📝 Abstract

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. In the present study, the novel concept of that copper was adopted as the substrate instead of silicon, which is conventionally used, was proposed. The micro/nano structures on the copper substrate could be fabricated by chemical/electrochemical etching or electroforming ; following by the patterns have been transferred onto the substrate using LAN process. Alternatives of the substrate materials could lead versatile applications in micro/nano-fabrication. To demonstrate the feasibility of this concept numerically, this study introduced optical multiple reflection theory to perform both analytical and numerical modeling during the process and to predict the thermal response theoretically.

💡 Analysis

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. In the present study, the novel concept of that copper was adopted as the substrate instead of silicon, which is conventionally used, was proposed. The micro/nano structures on the copper substrate could be fabricated by chemical/electrochemical etching or electroforming ; following by the patterns have been transferred onto the substrate using LAN process. Alternatives of the substrate materials could lead versatile applications in micro/nano-fabrication. To demonstrate the feasibility of this concept numerically, this study introduced optical multiple reflection theory to perform both analytical and numerical modeling during the process and to predict the thermal response theoretically.

📄 Content

9-11 April 2008 ©EDA Publishing/DTIP 2008

ISBN: 978-2-35500-006-5 Numerical Investigation of Laser-Assisted Nanoimprinting on a Copper Substrate from a Perspective of Heat Transfer Analysis

Chun-Ping Jen Department of Mechanical Engineering, National Chung Cheng University,
No. 168, University Rd., Min-Hsiung, Chia Yi, 62102, Taiwan, R.O.C.

Abstract- 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. In the present study, the novel concept of that copper was adopted as the substrate instead of silicon, which is conventionally used, was proposed. The micro/nano structures on the copper substrate could be fabricated by chemical/electrochemical etching or electroforming; following by the patterns have been transferred onto the substrate using LAN process. Alternatives of the substrate materials could lead versatile applications in micro/nano-fabrication. To demonstrate the feasibility of this concept numerically, this study introduced optical multiple reflection theory to perform both analytical and numerical modeling during the process and to predict the thermal response theoretically.

I. INTRODUCTION Nano-imprinting lithography (NIL) has been developed over a decade [1-5] and is now a promising method for nano-patterning and nano-fabrication. The basic concept of conventional nano-imprinting includes a mold, an etching resist layer and a sample substrate. The mold has some nano-scale features on the surface fabricated by either E-beam lithography or focus ion bean techniques. The thermo-plastic polymer such as poly-methylmethacrylate (PMMA) is usually used as the resist layer. By heating until above its glass transition temperature (Tg), the mold can impinge into the resist layer and form a pattern. Following by reaction ion etching, the nano-pattern is transformed to the resist layer and the substrate. It is sequent followed by standard lithography processes to achieve nano-structures on the substrate surface. However, the heating mechanism of conventional nanoimprinting is slow and usually causes misalignment due to the different thermal expansion between the mold and the substrate. Recently, laser-assisted nanoimprinting lithography (LAN) method illustrated in Figure 1a was proposed [6]. This new imprinting method shares the same concepts discussed above and combines the advantages of the traditional nano-imprinting and laser-assisted direct imprint [4]. The LAN process depicted schematically in Figure 1a utilizes a laser pulse to irradiate through a quartz mold and melt a thin polymer film (~200 nm) on the substrate. Upon the thin polymer film is melted, the pre-loaded mold is imprinted into the polymer resist layer. This LAN method has several obvious advantages over the thermal-based nano-imprinting technique in terms of shortening the processing time and reducing the heating of the substrate and in this way the misalignment due to the thermal expansion mismatch of the mold and substrate can be avoided [6]. This method shows a great potential for future nano-patterning and fabrication of nano-structures. In the present study, the novel concept of that copper was adopted as the substrate instead of silicon, which is conventionally used, was proposed. The micro/nano structures on the copper substrate could be fabricated using chemical/electrochemical etching or electroforming; following by the patterns have been transferred onto the substrate using LAN process.
Alternatives of the substrate materials could lead versatile applications in micro/nano-fabrication. To demonstrate the feasibility of this concept numerically, this study introduced optical multiple reflection theory to perform both analytical and numerical modeling during the process and to predict the thermal response theoretically. II. THEORETICAL MODELING During the heating process of the substrate by the pulsed laser, one-dimensional transient heat-diffusion equation can be employed herein. The physical domain for the heat-transfer system considered here is illustrated in Figure 1b.
Assuming that the laser spot is larger than the mold and all materials involved are homogeneous; therefore this system can be simplified as one-dimensional. The source term of heat-generation in the substrate originating from the energy absorption of a laser pulse can be described as:

) ( )

exp( ) , ( t I x A t x S S β β −

                                (1) 

where x and t are the spatial variable and time, respectively.
AS is the absorption of the incident light, β is the optical absorption coefficient which is related to the imaginary part of refractive index, κ , and the laser wavelength, λ, by λ πκ β 4

[8]. I(t) is the power density function

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