Cathodoluminescence (CL) is a powerful analytical technique that provides real-time feedback during electron beam lithography (EBL), enabling precise monitoring of material modifications at the nanoscale. By detecting the light emission resulting from electron-matter interactions, CL offers insights into structural, compositional, and electronic changes in semiconductors and other materials during EBL processing. This capability is particularly valuable for optimizing lithographic parameters, minimizing damage, and ensuring high-resolution patterning.

The fundamental principle of CL involves the generation of electron-hole pairs when a high-energy electron beam interacts with a material. Subsequent recombination of these pairs produces photons with energies corresponding to the material’s bandgap or defect states. In EBL, the electron beam not only exposes the resist but also interacts with the underlying substrate, making CL an ideal tool for in-situ monitoring. The emitted CL signal can reveal variations in material properties, such as crystallinity, doping levels, and defect densities, which are critical for process control.

One of the key advantages of CL in EBL is its ability to provide spatially resolved information. Since the electron beam is finely focused, the CL signal can be mapped with sub-micrometer resolution, allowing for direct correlation between exposure conditions and material response. For example, in gallium nitride (GaN) substrates, CL mapping has been used to identify defect clusters and inhomogeneities that arise during electron beam exposure. By adjusting beam parameters such as accelerating voltage, current, and dwell time in real-time, EBL processes can be optimized to mitigate unintended damage.

Real-time CL monitoring also enables dynamic feedback for resist exposure and development. Certain resist materials, such as polymethyl methacrylate (PMMA), exhibit CL signals that vary with exposure dose. Studies have shown that the CL intensity from PMMA decreases nonlinearly with increasing electron dose due to cross-linking and chain scission. By calibrating the CL response to exposure levels, it becomes possible to achieve precise dose control without post-exposure characterization. This reduces processing time and improves yield in high-throughput nanofabrication.

In compound semiconductors like GaAs or InP, CL provides critical feedback on stoichiometric changes and defect formation during EBL. For instance, electron beam exposure can induce arsenic or phosphorus desorption, leading to non-radiative recombination centers that quench CL emission. By tracking the CL spectrum shifts or intensity decay, operators can detect these modifications early and adjust beam conditions to preserve material integrity. This is especially important for optoelectronic devices where minority carrier lifetime is a key performance metric.

Another application of CL in EBL is the monitoring of quantum-confined structures. Quantum dots and nanowires exhibit size-dependent CL emission due to quantum confinement effects. During lithography, unintended beam-induced diffusion or oxidation can alter these structures, leading to shifts in emission wavelength. Real-time CL spectroscopy allows for immediate detection of such changes, facilitating corrective measures before further processing steps.

The integration of CL with EBL systems requires careful consideration of signal collection efficiency and spectral resolution. Most modern CL systems employ parabolic mirrors or fiber optics to maximize light collection, coupled with high-throughput spectrometers for rapid spectral analysis. Time-resolved CL can further enhance monitoring by capturing carrier dynamics, which is useful for assessing radiation-induced defects. However, challenges remain in signal-to-noise ratio optimization, particularly for low-emission materials or ultrathin films.

Despite these challenges, the benefits of CL as an in-situ monitoring tool for EBL are substantial. It provides non-destructive, high-resolution feedback that complements traditional inspection methods like scanning electron microscopy (SEM). By enabling real-time process adjustments, CL enhances the reproducibility and precision of nanofabrication, making it indispensable for advanced semiconductor manufacturing and research.

Future developments in CL-EBL integration may focus on automated feedback systems, where machine learning algorithms analyze CL data to dynamically optimize beam parameters. Such advancements could further reduce human intervention and improve process reliability. Additionally, combining CL with other in-situ techniques, such as energy-dispersive X-ray spectroscopy (EDS), could provide a more comprehensive understanding of material modifications during lithography.

In summary, cathodoluminescence serves as a versatile and effective tool for real-time monitoring in electron beam lithography. Its ability to detect material changes at the nanoscale ensures higher precision in patterning and reduces the risk of process-induced defects. As EBL continues to push the boundaries of nanofabrication, CL will remain a critical enabler for achieving consistent, high-quality results.