Fig. 1. Schematic diagram of DMD maskless projection lithography

Fig. 2. Principle of fly-eye lens and beam homogenizer

Fig. 3. Working principle of micromirror or micromirror array. (a) Structural diagram of single micromirror^[17]; (b) scanning electron microscope image of micromirror array^[17]; (c) photos of integrated DMD chips of different models^［18］; (d) schematic diagram of micromirror controlling light exit direction in optical path^[18]

Fig. 4. Development history of resolution of DMD maskless projection lithography. (a)~(b) 50 μm line width obtained by DMD maskless projection lithography experimentally in 2000^[27]; (c)~(e) 1.5~1.8 μm horizontal scanning line width and 1 μm diagonal scanning line width obtained by point array technique projection in 2003^[29]; (f) 600 nm line width obtained in 2005^[38]; (g) line array of 0.67 μm width obtained in 2010^[39]; (h)~(i) dot array with 900 nm period obtained in 2010^[40]; (j)~(k) helix structures with 400 nm minimum linewidth in 2013^[41]; (l) 357 nm feature line width obtained by introducing high NA and big magnification projection lens in 2020^[42]

Fig. 5. Linewidth resolution obtained by femtosecond laser maskless surface projection exposure.(a) 150 nm feature linewidth obtained by introducing high NA objective lens and femtosecond laser^[45]; (b) light field distribution diagram of single pixel width’s projection line^[46]; (c) schematic diagram of chemical nonlinear effect, where left column and right column images correspond to high and low light field intensity regions in (b)^[46], respectively; (d) objective lens with 100 × magnification and NA of 1.45^[45], and obtained fine line array; (e) 32 nm linewidth structure which breaks through diffraction limit to λ/12^[46]

Fig. 6. Photonics devices manufactured by DMD maskless projection lithography. (a)~(c) Arrayed waveguide grating pattern^[46]; (d)~(e) micronanofluid device pattern^[46]; (f)~(h) electrostatic comb micro-resonators^[46]; (i) chromium Fresnel zone plate fabricated with single exposure^[39]; (j)~(k) Fresnel zone plate with diameter of tens of micrometers, which has response at about 114 μm^[45]; (l)~(m) large area structure with high precision obtained by single exposure^[46]

Fig. 7. Biological scaffolds and bionic structures fabricated by DMD maskless projection lithography. (a) Process of 3D layer-by-layer sinking fabrication^[26]; (b) kidney-shaped 3D scaffold^[26]; (c) top view and side view photographs of hydrogel enhanced by scaffold^[50]; (d) scaffold enhanced hydrogel’s mechanical capabilities and now it can ‘stand’ on surfaces^[50]; (e) bionic tendon structure inspired from human calf, capable of lifting 1 kg weight^[51]

Fig. 8. Introduction of femtosecond laser can realize exposure of special materials using DMD maskless projection lithography. (a) Processing hard material structure with layer-by-layer fabrication^[52]; (b)~(c) micro metal woodpile structure and nano metal wire bridge^{fabricated by layer-by-layer process[52]; (d) schematic diagram of gray level represented by dot matrix density arranged uniformly in space, and simulated distribution of DMD reflected light field smoothed out by diffraction[53]; (e) graphene removed on catalysis substrate after exposure[53]; (f) graphene transferred to device substrate after exposure[53]}