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.