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Grayscale Lithography Creating Complex 2.5D Structures in Thick Photoresist by Direct Laser Writing

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Grayscale Lithography Creating Complex 2.5D Structures in Thick Photoresist by Direct Laser Writing EPIC Meeting on Wafer Level Optics Grayscale Lithography Creating complex 2.5D structures in thick photoresist by direct laser writing 07/11/2019 Dominique Collé - Grayscale Lithography Heidelberg Instruments in a Nutshell • A world leader in the production of innovative, high- precision maskless aligners and laser lithography systems • Extensive know-how in developing customized photolithography solutions • Providing customer support throughout system’s lifetime • Focus on high quality, high fidelity, high speed, and high precision • More than 200 employees worldwide (and growing fast) • 40 million Euros turnover in 2017 • Founded in 1984 • An installation base of over 800 systems in more than 50 countries • 35 years of experience 07/11/2019 Dominique Collé - Grayscale Lithography Principle of Grayscale Photolithography UV exposure with spatially modulated light intensity After development: the intensity gradient has been transferred into resist topography. Positive photoresist Substrate Afterward, the resist topography can be transfered to a different material: the substrate itself (etching) or a molding material (electroforming, OrmoStamp®). 07/11/2019 Dominique Collé - Grayscale Lithography Applications Microlens arrays Fresnel lenses Diffractive Optical elements • Wavefront sensor • Reduced lens volume • Modified phase profile • Fiber coupling • Mobile devices • Split & shape beam • Light homogenization • Miniature cameras • Complex light patterns 07/11/2019 Dominique Collé - Grayscale Lithography Applications Diffusers & reflectors Blazed gratings Other applications Eli - eye eye courtesy ShenZhenof Nahum - Moth Optical Technology Inc • Controlled light diffusion/reflection • Monochromators • Textured surfaces • Illumination • Spectrometers • MEMS/MOEMS • Back light units (LCD displays) • Sensors & communication • Decorative effect 07/11/2019 Dominique Collé - Grayscale Lithography The DWL Series DWL 2000 and DWL 4000 DWL 66+ Our fast and flexible high resolution pattern Our ultimate lithography research tool – now with the generator for mask making and direct writing of 2D High Resolution Mode: Our highest resolution system and 3D micro structures – a “workhorse” in large of all times! multi-user R&D labs and the “go to” system for advanced gray scale. • Maskless technique: fast & flexible prototyping • Up to 1000 gray level accessible for each pixel (minimum pixel size 50nm) • Scalable to large area: substrate size up to 1.4m x 1.4m 07/11/2019 Dominique Collé - Grayscale Lithography Input CAD Formats DXF STL IMAGE XYZ Layer 1 Layer 2 Layer 3 Layer 1: intensity level 1 Native 3D format Image format ASCII files Layer 2: intensity level 2 Height information BMP, PNG, JPG With the coordinates of Layer 3: intensity level 3 transferred into intensity RAW files the structure’s vertices level 07/11/2019 Dominique Collé - Grayscale Lithography Data Conversion: HiConvert-3D • Merge several input files • Step, repeat, rotate… • Multi-pass exposure • Gray value adjustment • Combine 2D & 3D • Outputs machine data for one exposure 07/11/2019 Dominique Collé - Grayscale Lithography DWL: Raster Scan Exposure • Spatial Light Modulator (SLM) : dynamic mask • Ultra fast light modulation between each pixel. • Up to 1000 gray levels are accessible for each pixel (minimum pixel size 50nm). • SLM combined with focusing optic and XY stage motion enables fast writing of high resolution over large areas. • The design is exposed stripe after stripe. 07/11/2019 Dominique Collé - Grayscale Lithography DWL: Raster Scan Exposure y Stage Position x 07/11/2019 Dominique Collé - Grayscale Lithography Stripes Stitching • Invisible in binary exposures • Small intensity variations at the border between stripes in thick photo resist. Stripe width Scan • More visible in deep areas Width 07/11/2019 Dominique Collé - Grayscale Lithography Stitching: N-Over & CI-Over N-Over CI-Over • N-fold overlapping of stripes • Same as N-Over, but with reduced energy at the edges of the stripes • Stripe shift = Stripe width / N • Creates smoother transition between • Each pixel is exposed N times stripes • Exposure time increased by factor N • Better results than N-Over: CI-Over 10 ~ N-Over 40 07/11/2019 Dominique Collé - Grayscale Lithography Stitching Optimization: N-Over & CI-Over Without Stitching Reduction N-Over 4 N-Over 10 N-Over 40 CI-Over 4 CI-Over 10 CI-Over 40 07/11/2019 Dominique Collé - Grayscale Lithography Exposure Time Considerations: • DWL 66+, WM-II • Photoresist: ma-P1275G, 30 µm, 500 mJ/cm2 Exposure Time 1-pass 2-pass 10-pass • Acceptable writing time for 1000 x 1000 50 x 50 mm2 70 min 140 min 12 hours mm2 : 100 x 100 mm2 4.5 hours 9 hours 2 days 10 days 2 200 x 200 mm 16.2 hours 1.4 days 6.8 days • Multi-beam approach 400 x 400 mm2 2.7 days 5.4 days 27 days to achieve higher throughput 1000 x 1000 mm2 16.2 days 32.4 days 162 days 07/11/2019 Dominique Collé - Grayscale Lithography From an Idea to a Useful Structure CAD Software Array of cones One pair of cones cut in hexagons arranged in a STL format honeycomb pattern Output Machine data Conversion software Array 3 x 20 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: 1st Step Target profile Energy too high Energy too low Laser Energy Focused Defocused Focusing lens Focusing 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: 2nd Step CHOOSE INITIAL GV DISTRIBUTION EXPOSURE 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: 2nd Step CHOOSE INITIAL GV DISTRIBUTION EXPOSURE MEASURE GEOMETRY AND COMPARE TO TARGET OK? Height X 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: 2nd Step CHOOSE INITIAL GV DISTRIBUTION EXPOSURE MODIFY GRAY VALUE MEASURE GEOMETRY AND DISTRIBUTION OR DESIGN COMPARE TO TARGET NO OK? Height X 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: 2nd Step CHOOSE INITIAL GV DISTRIBUTION EXPOSURE MODIFY GRAY VALUE MEASURE GEOMETRY AND DISTRIBUTION OR DESIGN COMPARE TO TARGET NO OK? YES Height FINAL EXPOSURE X 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: 2nd Step 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: 2nd Step WORKS WELL, BUT… • … can be time consuming • … requires compromises • … becomes complex for irregular designs 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: Proximity and Process Effects The beam waist is… Lateral development • …larger than the pixel size • …not constant along z-axis (not to scale) Output topograpy strongly depends on target geometry and both tool and process parameters 07/11/2019 Dominique Collé - Grayscale Lithography Shape Optimization: Genisys Beamer 3D PEC Tool & resist Design parameters Beam: Size FWHM, flare Resist optical parameters: absorption bleached & unbleached, refractive index Contrast curve Target depth 07/11/2019 Dominique Collé - Grayscale Lithography Application Example: Pyramids 50 µm Resist AZ4562 Thickness 56 µm Diode Laser 100 mW @ 405 nm 8 µm 25 µm 07/11/2019 Dominique Collé - Grayscale Lithography Application Example: Fresnel Lens Fresnel Formula: c×r2 where z r = target ( ) 2 2 1+ 1-(1+ k)×c ×r measured r = distance from centre c = 1/radius of curvature k = conic constant 07/11/2019 Dominique Collé - Grayscale Lithography Application Example: Cylindrical Lens Array 07/11/2019 Dominique Collé - Grayscale Lithography Application Example: DOE 07/11/2019 Dominique Collé - Grayscale Lithography Application Examples 30 µm Convex 30 µm 500 µm 20 µm 07/11/2019 Dominique Collé - Grayscale Lithography Application Examples 3D-view of height data 1.1 Cross section 07/11/2019 Dominique Collé - Grayscale Lithography Application Examples IGI - All pictures courtesy of Himaxcourtesy Allpictures 07/11/2019 Dominique Collé - Grayscale Lithography Application Examples All pictures courtesy of Kuraray courtesy Allpictures 07/11/2019 Dominique Collé - Grayscale Lithography Thermal Scanning Probe Lithography (t-SPL) • Resist direclty evaporated with a heated scanning probe • Vertical resolution <1nm • Lateral resolution <25nm (record 8nm) • Closed-Loop Lithography • Markerless overlay • 2D & 2.5D lithography • Pattern depth in PPA resist (Polyphthalaldehyde) limited to 150nm • Pattern can be amplified more than 100x to a depth of up to 4µm • No wet development • No damage or charge to the substrate • No vacuum needed Patented “Closed-Loop Lithography” • No proximity effect ensures high patterning accuracy 07/11/2019 Dominique Collé - Grayscale Lithography Grayscale Application of t-SPL 07/11/2019 Dominique Collé - Grayscale Lithography Thank you for your attention! 100µm 07/11/2019 Dominique Collé - Grayscale Lithography This presentation was presented at EPIC Meeting on Wafer Level Optics 2019 HOSTED BY GOLD SPONSOR DINNER SPONSOR SILVER SPONSORS BRONZE SPONSORS EU initiatives funded by www.photonics21.org.
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