Quartz Mold Research Articles

Atomic scale smoothing of nanoscale quartz mold using amorphous carbon films

Abstract Surface roughness control of end products is increasingly becoming significant, especially with the miniaturization trends in the semiconductor industry. Ultra-thin amorphous carbon (a-C) films offer a prime solution to optimize surface roughness due to their outstanding characteristics. In this study, hydrogenated a-C films are deposited on two-dimensional quartz plates and three-dimensional quartz molds to evaluate the growth mechanisms and changes in the surface roughness, which is supported by molecular dynamics simulations. Results reveal that surface roughness encounters multiple variations until it reaches stable values. These fluctuations are categorized into four different stages which provide a concrete understanding of various growing mechanisms at each stage. Different behavior of the atoms in the top layers is recorded in the cases of normal and grazing incidents of carbon atoms. Lower surface roughness values are obtained at low-angle deposition. Interestingly, surface smoothing is attained on the sidewalls of the nanotrench mold where the deposition occurs with high incident ion angles.

Effect of thickness of surface silicon oxide on liquid advancement in nanogaps between synthetic quartz mold and silicon substrate surfaces in UV nanoimprinting

To understand the phenomenon in which shear stress increases in nanogaps between the mold and substrate surfaces during alignment in UV nanoimprinting, we investigate the liquid advancement of UV-curable droplets on modified silicon surfaces. The droplets are pressed with a flat modified surface of a synthetic quartz mold, and the transformed droplets are cured individually. Subsequently, the mold is detached and the shapes of the transformed droplets are observed. Scanning electron microscopy is performed to determine whether the transformed shapes are affected by the pressing force and holding time under a fixed applied force. The areas on which the droplets spread on the modified silicon substrates are almost independent of the pressing force and holding time, whereas the thickness of the surface silicon oxide layer affects the liquid advancement of the UV-curable droplets sandwiched between the modified mold and substrate surfaces in the nanogaps.

Study on the morphology and distribution of Fe phase in solidification structure of Cu-15Fe alloy ingots

The realization of high strength of copper-iron (Cu-Fe) alloy is related to its solidification structure. The morphology and distribution characteristics of Fe phase in the solidification structure of Cu-15Fe alloy ingot were analyzed, and the deformation strength of the alloy was compared. The results show that the cooling conditions can affect the size, morphology and distribution of Fe phase in the solidified structure. The average distribution uniformity in the water-cooled copper mold ingot (W-ingot) is 0.45% higher than that in the quartz mold ingot (Q-ingot). The distribution quality of Fe phase in solidification structure can be evaluated by fractal dimension and average Fe phase area. The larger the fractal dimension is, the smaller the average Fe phase area is, where Fe phase is smaller and more uniform in the corresponding region. In the experiment, the strength of the strip increased from 510 to 547 Mpa corresponds to the Q-ingot and the W-ingot.

Fluorescence alignment simulation for atomic-scale position adjustment in ultraviolet nanoimprint lithography

The alignment process of ultraviolet (UV) nanoimprint lithography requires a further sophisticated method to detect infinitesimal misalignments between a synthetic quartz mold and a silicon substrate. Previously, we proposed a fluorescence-alignment method based on the analysis of the additive-type moiré fringes generated by the interferences of fluorescence emission from fluorescent UV-curable liquid filling the concave bar-mark arrays on a synthetic quartz mold and a silicon substrate. The proposed method significantly reduces the cost of mold fabrication and simplifies the in-liquid process compared to the conventional method based on multiplicative-type moiré fringes prevailing in the industry. This is because the fluorescence-alignment method is free from the problem of the refractive index matching between mold and UV-curable liquid materials. However, its position accuracy remains as large as sub-10 nm scales in principle. In this study, through simulation using image drawing and analysis software, we demonstrate that a sophisticated fluorescence alignment can realize atomic-scale precision for position accuracy by attempting the following concepts: (i) the application of the principle on position determination of a fluorescent single-molecule to that of an individual bar-mark fluorescence signal; (ii) effective use of high bit-depth of recent imaging devices; and (iii) accumulations of the information on the positions of multiple bar-marks with periodicities by fitting their fluorescence intensity profiles using a periodic function.

ИССЛЕДОВАНИЕ СВОЙСТВ СПЛАВА U-10 % Zr

Density, phase composition, microstructure and thermal conductivity of the U-10 wt. % Zr alloy manufactured by induction melting with subsequent casting into quartz molds and turning to size have been investigated at JSC “SSC RF - IPPE”. For comparison, the density and thermal conductivity of the U-10 wt. % Zr alloy produced by melting followed by extrusion and turning to size were investigated. To determine the density, a hydrostatic weighing method was used. The average density values of the cast and extruded alloy were respectively 98.8 and 97.5 % of the theoretical density, which was calculated according to the rule of mixtures. The results of studying the microstructure using a scanning electron microscope are presented. It is shown that the cast alloy U-10 % Zr is a metal matrix in which zirconium-enriched particles of arbitrary shape are distributed. In a metal matrix, the bulk of the volume is occupied by the α-U, and there are also precipitates of the δ-phase in the form of thin plates. A lower value of the microhardness of the alloy is noted in comparison with the data published in the known literature. The results of measuring the thermal conductivity at temperatures from 100 to 750 °C for the U-10 wt. % Zr alloy obtained by casting and extrusion are presented. The stationary axial heat flux method (or method of plate) was used to measure the thermal conductivity. Alloy samples made in different ways have almost the same thermal conductivity at 200 °C. With an increase in temperature, the discrepancy in thermal conductivity between the samples of the cast and extruded alloy gradually increases, and the thermal conductivity of the extruded alloy turns out to be lower, which is especially noticeable in the temperature range of 600-750 °C. The data obtained are compared with the results of published works. The measured values of the thermal conductivity of the cast alloy U-10 wt. % Zr up to a temperature of 750 °C do not disagree with the literature data. It was found that at a higher temperature, the alloy softens, which, in turn, leads to deformation of the test specimen and an increase in the measurement error when using the axial heat flux method.

Remote injection casting process with reduced material loss for fabrication of metallic fuels

The remote injection casting process was developed using a high-capacity casting system in a mockup facility to secure the key technology for the fabrication of transmutation metallic fuels in hot cells. Seventy-eight fuel slugs fabricated simultaneously through remote injection casting were confirmed to satisfy the fabrication specification. The reaction characteristics of the coating candidates for the reusable crucible were investigated by using sessile drop tests with U-10wt%Zr-5wt%RE at 1450 °C for 1 h and LaYO3 showed the smallest interaction width. The improvement in the adhesion of Y2O3 coatings on the inner walls of the quartz mold was effective in reducing the reaction between the melt and the mold. The mechanical and chemical cleaning processes were investigated to remove the surface contamination layer of the melt residue for recycling. Both cleaning methods were effective with the mechanical treatment favored owing to the operations in hot cells. The remote injection casting process equipped with fuel loss control components developed in this work will fabricate transmutation fuels in hot cells.

Design of a disulfide bond-containing photoresist with extremely low volume shrinkage and excellent degradation ability for UV-nanoimprinting lithography

UV-nanoimprinting lithography has the merits of high throughput and resolution, low cost of manufacture and room temperature operation, and thus finds wide applications in various fields. Herein, a novel disulfide bond-containing photoresist for UV nanoimprint lithography was designed and prepared based on the disulfide compound, 2,2-dithiodiethanol diacrylate (DTDA), isobornyl acrylate (IBOA) and methyl methacrylate (MMA). The addition of DTDA could obviously enhance the double bond conversion (97%), polymerization rate (19% s−1) and thermal stability of the photoresist, but slightly reduce the Young’s modulus and indentation hardness. Remarkably, the as-prepared photoresist exhibited very low volume shrinkage that was as low as 0.93% owing to the reversible nature of the disulfide bond under UV light irradiation. Meanwhile, it had an excellent degradation ability in the presence of tributyl phosphine (TBP) and easily was removed from the mold. More importantly, the photoresist manifested an outstanding pattern transfer ability and could precisely duplicate the pattern with the line width of 206 nm and the height of 108 nm in the quartz mold without distortion.

Fabricating metal wicks by LMC-like continuous directional freeze casting

A novel continuous directional freeze casting technique derived from LMC (liquid metal cooling) is developed in the present study, which is named as “LMC-like freeze casting”. In this novel freeze casting method, a quartz mold containing slurry is dipped into a low-temperature bath with a constant rate to achieve directional freezing of the slurry. Under quasi-steady state conditions, the solidification front is kept above the liquid level of the low-temperature bath at a constant distance. The heat released during freezing is conducted downward axially within the solidified slurry, and then is conducted axially and radially to the low-temperature bath through the mold wall. As a result, the thermal resistance between the solidification front and the low-temperature bath is kept constant, and the solidification velocity is exactly the same as the dipping rate of the casting mold. With casting molds made from quartz, a good compromise between high casting rate and unidirectional freezing is achieved without introducing complex temperature control systems. To demonstrate the feasibility of the LMC-like freeze casting, long wicks (about 10 cm) with uniform pore size along the freezing direction are freeze-casted from aqueous nickel slurry. Permeabilities and capillary performance parameter of the fabricated wicks are measured, proving that LMC-like freeze casting technique is feasible to fabricate biporous metal wicks with aligned porosity.

Thermal shaping of thin glass panels for hard X-ray telescope optics

We present a process for thermal forming of thin glass panels of borosilicate glass to produce mirror segments for X-ray telescope optics. The mirror segments are required to be shaped in a parabolic and hyperbolic shape in accordance with Wolter-I type design of X-ray telescope optics. Thermal forming of glass is a low-cost method to produce light-weight mirror segments. The process makes use of a semi-cylindrical quartz mold having surface roughness of the order of 1 nm. Flat glass sheets of 0.2 mm and 0.3 mm thickness are placed on the diametric edges of the mold. With a suitable thermal cycle, the glass sheets are thermally formed as per the shape of the mold. The shape of these formed glass sheets was measured using a non-contact optical setup. The surface quality measurements of the formed glass sheets were performed using atomic force microscope and they were found to be in the range of 0.04–0.33 nm. Once tested for acceptance, these glass sheets are coated using sputter deposition of multi-layers of high and low atomic number materials for hard X-ray reflection. Such mirror segments do not require polishing of the surface before being coated with multi-layers.

Evaluating Heat Resistance of Mold Shells in Investment Casting

The paper describes the theory of developing the heat-resistance criterion for disposable ceramic molds exposed to poured metal, creating a computational and experimental method for computing the heat resistance by rapidly heating the mold by an electric arc, as well as analysis of comparative data on quartz, dinas, and electric-corundum molds from the standpoint of the developed criterial-evaluation theory. In this case, the heat resistance is of one-time character, as this mold sustains only a single casting. Computational and experimental data indicate a low heat resistance of β-quartz, making them non-recommendable for annealing and metal pouring if there is not supporting filler. Molds based on electric-corundum or dinas fillers are free of such drawbacks, with the latter being considerably cheaper. The use of tridymited dinas powders is effective after grinding the spent dinas lining of electric furnaces.

Fabrication of Nanosized Structures on Nafion Membranes by Thermal Nanoimprinting

We demonstrated a novel technique to fabricate nanosized structures on a Nafion membrane, using thermal nanoimprinting with a 5 × 5 μm2 square pattern Si mold without any polymer damage. A 24 MPa thermal imprinting pressure was used for 10 min. We observed high aspect ratio (∼1:10) pillars on the surface after imprinting at 200°C. Finally, we used a novel quartz mold with a 200 nm resolution dot pattern.

Simple fabrication process for UV nanoimprint mold with embedded metal alignment marks for in-liquid alignment

In-liquid alignment is expected to be applied to UV nanoimprint lithography (UV-NIL) for the fabrication of integrated circuits that requires high-precision multilayer processes. It is not very easy to perform in-liquid alignment using quartz molds commonly used in UV-NIL, since alignment marks on the molds become invisible owing to the refractive index matching of quartz and UV-curable resin when alignment marks of a mold are filled with UV-curable resin. In this paper, we developed a simple fabrication process for quartz molds without the mentioned problem. We successfully fabricated Ti patterns, which served as high-contrast alignment marks, exclusively in the recess part of the mold mark. We also performed in-liquid alignment process using a mold with the marks and demonstrated less than sub-100-nm alignment accuracy.

Influence of mold and substrate material combinations on nanoimprint lithography process: MD simulation approach

A molecular dynamics (MD) study was performed to examine the effect of mold–substrate material composition on the pattern transferring and defects of the resist polymer in a thermal Nano Imprint Lithography (NIL) process. As candidate materials, single crystalline nickel (Ni), silicon (Si) and silica (SiO2, α-quartz) for the rigid mold substrate, and amorphous poly-(methylmethacrylate) (PMMA) thin film for the resist were considered for common applications in NIL processes. Three different material compositions of Si mold–Ni substrate, Ni mold–Si substrate, and quartz mold–Ni substrate were considered. In accordance with a real NIL process, a sequence of indentation–relaxation–release processes was quasi-statically simulated using isothermal ensemble simulation on tri-layer molecular structures consisting of a mold, resist, and substrate. To correlate the deformed shape and delamination of PMMA resist from the substrate in indentation and release processes, non-bond interaction energy between a rigid mold and resist was calculated for each combination of mold and substrate materials. The Si mold–Ni substrate combination shows successful pattern transfer to the resist polymer even without an anti-sticking layer as a result of the desirable balance of surface free energy for mold and substrate materials. However, Ni mold–Si substrate combination shows a critical delamination of the resist in the release process due to strong van der Waals adhesion between the resist and Ni mold. Similarly, the quartz mold–Ni substrate combination shows the same delamination in pattern transfer, but the adhesion of the resist to the quartz mold is attributed to electrostatic interaction. In order to provide guidelines for material selection in imprint-like processes where surface adsorption and wetting characteristics are critical design parameters, a simple PMMA-rigid plate model is proposed, with which consistent surface interaction characteristics in the full model NIL process simulation can be obtained.

Noncontact microembossing technology for fabricating thermoplastic optical polymer microlens array sheets.

Thermoplastic optical polymers have replaced traditional optical glass for many applications, due to their superior optical performance, mechanical characteristics, low cost, and efficient production process. This paper investigates noncontact microembossing technology used for producing microlens arrays made out of PMMA (polymethyl methacrylate), PS (polyStyrene), and PC (polycarbonate) from a quartz mold, with microhole arrays. An array of planoconvex microlenses are formed because of surface tension caused by applying pressure to the edge of a hole at a certain glass transition temperature. We studied the principle of noncontact microembossing techniques using finite element analysis, in addition to the thermal and mechanical properties of the three polymers. Then, the independently developed hot-embossing equipment was used to fabricate microlens arrays on PMMA, PS, and PC sheets. This is a promising technique for fabricating diverse thermoplastic optical polymer microlens array sheets, with a simple technological process and low production costs.

Novel Fluorinated Compounds that Improve Durability of Antistick Layer for Quartz Mold

Novel Fluorinated Compounds that Improve Durability of Antistick Layer for Quartz Mold

Formation of metal nanostructures by high-temperature imprinting

Metal nanostructures are used as wire grids for liquid crystal displays and lighting-receiving surface electrodes of solar cells. They are also integrated in emerging devices for chemical and biomedical detection and analyses carried out under various research and development programs. Currently, the mainstream fabrication method of metal nanostructures needs many manufacturing processes including patterning and metallization technologies. Here, our high-temperature nanoimprint technology for glass materials was applied to metals, which led to the development of technology to transfer nanopatterns onto a metal foil using a quartz mold. Although the glass transition temperature does not exist in metal but plastic deformation of metal is possible if the metal is made to re-crystallize at a high-temperature, but kept below its melting point. In our experiment, Al, Ag, and Cu foils of 100 μm thickness were bonded on a glass substrate of 1 mm thickness using an intermediation layer of the same metal. After that, a heated quartz mold was pressed against each metal foil, and nano-patterning was carried out. Within the limits of the specifications of a used thermal nanoimprint system, the optimal imprint temperature for Al, Ag, and Cu foils was 500, 600, and 650 °C respectively. For all metals the imprint pressure and holding time were set as 20 MPa and 1 h. As a result of trial experiments, on the three kinds of metal foils we succeeded in forming line/space with a minimum linewidth of 350 nm; and concave and convex square dotted patterns with a minimum width of 500 nm. This technique required imprint pressure less than used in conventional direct-nanoimprinting at the room temperature. With this technique of nanofabrication, molds with a low mechanical strength could be used.

Fabrication of sub 20-nm wide grooves in a quartz mold by space narrowing dry etching

This paper describes a simple fabrication process of fine groove structures for quartz molds used in UV nanoimprint lithography. Grooves that are finer than the ''spaces'' in line/space resist patterns can be obtained on a quartz substrate with the aid of thin Cr layer and a dry etching process using CHF3. The main cause of the groove width narrowing is deposition of fluorocarbon polymer. By changing etching conditions, a large amount of space narrowing is realized. Grooves with widths of 18nm and 62nm were successfully obtained from 85-nm and 200-nm wide space resist patterns, respectively.

Electroless deposition of biocompatible Ag/W on quartz for the purpose of variotherm micro molding

Variotherm micro/nano molding demands lower heat capacity but higher thermal conductivity on being electrically heated part. Quartz mold can provide nano/micro features with high accuracy but failed to be used in real molding process due to its low thermal conductivity, which may be elevated by coating metals on it. In this paper, a novel electroless plating solution with ammonia and malic acid as double complexing agents was developed to deposit Ag/W alloys on quartz surface. A suitable surface roughness of quartz glass for Ag/W deposition was obtained at volumetric ratio (HF:H2SiF6:H2O) of 1.4:1:2. The effects of malic acid concentration on the compactness, adhesion, composition, resistivity and deposition rate of the Ag/W coating were investigated. A kinetic model was established for adjusting and predicting Ag/W deposition rate in the coating fabrication process.

Large-Area Nanotemplate Process and Its Application to Roll Imprint

This study developed a stitching process for unit element nanotemplates based on step and repeat imprinting for use in enlarged soft mold fabrication. This mold was subsequently used for the custom-developed roll-to-plate UV nanoimprint process. The distinctive features of roll UV imprinting include the following: (1) the UV source is embedded within a roll mold made of quartz so that it can illuminate a resist coated on either a transparent or an opaque substrate, (2) the press-contact between the resist and soft mold wrapped around the quartz mold was designed to synchronize the rolling operation with the linear motion of the substrate, which helped minimize the residue thickness, and (3) a compressed pneumatic force was applied along the contact line of the roll imprint, which helped attenuate any possible level mismatch on the stitched mold surface.

Fabrication and characterization of sub-500 nm channel organic field effect transistor using UV nanoimprint lithography with cheap Si-mold

P-type poly (3-hexylthiophene) (P3HT) organic field effect transistors (OFETs) with channel length down to 500nm were fabricated. The gold source and drain electrodes were patterned using UV-based nanoimprint lithography and a lift-off process. To reduce mold costs, an opaque silicon nanoimprint-mold was used instead of expensive quartz molds for UV-nanoimprint. This new technique, called non-transparent UV-nanoimprint lithography, can be applied due to the impact of indirectly propagating light. Finally, the electrical performance of OFETs was tested. However, the OFETs with short channels show inhibited saturation ability and a weak gate control. The reasons for this short channel effect were discussed.