Template-assisted nanofabrication using photoresist or electron-beam (e-beam) resist patterns as sacrificial templates has become a cornerstone of modern semiconductor manufacturing and nanophotonics. These resists serve as temporary masks, enabling precise pattern transfer onto underlying substrates through etching or lift-off processes. The choice of resist material, exposure method, and development parameters directly influences the achievable resolution, fidelity, and final nanostructure performance.

Photoresists are photosensitive polymers that undergo chemical changes upon exposure to ultraviolet (UV) or deep ultraviolet (DUV) light. Positive-tone resists become soluble in developer solutions after exposure, while negative-tone resists crosslink and become insoluble. In semiconductor manufacturing, photolithography using DUV (193 nm wavelength) or extreme UV (EUV, 13.5 nm) enables patterning of features down to sub-20 nm scales. The resolution is governed by the Rayleigh criterion, where shorter wavelengths and higher numerical aperture lenses reduce the minimum feature size. Chemically amplified resists, which employ acid-catalyzed reactions to enhance sensitivity, dominate advanced nodes due to their high throughput and resolution capabilities.

Electron-beam resists, such as poly(methyl methacrylate) (PMMA) or hydrogen silsesquioxane (HSQ), offer higher resolution than photoresists because of the shorter de Broglie wavelength of electrons. E-beam lithography can achieve sub-10 nm features but suffers from low throughput due to its serial writing process. Resist performance depends on parameters like molecular weight, sensitivity, and contrast. High-contrast resists provide steeper sidewalls, critical for pattern transfer fidelity. For example, HSQ, a negative-tone inorganic resist, can achieve sub-5 nm resolution due to its high contrast and small molecular size.

After exposure and development, the resist pattern serves as a template for etching or lift-off. In etching, the resist masks areas of the substrate while reactive ions or plasma remove unmasked regions. Dry etching techniques like reactive ion etching (RIE) or inductively coupled plasma (ICP) etching provide anisotropic profiles, crucial for high-aspect-ratio nanostructures. The selectivity between resist and substrate must be optimized to prevent premature resist erosion. For instance, silicon etching with fluorine-based plasmas requires resists with high etch resistance, such as SU-8 or metal-hardened layers.

Lift-off processes involve depositing a material (e.g., metal or dielectric) over the resist pattern and subsequently dissolving the resist to leave behind the desired pattern. This method is widely used for creating metallic nanostructures in nanophotonics, such as plasmonic antennas or grating couplers. Successful lift-off demands resist profiles with undercuts or re-entrant angles, achievable using bilayer resists or image reversal techniques. For example, a PMMA/MAA copolymer top layer over a thicker PMMA underlayer can generate undercut profiles ideal for clean lift-off.

Resolution limits are dictated by resist chemistry, exposure tools, and pattern transfer methods. Photoresists face diffraction limits, while e-beam resists contend with electron scattering (proximity effects) that broadens exposed regions. Advanced strategies like dose modulation or multi-pass exposure mitigate these effects. In etching, sidewall roughness and line-edge roughness (LER) degrade resolution. LER below 2 nm is achievable with optimized resist formulations and plasma conditions. For lift-off, resist swelling during dissolution can distort features, necessitating careful solvent selection.

In semiconductor manufacturing, resist templating enables the fabrication of fin field-effect transistors (FinFETs), gate-all-around nanosheets, and interconnect vias. The transition to EUV lithography at the 7 nm node and beyond relies on resist materials with low stochastic defects and high sensitivity. Metal-oxide resists, such as hafnium oxide hybrids, are emerging as promising candidates due to their high etch resistance and sub-10 nm resolution.

Nanophotonics leverages resist templates to create optical metasurfaces, photonic crystals, and waveguide devices. Plasmonic nanostructures, such as gold nanodots or silver bowtie antennas, require precise control over feature size and spacing to tune optical resonances. E-beam lithography followed by lift-off is the preferred method for these applications, enabling sub-wavelength feature sizes critical for manipulating light at the nanoscale. For instance, arrays of sub-100 nm gaps between nanoparticles can enhance Raman scattering for surface-enhanced spectroscopy.

Challenges persist in resist-based templating, including pattern collapse due to high-aspect-ratio structures, resist shrinkage during processing, and defect formation. Techniques like critical point drying or supercritical CO2 treatment minimize collapse, while advanced resist formulations reduce shrinkage. Defect control is paramount in high-volume semiconductor production, where even nanometer-scale defects can impact device yield.

Future directions include the development of resist materials with higher sensitivity and lower line-edge roughness, as well as hybrid approaches combining top-down lithography with bottom-up self-assembly. Directed self-assembly of block copolymers, guided by resist templates, can further enhance resolution and reduce costs. Additionally, emerging resist chemistries, such as two-photon absorption materials or quantum dot resists, may push the limits of nanofabrication beyond current capabilities.

The versatility of resist-based templating ensures its continued dominance in nanofabrication. From enabling Moore’s Law in semiconductors to unlocking new functionalities in nanophotonics, sacrificial resist patterns remain indispensable tools for engineering materials at the nanoscale. As demands for smaller features and greater complexity grow, innovations in resist chemistry and pattern transfer techniques will drive progress across multiple disciplines.