Process technology

Process Technology 2 MMIC-HEMT, ETH Zürich Electrical nm contacts, Uni Basel Luft InP 70 nm DFB Laser, WSI München Applications: Nano Devices  =230 nm Nanoelectronics Optics Basic Research Nano-“mechanics“ „Nanopendulum“, LMU TH Aachen Magnetoelectronics EBL

Process Technology 3 Coating or stripping step Remover Lift-Off Etching metal Remover Pattern Transfer substrate resist substrate Spin coating Exposure substrate Developing Wafer After x process steps Process Technology

4 Remover Lift-Off Etching metal Remover Pattern Transfer substrate resist substrate Spin coating Exposure substrate Developing Process Technology metal Etching substrate EBID gas injection

Process Technology 5 Raith support Special Knowledge, e.g. EBL resist database General Knowledge substrate resist substrate Spin coating Exposure substrate Developing Remover Lift-Off Etching metal Remover Pattern Transfer Process Technology

6 Raith Application Lab: Typical Instrumentation Process step substrate Spin coating Exposure substrate Developing Cleaning Spin coating Film thickness measurement Exposure DevelopingInspection Instrumentation Film thickness measurement Cleaning Spin coating Exposure Developing Inspection wet bench (eye-) shower for accidents with acids storage for chemicals stove / hotplate refrigerator spin coater stove / hotplate Film Thickness Probe Raith 150 / R50 FE wet bench storage for chemicals optical microscope sputtering machine Raith 150 / R50 FE

Process Technology 7 Lift Off Tips & Tricks obtain an undercut resist profile by if possible use evaporation, not sputtering using a double layer resist using low beam energy overexposure or overdeveloping use an aspect ratio of resist: metal as large as possible

Process Technology 8 Resist Wafer apply postbake to improve resist stability during etching for organic resists avoid etching processes with oxygen Wafer Tips & Tricks obtain cross-sections without undercut or overcut by using high beam energy avoiding overexposure and overdeveloping Etching

Process Technology 9 Process Steps substrate resist substrate Spin coating Exposure substrate Developing Wafer e.g. electron beam lithography inspection e.g. resist thickness measurement inspection optical microscope SEM metrology

Process Technology 10 How to Avoid Charging Effects On isolating samples an additional metal layer between resist an substrate or on top of the resist is required, e.g. use additional Al layer on top of the resist. thickness should be 10 nm to 20 nm remove with KOH With an additional isolating interlayer, e.g. SiO layer use a higher acceleration voltage, e.g. 25 kV for 1 µm SiO.

Process Technology 11 Dependence of thickness on spin speed open cover closed cover Resist Characterization I:

Process Technology 12 Contrast curves Resist Characterization II:

Process Technology 13 application dose resolution comments µC/cm nm High resolution: PMMA~200<10dry etch (--), low sensitivity or low contrast ZEP xx~ 50<20dry etch(3x better than PMMA), adhesion (-) Mask making: EBR-9~20>200long shelf life, large process latitude PBS~2>250low contrast, difficult process (--) AZ5206~20~250 high contrast, good etch resistance Double layer with PMMA (e.g. lift-off): P(MMA-MAA)~ 70<200 PMGI~ 40<100 Positive EBL Resists more info at:

Process Technology 14 Applicationdose resolution comments µC/cm nm High resolution Calixarene~4000<10very low sensitivity, high resolution (+) HSQ~300<20dry etch(+) ma-N2400~100<70DUV & E-beam sensitive NEB xx~ 20<40dry etch(+), adhesion (-) SAL~10<100high contrast, dry etch (+) SU8~2<1003D EBL applications COP~1>1000difficult process (--) Mask making Negative EBL Resists more info at:

Process Technology 15 Which Resist for Which Task? decide about positive or negative resist with respect to the minimum area that will be exposed check literature and resist suppliers for resist performance with respect to e.g. resolution sensitivity etching stability check suitability for your lab, e.g. required baking steps and chemicals

Process Technology 16 Getting Started As an EBL beginner, use resists that are easy to handle : avoid chemically amplified resist because they need a carefully controlled post exposure bake avoid very sensitive resists make first tests with positive resist, because several tests can be made on one sample  use for example PMMA 950K from Raith’s EBL starter kit