Lithography

About: Lithography is a research topic. Over the lifetime, 23507 publications have been published within this topic receiving 348321 citations.

Electrochemical AFM "dip-pen" nanolithography.

Abstract: In recent years, SPM-based lithography has attracted great attention because of its simplicity and precise control of the structure and location Many SPM lithography techniques based on mechanical scratching,1 anodization of Si surfaces,2 electrochemical decomposition of self-assembled monolayers,3 electric field-induced chemical reactions,4 electrochemical reactions in solution using electrochemical STM tips5 have been developed in the past decade Comprehensive reviews of SPM-related lithography can be found in the literature6 More recently, a “dippen” nanolithography (DPN) method has been invented that uses an atomic force microscope (AFM) tip as a “nib” to directly deliver organic molecules onto suitable substrate surfaces, such as Au7 By using this technique, organic monolayers can be directly written on the surface with no additional steps, and multiple inks can be used to write different molecules on the same surface However, the current “dip-pen” method can only be used to deliver organic molecules to the surface The long-term stability of the created structures is a potential problem Here we report a new electrochemical “dip-pen” lithography technique that can be used to directly fabricate metal and semiconductor nanostructures on surfaces This technique has all the advantages of the previous “dip-pen” technique and improves the thermal stability and chemical diversity of the structures because they now could be made of various inorganic materials Furthermore, the ability to directly fabricate metal or semiconductor nanostructures on surfaces with a high degree of control over location and geometry is of significant interest in nanotechnology Potentially, one could use this method to fabricate nanodevices with multiple metal and semiconductor components When AFM is used in air to image a surface, the narrow gap between the tip and surface behaves as a tiny capillary that condenses water from the air This tiny water meniscus is actually an important factor that has limited the resolution of AFM in air “Dip-pen” AFM lithography uses the water meniscus to transport organic molecules from tip to surface7 In our new technique, we also use the tiny water meniscus on the AFM tip as the transfer medium However, unlike in the previous AFM “dip-pen” method where water is only used as a solvent for the molecules, we have used this tiny water meniscus as a nanometer-sized electrochemical cell in which metal salts can be dissolved, reduced into metals electrochemically, and deposited on the surface (Figure 1) Although electric field-induced chemical reactions,4 electrochemical reactions in solutions using electrochemical STM,5 and electrochemical deposition using self-assembled monolayer as resist3c have been previously used to create metallic nanostructures, our method is the first that combines the versatility of electrochemistry with the simplicity and power of the DPN method to produce nanostructures with high resolution Electrochemical STM-based methods require that the substrates be metallic, but substrates used in our method do not have to be metallic since the control feedback of the AFM does not rely on the current between the tip and surface Si wafers coated with native oxide provides enough conductivity for the reduction of the precursor ions This development significantly expands the scope of DPN lithography, making it a more general nanofabrication technique that not only can be used to deliver organic molecules to surfaces but is also capable of fabricating metallic and semiconducting structures with precise control over location and geometry Because of the electrochemical nature of this new approach, we call this technique electrochemical “dip-pen” nanolithography (E-DPN) We have investigated the deposition of several metals and semiconductors on Si surfaces at room temperature using the E-DPN technique Here we show the deposition of Pt metal as an example8 The experiments were performed using a Nanoscape IIIa AFM (Digital Instruments) In a typical experiment, an ultrasharp silicon cantilever coated with H2PtCl6 is scanned on a cleaned P-type Si (100) surface with a positive DC bias applied on the tip During this lithographic process, H2PtCl6 dissolved in the water meniscus is electrochemically reduced from Pt(IV) to Pt(0) metal at the cathodic silicon surface and deposits as Pt nanofeatures according to the following equation:

Recent progress in high resolution lithography

Abstract: The nanotechnology revolution of the past decade owes much to the science of lithography, an umbrella term which encompasses everything from conventional photolithography to “unconventional” soft lithography and the self-assembly of block polymers. In this review, some of the recent advances in lithography are summarized with special reference to the microelectronics industry. The next generation photolithography, two-photon lithography, step-and-flash imprint lithography and nanofabrication using block copolymers are covered, in an attempt to describe more recent work in this vibrant and active field of research. Copyright © 2006 John Wiley & Sons, Ltd.

Organic light emitting devices with enhanced outcoupling via microlenses fabricated by imprint lithography

Abstract: High efficiency white organic light emitting devices (WOLEDs) with optical outcoupling enhanced by hexagonal polymethylmethacrylate microlens arrays fabricated by imprint lithography on a glass substrate are demonstrated. Monte Carlo and finite difference time domain simulations of the emitted light are used to optimize the microlens design. The measured enhancement of light outcoupling and the angular dependence of the extracted light intensity are in agreement with the simulation. Using microlens arrays, we demonstrate a fluorescent/phosphorescent WOLED with a maximum external quantum efficiency of (14.3±0.3)% at 900cd∕m2 and power efficiency of 21.6±0.5lm∕W at 220cd∕m2. The electroluminescent spectra at viewing angles from normal to the substrate plane, to 60° off normal, remain almost unchanged, giving a color rendering index of 87.

Nanolithography using high transmission nanoscale bowtie apertures.

Abstract: We demonstrate that bowtie apertures can be used for contact lithography to achieve nanometer scale resolution. The bowtie apertures with a 30 nm gap size are fabricated in aluminum thin films coated on quartz substrates. Lithography results show that holes of sub-50-nm dimensions can be produced in photoresist by illuminating the apertures with a 355 nm laser beam polarized in the direction across the gap. Experimental results show enhanced transmission and light concentration of bowtie apertures compared to square and rectangular apertures of the same opening area. Finite different time domain simulations are used to explain the experimental results.

Polymerization optimization of SU-8 photoresist and its applications in microfluidic systems and MEMS

Abstract: In this paper, SU-8 EPON-based photoresist (PR) polymerization optimization and its possible microfluidic and MEMS applications are reported. First, the optimization results of SU-8 under UV lithography are reported. The parameters which could have an influence on the lithography quality were chosen and optimized by a three-level, L9 orthogonal array of the Taguchi method. By optimization, the optimal parameter range and the weighted per cent of a parameter on the final results were determined. For SU-8-5 and SU-8-50, many microstructures with thicknesses of more than 100 and 500 µm and aspect ratios of more than 20 and 50 were obtained with high resolution. The optimization results show that the prebake time plays the key role in the quality, which is different from the previously published results. With the optimization results obtained, some possible applications of SU-8 were developed and demonstrated. These applications included using SU-8 as a structural material for a microfluidic system, as a micromold for electroplating, as a master for plastic hot-embossing, and even as a mask for some wet-etching processes.