Double-Exposure Grayscale Photolithography

• Published in: Journal of microelectromechanical systems Vol. 18; no. 2; pp. 308 - 315
• Main Authors: Mosher, L., Waits, C.M., Morgan, B., Ghodssi, R.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.04.2009; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Calibration; Design engineering; Electronics; Empirical analysis; Exact sciences and technology; Exposure; Fabrication; Gray-scale; Grayscale lithography; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Laboratories; Lithography; Masks; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Microelectromechanical systems; microelectromechanical systems (MEMS); Microelectronic fabrication (materials and surfaces technology); micromachining; Micromechanical devices; Micromechanical devices and systems; Optical sensors; Photolithography; Photoresists; Physics; Precision engineering, watch making; Resists; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Space technology; Three dimensional; three-dimensional (3-D) lithography; Photofabrication; High resolution; Grayscale lithography; microelectromechanical systems (MEMS); Lithography; three-dimensional (3-D) lithography; Micromachining; Calibration; Gray scale; Exposure time; Photolithography; Alignment defect; Microelectromechanical device; Photoresist; Production process
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2008.2011703

A double-exposure grayscale photolithography technique is developed and demonstrated to produce three-dimensional (3-D) structures with a high vertical resolution. Pixelated grayscale masks often suffer from limited vertical resolution due to restrictions on the mask fabrication. The double-exposure technique uses two pixelated grayscale mask exposures before development and dramatically increases the vertical resolution without altering the mask fabrication process. An empirical calibration technique was employed for mask design and was also applied to study the effects of exposure time and mask misalignment on the photoresist profile. This technology has been demonstrated to improve the average step between photoresist levels from 0.19 to 0.02 mum and the maximum step from 0.43 to 0.2 mum compared to a single pixelated exposure using the same mask design.