Digital projection photochemical etching defines gray-scale features

Chris Edwards,Gabriel Popescu,Renjie Zhou,Lynford L Goddard,Kaiyuan Wang,Basanta Bhaduri

doi:10.1364/oe.21.013547

Abstract

We demonstrate a maskless photochemical etching method that is capable of performing one-step etching of multi-level structures. This method uses a digital projector to focus an image onto the sample and define the etching pattern. By combining digital projection photochemical etching with diffraction phase microscopy, etch heights can be measured in situ in a non-destructive manner. This method is single shot, eliminating the need for expensive gray-scale masks or laser scanning methods. The etch rate is studied as a function of the wavelength and irradiance of the projected light. A lateral etch resolution of 2 μm is demonstrated by etching selected portions of the USAF-1951 target. Micropillars, multi-level plateaus, and an Archimedean spiral are etched, each in a single processing step, to illustrate the unique capabilities.

Highlights

Photochemical etching (PC etching) is a technique that can enable low-cost fabrication of semiconductor devices with grayscale topography
The solid lines represent the light path for the PC etching and the dotted lines represent the light path for the epi-illumination diffraction phase microscopy (epi-DPM) imaging system, which are both part of the same setup
This image was created in Microsoft PowerPoint using the standard eight bit red-green-blue (RGB) color scheme

Summary

Introduction

Photochemical etching (PC etching) is a technique that can enable low-cost fabrication of semiconductor devices with grayscale topography. Various structures have been fabricated using laser-assisted wet etching, which requires the aid of proximity masking in order to achieve competitive results [7,8,9]. For multi-level structures, gray-scale masks are used which allow varying amounts of light to pass through. These masks are very expensive and may require several iterative purchases as the process is perfected. Focus has been shifted to direct writing techniques which use lasers as the etching tool, rather than gray-scale masks [10]. More complex structures can be created if laser scanning is used [11,12,13] This serial laser writing technique requires precise scanning equipment and software control, and the throughput is relatively low. The interference of multiple laser beams has been employed to bypass the diffraction limit and obtain sub-micron gratings [9, 14, 15] and nanostructures [16]

Methods

Results

Conclusion