Abstract
Micropatterning on oblique and multiplane surfaces remains a challenge in microelectronics, microelectromechanics, and photonics industries. We describe the use of numerically optimized diffractive phase masks to project microscale patterns onto photoresist-coated oblique and multiplane surfaces. Intriguingly, we were able to pattern a surface at 90 deg to the phase mask, which suggests the potential of our technique to pattern onto surfaces of extreme curvature. Further studies show that mask fabrication error of below 40-nm suffices to conserve pattern fidelity. A resolution of 3 μm and a depth-of-focus of 55 μm are essentially dictated by the design parameters, the mask generation tool, and the exposure system. The presented method can be readily extended for simple and inexpensive three-dimensional micropatterning.
Highlights
Microstructures on oblique and nonplanar surfaces enable unique functionalities in photonics,[1,2] electronics,[3] and microelectromechanics,[4,5] and provide a broad array of interesting applications in high-gain antennas,[6] radio-frequency identification devices,[7] metamaterials,[8] and transformation optics.[9]
These limitations can be avoided by lens-less lithography that utilizes computer-generated holograms (CGHs) to directly project patterns onto the photoresist surface.[15]. These approaches only project the pattern onto a single plane surface. We extend this technique by designing diffractive optics that can manipulate the intensity of light in 3-D space, and thereby allow for patterning onto nonplanar and oblique surfaces
The samples for lithography were silicon wafers coated with a 1.3-μm-thick photoresist (Shipley 1813) and mounted on a holder that was placed at 45 deg to the optical axis
Summary
Microstructures on oblique and nonplanar surfaces enable unique functionalities in photonics,[1,2] electronics,[3] and microelectromechanics,[4,5] and provide a broad array of interesting applications in high-gain antennas,[6] radio-frequency identification devices,[7] metamaterials,[8] and transformation optics.[9]. It is difficult to utilize OPL to pattern nonplanar or oblique surfaces due to the limitations of the imaging optics. These limitations can be avoided by lens-less lithography that utilizes computer-generated holograms (CGHs) to directly project patterns onto the photoresist surface.[15] far, these approaches only project the pattern onto a single plane surface. We extend this technique by designing diffractive optics that can manipulate the intensity of light in 3-D space, and thereby allow for patterning onto nonplanar and oblique surfaces. An alternative approach for lithography on nonplanar and oblique surfaces is to utilize a flexible template that contains a master pattern and apply this template conformally over the substrate. The pattern may be transferred via an imprint process[16,17,18] or by exposure
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