The continuous scaling of semiconductor devices and nanophotonic components demands lithography techniques capable of achieving higher resolution, lower cost, and greater flexibility. However, conventional photolithography relies heavily on physical masks and complex fabrication infrastructures, which significantly increase cost and limit design flexibility. Meanwhile, maskless digital projection lithography, although promising for rapid prototyping and customized manufacturing, is fundamentally constrained by optical diffraction and pixel coupling effects, which restrict its resolution at subwavelength scales.
In a recent paper published in Light: Advanced Manufacturing , a team of scientists led by Prof. Xuan-Ming Duan and Prof. Yuan- Yuan Zhao at Jinan University proposed a novel digital phase-shift mask projection lithography (PSM-DPL) strategy to overcome these limitations. The approach integrates phase-shift mask principles into a programmable maskless lithography platform by employing a dual-spatial light modulator (dual-SLM) architecture, enabling independent modulation of both amplitude and phase of the optical field.
By introducing a controlled phase difference close to π between adjacent pixels, the system exploits destructive interference to enhance image contrast and suppress sidelobe intensity. This mechanism significantly improves the image log slope (ILS), thereby enabling sharper feature boundaries and higher-resolution patterning beyond the conventional diffraction limit.
Experimental results demonstrate that the proposed system can achieve approximately 60 nm line-width (0.16λ/NA) structures and a 235 nm pitch resolution (half pitch ~0.32λ/NA) in a single exposure using a 517 nm femtosecond laser combined with a 100X scaled objective lens (NA1.4). Through double-exposure strategies, the pitch can be further reduced to 158 nm (half pitch ~0.21λ/NA), approaching the physical limits of digital lithography systems. The method has also been validated through the fabrication of representative integrated circuit metal-layer layouts, where dense and complex patterns with sub-300 nm spacing (half pitch <0.5λ/NA) were successfully realized.
Importantly, unlike conventional lithography techniques, the proposed method is maskless, programmable, and cost-efficient. It enables rapid switching between different pattern designs without physical mask fabrication, making it highly suitable for small-batch, multi-variety semiconductor manufacturing, as well as rapid prototyping of nanophotonic devices such as metasurfaces and diffractive optical elements.
The research team summarized the core concept of their approach as follows:
“We introduce a dual-SLM-based phase-controlled projection lithography system in which amplitude and phase are independently engineered in a digital manner. By carefully tuning the phase difference toward π, destructive interference is utilized to enhance contrast and achieve sub-diffraction-limited patterning in a flexible and programmable framework.”
They further noted that:
“The proposed platform provides a general route for extending maskless lithography toward sub-100 nm regimes while preserving the advantages of digital programmability and system scalability.”
The authors also emphasized that this approach is compatible with a wide range of optical sources and can be integrated with advanced computational lithography and multi-exposure strategies, offering a promising pathway toward next-generation low-cost nanomanufacturing technologies.
Light: Advanced Manufacturing
Digital phase-shift mask projection lithography enabling sub-diffraction-limit resolution for dense nanoscale patterning