Fig. 1. Photolithography basic process flow chart

Fig. 2. Schematic of projection optical lithography

Fig. 3. 88 mm×88 mm superconducting integrated circuit fabrication process^[44]. (a) 2D view; (b) 3D view

Fig. 4. EUV lithography working principle (ASML)

Fig. 5. Application and characterization of EUVL in nanoscale patterning: from computational aerial images to SEM analysis^[46]. (a) Calculated aerial image for a 7.8 nm HP; (b) the corresponding SEM image of HSQ resist showing line/space patterning; (c) SEM image intensity averaged along the line direction; (d) calculated NILS for an EUV beam with 4% bandwidth; (e) computed contrast of the aerial image and the SEM image; (f) line/space patterning of 5 nm HP

Fig. 6. E-beam lithography system diagram

Fig. 7. Experimental and simulated behavior of sub-5 nm nanogap metasurfaces^[53]. (a) Scanning electron microscopy image for the 2 nm nanogap bow-tie; (b)‒(c) measured transmission spectra for 2 and 3 nm gaps and the corresponding numerical simulations; (d) simulated distribution of the modulus of the optical field for a 3 nm nanogap metasurface at CR (824 nm) and LSPR (1113 nm) positions

Fig. 8. Ion beam lithography system^[58]

Fig. 9. XRL system and its application in wafer-scale high-efficiency production. (a) Schematic diagram of XRL system^[64]; (b) 1800 gray-level micro-optical components on a 4.8 mm×2.4 mm chip fabricated by XRL technology^[65]; (c) image of wafer scale microchips, where 148 chips in wafer achieved through single exposure run and the zoom out of individual chips at the left and right end of the wafer^[65]

Fig. 10. Basic flow chart of NIL

Fig. 11. Application of nanoimprinting and etching processes for silicon patterning and pattern transfer and seam treatment^[77]. (a) Scheme of the first and second cross-nanoimprinting and etching process; (b) large-area nanoimprinted silicon pattern measuring 5 mm×30 mm; (c)‒(d) the hole pattern transferred onto the silicon substrate after the first and second nanoimprinting and etching processes, respectively; (e)‒(f) the seams between the first nanoimprinted-etched pattern and the second nanoimprinted-etching pattern: (e) the seam is in the edge, (f) the seam is in the middle

Fig. 12. Printed transparent MAS ceramics after sintering and TPL^[91]. (a)‒(b) Octet lattice consisting of struts with a diameter of about 80 μm; (c)‒(d) Schwarz P 3×3×3 array with a wall thickness of 34 μm; (e) SEM image of a gyroid structure after sintering and hot isostatic pressing (HIP), where the inset shows a feature size of only 13 μm; (f) scheme for the demonstration of the functionality of a microlens array by focusing through the lenses on an “M” below the printed part; (g) SEM image of the micro lens array after HIP; (h) demonstrated functionality of the lenses according to the scheme in Fig. (f); (i) WLI measurement of the printed microlens array in Fig.(g)

Fig. 13. Construction of nanoscale HSQ features by FsLDW^[92]. (a) Illustration of patterning HSQ with sub-diffraction feature size by FsLDW through nonlinear absorption process; (b) scheme of HSQ features fabricated by FsLDW with single-scanning and cross-scanning methods, resulting in 33 nm and 26 nm feature sizes, respectively; (c) SEM image of HSQ nanowires fabricated by FsLDW with different laser scanning speeds

Fig. 14. MoTe₂ surface patterning^[98]

Fig. 15. SEM images of graphene nanoribbon and nanomesh patterns fabricated by a PSM modulated laser beam^[106]. (a)‒(b) Nanoribbon and its partial magnification; (c)‒(d) nanomesh and its partial magnification

Fig. 16. Fabrication of sub-20 nm line diagrams by DSA using PS-b-PG^[110]. (a) Schematic of the DSA process using PS-b-PG;

Fig. 17. Typical setups for STED microscopy and STED lithography^[128]

Fig. 18. Performance of LMC-MPL and light confining mechanism^[129]. (a) Schematic diagram of LMC-MPL; (b) standard pattern for light confining capability tests; (c) schematics of a 3D woodpile structure (left) and voxels (right); (d) woodpile structures made by multi-photon lithography (MPL), matter-confined lithography (MC-MPL), and LMC-MPL; (e) light confining capability test patterns of two chemical quenchers; (f) linewidth versus inhibition beam power for light-confined multiphoton lithography (LC-MPL) and LMC-MPL under different excitation beam powers P_ex; (g) CD lines for LC-MPL (Pr1) and LMC-MPL (Pr2) correspond to points C and D in Fig.(f); (h) schematic diagram of different light confining paths; (i) energy level transition for LMC-MPL

Fig. 19. Synthesis of HABI-PU photoresist and study of its lithographic properties^[133]. (a) Synthesis of HABI-PU photoresist and its decomposition in the photolithography process. Optical microscopy images of the HABI-PU photoresist with different contents of HABI after lithography and development at different exposure doses: (b) exposure dose is 4096 mJ/cm² and molar percentage of HABI is 6%; (c) exposure dose is 2046 mJ/cm² and molar percentage of HABI is 9%; (d) exposure dose is 256 mJ/cm² and molar percentage of HABI is 12%

Fig. 20. Molecular structure of the polymer chain^[136]: three functional units, AG (red), TPSn (purple), and acid reactive (AR) unit (green), attached to a single polymer chain. The right image shows 18 nm HP pattern under SEM

Fig. 21. High-resolution SEM images of BPA-6-epoxy for HP 25 nm and HP 22 nm^[139]. The critical dimensions are 25 and 22 nm with line-space-ratio of 1∶1, respectively (film thickness: 34 nm). PR-1: BPA-6-epoxy with a mass fraction of 10% 2-aminoanthracene; PR-2: BPA-6-epoxy without 2-aminoanthracene

Fig. 22. SEM images of PS-I_0.58 photoresist with different thicknesses^[145]. (a) 29 nm; (b) 25 nm

Fig. 23. High-resolution SEM images of line-space patterns (top view) for SP-BOC photoresist at various exposure doses^[152], where the grating and pattern periods are 280 and 140 nm, respectively

Fig. 24. E-beam exposure patterns for PMMA-Al₂O₃ prepared using different numbers of SIS cycles^[156]

Fig. 25. Zn-mTA clusters and their formation of sub-15 nm patterns^[161]

Fig. 26. Multicolored PQD patterns prepared by direct in situ photolithography^[170]. (a)‒(c) Green cartoon, red letter, and blue snowflake patterns and their corresponding pixels; (d) red, green, and blue stripe pattern; (e) blue stripe pattern with a period of 10 μm; (f) blue circular pattern with a diameter of 5 μm; (g) a photograph showing a green logo pattern on a flexible PET; (h) a photograph showing a green school badge pattern on a silicon wafer

Fig. 27. EUV exposure results of zinc organic cluster photoresist on underlayers^[172]

Fig. 28. High sensitivity two-photon initiator CCK-Th^[177]

Fig. 29. Ultrafast multiphoton lithography of PVA hydrogel objects^[179]. (a) Schematic of multiphoton lithography; (b) well-defined hydrogel lines are written with a large processing window; (c) a model of artificial bacterial flagella (ABF) (left) and projected confocal image of a microarray of ABF gel structures (right); (d) a 3D model of multilayered tissue-mimicking scaffold (left) and projected confocal image of the microfabricated scaffold (right)

Fig. 30. Architectures manufactured with cellulose-based photoresists^[181]

Fig. 31. Schematic illustration of the formation of PRGO composites^[184]

Fig. 32. Magnetic-field driven hydrogel micro-nail^[186]. (a) Schematic of the design strategy; (b)‒(f) micrographs of the micro-nail at its original position (b) and other positions under external magnetic actuation, where the insets showing the schematic of corresponding state of hydrogel micro-nail

Fig. 33. Characterization of the SU8-m-PD conjugated thin film^[187]. (a) High-resolution SEM image of the SU8-m-PD conjugated film in normal mode; (b) high-resolution SEM image of a cross-section of the SU8-m-PD conjugated film on a substrate, captured in backscatter mode; (c) high-resolution AFM image of a 5×5 µm area of the SU8-m-PD film; (d) confocal images in XY, XZ, and YZ planes of the SU8-m-PD film deposited on a glass substrate under 488 nm excitation

Fig. 34. Preparing polymers with RAFT method to improve photoresist performance^[191]

Fig. 35. Liquid PMMA microstructures prepared using microlithography^[195]. (a) A Tesla mixer cascade directly structured using microlithography; (b) micropores with a width of 100 μm and a depth of 50 μm; (c) the logo of a group with a minimum feature size of 60 μm; (d) white light interferometry measurement of the structure shown in Fig.(c)