High throughput i line grayscale exposure for 3D optical components and MEMS applications

i-line grayscale reticle based exposure has the advantage to offer high throughput and can be used in existing i-line tools in the industry: ◼Tuning the slope of sidewalls ◼Implementing different height level −Reducing Lithography/Etching Steps →Cost Reduction →New Design Possibilities Introduction High throughput i-line grayscale exposure for 3D optical components and MEMS applications — Sebastian Schermera, Stephen DeMoorc, Andrew Zanzalc, Patrick Reynoldsc, Christian Helkea,b, Anja Voigtd and Danny Reutera,b aFraunhofer Institute for Electronic Nano Systems (ENAS), Chemnitz, Germany b Technische Universität Chemnitz, Center for Microand Nanotechnologies (ZfM), Chemnitz, Germany c Benchmark Technologies, 7 Kimball Lane, Building E Lynnfield, MA 01940, USA d Micro Resist Technology (MRT) GmbH, Köpenicker Str. 325, 12555 Berlin, Germany ACKNOWLEDGEMENT This project has received funding from the European Union’s Horizon Europe research and innovation programme under grant agreement no 101137624; and has received funding from the Swiss State Secretariat for Education, Research and Innovation (SERI). UK participants are supported by UKRI grant number 10102121. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union. Neither the European Union nor UKRI can be held responsible for them. The authors also would like to thank all involved colleagues of Fraunhofer ENAS and ZfM of Technical University of Chemnitz for their support. M.Sc. Sebastian Schermer — Group Lithography and Photonic Micro-/ Nanostructures Department Nano Device Technologies Tel. +49 371 45001-459 [email protected] Fraunhofer ENAS Technologie-Campus 3 / 09126 Chemnitz / Germany 2.5D structures can be achieved by using grayscale lithography, which can be done with maskless patterning technologies like electron beam (e-beam), or direct laser writing1,2. These technologies offer a high resolution, but the downside of this sequential exposure / direct writing tools are low writing speeds, which hampers scalability to high volume1.To overcome those limitations and enable higher volume manufacturing, an 5x i-line stepper lithography is used. Therefore a stepper reticle based on mask aligner contrast curve was fabricated. Project Partner - Process Development: Fraunhofer ENAS, Germany - Resist Development: Micro Resist Technology, Germany - Reticle Design: Benchmark Technologies, USA Experimental References [1] Grushina, A. "Direct-write grayscale lithography." Advanced Optical Technologies 8.3-4, 163-169 (2019). [2] McKenna, C., et al. "Maskless direct write grayscale lithography for MEMS applications." 2010 18th Biennial University/Government/Industry Micro/Nano Symposium. IEEE, (2010). [3] Gan, O., et al. "Programmed resist sidewall profiles using subresolution binary grayscale masks for Si-photonics applications." Advanced Fabrication Technologies for Micro/Nano Optics and Photonics V. Vol. 8249. SPIE, (2012). [4] Heller, M., et al. "Grayscale lithography: 3D structuring and thickness control." Optical Microlithography XXVI. Vol. 8683. SPIE, (2013). Processing Parameter Substrate preparation Dehydration bake: Oven, 30 min at 200 °C Spin - coating, resist ma-P 1200 series, low contrast positive tone resist, thicknesses from 1 µm up to 10 µm Softbake Hotplate, 90 s to 600 s @ 105 °C Exposure NIKON NSR2205i11D i-line Stepper Development No post exposure bake; mr-D 526/S ma-D 532/S Table 1: Processing Parameter for ma-P 1200G positive tone resist series. Contrast curve and Selectivity Useable Grayscale transition Area Useable Grayscale transition Area Figure 1: Contrast Curves of a) ma-P 1215G with a resist thickness of 1.8 µm and b) ma-P 1275G with a resist thickness of 8.1 µm Mask Fabrication ◼6”X 6”X 0.25”Reticle designed on a 1 nm grid at 5x for writing on a variable shaped e-beam tool; gray level are modulated using half-toning technique3,4 ◼Writer grid and resolution capability allow for ~ 1900 gray levels for a 64 µm diameter lens design (at wafer scale) ◼Adapted reticle used contrast data from a previous grayscale reticle ◼Structure fidelity relies on known contrast curves; for structure transfer via etching also the contrast curve after etching is necessary Applications MEMS Photonic Applications Figure 2: SEM Image and AFM line Scan of lines with slopes sidewalls in ma-P 1215G with a resist thickness of 2 µm. a) b) Fig. 3: a) Schematic view and SEM image of waveguide with out-of-plane mirror at both ends in 8.1 µm ma-P 1275G; b) Detail view of out-of-plane mirror. a) b) 5 µm 5 µm 5 µm 5 µm 10 µm 20 µm 5 µm 10 µm 10 µm Fig. 5: SEM images of different structures in ma-P 1275G with 8.1 µm thickness. ◼High throughput grayscale process with i-line wafer Stepper for different applications and specific customers needs ◼SEM-images (stage 45°) of fabricated structures in different resist thicknesses (Lenses, Pyramids, Slanted Gratings, Pixel Array, Needles) Various Applications Fig. 4: SEM Image of Lens Array in 2 µm ma-P 1215G resist.