In the conference room of the domestic lithography R&D center, the air hung so heavily it felt like it could be wrung out. Around the long rectangular meeting table sat the heads of various subsystems—light source, optics, mechanics, control—along with Chief Engineer Li, the project lead. Smoke curled in the air; most faces were creased with worry, eyes fixed on the anxiety-inducing data chart projected on the screen. The current dry‑based DUV lithography technology was approaching its theoretical resolution limit, unable to meet the finer line‑width requirements of next‑generation chip fabrication.
The technical roadmap had reached a fork. Should they continue struggling down the traditional "dry" path, squeezing out every nanometer of potential, or dare to turn toward a new route that promised great prospects but was fraught with unknowns and challenges?
Xiuxiu sat near the screen, her heartbeat slightly quickening. She knew the kind of waves her proposal would stir within the team. Although the Swiss laboratory contacted indirectly through Mozi offered a novel frequency‑stabilization technology based on optical frequency combs—a way to bypass embargo restrictions—the technology itself was immature. Engineering it and integrating it into the existing light‑source system would still take considerable time. Yet chip‑process iteration was urgent; they had to find a breakthrough that could achieve a leapfrog improvement on their current foundation.
Her gaze swept over the faces of every senior engineer present. She saw exhaustion, anxiety, and the ingrained mindset born of path dependence. Taking a deep breath, she operated the computer and switched slides. The screen now displayed bold characters: **Exploration of Immersion Lithography Technology Path**.
As expected, the moment the term appeared, a muffled stir and low whispers rippled through the conference room. Several senior engineers exchanged glances, their expressions plainly skeptical.
"Engineer Xiuxiu," Deputy Chief Engineer Wang, responsible for the optical system, spoke first. A veteran with thick glasses and high prestige in optical design, his tone carried distinct doubt. "Immersion lithography? That concept was proposed internationally over a decade ago. Theoretically it can boost resolution, but you must realize how enormous the engineering challenges are! It means adding something between the lens and the wafer—direct contact! Any tiny bubble, impurity, or fluctuation in the liquid would be catastrophic! We haven't even perfected the stability of dry lithography, and now we're jumping into this 'wet' scheme. Isn't that too rash?"
His words echoed the thoughts of many. In lithography, where precision reaches the nanometer scale, introducing liquid was akin to injecting an uncontrollable variable into heart surgery. Traditional "dry" lithography, where light travels in air (refractive index n ≈ 1.0), had limited resolution, but the environment was relatively "clean" and "stable."
Xiuxiu did not fluster at the challenge; she had anticipated such reactions. She stood up, walked to the screen, and let the laser pointer's dot land on the core schematic. It was time to use the clearest physical picture and the most persuasive logic to explain this path that might lead them through the fog.
"Engineer Wang raises a crucial point—exactly the core challenge of immersion technology," Xiuxiu first acknowledged the concern, then shifted her tone. "But before discussing the challenges, we must first understand why immersion technology can bring revolutionary improvement in resolution. It stems from a fundamental law of physical optics—**the Rayleigh criterion**."
She quickly wrote the Rayleigh criterion formula on the whiteboard: **CD = k₁ * λ / NA**. Here CD is the critical dimension (resolution), λ is the source wavelength, NA is the numerical aperture, and k₁ is the process constant.
"Everyone, look: three key factors determine the smallest line width CD we can etch. k₁ we can reduce through process optimization, but space is limited. λ—our ArF source wavelength is 193 nm, practically the DUV limit; it's very hard to shorten further." Her laser pointer circled the third parameter emphatically. "**Numerical aperture NA!**"
"NA = n * sinθ." She enunciated the formula clearly. "Here, θ is the aperture angle of the objective lens—the maximum angle at which the lens collects light. The maximum of sinθ is theoretically 1, but in practice it's constrained by lens design, rarely exceeding 0.93. And **n is the refractive index of the medium between the lens and the wafer!**"
Her voice rose a little, carrying the force of revealing a secret. "In conventional dry lithography, the medium is **air, n ≈ 1.0**. So the maximum NA is limited to slightly below the maximum sinθ."
She paused, letting everyone digest this basic concept. Then the laser‑pointer dot pressed hard on the "n" in the formula.
"**The essence of immersion technology lies in changing this 'n'!**" Xiuxiu's gaze swept across the room. "We don't expose in air; instead, we fill the gap between the last lens surface and the photoresist on the wafer with a **high‑refractive‑index, ultra‑pure liquid**! The most mature option now is **ultra‑pure water**, whose refractive index n ≈ 1.44!"
She wrote "1.44" in red, conspicuously, in the "n" position of the NA formula.
"What does this mean?" she asked rhetorically, her tone holding irrefutable logical power. "It means that, with the same aperture angle θ, the system's **effective numerical aperture NA is magnified 1.44‑fold**! According to the Rayleigh criterion, resolution CD is inversely proportional to NA! A 1.44× increase in NA theoretically reduces the resolution to 1/1.44 of the original—roughly **equivalent to using a 134 nm source instead of 193 nm**!"
Silence filled the conference room; only Xiuxiu's clear voice reverberated. With this fundamental physical law laid out so plainly, the enormous performance gain was undeniable. Even some of the initially opposing engineers showed thoughtful, wavering expressions in their eyes.
"Of course, Engineer Wang is right—opportunity comes with immense challenge." Xiuxiu did not evade the issues and began dissecting them one by one. "First, **defects introduced by the liquid**. Any nanoscale bubble, particulate contaminant in the water would cause pattern defects during exposure. This demands extremely precise **fluid‑control systems**—achieving bubble‑free liquid filling, stable flow under constant‑speed scanning, perfect liquid recovery and filtration."
She switched slides, displaying international research literature on flow dynamics and defect control in immersion technology. "Second, **aberration caused by the liquid**. Water's refractive index changes minutely with temperature; the thickness and uniformity of the liquid layer must be controlled at the nanometer level, otherwise it introduces optical aberrations hard to compensate. This requires **precise temperature‑control systems** and **real‑time gap measurement and control between the stage and the lens**."
"Third, **material compatibility**. High‑refractive‑index liquids (in the future maybe not just water) may interact with the lens's protective coating or the photoresist on the wafer, necessitating rigorous material screening and surface‑treatment processes."
She listed each challenge clearly and gravely. But after every challenge, she promptly suggested preliminary solutions and technical‑research directions, showing she was not blindly optimistic but had conducted in‑depth feasibility studies.
"I know this road is difficult," Xiuxiu concluded, her voice calm again yet imbued with a steadfast strength. "It demands coordinated breakthroughs across many fields—precision mechanics, fluid control, materials science, thermal management. But, please consider—"
Her gaze swept the room once more, meeting the eyes of every core member.
"If we continue deepening the dry path, we might raise the yield a few percentage points, push resolution a negligible fraction closer to the physical limit. But the target we're chasing won't stop and wait for us. They have already fully switched to immersion and are moving toward EUV. If we dare not cross this seemingly perilous river, we will forever be stranded outside the mainstream technology track, watching the gap widen!"
"Immersion technology is the **essential bridge** to more advanced process nodes. Bypass it, and we have nowhere to go! The bridge indeed sways, indeed brims with risk, but on the other side lies the dawn of resolution enhancement—the ticket that truly admits us into the arena of high‑end chip manufacturing."
She paused a moment, letting the words settle in the quiet.
"Risks we can manage and reduce through finer design, stricter processes, more thorough testing. But opportunity, once missed, could mean falling behind an entire era. I believe we have the capability, and we must have the capability, to conquer the engineering hurdles of immersion technology. This isn't merely a choice of technical route; it concerns the future position of our team, our nation, in the entire semiconductor industry!"
Xiuxiu finished and slowly sat down. The conference room sank into prolonged silence. No one spoke immediately; each person digested her words, weighing the risks and opportunities.
Chief Engineer Li stubbed out his cigarette, slowly lifted his head, and looked deeply at Xiuxiu, then around at everyone present.
"Engineer Xiuxiu's analysis is thorough," he said, his voice steady, bearing the weight of a decision‑maker. "Advantages and disadvantages are laid on the table. The dry road has a visible ceiling. The immersion road shows a threshold, but also the vast space beyond the door."
He deliberated briefly, then made the call. "I agree to launch the pre‑research andbreakthrough project on immersion technology. Xiuxiu will serve as the project's technical chief, coordinating resources of all subsystems, and deliver a detailed technical plan and risk‑assessment report as soon as possible."
The decision fell like a boulder into a calm lake. It meant the team would commit enormous resources, betting on a technology route full of uncertainty, and the one shouldering this heavy responsibility was this relatively young, recently‑returned female engineer whose seniority was not the deepest.
Xiuxiu felt her heart contract, then the solid weight of responsibility settle on her shoulders. She saw lingering doubts on Engineer Wang's face, but also saw in many other eyes a kindled fighting spirit—a willingness to challenge the difficulties.
"Thank you for Chief Engineer Li's trust, and for everyone's support." She stood up again, her tone firm, gaze clear. "I'm fully aware of the heavy responsibility. I will work closely with colleagues from every subsystem, spare no effort, and together overcome every obstacle of immersion technology."
After the meeting ended, Xiuxiu sat alone in the conference room for a while. Outside the window, dusk approached; the sunset gilded the campus with a golden glow. She felt unprecedented pressure, but also a force breaking out of a cocoon.
She was no longer merely the returned expert with ASML experience. She had proposed the key technical route that would lead the team forward, and amid fierce contention, through professionalism, logic, and courage, had earned recognition and taken on the leadership of atackling the hardest challenges mission.
The dawn of immersion was not only the hope of a technological breakthrough, but also the beginning of her own transformation in this technological Long March—from a technical executor into a technical leader and strategist. The road ahead would inevitably be rugged, but that gleam of light emanating from the depths of physical law, pointing toward higher resolution, now shone clearly on her shoulders, and on the path the whole team must walk. She knew that from this moment onward, she must lead her comrades‑in‑arms, resolutely, into that "deep‑water zone" full of challenges yet also full of promise.