Measurement and statistical analysis toward reproducibility validation of AZ4562 cylindrical microlenses obtained by reflow

• Published in: Measurement : journal of the International Measurement Confederation 2014-03, Vol.49, p.60-67
• Main Authors: de Jesus Maciel, Marino, Rocha, Rui Pedro, Carmo, João Paulo, Correia, José Higino
• Format: Article
• Language: English
• Subjects: Arrays; Cross sections; Measurement; Microlenses; Microlenses fabrication; Photolithography; Photoresists; Reproducibility; Reproducibility validation; Standard deviation; Statistic analysis; Statistical analysis
• ISSN: 0263-2241; 1873-412X
• DOI: 10.1016/j.measurement.2013.11.056

•Microlenses (MLs) fabrication process: statistical validation of their high-reproducibility feature.•MLs fabrication: lithographic process based on thermal reflow and rehydration.•Optical microsystems: MLs for direct fabrication on top of planar photodetectors.•Diameter before/after reflow: maximum mean difference=2.78±0.22μm of SD/2.34±0.35μm of SD.•Height before/after reflow: maximum mean difference=0.76±0.10μm ofSD/12.24±0.24μm ofSD. This paper presents the statistical analysis applied into the shape of microlenses (MLs) for validating the high-reproducibility feature of their fabrication process. The MLs were fabricated with the AZ4562 photoresist, using photolithography and thermal reflow processes. Two types of MLs arrays were produced for statistical analysis purposes: the first with a cross-sectional diameter of 24μm and the second with a cross-sectional diameter of 30μm, and both with 5μm spacing between MLs. In the case of 24μm diameter arrays, the measurements showed a mean difference in diameter of 2.78μm with a standard deviation(SD) of 0.22μm (e.g., 2.78±0.22μmofSD) before the reflow, and 2.34±0.35μm ofSD after the reflow. For the same arrays, the mean difference in height obtained was, comparatively to the 5.06μm expected, 0.76±0.10μm ofSD before the reflow and 1.91±0.15μm of SD after the reflow, respectively. A mean difference in diameter of 2.64±0.41μm ofSD before the reflow, and 1.87±0.34μm of SD after the reflow was obtained for 30μm diameter MLs arrays. For these MLs, a mean difference in height of 0.71±0.12μm of SD before the reflow and 2.24±0.24μm of SD after the thermal reflow was obtained, in comparison to the 5.06μm of height expected to obtain. These results validate the requirement for reproducibility and opens good perspectives for applying this fabrication process on high-volume production of MLs arrays.