Maskless lithography using silicon oxide etch-stop layer induced by megahertz repetition femtosecond laser pulses

Amirkianoosh Kiani,Bo Tan,Krishnan Venkatakrishnan,Venkat Venkataramanan

doi:10.1364/oe.19.010834

Abstract

In this study we report a new method for maskless lithography fabrication process by a combination of direct silicon oxide etch-stop layer patterning and wet alkaline etching. A thin layer of etch-stop silicon oxide of predetermined pattern was first generated by irradiation with high repetition (MHz) ultrafast (femtosecond) laser pulses in air and at atmospheric pressure. The induced thin layer of silicon oxide is used as an etch stop during etching process in alkaline etchants such as KOH. Our proposed method has the potential to enable low-cost, flexible, high quality patterning for a wide variety of application in the field of micro- and nanotechnology, this technique can be leading to a promising solution for maskless lithography technique. A Scanning Electron Microscope (SEM), optical microscopy, Micro-Raman, Energy Dispersive X-ray (EDX) and X-ray diffraction spectroscopy were used to analyze the silicon oxide layer induced by laser pulses.

Highlights

Photolithography is considered to be an important method in a wide range of applications such as fabrication of information storages, micro and nano photonics, nanoelectromechanical systems (NEMS), microelectromechanical systems (MEMS), microfluidics and lab On a Chip Systems [1,2,3,4,5,6,7]
We attempt to use this oxidized layer as an etch stop in alkaline etchant, such as KOH to develop a unique approach for single step maskless lithography by a combination of direct-write femtosecond laser oxidation of silicon and chemical wet etching
Scanning Electron Microscope (SEM) images show bump lines around 7 μm width and 500 nm height induced with femtosecond laser pulses with a power of 3.3 W supplied at 26 MHz

Summary

Introduction

Photolithography is considered to be an important method in a wide range of applications such as fabrication of information storages, micro and nano photonics, nanoelectromechanical systems (NEMS), microelectromechanical systems (MEMS), microfluidics and lab On a Chip Systems [1,2,3,4,5,6,7].Patterning layers of etch stop materials on the substrate materials (such as silicon) is one of the most important issues in the photolithography process. Over the past few years, a number of novel techniques such as scanning electron beam lithography (SEBL) [19,20,21] focused ion-beam (FIB) lithography [22,23], multi-axis electron beam lithography (MAEBL) [24], interference lithography (IL) [25,26] maskless optical projection lithography [27], easy soft imprint nanolithography (ESNIL) [28], scanning-probe and dip pen lithography (SPL, DPL) [29,30], and Tribo Nano Lithography (TNL) based on atomic force microscope (AFM) [31,32,33,34] have been reported for maskless replication of micro/nanoscale patterns of silicon oxide on silicon substrate These techniques have some advantages, they suffer from problems of high cost, low throughput and pattern placement inaccuracy [35]; most of these techniques entail time consuming processing steps and employ complex and expensive equipments which are influenced by environment, they are only applicable to micron-sized devices and for large scale manufacturing, cell stitch must be performed which can be very challenging due to the small dimension of each cell. In addition this method allows for the large-area patterning (in mm-scale) at fast writing speed under ambient conditions

Methods

Results

Conclusion