[INVITED] Total-internal-reflection-based photomask for large-area photolithography. (May 2016)

• Record Type: Journal Article
• Authors: Hung, Shao-Kang; Lin, Kung-Hsuan; Chen, Cheng-Lung; Chou, Chen-Hsun; Lin, You-Chuan
• Is Part Of: Optics & laser technology. Volume 79(2016)
• Page Start: 39
• Page End: 44
• Publication Date: 2016-05
• Subjects: Optics -- Periodicals; Lasers -- Periodicals; Electronic journals; 621.366
• DOI: 10.1016/j.optlastec.2015.11.016
• Languages: English
• ISSNs: 0030-3992

Abstract

Abstract: Photolithography has been widely implemented with a photomask in contact or in close proximity to the photoresist layer. The flatness of the substrates is a crucial factor to guarantee the quality of the entire patterned photoresist (PR) layer especially for large-area photolithography. However, some substrates, such as sapphire wafers, do not possess highly uniform thickness as silicon wafer does. In this work, we demonstrate that a flexible polydimethylsiloxane (PDMS) photomask with optical total-internal-reflection structure can effectively circumvent this problem for mass production. Different from conventional photomask that the light is blocked by the patterned reflective/absorbing materials, the distributions of light intensity on the PR is engineered by the geometric structure of the transparent PDMS photomask. We demonstrate that 4 in. patterned sapphire wafers can be successfully fabricated by using this PDMS photomask, which can be easily integrated into the present techniques in industry for mass production of substrates for GaN-based optoelectronic devices. Highlights: We design flexible photomasks for large-area warped substrates like sapphire. Our concave/single-material design overcomes drawbacks in previous designs. Throughput of our method is 15-fold faster than the dominant way in industry.