Microstructuring of resist double layers by a femtosecond laser ablation and UV lithography hybrid process

Transcription

1 Microstructuring of resist double layers by a femtosecond laser ablation and UV lithography hybrid process Tamara Pacher 1, Adrian Prinz 2, Stefan Partel 1, Sandra Stroj 1 1 Josef-Ressel-Center for material processing with ultrashort pulsed lasers, Research Center for Microtechnology, Vorarlberg University of Applied Sciences, Hochschulstrasse 1, 6850 Dornbirn, Austria 2 Sony DADC Austria AG, Sonystrasse 20, 5081 Anif, Salzburg, Austria Overview Introduction and motivation Experimental Material system Process parameters AZ n-lof 2070 Ultra-short pulse laser system Selective ablation Determination of ablation thresholds Results UV photolithography Protective layer Selective laser ablation Laser ablation glass substrate Summary and conclusion 2 1

2 Josef-Ressel-Center for material processing with ultrashort pulsed lasers a cooperation of HighQLaser / Spectra-Physics and the Vorarlberg University of Applied Sciences 3 Josef-Ressel-Center for material processing with ultrashort pulsed lasers 5 Years Project Funded by the Austrian Federal Ministry of Economy, Family and Youth and the National Foundation for Research, Technology and Development Focus on physical mechanisms of laser ablation (material removal) with ultrashort laser pulses possible applications materials and material systems, respectively, which are considered as promising for future microsystems 4 2

3 Josef-Ressel-Center for material processing with ultrashort pulsed lasers Project partner founded in 1999 ultra-short pulse lasers (picosecond / femtosecond) since 2011 part of Newport / Spectra-Physics Laser Division #1 in ultrafast broadest installed base of ultrafast lasers 5 Motivation Aim: Selective structuring of photoresist with femtosecond laser pulses in combination with conventional UV photolithography Rendered design of a structure containing both micro- and milimeter patterns Selective laser ablation Laser ablation substrate UV photolithography 6 3

4 Material system structure created with UV photolithography sacrificial layer for debris removal Femtosecond laser structure created with laser ablation Substrate Laser debris 7 Process parameter AZ n-lof 2070 Equipment for exposure: SUSS Mask Aligner MA6 Step no. Process Parameters 1 Cleaning of substrate (soda-lime glass Acetone and isopropyl alcohol and cross-linked SU-8) 2 Dehydration 160 C for 10 min 3 Adhesion promoter AZ Ti-Prime Softbake at 65 C for 2 min followed by a second step at 100 C for 2 min 4 Rehydration cold down to RT 5 Spin-coating of AZ n-lof 2070 Softbake at 65 C for 2 min followed by a second step at 100 C for 10 min 6 Exposure UV broadband VAC mode (100 mj/cm²) 7 Post exposure bake 110 C for 2 min 8 Development AZ 826 MIF for 80 sec 9 Hardbake ramped at RT to 110 C within 10 min, kept for 30 min at 110 C 8 4

5 Schematic representation of ultra-short pulse laser system Laser system: Spirit TM 4W ultra-short pulse laser (HighQLaser), microstruct vario τ = 400fs, f = 50kHz to 1MHz 9 Selective ablation Femtosecond laser resist-substrate system for selective ablation process window 10 5

6 Determination of the ablation thresholds F F solving the equation for slope 2 F F ablation threshold Decrease of power Multipulse threshold fluence SU-8: 0.3 J/cm² Soda-lime glass: 0.99 J/cm² for (point of intersection with the x-axis) Measurement methode from J. M. Liu, Simple technique for measurements of pulsed Gaussian-beam spot sizes, 11 Results UV photolithography 12 6

7 Protective layer Without protective layer With protective layer Structure created with laser ablation, edge damage caused by the debris Structure created with laser ablation after removing the PVA with warm water 13 Results selective laser ablation Parameter Step no. 1 Step no. 2 Value Unit Value Unit Repetition rate 500 khz 500 khz Fluence J/cm² 0.3 J/cm² Hatch distance mm mm Speed of operation 500 mm/s 500 mm/s Number of cycles

8 Results selective laser ablation 15 Results laser ablation soda-lime glass Parameter Value Unit Repetition rate 500 khz Fluence 2.23 J/cm² Hatch distance mm Speed of operation 300 mm/s Number of cycles

9 Results laser ablation fused silica Parameter Value Unit Repetition rate 500 khz Fluence 2.23 J/cm² Hatch distance mm Speed of operation 300 mm/s Number of cycles Summary and conclusion Combination of photolithography and laser ablation offers possibilities in fabrication of multilayer structures A suitable material system was found The required structure qualities can be achieved It was demonstrated that it is possible to generate cavities into the glass substrate This allows photoresist patterning and substrate processing within one laser processing step Cutting the structured wafer into single chip devices Enables fast and flexible process steps 18 9

10 Acknowledgements The financial support by the Austrian Federal Ministry of Economy, Family and Youth and the National Foundation for Research, Technology and Development is gratefully acknowledged. 19 Thank you for your attention 10