material libraries that can be stacked in freestanding form.

Sn is the one of the materials that can be used for next generation extreme ultraviolet (EUV) mask material having a high absorption coefficient and, for the fabrication of the next generation EUV mask, a precise etching of Sn is required. In this study, the atomic layer etching (ALE) process was performed for the precise etch thickness control and low damage etching of Sn by the formation SnHxCly compounds on the Sn surface using with H and Cl radicals during the adsorption step and by the removal of the compound using Ar+ ions with a controlled energy during the desorption step. Through this process, optimized ALE conditions with different H/Cl radical combinations that can etch Sn at ∼2.6 Å cycle−1 were identified with a high etch selectivity over Ru which can be used as the capping layer of the EUV mask. In addition, it was confirmed that not only the Sn but also Ru showed almost no physical and chemical damage during the Sn ALE process.

Phase change random access memory (PCRAM) is one of the most industrially applicable memory devices because of its advantages such as non-volatility, high speed, scalability, and low power consumption. Ovonic threshold switch (OTS) materials are used in selector devices in PCRAM circuits and are generally composed of chalcogenide compounds. In this study, etch characteristics of OTS material composed of Ge-As-Te has been investigated using reactive ion etching (RIE) by hydrogen-based gases such as H2, CH4, NH3, etc. Among the investigated hydrogen-based plasmas, NH3 showed the highest etch rate due to the high vapor pressures of the hydrides of the OTS material, but the formation of nitride compound and the increased roughness were observed on the OTS surface. In the case of CH4 plasma, due to the carbon on the OTS surface, a polymer layer was deposited. Even though H2 showed the better surface smoothness due to the no surface residues or compounds on OTS surface related to carbon or nitrogen, the etch rates were lower than NH3. In this presentation, the effects of various hydrogen-based gases on the etch characteristics of OTS material will be discussed in details.

In order to etch CoFeB and MgO constituting the magnetic tunnel junction (MTJ) layer of magnetic random access memory, rf-biased reactive ion beam etching (RIBE) with a H2:NH3 gas mixture was introduced and the etching characteristics were investigated. The H2:NH3 gas mixture of 8:1 was used for rf-biased RIBE because the etch selectivity is increased with H2 percentage in the H2:NH3 gas mixture while the etch rates of MTJ materials are the highest between 2:1 and 1:1 ratio of H2:NH3 due to the synergy effect of H2 and NH3 in the etching of MTJ materials. When a high rf power was applied to the substrate (high rf-biasing) during RIBE, even though etch rates of MTJ materials were increased, the etch selectivities of MTJ materials over hard mask materials were decreased possibly due to the high physical sputtering effect. However, when small rf-biasing was added to the substrate during RIBE, improved etch characteristics such as higher etch selectivity of MTJ over the top electrode (TE) material, improved etch anisotropy of the MTJ pattern masked with TE, and a thinner sidewall residue on the MTJ pattern could be observed. The improvement in etch characteristics by the addition of small rf-biasing during RIBE is believed to be related to the increased chemical etching effect through H2/NH3 gas dissociation and the increased H/NH ratio in the plasma generated just above the substrate without increasing the physical sputtering effect. Specifically, for the substrate located on the insulating substrate holder, the charging of the substrate could be removed without using an electron emitting neutralizer by supplying electrons from the plasma generated by rf-biasing during RIBE.

Directed self-assembly of vertically aligned block copolymer (BCP) thin films has been extensively explored as one of the possible bottom-up routes for sub-10 nm patterning technology. To achieve a vertical orientation, it has been imperative to incorporate neutralization layers to balance the interfacial energy difference, which inevitably accompanies processing complexity. Here, a gradient random-copolymer block copolymer system, poly[(styrene-gradient-pentafluorostyrene)-b-methyl methacrylate] [P(S-g-PFS)-b-PMMA] BCP, which realizes universal vertical alignment of sub-10 nm block copolymer lamellae without any top-coat and neutral brush layers, is demonstrated. The surface energy difference between the block junction region and the tail of the gradient random-copolymer block provides a strong energetic preference for vertical lamellae on almost any type of surface, which is well supported by a thermodynamic model. Furthermore, we show that the gradient BCPs can be assembled on EUV lithography patterns to enhance their aspect ratios. This strategy of encoding surface energy balance could be potentially extended to a variety of other self-assembling systems, realizing universal orientation-controllability of nanoscale objects.

Freestanding graphene on a trench has been fabricated extensively using a transfer process of chemical vapor deposition grown graphene. Here, we demonstrate that freestanding graphene can be grown directly on a trench without a transfer process. A shallow trench was made on a 6H–SiC(0001) wafer using a focused ion beam lithography. The shallow trench was heated to a high temperature under Ar atmosphere. The heat treatment made the shallow trench become deeper and wider. Subsequently, epitaxial graphene was floating on the trench, resulting in freestanding graphene, where underlying bulk SiC was self-etched after the growth of epitaxial graphene. The freestanding graphene on a trench was characterized using Raman spectroscopy and atomic force microscopy. Such freestanding graphene writing can be applied to semiconductor fabrication process of freestanding graphene devices without a transfer process.

Next generation semiconductor devices require ultra low dielectric constant (ULK) materials such as porous SiCOH on the back end of line structure for lower resistance and capacitance (RC) time delay, however, these ULK materials are easily damaged by the exposure to plasmas during the etching. In this study, etch characteristics of nanoscale TiN masked porous SiCOH such as etch rate, etch profile, surface damage, etc. and plasma characteristics by using C3H2F6 based gases have been investigated with a dual-frequency capacitively coupled plasma system (DF-CCP) and the results were compared with those by using conventional C4F8 based gases used for low-k dielectric etching. The results showed that, for the similar etch rates and etch profiles of porous SiCOH, lower sidewall damage was observed for the etching with the C3H2F6 compared to the C4F8. The analysis showed that it was related to less UV (less than 400 nm) emission and less fluorine radicals in the plasma for C3 H2F6 compared to C4F8, which leads to less fluorine diffusion to the sidewall surface of the etched porous SiCOH by the fluorine scavenging by hydrogen in C3H2F6.

In this study, the SiO2 etch characteristics of perfluorocarbon such as C4F8, C5F8, and C7F8 were investigated using inductively coupled plasmas (ICPs) to study the effect of a high C/F ratio on the etch characteristics of SiO2 for the ICP. The SiO2 rates and etch selectivities over Si3N4 and amorphous carbon layer (ACL) were measured by using the mixtures of Cx(x = 4, 5, 7)F8/Ar/O2. The higher C/F ratio of perfluorocarbon showed lower SiO2 etch rate but exhibited higher etch selectivities over Si3N4 and ACL due to the higher C2 while keeping the similar F in the plasma as observed by optical emission spectroscopy and due to the thicker fluorocarbon layer with more carbon-rich fluorocarbon on the materials surface as observed by X-ray photoelectron spectroscopy. Especially, C7F8 is environmentally benign material because it not only has a relatively low global warming potential but also can be captured easily using a capture system (a liquid state at the room temperature). Therefore, C7F8 could be applicable as one of the next generation perfluorocarbon etching materials.

In order to reduce the interconnect resistance and capacitance (RC) time delay of a semiconductor integrated circuit, a more porous dielectric material is used in recent interconnection for lower dielectric constant. However, it is difficult to use highly porous low-k dielectric materials at the narrow pitch because it is easily damaged during the plasma etching processes. In this study, as one of the plasma induced damage reduction methods in the etching of porous low-k dielectric, RF pulsed plasma methods have been investigated by using a dual frequency capacitively coupled plasma etching system. RF pulsed plasmas generated more polymerizing species and less UV compared to continuous wave plasmas and showed reduced damaged layer compared to the conventional continuous wave plasma etching. Porous SiCOH dielectric patterned with a TiN hard mask was etched using the RF pulsed plasmas and the results showed more anisotropic etching profiles with less sidewall damages, which was estimated by the thickness loss of sidewall low-k material after dipping into a diluted HF solution. Therefore, it is believed that the RF pulsed plasma etching process of ultra low-k dielectric materials can improve the RC time delay related to plasma damage for the next interconnect manufacturing technology.

Adjusting the intrinsic properties of 2-dimensional (2D) transition metal dichalcogenide materials is important for their various applications in electronic devices. Among them, molybdenum disulfide (MoS2) is one of the most attractive layered 2D materials because of its excellent electrical properties as well as good thermal and oxidation stability. Controlling the doping process and analyzing how the dopant atoms affect the device properties are crucial for advanced applications of TMDs. In this study, a simple and controllable chlorine doping method of MoS2 using a remote inductively coupled plasma (ICP) was studied and the effect of doping on the properties of MoS2 was investigated by adjusting the work function of MoS2. Kelvin probe force microscopy (KPFM) shows a gradual decrease of the work function with increasing chlorine radical treatment time. Chlorine doped MoS2 field effect transistors (FETs) exhibited improved electrical characteristics such as the field effect mobility and on current level as demonstrated by the transfer characteristics (Id–Vgs). Especially, the chlorine doped MoS2 FETs showed increased photoresponsivity by 1.94 times (from 424 to 824 A W−1) for green light (λ = 520 nm) and, much more interestingly, 8.59 times (from 37.6 to 323 A W−1) for near-infrared (NIR) light (λ = 785 nm).

Etch characteristics of ovonic threshold switch (OTS) materials composed of Ge–As–Te for a phase-change random access memory (PCRAM) has been investigated using reactive ion etching via hydrogen-based gases such as H2, CH4, NH3, CH4 + H2, and CH4 + NH3. Among the investigated hydrogen-based gases, NH3 showed the highest etching rate of about 0.52 nm s−1, but the formation of nitride compounds and the increased roughness were observed on the OTS surface by nitrogen. The use of other hydrogen-based gases such as CH4 and CH4 + H2 showed the deposition and low OTS etch rate, respectively, due to the presence of carbon in CH4. Even though H2 showed the better etch characteristics due to the no surface residues or compounds on the OTS surface related to carbon or nitrogen in the etch gases, the best OTS etch characteristics such as the second highest etch rate of 0.45 nm s−1, the lowest surface roughness of 0.21 nm, and no surface residues or compounds were observed with CH4 + NH3 due to the removal of carbon and nitrogen on the surface by the formation of volatile CN compounds while maintaining a high hydrogen atomic concentration in the plasma.

Low-hydrogen-containing amorphous silicon (a-Si) was deposited at a low temperature of 80 °C using a very high frequency (VHF at 162 MHz) plasma system with multi-split electrodes. Using the 162 MHz VHF plasma system, a high deposition rate of a-Si with a relatively high deposition uniformity of 6.7% could be obtained due to the formation of high-ion-density (10

Precise and selective removal of silicon nitride (SiN

Transparent heat films (THFs) are attracting increasing attention for their usefulness in various applications, such as vehicle windows, outdoor displays, and biosensors. In this study, the effects of induction power and radio frequency on the welding characteristics of silver nanowires (Ag NWs) and Ag NW-based THFs were investigated. The results showed that higher induction frequency and higher power increased the welding of the Ag NWs through the nano-welding at the junctions of the Ag NWs, which produced lower sheet resistance, and improved the adhesion of the Ag NWs. Using the inductive welding condition of 800 kHz and 6 kW for 60 s, 100 ohm/sq of Ag NW thin film with 95% transmittance at 550 nm after induction heating could be decreased to 56.13 ohm/sq, without decreasing the optical transmittance. In addition, induction welding of the Ag NW-based THFs improved haziness, increased bending resistance, enabled higher operating temperature at a given voltage, and improved stability.

Flexible, stretchable, and bendable materials, including inorganic semiconductors, organic polymers, graphene, and transition metal dichalcogenides (TMDs), are attracting great attention in such areas as wearable electronics, biomedical technologies, foldable displays, and wearable point-of-care biosensors for healthcare. Among a broad range of layered TMDs, atomically thin layered molybdenum disulfide (MoS2) has been of particular interest, due to its exceptional electronic properties, including tunable bandgap and charge carrier mobility. MoS2 atomic layers can be used as a channel or a gate dielectric for fabricating atomically thin field-effect transistors (FETs) for electronic and optoelectronic devices. This review briefly introduces the processing and spectroscopic characterization of large-area MoS2 atomically thin layers. The review summarizes the different strategies in enhancing the charge carrier mobility and switching speed of MoS2 FETs by integrating high-κ dielectrics, encapsulating layers, and other 2D van der Waals layered materials into flexible MoS2 device structures. The photoluminescence (PL) of MoS2 atomic layers has, after chemical treatment, been dramatically improved to near-unity quantum yield. Ultraflexible and wearable active-matrix organic light-emitting diode (AM-OLED) displays and wafer-scale flexible resistive random-access memory (RRAM) arrays have been assembled using flexible MoS2 transistors. The review discusses the overall recent progress made in developing MoS2 based flexible FETs, OLED displays, nonvolatile memory (NVM) devices, piezoelectric nanogenerators (PNGs), and sensors for wearable electronic and optoelectronic devices. Finally, it outlines the perspectives and tremendous opportunities offered by a large family of atomically thin-layered TMDs.

A novel adhesion process called “plasma press” has been investigated for achieving stronger bonding between two different materials. It was first developed to be applied in multilayer flexible printed circuit boards for next generation flexible mobile electronics. The plasma process is a hot pressing method employing plasma between the two materials in order to activate the material surfaces. Compared to the conventional hot-pressed sample, the plasma-pressed sample exhibited up to 130% higher adhesion strength. The stronger bond strength achieved in the plasma-pressed sample is attributed to the formation of active carboxyl functional groups and dangling bonds on the material surfaces by the presence of the plasma during the hot pressing process for bonding.

Tungsten (W) is actively investigated as one of the future metallization materials which can replace Cu for the metal thickness lower than tens of nanometer due to its sfmall electron mean free path of 19 nm and high melting temperature of 3673 K. In this study, inductively coupled plasma (ICP) assisted DC magnetron sputtering of W has been investigated for the lower resistivity of nm scale W film (30 nm). When the characteristics of W thin films deposited with and without ICP assistance were investigated, the decrease of the W thin film resistivity with the increase of deposition rate was observed as the ICP power is increased regardless of substrate heating. The decrease of W thin film resistivity by the ICP assisted DC sputter deposition was related to the change of crystal structure from A-15 to BCC, decreased oxygen incorporation in the film, decreased surface roughness, and increased grain size due to the increased ion flux to the substrate.

Tungsten diselenide (WSe2) has received significant attention because it shows the pristine ambipolar property arising from the Fermi level located near the midgap and can be converted to uni-polar form. In this study, we observe the formation of tungsten oxide (WOx) on the WSe2 surface after oxygen plasma treatment and show that the p-type WOx dopes WSe2. In our devices that underwent plasma treatment, it was interesting to find a strong correlation between the changes in the work function of WSe2 and a gold electrode, and the channel and contact resistances. The channel resistance changes very sensitively at a rate of 64 meV per dec with the increase in the WSe2 channel work function, which is close to the thermal limit; this indicates the defect-free oxidized WSe2 channel. The carrier transport in the oxidized WSe2 FET is shown to change to a high performance p-type device with greatly reduced channel and contact resistances with the increase in the plasma oxidation time.

In this study, cobalt films were deposited by plasma enhanced atomic layer deposition (PEALD) with cobaltocene (Co(Cp)₂) using two different very high frequency (VHF) NH₃ plasmas (60 MHz, 100 MHz), and the effect of different frequencies of VHF on the characteristics of NH₃ plasmas and the properties of cobalt films were investigated. It is found that the higher frequency showed the higher plasma density at the same input power and, the NH radicals, which are required to remove the ligands of the cobalt precursor during the plasma exposure step in the ALD cycle, were higher at 100 MHz than those at 60 MHz. The RMS surface roughness and carbon impurity percentage of the deposited cobalt films were lower at the higher frequency possibly indicating denser films due to more active surface reactions at the higher frequency. As a result, it is expected that the cobalt thin films deposited by the higher VHF PEALD will improve the characteristics of deposited thin films.

Magnetic tunneling junction (MTJ) materials such as CoFeB, Co, Pt, MgO, and the hard mask material such as W and TiN were etched with a reactive ion beam etching (RIBE) system using H

Silicon nitrides, deposited by capacitively coupled plasma (CCP)-type plasma enhanced atomic layer deposition (PEALD), are generally applied to today’s nanoscale semiconductor devices, and are currently being investigated in terms of their potential applications in the context of flexible displays, etc. During the PEALD process, 13.56 MHz rf power is generally employed for the generation of reactive gas plasma. In this study, the effects of a higher plasma generation frequency of 162 MHz on both plasma and silicon nitride film characteristics are investigated for the purpose of silicon nitride PEALD, using bis(diethylamino)silane (BDEAS) as the silicon precursor, and N2 plasma as the reactant gas. The PEALD silicon nitride film deposited using the 162 MHz CCP exhibited improved film characteristics, such as reduced surface roughness, a lower carbon percentage, a higher N/Si ratio, a lower wet etch rate in a diluted HF solution, lower leakage current, and higher electric breakdown field, and more uniform step coverage of the silicon nitride film deposited in a high aspect ratio trench, as compared to silicon nitride PEALD using 13.56 MHz CCP. These improved PEALD silicon nitride film characteristics are believed to be related to the higher ion density, higher reactive gas dissociation, and lower ion bombardment energy to the substrate observed in N2 plasma with a 162 MHz CCP.