Detachment Lithography of Photosensitive Polymers: A Route to Fabricating Three‐Dimensional Structures

Abstract

A technique to create arrays of micrometer‐sized patterns of photosensitive polymers on the surface of elastomeric stamps and to transfer these patterns to planar and nonplanar substrates is presented. The photosensitive polymers are initially patterned through detachment lithography (DL), which utilizes the difference in adhesion forces to induce the mechanical failure in the film along the edges of the protruded parts of the mold. A polydimethylsiloxane (PDMS) stamp with a kinetically and thermally adjustable adhesion and conformal contact can transfer the detached patterns to etched or curved substrates, as well as planar ones. These printed patterns remain photochemically active for further modification via photolithography, and/or can serve as resists for subsequent etching or deposition, such that photolithography can be used on highly nonconformal and nonplanar surfaces. Various 3D structures fabricated using the process have potential applications in MEMS (micro‐electromechanical systems) sensors/actuators, optical devices, and microfluidics.

Method to pattern etch masks in two inclined planes for three-dimensional nano- and microfabrication

“…Certain 3D structures can be formed by underetching and the subsequent deposition of new materials. 6,7 Another example is the fabrication of multilevel structures, 8,9 that can be used to obtain relatively simple 3D structures without buried features. Each subsequent level of the multilevel structures suffers from limitations imposed by the geometry of the previous level(s).…”

Moderate Reynolds number flow through microchannels filled with arrays of micro-cylinders

“…A 1-mmthick microscope slide was cut into small pieces whose size is same as a Si die. After cleaning, a thin layer of thermally curable epoxy-based adhesive [33] was transferred to a Si die via detachment lithography [34]. A glass top was then pressed down onto the adhesivecoated Si die on a 130ºC hotplate to create a gas-tight seal.…”

“…A glass top was then pressed down onto the adhesivecoated Si die on a 130ºC hotplate to create a gas-tight seal. The thickness of the adhesive is less than 1 micron and applied to the substrate via transfer printing process [34]. Therefore, the reflow of the adhesive during bonding is minimal, and the overall microchannel dimensions are unaltered even after bonding.…”

Theory, fabrication and applications of microfluidic and nanofluidic biosensors

“…Though UV lithography is a relatively cost-effective method, problems with uneven photoresist coverage often occur when patterning hierarchical nanostructures. Methods such as detachment lithography [117] and alterations to the photoresist spin step [118] have been shown to resolve this issue. This method is frequently used in micro/nanofluidic-based biosensors to fabricate fluidic channels [6,20,127] and is also used in the fabrication of silicon nanowires [24,95].…”

“…After annealing and rapid peeling, the protruding areas of the silicon substrate become coated with photoresist. The substrate can then be patterned using other lithographic methods to produce more complicated structures [117]. Of these methods, nanoimprint lithography has been used by many researchers for the fabrication of PDMS fluidic channels for biosensors [3,11,25,26,45,61].…”