Quartz Mold Research Articles

Investigation of Thermal Analysis on the Process of Laser-Assisted Nanoimprinting Lithography

The technique of laser-assisted nanoimprinting lithography (LAN) has been proposed to utilize an excimer laser to irradiate through a quartz mold and melts a thin polymer film on the substrate for micro- to nano-scaled fabrications. This study introduces optical multiple reflection theory to demonstrate both analytical and numerical modeling during the LAN process and to predict the thermal response theoretically. Furthermore, the capability of energy absorption for polymer resist is examined herein. The temperature of polymer resist with the capability of energy absorption is much higher than that without energy absorption. This study demonstrates the characteristics of the energy absorption for polymer materials could improve the performance of the LAN process for the reason that the thermally affected region is extremely limited.

Micro-nano mixture patterning by thermal-UV novel nanoimprint

Hybrid patterning by thermal and UV nanoimprint lithography (NIL) is demonstrated to fabricate micro and nano mixed structures. The SU-8 resist is thermally imprinted using a quartz mold, which has fine nanostructures and micro Cr mask patterns. After the thermal nanoimprint, UV light is exposed to the resist through the mold. Then, the mold is released and the resist is developed to fabricate microstructures. Using this process, nanodots having 200nm feature sizes are successfully demonstrated on the microgratings with 40μm width and 20μm height. Also, fabrication of nanocorn array on the bottom of the deep microwell is demonstrated using Ni mold replicated from the resist master structure fabricated by the hybrid NIL.

Fabrication of three dimensional structures for an UV curable nanoimprint lithography mold using variable dose control with critical-energy electron beam exposure

In three dimensional (3D) printing the most challenging aspect is in the mold making process. The authors have developed a process for making 3D structures in a simple two-step process. The 3D profiles are created on a negative tone photoresist using electron beam lithography with variable dose and critical-energy electron beam exposure. Resist contrast profiles have been obtained with a negative tone photoresist from Microresist (ma-N2403) and subsequently have been utilized as the 3D masking layer. The 3D patterns have been transferred into a quartz mold by single-step reactive ion etching (RIE) with suitable resist-to-substrate selectivity. The precision of the fabricated structures is important, especially for micro-optic devices. Surface roughness below 2nm has been achieved when the RIE process pressure is lower than 6mTorr. The differences between intended and final dimensions are also analyzed. By employing this technique, complex structures for 3D quartz molds can be fabricated with simplified steps.

Pattern Transfer Process Using Innovative Polymers in Combined Thermal and UV Nanoimprint Lithography (TUV-NIL)

ABSTRACTWe performed combined thermal and ultraviolet nanoimprint lithography (TUV-NIL) using a recently developed nanoimprint polymer (mr-NIL 6000 from Micro Resist technology GmbH) and achieved an imprinted feature size of 50 nm. We used commercially available 2-inch-diameter transparent quartz molds (NIL Technology, Denmark and Obducat, Sweden) comprising 150 nm to 190 nm-deep features of various shapes and aspect ratios with lateral dimensions ranging between 50 nm and 300 nm. The imprint polymer was spun onto a silicon substrate, covered with an oxide layer. After the TUV-NIL step, residual polymer layers at the bottom of the imprinted features were removed by oxygen plasma etching. Imprinted patterns were then transferred into the silicon oxide layer underneath by reactive ion etching (RIE). In a final step the residual polymer was stripped off the silicon oxide surface in an oxygen asher. All imprinted features as well as the corresponding pattern transfer results showed good surface and sidewall characteristics.

Hybrid mold reversal imprint for three-dimensional and selective patterning

Three-dimensional (3D) nanostructures are needed in many applications including sensors, actuators, and microanalysis systems. In this work, a novel technology combining UV lithography, hybrid mold, and reversal imprint for fabricating 3D structures is developed. A hybrid mold made from quartz is used. The mold has structures patterned by lithography and dry etching. The quartz mold also has selected patterns formed by 50nm thick Cr. A layer of UV definable SU-8 polymer is spin coated onto the hybrid mold and patterned by optical lithography. The mold with the patterned SU-8 layer and no residue is then transferred to a substrate with topography by reversal imprint with temperatures as low as 50°C and pressures of nominally 2MPa. Depending on the dimensions of patterns on the mold compared to the ones on the substrate and the imprint pressure, patterns can be selectively transferred to substrates through reversal imprint. This technology greatly simplifies the fabrication process and provides more flexibility in building complex 3D structures.

Fast three-dimensional nanostructure fabrication by laser-assisted nanotransfer printing

The authors present a laser-assisted nanotransfer printing technique for transferring metal nanopatterns onto prepatterned substrates. A fused quartz mold covered with an array of chromium nanodots is pressed against the surface of a photolithographically patterned substrate, while a single laser pulse from a quadrupled-frequency solid state Nd:YAG laser is used to melt the thin metal structures. By controlling the laser fluence, selective metal pattern transfer can be realized only on the protruded area of the substrate upon separation of the quartz support. The transferred chromium nanodots are then used as an etch mask to pattern three-dimensional structures.

Control of Etched Pattern Profile in Quartz Dry Etching Processfor Fabricating Fine Quartz Mold of UV-Nanoimprint

Control of Etched Pattern Profile in Quartz Dry Etching Processfor Fabricating Fine Quartz Mold of UV-Nanoimprint

In‐situ curing analysis of photoreplicated objective lenses using Raman and IR spectroscopy

AbstractOptical pick‐up lenses are used in optical storage devices such as CD, DVD, and Blu‐Ray Disc. The production of such lenses is based on UV‐induced polymerization of a mixture of a dimethacrylate monomer and an initiator on a spherical glass substrate. The shape of the polymer layer is defined with an aspherical transparent mold. This means that the coating is completely surrounded by glassy materials during processing. Raman spectroscopy is applied in situ to monitor the polymerization reaction under conditions that closely resemble the actual production process. As a result improvements can be made to the reaction conditions if necessary. Data are compared to results obtained with IR spectroscopy in an off‐line approach. The value of the in situ characterization using Raman spectroscopy is illustrated by the observation that contrary to expectation, the local rate of polymerization is not influenced by shrinkage effects caused by local variations in volume relaxation in the wedge‐shaped sample volume. Instead, even quartz glass mold plates with a thickness of 30 times that of liquid monomer were deformed to accommodate for thermodynamically required volume shrinkage. The assumption of isochoric polymerization in a confined volume turned out to be incorrect. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1287–1295, 2006

An analytical modeling of heat transfer for laser-assisted nanoimprinting processes

Laser-assisted direct imprinting (LADI) technique has been proposed to utilize an excimer laser to irradiate and heat up the substrate surface through a highly-transparent quartz mold preloaded on this substrate for micro- to nano-scaled structure fabrications. While the melting depth and molten duration are key issues to achieve a satisfactory imprinting pattern transfer, many material property issues such as crystalline phase alteration, grain size change and induced film stress variation are strongly affected by transient thermal response. With one-dimensional simplification as a model for the LADI technique, the present paper has successfully derived an analytical solution for the arbitrary laser pulse distribution to predict the relevant imprinting parameters during the laser induced melting and solidification processes. The analytical results agree quite well with the experimental data in the literature and hence can be employed to further investigate the effects of LADI technique from laser characteristics (wavelength, fluence and pulse duration) and substrate materials (silicon and copper) on the molten duration, molten depth and temperature distributions. Three kinds of excimer laser sources, ArF (193 nm), KrF (248 nm) and XeCl (308 nm) were investigated in this study. For the silicon substrate, the melting duration and depth were significantly dictated by the wavelength of laser used, indicating that employing the XeCl excimer laser with longer pulse duration (30 ns in the present study) will achieve the longest molten duration and deepest melting depth. As for the copper substrate, the melting duration and depth are mainly affected by the laser pulse duration; however, the wavelength of laser still plays an insignificant role in LADI processing. Meanwhile, the laser fluence should properly be chosen, less than 1.4 J/cm2 herein, so as to avoid the substrate temperature exceeding the softening point of the quartz mold (~1950 K) and to make sure that the mold can still maintain the original features.

Laser-assisted photothermal imprinting of nanocomposite

We report on a laser-assisted photothermal imprinting method for directly patterning carbon nanofiber-reinforced polyethylene nanocomposite. A single laser pulse from a solid state Nd:YAG laser (10ns pluse, 532 and 355nm wavelengths) is used to melt/soften a thin skin layer of the polymer nanocomposite. Meanwhile, a fused quartz mold with micro sized surface relief structures is pressed against the surface of the composite. Successful pattern transfer is realized upon releasing the quartz mold. Although polyethylene is transparent to the laser beam, the carbon nanofibers in the high density polyethylene (HDPE) matrix absorb the laser energy and convert it into heat. Numerical heat conduction simulation shows the HDPE matrix is partially melted or softened, allowing for easier imprinting of the relief pattern of the quartz mold.

Study on optical intensity distribution in photocuring nanoimprint lithography

Optical intensity distribution in photocuring nanoimprint lithography is investigated. Its dependency on pattern size, optical index, and residual thickness of the photopolymer has been numerically evaluated using the finite-difference time-domain method. The irradiated beam propagates mostly in the photopolymer, where the optical index is larger than that of the quartz mold. If the pattern size is less than around 1/4 wavelength of the irradiated beam, optical intensity in the polymer decreases because the light propagates through both the polymer and quartz molds. In addition, the index difference between mold and polymer increases diffraction into the residual layer and causes optical intensity concentration at a particular position.

Large scale ultraviolet-based nanoimprint lithography

Limits in resolution and accuracy of large scale ultraviolet (UV)-based nanoimprint lithography using rigid quartz molds and spin coated UV curable resists are presented. The resolution and precision parameters are closely followed from pattern in the mold through imprints in the resist and finally compared with structures transferred into silicon by special etching processes. Specific attention is paid to the simultaneous patterning of nano and microscale structures. The applicability for functional nanoelectronic components is demonstrated by the fabrication of an NMOS transistor based on SOI, whose channel width is reduced to 50 nm.

NANOSTRUCTURES IN NANOSECONDS

A NOVEL METHOD FOR RAPidly imprinting nanostructures in silicon avoids the expensive photolithographic process currently used to fabricate silicon chips. new laser-assisted direct imprint (LADI) process uses a XeCl excimer laser with a pulse duration of 20 nanoseconds and a transparent patterned quartz mold to mechanically imprint the molten surface of a silicon wafer. surface quickly solidifies and, because there is no adhesion between the quartz and silicon, the mold can be removed without damage. technique was developed by professor of electrical engineering Stephen Y. Chou and graduate students Chris Keimel and Jian Gu at Princeton University's NanoStructure Laboratory { Nature , 417 , 835 (2002)}. group reports that the technique can be used to imprint 140-nm-wide gratings and other structural features such as rectangles with a resolution better than 10 nm on silicon wafers. embossing time is less than 250 ns. The biggest three advantages of the new method over other nanolithogra...

Measurement of Adhesive Force Between Mold and Photocurable Resin in Imprint Technology

In order to reduce the strong adhesive force between the mold and photocurable resin in UV-curable imprint lithography, release coating materials of the quartz mold and easy to release photocurable resin were examined. Furthermore, measurement methods of release properties of the imprint mold and photocurable resin were established using a tensile testing machine. The surface-treated slide-glass (SG) did not adhere to the resins and the adhesive forces were markedly reduced. For the release coating materials, the adhesive force for KP-801M was smaller than that for Aquaphobe CF. In the case of the photocurable resins, the adhesive force for PAK01 was smaller than that for TSR820. According to the measurement result of durability, Aquaphobe CF showed good durability compared with KP-801M using PAK01 as a photocurable resin. The fracture energies were measured by the double cantilever beam method, and the resultant values were 3.64 N/m and 2.77 N/m, respectively, for no-treatment SG and the surface-treated SG with Aquaphobe CF using PAK01 photocurable resin. The rectangular patterns of 1 µm×2 µm were imprinted with good fidelity without ripping on the PAK01 resin using a surface-treated quartz mold with Aquaphobe CF under 0.2 MPa pressure and 10 J/cm2 UV dose.

Multiple imprinting in UV-based nanoimprint lithography: related material issues

We will present resist and mold modifications which affect the adhesion forces at the mold/resist interface to assure multiple imprinting in a UV-based stepping process. A specifically modified resist is used in combination with an anti-adhesion layer on the quartz mold surface. The resist was modified with a fluorine-based additive, which migrates to the surface during spin-on processes creating a low energy surface. Auger spectroscopy clearly shows the enhancement of the fluorine at the surface of the resist. The anti-adhesion layer on the mold was characterized by electron spectroscopy for micro-analysis (ESMA) to determine its monolayer characteristic and uniformity. The surface energy of both the modified resist and the mold was determined as well. To demonstrate the success of these modifications, multiple imprints (up to 50 times) of different micro- and nanostructures were performed with one mold. After printing, the structures were transferred into silicon using conventional RIE processes.

Fabrication of nanostructures using a UV-based imprint technique

We present a modified NIL-technique for the fabrication of nm-structures. The approach is based on the photopolymerization of special resits through a quartz mold. The fabrication sequence for the molds as well as requirements and properties of new resist materials are presented. The resists are adapted to the process, making a low pressure and room temperature printing and an easy detachment of the mold possible. Special modification guarantees suitable etching rates and selectivities. With this technique 80% of the mold area was printed with a pressure of only 0.8 bar. Dot arrays with a single dot diameter of 80nm have been printed successfully.

Fabrication of titanium carbide and diboride specimens by the method of self-propagating high-temperature synthesis for plasma-arc growth of single crystals

Fabrication of long cylindrical specimens of TiB2, and TiC by burning homogeneous pressings of Ti + 2B and Ti + C mixtures with an additive of final combustion products (up to 30%) in quartz shells with the aim of growing single crystals by the method of plasma-arc remelting is considered. Dependences of the ultimate bending strength of rods of TiB2 and TiC on the percentage of the ballast, the dispersity of the components, and the density of the specimen are presented. Problems of shrinkage of the rods in the process of synthesis, contamination of the internal surface of the shells, repeated use of quartz molds, and withdrawal of SHS rods from the shells and the distribution of impurities over their length are discussed. It is shown that self-cleaning in the process of SHS using the shells reduces the content of some impurities in the rods by a factor of 2–3.

Performance of U-Pu-Zr fuel cast into zirconium molds

To investigate a means of eliminating quartz mold waste, U-3Zr and U-20.5Pu-3Zr fuel was injection cast into Zr tubes, or sheaths, and clad in 316SS. These elements and U-10Zr and U-19Pu-10Zr fuel elements, cast in the standard manner into disposable quartz molds, were irradiated in EBR-II to 2 at% burnup and removed for interim examination. Measurments of fuel column axial growth indicate that the Zr-sheathed fuel exhibited significantly less axial elongation than the standard-cast fuel (1.3 to 1.8% versus 4.9 to 8.1%). Fuel material extruded through the ends of the Zr sheaths, contacting the cladding in some cases. Transverse metallographic sections reveal cracks in the Zr sheath, indicating that the sheath is not a sufficient barrier between fuel and cladding to reduce fuel-cladding chemical interaction (FCCI). FCCI effects will be monitored as the elements attain higher burnup.