What Is Nanolithography?

Nanolithography is the set of processes used to create patterns with at least one dimension in the range of 1 to 100 nanometers on a substrate. It is the central patterning step in semiconductor device fabrication, photonic component manufacturing, and research-scale device prototyping. The goal of every nanolithographic method is to transfer a geometric pattern, defined either on a mask or written directly by a beam, into a material layer with fidelity sufficient to yield functional structures. The resolution limit of any lithographic method is fundamentally constrained by the wavelength or equivalent wavelength of the imaging radiation, the optical or beam-optics characteristics of the exposure system, and the resolution of the patternable material (the resist) in which the image is formed.

Nanolithography extends earlier microlithography methods, which used visible and near-ultraviolet light to print features in the micron range, by employing shorter wavelengths or particle beams whose effective wavelengths are below 1 nanometer. As documented in a comprehensive review of the evolution from microlithography to nanolithography published in Nanomaterials, each successive generation of lithographic technology has traded off resolution, throughput, and equipment cost in different ways, producing a toolkit of complementary methods rather than a single dominant approach.

Photon-Based Lithographic Methods

Optical lithography with deep-ultraviolet (DUV) light at 193 nanometers, using immersion optics and multiple-patterning sequences, has been extended to features well below its diffraction limit and remains the workhorse of high-volume integrated circuit production. Extreme ultraviolet (EUV) lithography operates at 13.5 nanometers, a wavelength that cannot propagate in air and requires reflective multilayer optics and a plasma light source in a high-vacuum environment. EUV scanners in production since 2019 print features below 10 nanometers in a single exposure, eliminating the additional process layers required by multi-patterning DUV schemes. The Nature Reviews Methods Primer on extreme ultraviolet lithography provides a detailed account of how EUV achieves its resolution and the engineering trade-offs in source power, mask inspection, and resist sensitivity that govern tool utilization.

Particle-Beam Methods

Electron-beam lithography (EBL) bypasses the diffraction limit of optical systems by using a focused electron beam, whose de Broglie wavelength is below 0.01 nanometers at 10 to 50 keV energy, to expose a thin resist film directly. EBL achieves sub-5-nanometer feature resolution and is used for photomask fabrication, quantum device patterning, and research prototyping where throughput is secondary to precision. Focused ion beam (FIB) lithography operates on a similar principle but uses gallium or other ions, enabling direct milling of material without a separate resist layer. Ion beams cause more lattice damage than electrons, which restricts FIB to applications such as cross-section preparation, circuit editing, and direct writing of conductive deposits. Both EBL and FIB are serial processes, writing one feature at a time, which limits their throughput compared to parallel exposure methods.

Soft Lithography

Soft lithography encompasses a family of methods that replicate patterns using elastomeric molds and stamps rather than radiation. In microcontact printing, a polydimethylsiloxane (PDMS) stamp inked with a self-assembled monolayer-forming molecule transfers a molecular pattern to a substrate by conformal contact, achieving feature sizes from micrometers down to tens of nanometers. Nanoimprint lithography presses a rigid or soft mold into a UV-curable or thermally softened polymer, reproducing the mold topography in the polymer layer with sub-10-nanometer fidelity and at throughputs that optical lithography cannot match for specialized applications. Soft lithographic techniques are particularly useful for patterning on curved or flexible surfaces, and for biological and microfluidic applications where the substrate cannot withstand the vacuum and high-energy radiation required by other methods. The NIST electron-beam lithography program provides metrology and standards support that underpins both particle-beam and soft lithographic process qualification.

Applications

Nanolithography has applications in a wide range of fields, including:

• Semiconductor integrated circuit manufacturing, where EUV lithography defines sub-10-nanometer transistor gates and contacts
• Photonic integrated circuits, including diffraction gratings, photonic crystal resonators, and plasmonic nanoantenna arrays
• MEMS and NEMS fabrication, where nanoscale mechanical structures require feature resolution beyond optical lithography limits
• Biosensors and microfluidic chips, patterned by soft lithography on flexible polymer substrates
• Quantum device research, where EBL defines superconducting qubit junctions and nanowire contacts