ELSEVIER Microelectronic Engineering 53 (2000) 539-542 /dlCROI~,I~rliONE www.elsevier.nl/locate/mee THREE-DIMENSIONAL MICROSTRUCTURE ELEMENTS FABRICATED BY ELECTRON BEAM LITHOGRAPHY AND DRY ETCHING TECHNIQUE R. Steingrtiber and M. Ferstl Heinrich-Hertz-lnstitut fib Nachrichtentechnik Berlin GmbH, Einsteinufer 37, D-10587 Berlin Phone:++49 (0)30 31002 236 Fax: ++49 (0)30 31002 558 e-mail: steingrueber@hhi.de The fabrication of three-dimensional microstructure elements by electron-beam lithography and dry etching technique is shown for the example of typical three-dimensional optical structures (Echelette gratings, computer generated diffractive optical elements and Fresnel zone lenses). Several different structures, mainly for use in micro-optics with feature sizes in the micrometer range and below were realised. The utilisation of electron-beam lithography thereby proved to be extremely flexible and precise. 1. INTRODUCTION Micro structures and elements play an important role in a wide range of applications in micro-system technology and micro optics. The state-of-the-art fabrication techniques of lithography and dry etching offer a high degree of accuracy and reproducibility to generate small structures in the micrometer or sub- micrometer range [1]. However in many cases it is not sufficient to generate simple binary, i.e. two-level elements. The efficiency of a diffractive optical element (DOE) can drastically be improved by increasing the number of phase levels, e.g. for a Fresnel zone lens from a theoretical value of 40.5 % in the case of a binary element to 95 % for the 8-level structure [2]. Other elements like blazed gratings simply require the existence of a multi-level three-dimensional structure. The usual methods of multiple photolithographic and dry etching steps indeed offer a rather high throughput, however they suffer from a lack of accuracy, precision and flexibility. In this paper we will report on the fabrication of multi-level diffractive phase elements, especially Echelette gratings, computer generated DOEs (CG DOEs) and Fresnel zone lenses (FZLs) by application of direct electron- beam writing. 2. FABRICATION OF THE ELEMENTS I varic ed g Reactive ion etching Fig. 1 Fabrication scheme for three- dimensional structures 0167-9317/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S0167-9317(00)00373-7