by Einar Digernes ([email protected])

Standard procedure that can be used to obtain features down to 50 nm.

Summary

Substrate: Silicon Resist: CSAR62 Resist Thickness: 450 nm Resolution: 50 nm Liftoff thickness: Up to ~100 nm Base dose: 250 uC/cm2

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Mask Preparation

Create mask in Clewin or other layout editor. Save as gds file.   

• Open BEAMER 
• Import mask 
• Heal mask to remove overlaps 
• Apply proximity effect corrections 
• Select PSF file: 500 nm PMMA on Si with 100 kV energy 
• Keep other settings unchanged 
• Export mask 
• Select Elionix .con file (avoid long file names and spaces) 
• Select file from drop down menu (check name...) 
• Write field size: 500 µm 
• Write field dots: 500 000 dots (-> Dot size 1 nm) 
• Pitch: 10 (-> Dot size 10x1 nm = 10nm) 
• Dose time: 0.0125 µs/dot (Yields base dose of 250 µC/cm2 @5 nA beam current. Note d_beam~5nm  < d_dot ~10nm.) 
• Zip folder and upload to nanonet 

Notes: 

• If exposing large areas consider bulk and sleeve in BEAMER 
• If exposing only small areas you can consider reducing beam current to 1 nA, pitch to 2 (2nm dot size). Base dose is now 250 uC/cm2 
• Work with the thinnest resist that is suitable for your next process step. For liftoff resist thickness should be 5x metallization thickness for e-beam evaporation and 10x for sputter coating.

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Laboratory

Substrate Preparation

• Create Si chip of desired size from Si wafer by scribing 
• Clean in Acetone in ultrasonic bath for 2 minutes 
• Rinse in IPA for 1 minute 
• Dry with nitrogen 
• Dehydration bake 150 C for 5 minutes 
• Plasma clean O2 with 50% flow and 50% power for 2 minutes

Spin Coat

• Create spin coat recipe 
• Step 1: 1000 RPM for 4 s with 1000 RPM/s acceleration 
• Step 2: 4000 RPM for 60 s with 1000 RPM/s acceleration 
• Put sample on spin coater chuck and control that it is in the center (off-centered sample may be thrown off at high RPM) 
• Apply vacuum (home->settings->...->vacuum). Check that vacuum is good (>7 mbar), if not sample might be thrown off. 
• Start program (home->program, select program, start) 
• Remove sample from spin coater 
• Remove resist form back side of sample using swab and ethanol 
• Put sample on a clean Si wafer 
• Soft bake on hot plate at 150 C for 1 minute 
• Cool on cold plate 
• Measure thickness with reflectometer. The film should be homogeneous and with few pin holes. 
• Clean spin coater parts with ethanol

Exposure

• Beam current: 5 nA

Develop

• Step 1: 546 for 60 s 
• Step 2: Dip in MIBK:IPA 1:3 for 1-2 s 
• Step 3: IPA for 60 s 
• Dry with N2 

Remove Resist (Liftoff or after etching)

• 2 minutes in ultrasonic bath at RT (19 C) using remover 71 
• Rinse in IPA 
• Dry with N2 

Inspect with optical microscope, SEM and/or AFM. If resist is not easily removed this may be due to 

• Etching process can harden the resist. Try oxygen plasma  
• Liftoff can be unsuccessful if thinfilm covers the sidewalls 
• Leave in resist remover overnight 
• If still uncessessful the process must be altered 
• Ensure that sample lies flat during thinfilm deposition to avoid sidewall deposition 
• Increase resist thickness or reduce thinfilm thickness

Inspect pattern in optical microscope and SEM. If pattern appears good go on to the next step.