Fabrication of suspended micro-structures using diffsuser lithography on negative photoresist

Abstract

We report the results of diffuser lithography applied to a negative-type thick photoresist to fabricate 3-dimensional microstructures suspended on supports. When UV light passes through a diffuser film, the direction of the light is randomized because of the irregular surface of the diffuser. By exposing through a diffuser on a Cr-mask, a circular or an elliptical cross-section of exposed region can be formed on a spin-coated photoresist. When applied to a negative-type thick photoresist, diffuser lithography gives a 3-dimensional circular cross-section of the exposed and cross-linked regions, which could be used for making suspended microstructures. The size of the exposed region has been controlled by the dose of the UV light. The current study clearly shows that the depth of exposed region of photoresist is affected by the geometry of the pattern. By controlling the depth of the exposed region using different pattern size, beam structures suspended on the support structures could be fabricated by single exposure process. The characteristics of the diffuser lithography process were investigated on a negative type photopolymer, SU-8, with different doses of UV-light and different geometry.

One-Step Mask-Based Diffraction Lithography for the Fabrication of 3D Suspended Structures

“…Some one-step lithography methods have also been proposed. No et al [22] achieved suspended microstructures by a single exposure process, during which an optical diffuser film was put on the Cr-masks. The diffuser film had a significant impact on the exposure process, leading to the deformation of photoresist patterns.…”

Dimensionally controlled complex 3D sub-micron pattern fabrication by single step dual diffuser lithography (DDL)

“…A relatively promising and simple approach was put forward when diffuser was introduced in the photolithography process and the process was named as '3D diffuser lithography' or 'backside 3D diffuser lithography' [20][21][22][23]. However, the mentioned processes have various limitations and are inconvenient and nonconventional not only in terms of diffusion angle, dimensional control, photoresist thickness, pattern types, soft bake time etc but also backside lithography is uncommon and is not possible for opaque substrates.…”

A facile fabrication of light diffusing film with LDP/polyacrylates composites coating for anti-glare LED application

“…On the basis of different diffusing principles, the light diffusing films can be classified into two types: the particle-diffusing type [9][10][11][12][13] and the surface-relief type [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

“…When the light passes through the surface with microstructure, a refraction event occurs between the interface of the film and the air, and the incident light is deflected from its course, resulting in light diffusion. There are various methods for fabricating surface-relief type such as replica molding method [14,15], embossing process [7,16,17], lithography [8,18,19], electrospray method [20,21], etching [22,23], holographic technology [24], etc. According to the different preparation methods, the micro-structure can be a hemisphere [14,15,20,21], paraboloidal shape [8], polygonal shape [3,26], pyramid [27,28], cylindrical lens [16], V-shaped mirror [17], or irregular type [4,19,22,23], etc.…”