J. Boussey

Improved release strategy for UV nanoimprint lithography

The adhesion between the fused silica mold and the resist remains a key issue in ultraviolet nanoimprint lithography (UV-NIL), especially in step and repeat processes. In this paper, we present results on antisticking layers (ASLs) of tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (F13-TCS) deposited in vapor phase and of a commercial product, Optool DSX™, from Daikin Chemical, deposited in liquid phase. The antisticking properties and structural morphologies of the formed self-assembled monolayer are investigated using contact angle, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy (XPS) measurements. Obtained surface energies are as low as 10mN∕m for both types of ASL. The stability of these formed layers during the UV-NIL process remains the main important issue. It was tested on an EVG® step and repeat UV-NIL equipment using acrylate-based resists. After only 50 prints, we observed a high increase in the surface energy of the mold, which indicates a drastic degradati...

Double-anchoring fluorinated molecules for antiadhesion mold treatment in UV nanoimprint lithography

In this work, the authors evaluate a new type of perfluoropolyether molecule (FLUOROLINK® S10) to be used as an antisticking mold treatment in UV nanoimprint lithography. Unlike currently used ones, this molecule has two anchoring ends groups allowing two covalent grafting sites of the molecule to the mold surface. Obtained results on this molecule are compared to Optool DSX’s ones. Using contact angle measurement, x-ray photoelectron spectroscopy, and electron spin resonance, the authors carried out chemical analysis of the evolution of antisticking treatments as a function of the number of imprints. It is found that both molecules have a roughly equivalent behavior. FLUOROLINK® S10 has shown less chemical resistance, attributed to its larger number of C–O bonds in the molecule, but an improved mechanical resistance, attributed to the double grafting mechanism.

Photopolymerization kinetic study of UV nanoimprint lithography dedicated resists

This article reports on the properties of ultraviolet nanoimprint lithography dedicated imprinting materials. Studied solutions are composed of a diacrylate-based monomer and a variable amount (1%, 2%, and 4% in weight) of three different photoinitiators from Ciba Specialty Chemicals (Irgacure 819, Irgacure OXE02, and Irgacure 379). Photopolymerization kinetic studies were conducted on these solutions. Quantity and type of photoinitiator could be optimized in order to obtain a polymerization rate higher than 95% with an exposure dose as low as 20mJ∕cm2. The etch resistance of this home-developed imprinting resist was characterized under standard plasma etching conditions. We observed that the polymerization rate has a large influence on the plasma etch resistance, and we show that the etch rates of our best material is comparable to the one measured for 193nm photolithography resists and makes it a very good candidate as a masking layer for direct pattern transfer.

Investigation of the resist outgassing and hydrocarbonaceous contamination induced in multi-electron-beam lithography tools

In emerging high-vacuum multi e-beams exposure tools, the release of hydrocarbonaceous species (precursor) by resists outgassing is unavoidable and leads to premature contamination of optics projection systems. In this work, we present an experimental methodology aiming at resist outgassing qualification. A specific experimental setup was designed to monitor the induced outgassing phenomena by irradiating resist coated on 100mm silicon wafer. The wafer can be exposed through specific silicon micromachined membranes (called mimics) that are representative of the optics projection system usually embedded in real multi e-beam exposure tools. A Quadrupole Mass Spectrometer (QMS) is plugged into the vacuum chamber and enables in-situ analysis of the by-products outgassing. Combining this tool with the Thermo Desorption - Gas Chromatography coupled to Mass Spectroscopy (TD-GC-MS) analysis, we could not only determine the outgassing amount of different resists but also identify all the outgassed by-products and their origin. Finally, the Focus Ion Beam combined to Scanning Electron Microscopy (FIB-SEM) and X-ray Photoelectron Spectroscopy (XPS) characterization techniques were used to determine the contamination layer thickness and elementary composition, respectively. A first process oriented conclusion from this work shows that the use of a thin topcoat layer can considerably reduce the resist outgassing amount and, consequently, the hydrocarbonaceous contamination layer induced on the mimics. The outgassing amount as well as the top-coat efficiency was shown to be mainly dependent on the resist chemical properties. The contamination layer growth was shown to be dependent on e-beam current density and hydrocarbon pressure in the vicinity of the mimics.

Assessment of carbon layer growth induced by resists outgassing in multi e-beams lithography

The development of multiple e-beam lithography equipment is seen as an alternative for next generation lithography. However, similarly to EUV lithography, this technology faces important challenges in controlling the contamination of the optics due to deposition of carbon layer induced by the outgassed chemical species from resist under electron bombardment. An experimental setup was designed and built at LETI to study the outgassed species and observe the carbon layer. In this setup, resist coated wafers 100 mm size are exposed under a 5 kV e-beam gun. During exposure, byproducts from outgassed species are monitored with a Residual Gas Analyzer (RGA). The identification of outgassed chemical species is done with an ex-situ TD-GC-MS analysis (ThermoDesorption-Gaz Chromatography-Mass Spectrometry). In a second part of this investigation, we observed the contamination carbon layer growth induced by the outgassing. Thereby, we fabricated a device which consists of a silicon membrane with micro-machined apertures. During e-beam exposure, this device simulates the multiple parallel beams of the optic system of a maskless lithography tool. The deposited contamination layer on device is then observed and thickness measured under SEM. In this paper, we present the results of outgassing and contamination on 3 chemically amplified resists showing that contamination is not directly dependent of the overall outgassing rate but on first order of the outgassing from Photo Acid Generator (PAG). It also reports on the performance in reducing outgassing and contamination of applying a top-coat layer on top of the resist and shows that reduction is more important for contamination than for outgassing.

Wind Measurement Based on MEMS Micro-Anemometer With High Accuracy Using ANN Technique

Estimating wind speed and direction in outdoor areas with high precision and resolution requires a large number of anemometers distributed in different locations. Compared with others conventional sensors, the micro electro mechanical system (MEMS) sensors are lighter and smaller, therefore, they can be integrated in large numbers. Moreover, due to their batch production, MEMS sensors are relatively low cost. Their main drawbacks are the dependence on the air temperature and the inability of detecting the flow direction. This paper deals with the design of a cylindrical-shaped probe equipped with two dual MEMS hot-film sensor chips calibrated in a wind tunnel. With the obtained results, a model based on artificial neural network is developed and implemented on Arduino board. This model is assigned to calculate the corresponding values of wind speed and direction with correcting the effect of temperature drift. Finally, outdoor tests are carried out at wind monitoring points measured by an opto-electronic anemometer and an opto-electronic wind vane. The obtained results are accurate and agree well.

Template flatness issue for UV curing nanoimprint lithography

UV curing Nanoimprint Lithography (UV-NIL) is an emerging lithographic technique, seen as a potential candidate for the 32nm node by the ITRS road map. As the stamp is in direct contact with the substrate, template flatness is a critical issue in addition to standard optical lithography mask requirements (high-resolution, low defectivity, CD control...). This is why we propose to study the impact of the template flatness on the reproduction quality and on the imprint uniformity. After having studied the Residual Layer Thickness (RLT) uniformity intra-dies and compared it to different stamps flatness, the impact of UV-NIL process optimisations, such as the substrate quality and filling times, on RLT uniformity intra- and inter-dies were evaluated. We observed that a high stamp waviness is always transferred into the resist, while a low stamp waviness (under a few hundreds of nanometers range) has no impact on the RLT uniformity.