The sunlight and waves of Yalong Bay seemed still imprinted on her skin; the salty‑brackish sea breeze seemed still lingering at her nostrils. Yet that brief, precious vacation had already faded like a sand painting smoothed by the tide, leaving only a warm, firm imprint in the heart. Returning to the "XianGuang Research Institute" in Zhangjiang, Shanghai, Xiuxiu almost instantly switched back to the mode of a decisive, sharp‑eyed top engineer. The successful breakthrough of the 250‑watt EUV light source did not bring complacency from achievement; instead, it acted like a potent catalyst, igniting to a new height the insatiable curiosity and drive for conquest that were ingrained in her bones. Before the celebration banquet's wine glasses had fully cooled, her gaze, like the most precise laser alignment instrument, had already locked onto the taller, steeper peak on the horizon of lithography technology—**High Numerical Aperture Extreme Ultraviolet Lithography**, or **High NA EUV**.
The ultra‑clean laboratory beneath the research institute remained that isolated, futuristic micro‑cosmos control center. Only, the area that once held the first‑generation EUV light source prototype and the "XianGuang One" mass‑production test platform had now been cleared, awaiting a new protagonist. The air was permeated with an atmosphere different from before—a blend of post‑success confidence and a highly focused excitement facing an entirely new, unknown challenge.
Xiuxiu stood before a large, writable electronic whiteboard. No complex mechanical schematics or optical paths were drawn yet; instead, a concise yet crucial formula was written:
**NA = n × sinθ**
She held an electronic pen, her posture erect, her eyes keen, like a general about to outline the strategy of a major campaign to her closest comrades. And her audience, at this moment, appeared in the center of the laboratory via encrypted high‑definition holographic projection—Mozi and Yue'er. Mozi seemed to be in his top‑floor office, the familiar urban skyline data streams in the background; Yue'er was in her study, piled with books and blackboards covered in formulas, her expression attentive.
"The 250‑watt milestone allowed us to overcome the 'source power' bottleneck of EUV lithography, ensuring **throughput** and making possible the large‑scale manufacturing of 7nm, 5nm, even 3nm process chips." Xiuxiu got straight to the point, her voice clear and forceful, without any pleasantries, cutting directly to the technical core. "But that is merely one waypoint in the long march of lithography technology. Moore's Law won't pause—or rather, our endless demand for computing power won't pause. To pack more transistors onto a single chip, to achieve more complex functions, we must make transistors smaller and wiring more refined. That means we need higher **resolution**."
She circled the formula on the whiteboard emphatically with her pen: "And the single most critical parameter determining the resolution limit of our lithography system is this—**Numerical Aperture, NA**."
Yue'er leaned forward slightly. She had a natural sensitivity toward abstract formulas and immediately grasped the mathematical structure behind this concise expression. Mozi's gaze remained calm; he needed to understand the physical significance and commercial value behind this parameter.
"This formula is simple," Xiuxiu continued, adept at presenting the most complex technical concepts in an intuitive way. "**NA** equals **n** times **sinθ**. Here, **n** is the **refractive index**, which can be simply understood as a measure of how much light 'bends' when traveling through a medium. In air, n is approximately 1. In immersion lithography we used before, we added a drop of water between the lens and the silicon wafer; water's refractive index is about 1.44, which significantly increased NA and thus achieved a breakthrough in resolution."
She paused, letting the concept sink in. "And **θ**, the **aperture angle**, can be understood as the maximum angle at which light can enter the lens. The larger the angle, the richer the light information collected from the mask, and theoretically, the finer the details that can be resolved."
"So, there are two paths to increasing NA." Xiuxiu's pen swept across the whiteboard. "Either increase **n**, using a **new high‑refractive‑index immersion liquid** that is higher than water; or increase **θ**, which means fabricating larger lenses capable of receiving light from wider angles."
Her tone grew solemn. "And High NA EUV is about pushing both paths to their absolute limits. It demands raising the NA value from the current EUV's roughly 0.33 to above 0.55—a massive leap!"
Even Mozi, less versed in technical minutiae, raised an eyebrow slightly at this number. He knew well that in high‑end manufacturing, any significant increase in a key parameter implied exponentially growing difficulty and investment.
"What does this mean?" Xiuxiu asked rhetorically, a challenging gleam in her eyes. "First, a **revolution in the optical system**. To achieve a larger aperture angle θ, the optical lenses for High NA EUV will become extraordinarily large and complex. It's not just about physical size; it's the ultimate test for optical design and fabrication precision. The required **asphericity** of the lenses will reach unprecedented levels. Any tiny deformation—whether residual from machining or induced during use by gravity, temperature changes—will cause aberrations, distorting and blurring the final light spot focused onto the silicon wafer, rendering it utterly useless for carving nanometer‑scale circuits."
She pulled up an exaggerated schematic, displaying a lens assembly so enormous it was breathtaking. "Moreover, larger lenses mean heavier weight, placing inhuman demands on the support structure and motion control systems. Meanwhile, EUV light itself is extremely prone to absorption, so the entire optical path must be under high vacuum, posing hellish challenges to the stability of such a large, precise structure."
"Second, **upgrading the light source again**." Xiuxiu switched the display, showing the "light‑devouring" effect of the High NA optical system. "Increasing NA means the optical system's efficiency in collecting and utilizing light changes; more light will be lost along the way. Although we've achieved 250‑watt source power, in a High NA system the effective light intensity that ultimately reaches the wafer for exposure could drop substantially. That might in turn require our EUV source power to advance toward 300 watts, even 500 watts. Or we must achieve unprecedented extremes in **collection efficiency** and **bandwidth control** just to maintain acceptable throughput under High NA."
"Finally, the **limits of materials and processes**." Her pen tip tapped heavily on the "n". "Finding an **immersion liquid** with a refractive index higher than water's 1.44, yet suitable for the EUV wavelength, is a world‑class challenge. Existing materials either offer limited refractive‑index increase, or are unstable under the high‑energy photon bombardment of EUV, prone to bubbling or decomposition, thereby introducing new defects. If no suitable liquid can be found, the entire burden of increasing NA will fall on enlarging the aperture angle θ, pushing the design and fabrication difficulty of the optical system up another notch."
Xiuxiu put down the electronic pen, her gaze sweeping over Mozi and Yue'er in the holographic projection. Her face showed no fear, only an almost devout focus and a burning fighting spirit.
"High NA EUV is the essential path to process nodes below 2nm, even exploring the 1nm era. It is the key battle to continue extending Moore's Law's lifeline. This fight will be far tougher than our previous conquests of DUV, immersion, even the EUV light source itself. It demands breakthroughs at the limits of nearly every engineering field: optics, materials, precision mechanics, thermal management, control software."
She took a deep breath, her voice carrying an unquestionable determination and an eager passion for sharing the dream: "But this is the road we must take. We cannot rest on the laurels of 250 watts. The world's technological race won't wait for us; future chip demand won't wait for us. I hope our 'XianGuang' can be the first team to truly overcome the commercialization barriers of High NA EUV! This is my next dream, and the battle we must devote ourselves to wholeheartedly next… the **next battle**!"
Silence filled the laboratory, only the low hum of equipment audible. In the holographic projection, Yue'er looked at Xiuxiu, her eyes full of admiration and understanding. She saw in Xiuxiu the courage of a true pioneer, the soul of an engineer who continually turns the unknown into the known. She nodded gently, silently conveying her support.
And Mozi—he listened quietly to Xiuxiu's exposition, from the dissection of the NA formula, through the layer‑by‑layer unraveling of technical challenges, to the resounding declaration at the end. He saw the difficulty of this path, the astronomical financial investment behind it, the unforeseeable technical risks, the long, uncertain R&D cycle. Any rational investor faced with such a project would likely weigh it repeatedly, perhaps even shy away.
But he saw more. He saw the unquestionable resolve and light in Xiuxiu's eyes—the intuition and daring of a top‑tier achiever, which he was willing to trust unconditionally. He saw that behind High NA EUV lay not just immense commercial returns, but also an absolute enhancement of national cutting‑edge manufacturing capability, yet another push on the boundaries of human computing. This perfectly aligned with the fundamental purpose of "XianGuang."
He didn't ask for a detailed budget, didn't assess potential risk‑return ratios, didn't hesitate for even a split second. In the moment of silence after Xiuxiu's words fell, Mozi's calm, firm voice came clearly through the holographic projection, filling the laboratory:
"The XianGuang Fund will provide unlimited financial support."
This statement, like a weighty yet power‑filled counterweight, settled firmly on one side of the scale. No flowery rhetoric, no complex conditions—just the simplest, most thorough trust and commitment.
Xiuxiu was stunned. She had anticipated Mozi's support, but not such a straightforward, unequivocal, no‑holds‑barred backing. A great warmth and indescribable emotion instantly breached her tough exterior as the technical commander. Her eyes grew slightly hot; she pressed her lips tightly together to keep her feelings in check. She didn't need to say anything; she simply nodded heavily—everything was understood without words.
A warm, gratified smile appeared on Yue'er's face. She looked at Mozi, at Xiuxiu, at this unbreakable alliance formed by the three of them. The power of capital, the dream of technology, the guidance of theory—all fused together perfectly once more.
Xiuxiu took a deep breath, forcibly suppressing the surging emotions. Her gaze sharpened again, focused, turning toward that empty waiting area, as if she already saw the majestic peak named "High NA EUV."
"Good." She uttered just one word, yet it seemed to sound the charge.
The next battle—the journey begins anew. And this time, behind them lies an even more solid alliance and an even firmer belief. The epic of lithography is about to turn a new page, one with higher resolution and greater challenges.