We demonstrate magnetic control of optical reflectance with no ferromagnetic material via combining the Faraday rotation and the surface plasmon resonance (SPR) in a Kretschman configuration under magnetic fields < 0.5 T. The SPR produces the polarization sensitive reflectance from the Au or Ag thin film coated on a N-BK7 prism in which the Faraday rotation occurs. The gold (Au) or silver (Ag) metal film as a plasmonic film somewhat acts as an incident angle-dependent reflection polarizer that can sensitively sense the polarization change induced by the Faraday rotation that occurs in a prism. We find that combination of Faraday rotation and the surface plasmon can induce a significant magnetic modulation of reflectance normalized with respect to that obtained with no magnetic fields at a specific incident angle of light. The magnetic control of optical reflectance presented may find an application in polarizer-free photonic devices with no ferromagnetic material for magneto-optical modulation.
We develop stable and printable precursor inks from binary metal halides; the inkjet-printed textile-based CuBrI thin-film transistors at a low temperature of 60 °C demonstrated the potential for printing complementary circuits in wearable electronic textiles.
Selective etching of Si3N4 to SiO2 is essential in the semiconductor fabrication process. In particular, as the number of alternating Si3N4/SiO2 multi-layered stacks increases, selective removal of Si3N4 without loss of SiO2 becomes difficult. In this study, the dissolution of Si3N4 was demonstrated in superheated water without addition of H3PO4, which has been widely used to etch Si3N4. The dissolution rates of Si3N4 and SiO2 in the superheated water depended strongly on the concentration of OH−, and the activation energy obtained for the dissolution of Si3N4 was 72.65 ± 0.95 kJ/mol. It is believed that the attack of the partially δ+ charged Si atoms in the Si3N4 by nucleophilic OH− was the key step in the dissolution of Si3N4 in the superheated water. Because a tradeoff between the dissolution rate of Si3N4 and the Si3N4-to-SiO2 etching selectivity was observed, H2SiO3 and HF were added to HCl-based superheated water for optimization. The HCl-based superheated water with the addition of 0.005 vol% HF and 0.01 M H2SiO3 allowed successful fabrication of a horizontal SiO2 trench structure on a patterned Si3N4/SiO2 15 pair-layered stack through selective etching of Si3N4 without thinning of the SiO2 layer.
Silicon nitride (Si 3 N 4 ) has been widely used as an insulating or sacrificial layer in various electronic devices. A removal of Si 3 N 4 is also required in the semiconductor manufacturing process. In particular, in the 3D NAND flash memory manufacturing processes, selective removal of Si 3 N 4 from the Si 3 N 4 /SiO 2 stack structure is one of the very critical processes. It is known that Si 3 N 4 is etched in high temperature phosphoric acid (H 3 PO 4 ). Si 3 N 4 is etched by nucleophilic attack of H 2 PO 4 - and H 2 O in H 3 PO 4 solution [1]. However, as the number of Si 3 N 4 /SiO 2 stacked layers increases to improve the memory density of 3D NAND, oxide regrowth on the SiO 2 layer and non-uniform top-to-bottom etching performance during Si 3 N 4 etching process are the issues that need to be solved [2]. In this study, a novel Si 3 N 4 etching in superheated water is investigated. As the temperature of H 2 O increases, the self-ionization of H 2 O is accelerated, thus the concentrations of H 3 O + and OH - ion increase. It was previously reported that Si 3 N 4 is etched by nucleophilic attack of OH - in superheated water [3]. However, in general, superheated water produced a low Si 3 N 4 etching rate with the attack of Si substrate, making it difficult to apply to the Si 3 N 4 etching process. Therefore, in this study, various additives were added to superheated water to selectively etch Si 3 N 4 without material loss of the SiO 2 and Si substrate. LPCVD Si 3 N 4 film was prepared on Si wafer. A patterned Si 3 N 4 /SiO 2 multi-stack structure was prepared the selective etching of Si 3 N 4 . Deionized (DI) water with a resistivity of 18.25 M was used to prepare superheated water in the reactor. Acetic acid, butyric acid, citric acid, formic acid, hexanoic acid, lactic acid or tartaric acid was added to DI water before heating. The etching of process was conducted 160 °C for 20 min. The thickness of the Si 3 N 4 film was measured using a spectroscopic ellipsometry and a field-emission scanning electron microscope. To increase Si 3 N 4 etching rate and suppress the material loss of the Si substrate during the Si 3 N 4 etching process, various carboxylic acids, which are acidic and nucleophiles, were added to superheated water. The etching rates of Si 3 N 4 in 1 M carboxylic-acid-containing superheated water at 160 °C were shown in Fig. 1(a). To reduce the effect of OH - and investigate the effect of carboxylic acid on Si 3 N 4 etching, HCl was added to superheated water, adjusting the pH of the solution at 1, 2 and 3. Etching rates of Si 3 N 4 are shown in Fig. 1(a). When either of tartaric acid, citric acid, lactic acid, or acetic acid was added to superheated water, Si 3 N 4 etching rate was increased at a given pH, as compared to that obtained in HCl-added superheated water. However, when butyric acid, hexanoic acid or formic acid was added to superheated water, similar or lower etching rates of Si 3 N 4 were observed as compared to the HCl-added superheated water. The results in Fig. 1(a) suggest that Si 3 N 4 etching kinetics differs depending on the type of carboxylic acid added to superheated water. To investigate the reason for different Si 3 N 4 etching rate with the type of carboxylic acid, the concentrations of carboxylate (RCOO - ) ion were calculated from the p K a values of carboxylic acids at 25 °C. As shown in Fig. 1(b), the etching rates of Si 3 N 4 increased with the concentration of carboxylate ions. Based on these results, it is thought that carboxylate ions play an important role in Si 3 N 4 etching in superheated water. To investigate the selective Si 3 N 4 etching ability of carboxylic-acid-containing superheated water, a Si 3 N 4 /SiO 2 multi pair-layered structure on Si wafer was etched in tartaric-acid-containing superheated water. The cross-sectional FE-SEM images before and after the Si 3 N 4 etching process were shown in Fig. 2. It is clearly shown that Si 3 N 4 was selectively etched without material loss of SiO 2 and Si substrate. Finally, eco-friendly and environmentally friendly carboxylic-acid-containing superheated water process can be a strong candidate that can replace the conventional Si 3 N 4 etching process. References [1] T. Park, C. Son, T. Kim, S. Lim, J. Ind. Eng. Chem. , 102 , 146−154 (2021). [2] T. Kim, C. Son, T. Park, S. Lim, Microelectron. Eng. , 221 , 111191 (2020). [3] C. Son, S. Lim, ECS J. Solid State Sci. Technol. , 8 , N85−N91 (2019). Figure 1
Pairs of entangled photons are a key resource for photonic quantum technologies. The demand for integrability and multi-functionality suggests flat platforms, such as ultrathin layers and metasurfaces, as sources of photon pairs. Despite the success in the demonstration of spontaneous parametric-down-conversion (SPDC) from such flat sources, there are almost no works on spontaneous four-wave mixing (SFWM) - an alternative process to generate photon pairs. Meanwhile, SFWM can be implemented in any nanostructures, including isotropic and centrosymmetric ones, which are easier to fabricate than crystalline structures needed for SPDC. Here, we investigate photon pair generation through SFWM in subwavelength layers of amorphous silicon nitride (SiN) and study the effect of nitrogen content on the rate of pair emission. By observing two-photon interference between SFWM from the SiN layers and from the fused silica substrate, we find the third-order susceptibilities of layers with different nitrogen content. Finally, we demonstrate SFWM in lithium niobate, which is a second-order nonlinear material and where the direct SFWM can coexist with a cascaded process. Our results open a path for the implementation of SFWM in resonant flat structures, such as metasurfaces.
For the integration of 3D NAND, which has multiple Si 3 N 4 and SiO 2 pair-layer stack structure, highly selective etching of Si 3 N 4 to SiO 2 is required without decrease in the etching rate of Si 3 N 4 . While phosphoric acid is widely used as an etchant of Si 3 N 4 in actual processes [1], chemical additives are added to the phosphoric acid as accelerators or inhibitors to control the kinetics of the reaction. In general, etching of Si 3 N 4 is done at around 160 °C, but in the meantime, the process temperature may increase with the introduction of single wafer tool. In this study, we investigated the effects of various additives in H 3 PO 4 on the Si 3 N 4 etch rate and Si 3 N 4 /SiO 2 etch selectivity at a higher temperature. LPCVD Si 3 N 4 and SiO 2 blanker wafers were etched in H 3 PO 4 with the addition of various etching accelerators and inhibitors such as HF, NH 4 F, Si(OH) 4 , Si(OC 2 H 5 ) 4 , and H 2 SiF 6 at a temperature range from 160 to 200 °C. The thickness of the wafer before and after etching was measured by ellipsometry to measure etching rates of the films. When experiments were carried out with additives containing F, the etching rates of Si 3 N 4 and SiO 2 were increased by more than 30%. On the other hand, the Si 3 N 4 and SiO 2 etching rates decreased with the addition of the Si-based additives, but the decrease was remarkable in SiO 2 . In addition, the Arrhenius plots of Si 3 N 4 and SiO 2 were plotted to obtain activation energies of the reactions. As shown in Fig. 1(a), the F-containing additives act as catalyst in the Si 3 N 4 etching reaction, reducing activation energy than the conventional phosphoric acid process (54 kJ/mol·K). On the other hand, Si-based additive show no significant change in the activation energy for the etching of Si 3 N 4 (Fig. 1(b)). This is because addition of Si-based material to H 3 PO 4 does not change reaction pathway, but suppresses the rates of etching reaction by Le-Chateliers principle [2]. On the other hand, SiO 2 shows slightly different etching tendency. As shown in Fig. 2(a), the activation energy of the SiO 2 etching reaction decreased with the addition of F-containing additives than that of phosphoric acid process (81 kJ/mol·K). However, Si-containing additives increased activation energy as inactivating agents. In addition, fluorosilicic acid (H 2 SiF 6 ) was selected as an additive because it was expected that it reacts with water in aqueous solution to produce hydrates of Si and HF, giving effects of both F-containing and Si-containing additives. It was observed that the etching rate of Si 3 N 4 was increased, but the etching rate of SiO 2 was decreased (Data not shown here). In addition, the activation energy of the etching of Si 3 N 4 was lower than that of phosphoric acid. On the other hand, the activation energy of the SiO 2 etching increased. Therefore, it is suggested that the Si-inactivating effect is greater than the catalytic etching effect of fluorine. Based on the current study, it is concluded that a higher etch selectivity with an increased Si 3 N 4 etch rate is achievable with the addition of proper additives by controlling the activation energy. References [1] S. Aritome, NAND flash memory technologies, p. 273, John Wiley & Sons, Hoboken, NJ (2015). [2] D. Seo, J. S. Bae, E. Oh, S. Kim, S. Lim, Microelectron. Eng., 118, 66 (2014). Figure 1
As the number of stacked layers of the 3D NAND structure increases, the memory density of 3D NAND flash memory device increases [1]. In the fabrication of 3D NAND device, it is essential to selectively etch Si 3 N 4 by an etchant flowing along a narrow slit followed by metal deposition. However, as the number of Si 3 N 4 /SiO 2 multi-stack increases, selective etching of Si 3 N 4 becomes difficult. In order to increase the Si 3 N 4 -to-SiO 2 etch selectivity, SiO 2 etching inhibitor should be added to H 3 PO 4 . Unfortunately, most of SiO 2 etching inhibitors added to H 3 PO 4 generate oxide regrowth around SiO 2 layer on the Si 3 N 4 /SiO 2 multi-stack structure. In this study, the mechanism of oxide regrowth occurred on the 3D NAND structure was investigated. Patterned Si 3 N 4 /SiO 2 multi-stack structures were prepared. Etching experiments were performed using coupon wafers in 85% H 3 PO 4 or etching inhibitor-added H 3 PO 4 at 160 °C. The Si 3 N 4 and SiO 2 etching rates and Si 3 N 4 -to-SiO 2 etch selectivity were measured using spectroscopic ellipsometry and oxide regrowth on the Si 3 N 4 /SiO 2 multi-stack structure was analyzed using FE-SEM and HR-TEM. When the Si 3 N 4 /SiO 2 multi-stack structure was etched in the SiO 2 etching inhibitor-added H 3 PO 4 , oxide regrowth was observed on the SiO 2 layered trenches on the Si 3 N 4 /SiO 2 multi-stack structure, as shown in Fig. 1. The oxide regrowth occurred intensively at the corner of SiO 2 layered trench and oxide regrowth occurred heavily at the bottom of Si 3 N 4 /SiO 2 multi-stack structure as compared to the top. The overall amount of oxide regrowth on the SiO 2 layered trench increased as the concentration of SiO 2 etching inhibitor added to H 3 PO 4 increased. In addition, it is shown that generation rate of etching product is an important factor to occur oxide regrowth. Based on the results, it is suggested that etching inhibitor addition and high generation rate of etching product and mass transfer limitation are responsible for the oxide regrowth. Through their optimization, selective Si 3 N 4 etching on the Si 3 N 4 /SiO 2 multi-stack structure without oxide thinning and regrowth could be obtained, as shown in Fig. 2. References [1] S. Aritome, NAND flash memory technologies, p. 273, John Wiley & Sons, Hoboken, NJ (2015). [2] J. Jang, et al, in Symp. VLSI Tech. Dig. , 192 (2009). Figure 1
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