Spin-on Glass Research Articles

Directed self-assembly lithography for half-pitch sub-15 nm pattern fabrication process

ABSTRACTThis paper introduces a fabrication method to achieve sub-15 nm line-and-space (L/S) patterns by combining grapho- and chemo-epitaxy using poly(styrene-block-methyl methacrylate) copolymer (PS-b-PMMA). The fabrication method is simple, since it eliminates photoresist stripping and also does not require any special materials to form pinning patterns. In this process, the ridges formed on spin-on-glass (SOG) surface work as physical guides and the photoresists on them are utilized as a pinning layer. Fine PS-b-PMMA L/S patterns were obtained in sufficient critical dimension (CD) range of the guide patterns that corresponded to the 15% dose margin using ArF immersion lithography. 3-dimensional grid defects were found to be the origin of the short defects. The half-pitch (hp) 15 nm L/S patterns were transferred successfully to SOG/spin-on-carbon (SOC) stacked substrate.We also describe fabrication of sub-10 nm L/S patterns using a high-chi block copolymer (BCP).

Refractive Indexes of Porous Thin Films Prepared From Organic-templated Polymethylsilsesquioxanes

The rapidly developing microelectronics industry has shown a strong demand for high performance materials to improve device performance [1,2]. Nanoporous silicate thin films are considered as important materials for advanced electronics. The formation of air-filled nanopores is a key technology for preparing insulating materials [3-12]. Polymethylsilsesquioxane (PMSSQ), with the empirical formula of (CH3-SiO1.5)n, is a potential candidate for low dielectric spin-on glass [13]. It has the characteristics of low dielectric constant ranging from 2.7 to 2.9, high thermal stability, low moisture uptake, good adhesion to metal, and excellent mechanical properties [11,14]. In addition, star-shaped macromolecules, such as hyperbranched poly(ecaprolactone) (PCL), are generally used as an organic template to generate nanometer-sized pores in the matrix polymer [11,15]. The organic templates dispersed in the polymer matrix are required to completely decompose at a relatively low temperature range (200°C ~ 400°C), and after the thermal calcination process, the derived nanopores need to be well distributed as a closedcell structure in the polymer matrix. The air-filled nanopores in a thin film can be generated by a method that disperses organic templates into an insulating matrix material, and decomposes them at elevated temperature. The mechanical strength of an insulating material will undoubtedly decrease, and the size and distribution of the as-made pores cannot be uniform, due to the organic templates, which leave pores behind from the thermal decomposition. Moreover, if the pores agglomerate, the insulating material may break down at low voltage. Therefore, the thermal decomposition and dispersibility of the organic templates in matrix polymers, and control of the nanopore generation, should be suitably considered for the structural design of organic templates. In order to effectively generate and thoroughly distribute nanopores in the whole matrix film, the organic templates should be completely dispersed in matrix polymers, and the miJung-Soo Kim and Dae-Geun Nam Energy Component and Material R&BD Group, Korea Institute of Industrial Technology, Busan 618-757, Korea

Fabrication of rigid stamp on a cylindrical substrate using hydrogen silsesquioxane/ZrO2 nanoparticle composite material for roll-to-roll nanoimprinting process

In this study, a hydrogen silsesquioxane (HSQ) and zirconium oxide (ZrO2, zirconia) nanoparticle composite was used for a nanopatterned roll stamp fabricated using the direct printing technique. HSQ, referred as a spin on glass (SOG) material have been used for direct printing process with polydimethylsiloxane mold. In order to enhance mechanical properties of SOG material without losing printable property, ZrO2 nanoparticles were dispersed with HSQ solution. After direct printing process of composite material, annealing process was done to convert polymeric HSQ structure into SiO2 in order to enhance mechanical properties. We evaluate the chemical, optical and mechanical properties of the HSQ/ZrO2 composite by FT-IR, a refractive index measurement, a nanoindentation test and a pencil adhesion test. At the mechanical property tests, the composite material shows a high hardness value and good adhesion properties with glass substrate. Considering the composite material properties, it is suitable for use as a master cylindrical stamp in a roll-to-roll process.

Case study: Root cause of fluorine detection during TiN ARC layer corrosion of AlSiCu metal lines

The present study examines the cause of fluorine detection during the corrosion of the TiN antireflection coat (ARC) layer of AlSiCu metal lines. When a crack is generated in the tetraethyl orthosilicate (TEOS) oxide or spin-on-glass (SOG) film of an LSI device, the corrosion of the TiN ARC layer (TiOxNy-oxidation) may occur due to residual moisture inside the device. In this case, concentrated fluorine is detected around the corroded TiN ARC layer by energy-dispersive X-ray spectroscopy (EDX) analysis. Fluorine concentration was correlated with the degree of corrosion on the TiN ARC layer, suggesting the contribution of fluorine to the corrosion of this layer. When a wider distribution of fluorine concentrations was evaluated, however, the concentration of fluorine and the degree of corrosion on the TiN ARC layer did not match; instead, a higher concentration of fluorine was observed near the crack of the TEOS oxide film. The corroded TiN ARC layer of the sample was then removed, and the Al line of the underlying layer was observed. Etching was observed on the Al line surface where a high concentration of fluorine was detected. More specifically, EDX analysis detected that fluorine reacted with the Al line in the underlying layer after diffusion through the TiOxNy film, causing decreased film density due to the corrosion of the TiN ARC layer.

Chemical bond structure and MOSFET device damages of electron beam cured siloxane spin-on-dielectric films

This paper presents the properties of electron beam cured SOG (spin-on-glass) films in terms of the chemical bond structure and accompanying device damages. It is observed that e-beam cured SOG films do not show the Si-CH bonds in the FT-IR spectra but still have the carbons in the film which are thermally stable. As for the device damage, the experimental result shows that the threshold voltage of nMOSFET decreases by positive charging of gate oxide after e-beam curing process and it shows antenna ratio independence. Also, the variation of threshold voltage is largely affected by the cathode voltage, which determines the electron energy and interlayer dielectric thickness.

Amorphous Si waveguides with high-quality stacked gratings for multi-layer Si optical circuits

To realize a stacked multi-layer silicon-based photonic device, a waveguide with a stacked grating was fabricated by using amorphous Si (a-Si) material, which is suitable for constructing layered structures. The fabrication method was based on forming a flat a-Si layer on a non-flat structure by using only spin-on-glass (SOG) coating technique. The a-Si grating was precisely constructed on the a-Si waveguide with gold alignment marks for electron beam lithography. Transmitted and reflected light power dependence on the grating period, wavelength, and polarization was systematically measured and compared with the designed dependence. As a result, the reflected light power exhibited a characteristic peak structure at a particular wavelength. Remarkable transverse electric/transverse magnetic (TE/TM) mode dependence was also observed. Furthermore, the measured and the designed properties were in excellent agreement with each other. Consequently, the designed structure was well reproduced in the actual stacked structure based on the a-Si material. These results pave the way for novel a-Si based integrated photonic devices such as polarization selectors and wavelength filters, indicating that a-Si is an excellent material for implementing Si-based multi-layer optical circuits.

Planarized ambipolar a-SiGe:H thin-film transistors: Influence of the sequence of fabrication process

This work presents the fabrication, characterization and modeling of inverted staggered a-SiGe:H TFTs with planarized gate electrode. Using this structure two different sequences of fabrication are presented, where spin-on glass and silicon nitride are used as passivation layer, respectively. The results show ambipolar and unipolar behavior in the a-SiGe:H TFTs depending on the fabrication sequence. Also, trap density and characteristic energies for the deep localized states in the a-SiGe:H film are obtained. Using these parameters the device modeling is presented.

Low-temperature spin-on-glass method involving high-pressure annealing for filling high-aspect-ratio structures

As semiconductor devices are being increasingly scaled down, complex and high-aspect-ratio (AR) structures become necessary. The spin-on-glass (SOG) method has been considered to be effective for filling high-AR (>50) structures, because it enables low-cost fabrication and it has greater amenability to such structures. However, this method requires high temperatures (>600 °C) that can lead to degradation (i.e., oxidation) of adjoining active regions, and additional processes to restore these regions are necessary. We propose a low process temperature (∼400 °C) SOG method involving high-pressure annealing, for the filling of high-AR structures without the creation of voids.

Effects of germane flow rate in electrical properties of a-SiGe:H films for ambipolar thin-film transistors

In this work, the study of germane flow rate in electrical properties of a-SiGe:H films is presented. The a-SiGe:H films deposited by low frequency plasma-enhanced chemical vapor deposition at 300°C were characterized by Fourier transform infrared spectroscopy, measurements of temperature dependence of conductivity and UV–visible spectroscopic ellipsometry. After finding the optimum germane flow rate conditions, a-SiGe:H films were deposited at 200°C and analyzed. The use of a-SiGe:H films at 200°C as active layer of low-temperature ambipolar thin-film transistors (TFTs) was demonstrated. The inverted staggered a-SiGe:H TFTs with Spin-On Glass as gate insulator were fabricated. These results suggest that there is an optimal Ge content in the a-SiGe:H films that improves its electrical properties.

Thermoelectric Device Based on Vertical Silicon Nanowires for On-Chip Integration

A fabricating process of prototype thermoelectric device based on vertical silicon nanowires (SiNWs) for on-chip integration was presented. The SiNWs with diameter of 200 nm and height of 1 μm were fabricated by electron beam lithography and inductively coupled plasma etching. The gaps between the NWs were filled by the spin-on glass, which isolated the top and bottom electrodes. A serpentine platinum resistance thermometer coil was formed on the NWs to create temperature gradient across the NWs and measure the temperature of the top of NWs. I-V characteristics of the vertical device before and after annealing were measured. The nonlinear I-V curves were obtained, but the annealed one demonstrated 1000-fold reduction in resistance than the unannealed one.

Nanopatterned yttrium aluminum garnet phosphor incorporated film for high-brightness GaN-based white light emitting diodes

In this study, we fabricated high-brightness white light emitting diodes (LEDs) by developing a nanopatterned yttrium aluminum garnet (YAG) phosphor-incorporated film. White light can be obtained by mixing blue light from a GaN-based LED and yellow light of the YAG phosphor-incorporated film. If white light sources can be fabricated by exciting proper yellow phosphor using blue light, then these sources can be used instead of the conventional fluorescent lamps with a UV source, for backlighting of displays. In this work, a moth-eye structure was formed on the YAG phosphor-incorporated film by direct spin-on glass (SOG) printing. The moth-eye structures have been investigated to improve light transmittance in various optoelectronic devices, including photovoltaic solar cells, light emitting diodes, and displays, because of their anti-reflection property. Direct SOG printing, which is a simple, easy, and relatively inexpensive process, can be used to fabricate nanoscale structures. After direct SOG printing, the moth-eye structure with a diameter of 220nm was formed uniformly on the YAG phosphor-incorporated film. As a result of moth-eye patterning on the YAG phosphor-incorporated film, the light output power of a white LED with a patterned YAG phosphor-incorporated film increased to up to 13% higher than that of a white LED with a non-patterned film.

Comparison of silicone and spin-on glass packaging materials for light-emitting diode encapsulation

Traditional white light light-emitting diode (LED) encapsulation is performed by mixed phosphors and silicone coating on LED die. However, this encapsulation with silicone coating incurs overheated temperatures and yellowing problem. Therefore, this work attempts to replace silicone paste by using spin-on-glass (SOG) materials. Experimental results indicate that although initial brightness of SOG-based packaging is lower than that of silicone packaging, its light attenuation is significantly lower than that of silicone for a long lighting time. After the LED power is turned on for 12h, the brightness of LED with silicone and SOG material packaging decreases from 84 to 48lm and 73 to 59lm, respectively. Therefore, SOG material provides an alternative packaging solution for high power LED lighting applications.

Graphene film formation on insulating substrates using polymer films as carbon source

Graphene films were formed on sapphire surfaces using polymethylmethacrylate (PMMA) polymer films as a carbon source and characterized by Raman spectroscopy. For large-scale, uniform growth, a spin-on-glass (SOG)/Cu-catalyst/PMMA/sapphire layered structure was annealed in Ar–H2 flow at atmospheric pressure. We found that the SOG cover layer is effective to suppress evaporation and agglomeration of the Cu film. We also confirmed that morphology and quality of grown graphene films are dramatically improved by hydrogen etching of buried bulky carbon produced by the polymer pyrolysis at the Cu/sapphire interfaces. Quality of graphene films grown at the catalyst-layer/sapphire interface was compared with that on the catalyst surface using Ni/PMMA, PMMA/Ni and Ni/PMMA/Ni layered structures. Quality of graphene films grown at the Ni/sapphire interfaces was found to be lower than that on the Ni surfaces, suggesting that strain engineering at the buried Ni/graphene/sapphire interfaces and/or etching technique to remove the wastes of polymer pyrolysis should be improved.

Transparent Conducting Oxides for High Temperature Processing

Indium tin oxide (ITO) thin films were deposited by magnetron sputtering from a ceramic target, and annealed at temperatures up to 1000°C in N2 atmosphere. Some samples were capped in a-Si:H or spin-on glass to prevent residual oxygen contamination from the annealing ambient, and annihilation of oxygen vacancies. The electrical and optical properties were measured before and after annealing. It is found that the protecting layer effectively limits the ITO degradation up to 900°C, whereas high transparency is preserved in all cases. The results indicate the applicability of the procedure to high temperature devices, and opens the way to the application of a variety of nanostructured materials in advanced photovoltaic devices.

Using Thin Films of Rutile-Phase TiO2 Nanoparticles as Photoactive Material in Metal-Semiconductor Structures with Low Thermal Processing

Rutile-phase TiO2 nanoparticles are embedded within an organic SiO2 matrix (Spin-On Glass) and the final suspension is deposited by spinning on (a) thin aluminum stripes or (b) in between thin aluminum films and ultra-thin titanium stripes. The maximum processing temperature for both devices is 220 � C. The first device is a “horizontal” TiO2:SiO2/Al/Glass photoactive structure which is then electrically characterized under dark and illuminated conditions (I–V -Light) so that the total resistance of a simple aluminum stripe is measured before/after ultraviolet-visible (UV-Vis) irradiation. Compared to dark conditions, excess carriers are photogenerated within the TiO2 nanoparticles during light exposure and they are transferred to both ends of the aluminum stripe after applying a low potential difference. A large decrease in the resistance of the aluminum stripe (down to 43% of its original value) is obtained when this horizontal structure is irradiated with UV-B light thus acting as a photoresistor. The second device is a “vertical” Ti/TiO2:SiO2/Al/Glass photoactive structure. Here, the path for photogenerated and electrically-driven carriers occurs vertically, or inside a Metal-Insulator-Metal (MIM) capacitor. Because of the ultra-thin titanium layer (100 A in thickness), this gate electrode is highly transparent to most of the UV-Vis irradiation so that when all carriers are being photogenerated, they are almost immediately separated at the top/bottom electrodes by a small applied electric field due to the thin and high-dielectric constant of the photoactive TiO2:SiO2 film. This way, a fast and large increase/decrease in gate current (about 4–7 orders of magnitude) is observed when this device is under illumination/dark conditions. This vertical structure operates as a photocapacitor, where all photogenerated carriers could be efficiently stored within the MIM capacitor itself and thus, enable simultaneous conversion and storage of solar energy in the same device.

Three-dimensional hologram-read-only memory duplication by nanoimprint lithography

Because the amount of multimedia data is continually increasing, there is growing demand for high-speed, large-capacity, read-only memory (ROM) to facilitate data distribution. Computer-generated hologram-ROM (CGH-ROM) has received considerable attention in relation to its potential to meet this rising demand. CGH-ROM requires a nanoscale-precision structure, as well as nanosteps. Because of its process simplicity, nanoimprint lithography (NIL) is a promising method for cost-effective fabrication of complex and high-precision patterns. The authors have demonstrated CGH-ROM duplication by ultraviolet NIL (UV-NIL) from a three-dimensional (3D) master mold fabricated by electron-beam lithography (EBL). The calculated depths of the CGH were converted into four tones to permit easy fabrication of the CGH while retaining a high diffraction efficiency. EBL using a spin-on glass and super-resolution technique with a postexposure bake was used to fabricate the 3D master mold. The developed depth was controlled by changing the EB exposure dose, with higher EB doses tending to produce deeper patterns. The pattern was duplicated by means of UV-NIL and the reconstruction image corresponded to the design pattern. Moreover, the authors have succeeded in fabricating a gray-scale multilevel CGH-ROM and in producing its reconstruction.

Selective Removal of Ashed Spin-On Glass

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Fabrication and characterization of VCSELs applying quantum well intermixing using spin‐on‐glass

AbstractThe applicability of the quantum well intermixing using a spin‐on‐glass (SOG) to the fabrication process of a vertical cavity surface emitting laser (VCSEL) was investigated to control the carrier confinement in the active layer. The intermixing by using the non‐doped SOG showed a large emission energy shift. The SOG coating of the mesa side‐wall of the VCSEL and following heat‐treatment are simple processes that can add to the conventional one. The fabricated VCSELs with a 30 μm‐square mesa showed lasing operation, and therefore the technique can be applicable as the VCSEL process for improving the performance of the small mesa devices. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanoimprint Lithography of 20-nm-Pitch Dot Array Pattern Using Tone Reversal Process

The nanoimprint lithography (NIL) of a hexagonal dot array pattern with 20 nm pitch was demonstrated using a tone reversal process. The dot array was formed by the self-assembled polystyrene–poly(dimethylsiloxane) (PS–PDMS) diblock copolymer. The dot pattern was transferred to a hole pattern on the imprint resist layer by a UV-NIL process. The hole pattern was filled with spin-on-glass (SOG). By removing the imprint resist matrix, the SOG dot pattern was formed as a final mask layer. The surface tension of the imprint resist was adjusted to achieve high-quality pattern transfer and demolding. The standard deviation of the diameter and pitch of the dot pattern suffered about 1% drop through the UV-NIL and tone reversal process.

Towards a ‘catalyst activity map’ regarding the nucleation and growth of single walled carbon nanotubes

Quantification using scanning electron microscopy (SEM) of single walled carbon nanotubes (SWNTs) grown per unit area using a Co-Fe (50:50) catalyst system, prepared by the incorporation of the appropriate metal salts into a Spin-On Glass substrate, at 900°C. The effects of substrate, as well as catalyst precursor concentration, were investigated. SWNT growth density is maximised with a catalyst precursor concentration of ≥2.5 mM, associated with the formation of catalyst nanoparticles of a critical size for SWNT nucleation. Samples were subjected to secondary growth, using a range of H2:CH4 ratios to determine the optimum precursor composition. It was found that nucleation and growth stages are optimal under different conditions. Optimum conditions for nucleation resulted in >10× increase in SWNT density. Optimisation is dependent on temperature and the partial pressure of reagent gas species.