HSQ FOx-12 negative resist – Process Information
Version 2.1, April 24, 2008
Bing Dai, Filip Crnogorac, James Conway
Stanford Nanofabrication Facility, Stanford University
HSQ is very high resolution negative tone resist, with smaller line edge roughness
compared to PMMA. The resist is an organic polymer (flowable oxide), which crosslinks
upon exposure to form silicon oxide. The resist needs to be kept refrigerated (4°C), and has
a shelf life of 6 months. Contact with air should be minimized, and avoid letting resist
reach room temperature.
HSQ FOx-12 E-beam Resist Process:
1. HMDS prime
2. Spin 3500 rpm for 60 seconds. Thickness = ~100 nm.
3. Post Application Bake: 2 min. at 150°C followed by 2 min. at 220°C.
4. Exposure
Raith Dose: (refer to appendix for more detailed info)
100 C /cm2 @ 10 kV for Areas (>1 μm)
~200 C /cm2 or higher for smaller features (sub 400 nm)
1000 pC /cm for Single Pixel Lines
0.020 pC for isolated dot shots.
All are highly dependent on proximity effects.
5. Develop in MF319 developer for 60 seconds with very gentle agitation.
6. STOP1: Rinse in 1:9 MF319:H2O mixture for 15 seconds.
7. STOP2: Rinse in DI water for 30 seconds.
8. Dry: N2 Blow dry.
9. Post Process: RIE etching suitable to process result desired.
10. Optical Microscope Inspection: 50 and 500 or 1000 X Magnification.
SEM Inspection: CD Measurements and dose determination.
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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Spin curve information
References
H. Namatsu et al. Microelectronic Eng. 41/42 (1998) 331-334.
Haifang Yang et al. Microelectronic Eng. 83 (2006) 788-791.
A.E. Grigorescu et al. Microelectronic Eng. 84 (2007) 822.
http://dsa.dimes.tudelft.nl/usage/process_data/resist_processes.html
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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1 μm wide rectangle at 80 and 90 μC/cm2 area dose. At higher doses, the width of the
pattern increases (i.e. corners get rounded). Both are narrower than the 1 μm wide
specification.
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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For smaller features, larger doses are required in order to reach specified dimensions. At
110 μC/cm2, the squares are all smaller than the specification. For isolated features dose
required is higher (see images below).
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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At 200 μC/cm2, the feature dimensions matched the design, however, scumming of resist
appears due to proximity effects in dense patterns.
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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SPL dose array shows a minimum dose of 1000 pC/cm2, for a 100nm thick resist,
producing a line ~15nm wide. See below.
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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Dot shots at 0.05 pC are overdosed (see above). Optimal doses are to shown below.
HSQ chip No 3
T = 97nm on Si
Acc. Volt. = 10 kV
Ap=10, WF=25μm
Dose = 0.02 pC
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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Isolated Dots dose determination matrix (all at 150,000 X mag.)
0.045 pC
(mag: 121,000 X)
0.030 pC
0.015 pC
0.040 pC
0.035 pC
0.025 pC
0.020 pC
0.010 pC
0.005 pC
Image drift was a major problem during imaging. Not sure if it is related to sample
charging or some other effect.
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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For the smallest dot shot dose (0.005 pC), the dot diameter is so small (25nm) that some of
the resist pillars fell over on their side as seen on the micrograph below.
HSQ chip No 3
T = 97nm on Si
Acc. Volt. = 10 kV
Ap=10, WF=25μm
Dose = 0.005 pC
Resist pillars fallen over
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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Typical results for 25um write field size, 10um aperture, 10kV and 800 pC/cm SPL dose.
F. Crnogorac, B. Dai, J.W. Conway - Stanford Nanofabrication Facility
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