Microfabrication on a curved surface using 3D microlens array projection

Abstract

Accurate three-dimensional microstructures on silicon or other substrates are becoming increasingly important for optical, electronic, biomedical and medical applications. Traditional microfabrication processes based on cleanroom lithography and dry or wet etching processes are essentially two-dimensional methods. In the past, complicated procedures were designed to create some three-dimensional microstructures; however, these processes were mainly used to create features on planar silicon wafer substrates using the bulk silicon machining technique. In a major departure from previous micromachining processes, a microfabrication process based on microlens projection is presented in this paper. The proposed microfabrication system will have the capabilities of a typical conventional micromachining process plus the unique true three-dimensional replication features based on microlenses that were created on a steep curved substrate. These microlenses were precisely fabricated with a specific pattern on the curved surface that can be used to create microstructures on a pre-defined nonplanar substrate where a layer of photoresist was spin coated. After proper exposure and development, the desired micro patterns are created on the photoresist layer. These micro features can eventually be replicated on the substrate via wet or dry etching processes. The results show that the fabricated three-dimensional microlens array has very high dimensional accuracy and the profile error is less than 6 μm over the entire surface.

Fabrication of Microlens Array and Its Application: A Review

“…Ultraprecision machining was also applied to fabricate 3D compound eye lens arrays [63,64]. It was reported that 601 individual compound eye microlenses (aperture of 0.58 mm) and the related microprisms were produced in a 20 mm diameter area, providing a large light deviation angle of 18.43° and maximal FOV of 180°, if the entire hemispherical surface is fabricated with microlenses.…”

Fast fabrication of curved microlens array using DMD-based lithography

“…Various methods for the fabrication of curved microlens array have been developed, including, but not limited to, reflow process, 4 laser direct-write, 5,6 3D microlens array projection 7 and soft lithography. 8 Most of these methods are processed on a curved substrate or by deforming the planar microlens array on elastomeric membrane into curved microlens array.…”

“…8 Most of these methods are processed on a curved substrate or by deforming the planar microlens array on elastomeric membrane into curved microlens array. 9 The fabrication methods processed on a curved substrate such as direct writing, [10][11][12] which employ a focused laser beam or an electron beam with a quasi continuous intensity modulation, have a long production cycle and high production costs. Although the fabrication deforming a planar microlens array is flexible, the complex process and harsh control condition may restrict its development.…”

Predictive modeling of surface roughness in lenses precision turning using regression and support vector machines

“…Toric and progressive addition lenses (PAL) are a kind of opthalmic lenses with freeform surface, and their application is limited for a long time by the difficulty to design and manufacture. At present, freeform surfaces can be machined by fast tool servo [1][2][3][4], micro-milling [5][6][7], fly-cutting or raster milling [8,9], and slow tool servo (STS) [10][11][12][13][14] etc. Among these technologies, with the advantages of high surface accuracy and high machining efficiency, STS is gradually applied to machine freeform surface.…”

“…One of such improvements can be made to STS turning by developing predictive models for surface roughness. There were a few papers discussing fabrication of freeform surface using STS [10][11][12][13][14], and path planning and error compensation [10,15,16] were also reported. However, little literature dealt with the prediction of surface topography using STS.…”