Characterization and application of a UV-based imprint technique

doi:10.1016/S0167-9317(01)00536-6

Microelectronic Engineering

Volumes 57–58, September 2001, Pages 361-366

https://doi.org/10.1016/S0167-9317(01)00536-6 Get rights and content

Abstract

We have investigated a UV-based nanoimprint technique with regard to its potential for large area applications. One aspect is the investigation of the residual resist thickness h_r, which depends on the geometry of the mold. If the geometry of structures to be printed varies strongly across the mold, fluctuations of the residual resist thickness and incomplete filling of the structures can occur. As a consequence, best results will be obtained with periodic structures and periodically arranged structures as is demonstrated with imprinted metal–semiconductor–metal (MSM) patterns.

Introduction

Nanoimprint lithography (NIL) offers some decisive technical potentials for replacing expensive lithography tools by a low cost version for the mass production of nanostructures. Research in the field of NIL has mainly been concentrated on the hot embossing technique, in which patterned molds are pressed into thermoplastic materials at relatively high levels of temperature and pressure [1]. Since alignment and overlay issues found in the microelectronic device fabrication could be adversely affected by these process conditions, alternative approaches to NIL have been developed, in which low viscosity, UV-curable materials are used as resists [2], [3]. In these UV-based NIL techniques, the mold is pressed into the UV-curable solution at room temperature after which the solution is photopolymerized by UV-irradiation. Due to the low viscosity of the resists, only low pressure is needed to press the mold into the resist. After the detachment of the mold, a replica of the mold’s topography remains in the resist layer. The residual resist thickness which remains in the recessed areas of the resist layer is then removed as a first step of the subsequent pattern transfer. For a successful pattern transfer of large imprinted areas, a uniform resist thickness over the entire imprinted area is essential.

In this article, basic considerations of this UV-based imprint technique are made and then compared to experimental results.

Section snippets

Basic consideration

The imprint process can be characterized on the basis of the residual resist thickness h_r, an important value for the evaluation of imprinted structures. To simplify the problem we will assume the following: (i) parallel contact between the surfaces of the mold and the substrate; (ii) no surface waviness of both the mold and substrate surfaces; and (iii) surface tensions and capillary forces are neglected. Additional assumptions concerning the geometry of the mold are (see Fig. 1): (i) the mold

Experimental results

To check the validity of this approach, experiments were performed to determine the parameters that the residual resist thickness h_r depends on. For this we used circular, UV-transparent quartz molds with a diameter of 2.5 cm and a thickness of 500 μm. The structures on the mold were lines and spaces both having a width of 4 μm, i.e. the molds had a local ratio A_e/A_r of 1. The height of the structures ranged from 200 to 400 nm for different molds. We used acrylate based resists with a

Discussion

In the UV-based nanoimprint process the residual resist thickness h_r depends only on the initial film thickness h_i and the geometry mold according to the flat regime of Eq. (1). Thus, h_r can be controlled by adjusting h_i according to the geometry of a given mold. This is simplified further by the process being independent of the applied imprint force and duration.

However, the A_e/A_r-dependency of h_r has a decisive influence on the uniformity of h_r and h_s across the imprinted area. A_e/A_r is

Conclusion

We investigated UV-based nanoimprint lithography, an imprint technique that allows the use of low viscosity resists. Within certain limits the residual resist thickness h_r is independent of the imprint pressure and the duration of applied pressure. It depends only on the initial film thickness and the geometry of the mold. If the geometry of structures to be printed varies strongly across the mold, fluctuations of the residual resist thickness and incomplete filling of the structures can occur.

Acknowledgements

The authors thank B. Vratzov of AMO GmbH, Aachen for the fabrication of the quartz molds and A. Berni at INM (Institut für Neue Materialien GmbH) for the development and modification of the resist materials. The work was supported by the German BMBF under the contract No. 13N7400/6.

References (3)

M. Bender et al.
Microelectron. Eng.
(2000)

There are more references available in the full text version of this article.

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