| Literature DB >> 26956598 |
Andrew Im Greer1, Benoit Della-Rosa2, Ali Z Khokhar2, Nikolaj Gadegaard2.
Abstract
The conversion of a computer numerical control machine into a nanoimprint step-and-repeat tool with additional laser- and photolithography capacity is documented here. All three processes, each demonstrated on a variety of photoresists, are performed successfully and analysed so as to enable the reader to relate their known lithography process(es) to the findings. Using the converted tool, 1 cm(2) of nanopattern may be exposed in 6 s, over 3300 times faster than the electron beam equivalent. Nanoimprint tools are commercially available, but these can cost around 1000 times more than this customised computer numerical control (CNC) machine. The converted equipment facilitates rapid production and large area micro- and nanoscale research on small grants, ultimately enabling faster and more diverse growth in this field of science. In comparison to commercial tools, this converted CNC also boasts capacity to handle larger substrates, temperature control and active force control, up to ten times more curing dose and compactness. Actual devices are fabricated using the machine including an expanded nanotopographic array and microfluidic PDMS Y-channel mixers.Entities:
Keywords: Flash; Imprint; Nanolithography; Replication; Resist; Stepping
Year: 2016 PMID: 26956598 PMCID: PMC4783314 DOI: 10.1186/s11671-016-1341-9
Source DB: PubMed Journal: Nanoscale Res Lett ISSN: 1556-276X Impact factor: 4.703
Fig 1a Annotated photograph of the converted CNC machine. b Annotated photograph of the custom-built lithography tool attachment for the CNC X-Y-Z head. c Schematic representation of the three discrete lithographic disciplines available on the converted CNC machine
Performance characteristics of the custom-built multifunctional UV-lithography tool
| Characteristic | Minimum | Maximum |
|---|---|---|
| LED irradiance (mW/cm2) | 45.0 | 102.0 |
| Laser power (mW) | 0.18 | 1.00 |
| Imprinting load (kg) | 0.10 | High (not measured) |
| Length displacement (mm) | 0.001 | 390.000a |
| Breadth displacement (mm) | 0.001 | 290.000a |
| Head speed (mm/s) | 0.001 | 25.000 |
| Working temperature (°C) | Room Temperature | 150 |
aAlthough the CNC head may displace to the tabulated maximum, with the documented hotplate functioning as the substrate mount, the displacement is limited to the mount area of 150 mm square
Comparison of the converted CNC machine criteria to purposely built commercial counterparts (data for which was determined from official data sheets; Suss power density was given for the discrete wavelength, whereas EVG was approximated for broadband spectrum range 300–500 nm)
| Model | Custom tool | Suss MA/BA6 | EVG 770 NIL Stepper |
|---|---|---|---|
| Price | $ | $$$$ | $$$$$ |
| Power density (mW/cm2) @ 365 nm | 102.0 | 7.1 | ~20.0 |
| Desktop unit | Yes | No | No |
| X/Y accuracy (μm) | <50.0 | 0.5 | 0.5 |
| Optical alignment | No | Yes | Yes |
| Maximum substrate (mm) | 390 | 150 | 300 |
| Active force control | Yes | No | Yes |
| Imprint environment | Air | Air | Vacuum/inert gas |
| Temperature control | Yes | No | No |
| Laser lithography | Yes | No | No |
Tested resist performance criteria
| Performance criteria | AMO NIL MMS4 | DELO-KATIOBOND OM VE 110707 |
|---|---|---|
| Imprint pressure (kPa) | 475 | 376 |
| Curing dose (J/cm2) | 8.0 | 0.4 |
| Etched by O2 plasma | No | Yes |
| Si:resist etch ratio | 1:1 | 4.87:1 |
| Maximum iterations/soft-PDMS stamp | 14 | 34 |
| Radiation bleed (μm) | 300 | 70 |
Fig. 2a Photograph of the custom-built tool being used to pattern a 4-in. Si wafer. Scale bar = 8 cm. b Photograph of a 4-in. Si wafer coated with Delo-Katiobond featuring stepped out 7 mm2 imprints of disordered nanopillars. Scale bar = 14 mm. c Top-down SEM image of the imprinted 200-nm diameter disordered nanopillars in Delo-Katiobond. Scale bar = 1 μm. d Cross-section at 90° tilt of the same sample as c following Si etching. Scale bar = 500 nm. e Photograph of the 4-in. wafer shown in b following Si etching and stripping of the resist in piranha etch
Optimum machine parameters for photolithographic exposure of various popular photoresists using the UV-LED light source and a grating mask of 5 μm × 7 mm openings at 200 μm pitch, (inset: profile from dashed lines)
| Resist | Microposit S1805 | Clariant AZ 4562 | MicroChem Nano SU-8 3005 |
|---|---|---|---|
| LED current | 700 mA | 700 mA | 700 mA |
| Dose | 135 mJ/cm2 | 404 mJ/cm2 | 359 mJ/cm2 |
| resist thickness | 0.5 μm | 4.5 μm | 5.7 μm |
| Line width | 13.0 μm | 7.3 μm | 26.0 μm |
| Optical micrograph |
|
|
|
Image scale bars = 200 μm
Fig. 3Optical micrographs of developed exposures in S1805 resist (all images are at the same magnification and the scale bar of (a) 200 μm): a a single exposure of the mask (inset: profile from dashed line), b a double exposure where the mask has been moved 100 μm in the transverse direction to the grating between exposures, c a triple exposure where the mask has been moved in 65 μm steps in the transverse direction to the grating between exposures, d a double exposure where the mask has been moved 30 μm in the transverse direction to the grating between exposures to create a 10 μm wide protrusion (inset: profile from dashed line), e a double exposure where the mask has been moved 20 μm in the transverse direction to the grating between exposures to widen the grating features and f a double exposure where the mask has been moved 7 mm in the direction of the grating between exposures to double the length of the features (the dashed black line indicates the stitch position). (Inset) ×2 magnified close-up of the stitch position for one line of the grating
Fig. 4a Screen capture of the microchannel mixer design being exposed with the laser lithography tool. Scale bar = 600 μm. b Photograph of a developed SU-8 pattern on Si. Scale bar = 2.5 mm. c Photograph of a relieved PDMS casting from the sample shown in b bonded to a quartz slide to seal the hollow channel. Scale bar = 2.5 mm. d–e Optical micrograph showing part of the design exposed via laser lithography into d S1805 and e Nano SU-8 post development. f Optical micrograph of the PDMS/quartz device shown in c. d–f At the same magnification, scale bar shown in d = 150 μm