Antisticking Layer Research Articles

Temporary polymer bonding for the manufacturing of thin wafers: An innovative low temperature process

The study deals with the handling of thin wafers in 3D integration. It concerns the fabrication of 300 mm wafers in industrial tools. Usually, the manufacturing is based on a temporary bonding process performed at 200 °C using a thermoplastic adhesive. In that condition bonding, thinning and dismounting are satisfactory. Moreover, the adhesive flattening during bonding results in an excellent thickness uniformity of the bonded pairs, with a small total thickness variation (TTV) value suitable for 3D integration. If the temperature is 150 °C or lower, the adhesive thickness uniformity is not acceptable anymore. An innovative temporary bonding process at low temperature has thus been developed. It consists in a carrier fabrication with highly uniform adhesive thickness. The standard coated adhesive is flattened with a first reversible temporary bonding at 210 °C. After a first dismounting, this carrier is then bonded to the target device wafer with a low bonding temperature, from 110 °C to 150 °C. Due to the pre-flattening, 80 μm thick silicon films with an excellent TTV value can thus be obtained even with a low bonding temperature required by the device wafer. Moreover, after the device wafer thinning, the final dismounting can be performed without any antisticking layer.

Replication of the Surface Wettability of Plant Leaves with Different Surface Morphologies Using Soft Lithography

Naturally occurring surfaces which display interesting surface wetting properties such as superhydrophobicity, superoleophobicity and directional wettability are found in most aquatic plants. These phenomena arise from the micro/nano structures present on these surfaces complimented by their surface chemistry. The replication of such surface structures is highly pursued due to their potential in applications such as self-cleaning (Lotus effect), microfluidic devices and antifouling surfaces. Soft lithography is a technique that has been used to replicate micro/nano structures with varying degrees of success. Nevertheless, in the context of natural surfaces, the technique has been mostly limited to the replication of the lotus leaf structure. Therefore, a systematic investigation could be fruitful since it has the potential to be scaled up to replicate different surface structures as well as large-area patterning. In this study, the feasibility of soft lithography technique on natural leaf surfaces was investigated using five plant species with different surface morphologies. The negatives of these primary molds were replicated using polydimethylsiloxane (PDMS) and the final positive replica was successfully replicated from PDMS while using hydroxypropyl methylcellulose (HPMC) as an anti-stick layer. The structures were characterized based on SEM images and contact angle measurements. Additionally, the effect of HPMC was also investigated. The technique can easily be extended to broader applications in other areas that require micro/nanostructured surfaces such as anti-reflection coatings, chemical sensors and anti-microbial surfaces.

A Cr Anti-Sticking Layer for Improving Mold Release Quality in Electrochemical Replication of PVC Optical Molds.

This paper addresses the issue of mold release quality in an electrochemical replication of an optical polyvinyl chloride (PVC) mold, which has microlens array or microprisms array on its surface. The main idea is to deposit a nanoscale Cr thin layer as an antisticking layer on the PVC mold surface, followed by Ag film deposition as the conductive layer using magnetron sputtering, and finally, a nickel layer is electrochemically deposited on the Ag surface. By doing so, the upripping of the nickel mold from the PVC mold becomes easier, resulting in better mold release quality. The experiment results showed that when the Cr antisticking layer was used, the release strength between the nickel mold and the PVC substrate reduced from 1.94 N/cm to 1.43 N/cm, the surface roughness of the PVC substrate after mold release reduced from 0.60 μm to 0.55 μm, the surface roughness of the nickel mold reduced from 0.63 μm to 0.49 μm, the retroreflection coefficient of the nickel mold increased from 1600 cd·lx−1·m−2 to 2100 cd·lx−1·m−2, and the surface energy of the PVC substrate reduced from 31.47 mN/m to 15.53 mN/m.

Fluorinated low-viscosity copolymer with enhanced release property for roll-to-plate UV nanoimprint lithography

A new fluorinated low-viscosity copolymer resin with enhanced release properties has been developed to provide higher fidelity for roll-based ultraviolet (UV) nanoimprint lithography (NIL) and simplify the process. The properties are optimized by blending (2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononyl) oxirane (EP-F8) and 1,4-butanediol divinyl ether (BDDVE) with 3,4-epoxycyclohexylmethyl-3,4-epoxy cyclohexane carboxylate. The cured resin renders the hydrophobicity and allows demolding from the stamp mold without an anti-stick layer (ASL), as further verified by the contact angle and the work of adhesion measurements. Due to the addition of BDDVE, our resin also has much lower viscosity compared to commercially available low-viscosity resins. These properties enable the transfer of high-density dot patterns by roll-to-plate (R2P) UV NIL in the newly developed resin without adding solvent or coating it with an ASL. These results demonstrate that our resin is a good option for high-quality, low-cost R2P UV NIL, as its use eliminates several steps in the imprinting process, making it applicable to the scalable fabrication of flexible devices.

Development and adhesion characterization of a silicon wafer for temporary bonding

The development of a silicon temporary carrier for thin wafer handling for 3D applications was investigated. Process selection and optimization ended up with a silicon carrier entirely covered with an antistick layer based on a fluorinated polymer. The carrier preparation was quite easy because only one coating was used and no sticking edge zone was needed onto the carrier. The fluorinated coating led to a very hydrophobic behavior. When bonded with a thermoplastic glue, it also exhibited very antiadhesive properties because the adherence was as low as 0.4J/m2 and lower than the adherence of a stack without any antiadhesive layer (above 4J/m2). The carrier was nevertheless suitable for different back side processes in 300mm: grinding, chemical cleaning, chemical mechanical polishing and silicon oxide deposition. Compared with a commercial carrier, it exhibited the same level of performance for the integration. The proposed carrier was compatible with a mechanical debonding of a thinned bonded structure with a silicon device wafer of 80µm. The carrier recycling was possible without any new preparation.

A full-process chain assessment for nanoimprint technology on 200-mm industrial platform

Abstract To evaluate the maturity of the wafer-scale NanoImprint lithography (NIL) process, laboratory of electronic and communication technology (LETI) and EV Group (EVG) launched the Imprint Nanopatterning Solution Platform for Industrial Assessment program (INSPIRE), which aims at building a nanoimprint solution platform for industrial assessment and provide a unique open ecosystem for the standardization of the nanoimprint process. This program enabled to gather EVG know-how for the tool manufacturing and its long expertise in bonding activities, and the established methods and advanced microelectronic environment. Presented as an upstream phase, metrology and defectivity were performed on dedicated assessment designs to address critical dimension uniformity (CDU) at wafer scale for a large number of imprints, defectivity on imprints and masters, and alignment capabilities of the nanoimprint HERCULES® platform of EVG. We demonstrate that the critical points are the anti-sticking layer for the defectivity, the CD shrinkage for the CDU, and the stiffness of the soft stamp for the overlay uniformity. Thus, we bring to light the actual capabilities of the HERCULES® platform, and open the discussions on the opportunities for this technology with the possible improvements for the process.

Imprint strategy for directed self-assembly of block copolymers

The directed self-assembly (DSA) of block copolymers (BCP) has attracted high interest for the definition of nanostructures in an almost self-forming way when adequate boundary conditions are given. At present, grapho- and chemo-epitaxy are the workhorses but they require precisely patterned substrates to serve as the guiding pattern. Nanoimprint may replace this laborious pre-patterning of each substrate by employing an adequate stamp that can be used multiple times, inducing the guided DSA from the top of the film. Here, the DSA of BCPs is revisited in view of the specific nanoimprint situation. As a consequence, the BCP layer is imprinted in a partial cavity-filling mode, using a stamp of sufficient height provided with a conventional anti-sticking layer; substrate pre-treatment is minimized or rather avoided. Even with a highly preferential substrate it is possible to obtain vertical lamellae that are largely oriented in parallel to the stamp edges in PS-b-PMMA (polystyrene-block-polymethyl methacrylate) already after 3min of imprint. The vertical lamellae are at least 70nm high, freestanding on the substrate. Though optimization is required the results indicate the high potential of nanoimprint to simplify the DSA of BCPs for technical applications, also beyond Si technology.

Thermal stability and separation characteristics of anti-sticking layers of Pt/Cr films for the hot slumping technique**Supported by CAS XTP project XDA04060605

The thermal stability and separation characteristics of anti-sticking layers of Pt/Cr films are studied in this paper. Several types of adhesion layers were investigated: 10.0 nm Pt, 1.5 nm Cr + 50.0 nm Pt, 2.5 nm Cr + 50.0 nm Pt and 3.5 nm Cr + 50.0 nm Pt fabricated using direct current magnetron sputtering. The variation of layer thickness, roughness, crystallization and surface topography of Pt/Cr films were analyzed by grazing incidence X-ray reflectometry, large angle X-ray diffraction and optical profiler before and after heating. 2.5 nm Cr + 50.0 nm Pt film exhibits the best thermal stability and separation characteristics according to the heating and hot slumping experiments. The film was also applied as an anti-sticking layer to optimize the maximum temperature of the hot slumping technique.

Fabrication of III–V compound nanowires via hot embossing nanoimprint lithography

In this study, the nanoimprint lithography (NIL) technique used to fabricate III–V compound nanowires was investigated. A silicon mold and thermoplastic polymer mr-I 7010R were used for hot embossing nanoimprint lithography. The mold was patterned by e-beam lithography with two masks exposed with different dosages to reduce the proximity effect. The filling capability and residual layer thickness of the thermoplastic polymer were optimized at the embossing temperature of 125 °C. A 73 nm GaAs nanowire was obtained by the mold coated with an antisticking layer.

Method for high temperature nanoimprint of an organic semicrystalline polymer

Performance and functionality of devices prepared from organic semicrystalline polymers strongly depend on the size and the orientation of the ordered crystalline domains, as the conductivity is distinctly different in the different lattice directions. This investigation addresses the potential of thermal nanoimprint to control the size of the ordered domains as well as their orientation with respect to the substrate. Poly-3-hexylthiophene (P3HT) is chosen as one of the prominent semicrystalline polymers available at high quality. In order to control the ordering of the domains freely, the imprint is performed at a temperature beyond the melting point to eliminate the domains already existing after spin-coating and soft-bake. To avoid a degradation of P3HT at such a high temperature under oxygen contact—the imprint system used operates in air—a novel imprint procedure is employed, where a distinct prepressure is applied already during the heating of the imprint stack (stamp/substrate with P3HT layer). To enable efficient recrystallization in the form “shaped” by the imprint mold, the novel procedure features, in addition, a slow cool-down from the processing temperature (245 °C) down to 150 °C. During recrystallization the orientation of the ordered domains is driven primarily by the interaction of the side-chains of the P3HT molecules with the antisticking layer of the mold, where the pressure still applied forces ordering, too. The potential of this approach is characterized by x-ray diffraction measurements. The results clearly show that the novel procedure investigated here is effective not only to avoid the degradation of P3HT at a high temperature but also to provide ordered domains that are more than two times larger than those existing before imprint, after spin-coating. The results obtained so far with grating patterns are encouraging and indicate new possibilities of controlling the conductivity of devices prepared from semicrystalline organic polymers.

Evaluation of the fluorinated antisticking layer by using photoemission and NEXAFS spectroscopies

The electronic structures of four kinds of fluorinated self-assembled monolayers (F-SAMs) with different chain length, which were used for an antisticking layer, were investigated by the photoemission and the near-edge X-ray absorption fine structure (NEXAFS) spectroscopies. From the photoemission spectra in the wide and in the C 1s core-level regions, chemical compositions and components of the F-SAMs with different chain length were evaluated. By using the curve fitting analysis of the photoemission spectra in C 1s core-level region, it was found that the CF3 site is located at the top of the surface in the C sites of the F-SAM. From the C K-edge NEXAFS spectra of the F-SAMs as a function of the incidence angle of the excitation photon, it was shown that the σ*(C–F) and σ*(C–C) orbitals in the F-SAMs are parallel and perpendicular to the surface, respectively. This indicates that the C–C chain in (CF2) n part of the F-SAMs is perpendicular to the surface. Based on these results, the electronic structures of the F-SAMs are discussed.

Anti-sticking layers for nickel-based nanoreplication tools

Graphical abstractDisplay Omitted HighlightsReliable anti-sticking coatings on nickel surfaces are produced based on perfluoro-alkyl phosphates and -phosphonates.Oxygen plasma pre-treatment yields ...

A scalable anti-sticking layer process via controlled evaporation

We developed a novel process for the deposition of anti-sticking layers from the gas phase based on the use of evaporation cells. The cells are prepared from Teflon and consist of small silane containers with an orifice. Temperature is used to provide a silane-containing gas phase in the containers; the temperature is well below the boiling point of the silane. The number of cells can be varied to improve the uniformity with respect to surface energy, to scale-up the process to larger diameters and to reduce the processing time required. The impact of cell number, processing temperature and processing time is investigated with respect to uniformity and with respect to the minimum times and temperatures required. The concept works well and shows potential for the control of surface energy beyond anti-sticking purposes.

Anti-sticking layers for nickel-based nanoreplication tools

Nickel is the preferred material for molds used in high throughput micro injection molding and roll-to-roll processes. We present different solutions for anti-sticking layers for nickel-based nanoreplication tools, which are highly desired for replication of features in the sub-micrometer and nanometer scale. Layers of fluorocarbon molecules, bound to nickel via different head groups, were evaluated via friction force and contact angle measurements, X-ray photoelectron spectroscopy and imprint tests. The robustness of fluorinated phosphates and phosphonates applied to nickel pre-treated in oxygen plasma is similar to silanes used on silicon molds.

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.

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

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

Effect of Fluorosurfactant contained in Resin for Anti-sticking Layer Free UV Nanoimprinting

We evaluated the effect of DSN4034 (fluorosurfactant) to carry out ASL free UV nanoimprinting. The water contact angle of C-TGC-02 (UV nanoimprint resin) with DSN4034 decreased with increase in additive amount of DSN4034. We assumed that this phenomenon was caused by large amount of PEO chain and OH group in DSN4034. However, it is necessary to investigate the phenomenon by X-ray photoelectron spectroscopy and atomic force microscopy. When both the mold and the substrate were the equivalent hydrophilic surface treated by O2 RIE, the resin was peeled from the substrate. By putting the difference of interface between the mold and the substrate, we succeeded ASL free UV nanoimprinting.

Fabrication of Micro-Polymer Lenses With Spacers Using Low-Cost Wafer-Level Glass-Silicon Molds

A novel low-cost molding process to prepare polymer-based micro-lens arrays with spacers for optical applications was investigated in this paper. The process consists of the following steps: 1) hemispherical glass bubble arrays, used as the upper part of the molds, was prepared by combining a hot-forming process and a chemical-foaming process; 2) the silicon mold, used as the lower part of the molds, was fabricated by etching; 3) an anti-stick layer was coated on the concave surface of the glass mold; and 4) the lens material, UV-curable glue, was dispensed into the concave molds, followed by curing and de-molding. The optical properties of the lens were characterized by a profile meter and a beam analyzer. The results showed that the micro-polymer lens arrays with spacers were successfully prepared using the low-cost wafer-level glass-silicon mold. The results indicate that the micro-lenses have hemispherical structures and smooth surface.

Evaluation of resistless Ga+ beam lithography for UV NIL stamp fabrication

This paper presents an alternative rapid prototyping approach for the fabrication of stamps for UV nanoimprint lithography. In this process, areas implanted with gallium serve as an etch mask for the dry etching of quartz. The implantation is performed using a focused ion beam system. To avoid charging of the quartz substrate the use of thin layers of chromium or carbon on the quartz substrate has been evaluated. The resulting quartz structures exhibit very smooth surfaces after dry etching, if the implantation dose is high enough to form a stable etch mask. Furthermore, anisotropic etching could be realized by optimization of a quartz etching process involving C4F8 and O2 after the use of resistless Ga+ beam lithography. Finally, imprints into a UV curing resist are performed successfully with the manufactured stamps, proving that the presence of Ga rich areas on the stamp is not detrimental to the curing of the resist or the functionality of the anti-sticking layer.

Mold cleaning with polydimethylsiloxane for nanoimprint lithography

We present a simple and effective mold cleaning method for nanoimprint lithography. Polydimethylsiloxane (PDMS) prepolymer is spin-coated onto a contaminated imprint mold, thermally cured in an ambient environment, and then peeled off afterwards. Contaminants of 100 s μm to sub-50 nm sizes are effectively cleaned within one cycle. During the cleaning process, a very thin PDMS film (1–2 nm) is uniformly coated onto the mold surface, serving as a protection and anti-sticking layer.