Diffractive microlens with a cascade focal plane fabricated by single mask UV-photolithography and common KOH:H2O etching

• Published in: Journal of micromechanics and microengineering Vol. 20; no. 10; p. 105029
• Main Authors: Zhang, Xinyu, Li, Hui, Liu, Kan, Luo, Jun, Xie, Changsheng, Ji, An, Zhang, Tianxu
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.10.2010; Institute of Physics
• Subjects: Applied sciences; Cascades; Circuit properties; Diffraction; Electric, optical and optoelectronic circuits; Electronics; Etching; Exact sciences and technology; Focal plane; Focusing; Integrated optics. Optical fibers and wave guides; Machinery and processing; Masks; Microelectronic fabrication (materials and surfaces technology); Moulding; Optical and optoelectronic circuits; Plastics; Polymer industry, paints, wood; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Silicon; Silicon dioxide; Technology of polymers; Embossing; Potassium hydroxide; Electrochemical method; Evolutionary algorithm; Submicrometer; Roughness; Optics; Rough surface; Chemical vapor deposition; Nanometer scale; Microlens; UV lithography; Silicon oxides; Hot forming; Silicon; PECVD; Microelectromechanical device
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/20/10/105029

A diffractive microlens with a cascade focal plane along the main optical axis of the device is fabricated using a low-cost technique mainly including single mask ultraviolet (UV) photolithography and dual-step KOH:H2O etching. Based on the evolutionary behavior of converse pyramid-shaped microholes (CPSMs) preshaped over a {1 0 0}-oriented silicon wafer in KOH etchant, the first-step KOH etching is performed to transfer initial square micro-openings in a SiO2 film grown by plasma enhanced chemical vapor deposition (PECVD) and patterned by single mask UV-photolithography, into CPSMs with needed dimension. After completely removing a thinned SiO2 mask, basic annular phase steps with a relatively steep sidewall and scheduled height can be shaped in the overlapped etching region between the neighboring silicon concave-arc microstructures evolved from CPSMs through the second-step KOH etching. Morphological measurements demonstrate a desirable surface of the silicon microlens with a roughness in nanometer scale and the feature height of the phase steps formed in the submicrometer range. Conventional optics measurements of the plastic diffractive microlens obtained by further hot embossing the fine microrelief phase map over the nickel mask made through a common electrochemical method indicate a highly efficient cascaded focusing performance.