<svg viewBox="0 0 760 470" xmlns="http://www.w3.org/2000/svg" font-family="-apple-system,Segoe UI,Roboto,Helvetica,Arial,sans-serif"><rect x="0" y="0" width="760" height="470" rx="14" fill="#0d1117"/><text x="20" y="30" fill="#e6edf3" font-size="19" font-weight="700">Photolithography: print the circuit pattern with light and resist</text><text x="20" y="50" fill="#8b949e" font-size="12.5">Coat the wafer in a light-sensitive resist, expose it through a mask, develop it &#8212; the pattern is now a stencil for etch</text><!-- Panel 1: the cycle --><rect x="20" y="66" width="226" height="298" rx="7" fill="#0c141d" stroke="#30363d"/><text x="32" y="88" fill="#7ee6c0" font-size="13" font-weight="700">1 &#183; Coat &#8594; expose &#8594; develop</text><text x="32" y="106" fill="#8b949e" font-size="10.5">three core steps, repeated per layer</text><!-- step a: coat --><rect x="42" y="118" width="182" height="44" rx="3" fill="#111a24" stroke="#30363d"/><rect x="52" y="146" width="60" height="8" fill="#38506a"/><rect x="52" y="140" width="60" height="6" fill="#e0b13a"/><text x="120" y="134" fill="#e0b13a" font-size="9" font-weight="700">coat resist</text><text x="120" y="150" fill="#8b949e" font-size="8">spin on a thin, uniform film</text><!-- step b: expose --><rect x="42" y="168" width="182" height="52" rx="3" fill="#111a24" stroke="#30363d"/><!-- light --><g stroke="#9fd8ef" stroke-width="1"><line x1="55" y1="174" x2="55" y2="184"/><line x1="65" y1="174" x2="65" y2="184"/><line x1="85" y1="174" x2="85" y2="184"/><line x1="95" y1="174" x2="95" y2="184"/></g><!-- mask --><rect x="50" y="186" width="20" height="5" fill="#6b5fb0"/><rect x="80" y="186" width="20" height="5" fill="#6b5fb0"/><text x="108" y="182" fill="#9fd8ef" font-size="9" font-weight="700">expose thru mask</text><rect x="52" y="200" width="56" height="8" fill="#e0b13a"/><!-- exposed regions --><rect x="70" y="200" width="10" height="8" fill="#34d399"/><text x="108" y="198" fill="#8b949e" font-size="8">light hits gaps, changes resist</text><text x="118" y="214" fill="#8b949e" font-size="8">lens shrinks the mask 4&#215;</text><!-- step c: develop --><rect x="42" y="226" width="182" height="46" rx="3" fill="#111a24" stroke="#30363d"/><rect x="52" y="252" width="56" height="8" fill="#38506a"/><rect x="52" y="246" width="18" height="6" fill="#e0b13a"/><rect x="90" y="246" width="18" height="6" fill="#e0b13a"/><text x="120" y="242" fill="#34d399" font-size="9" font-weight="700">develop</text><text x="120" y="258" fill="#8b949e" font-size="8">wash away soluble resist &#8594;</text><text x="120" y="269" fill="#8b949e" font-size="8">a patterned stencil remains</text><text x="32" y="292" fill="#adb5bd" font-size="9.5">The developed resist masks the wafer:</text><text x="32" y="307" fill="#adb5bd" font-size="9.5">the next etch or implant only touches</text><text x="32" y="322" fill="#adb5bd" font-size="9.5">the open areas. Then the resist is</text><text x="32" y="337" fill="#adb5bd" font-size="9.5">stripped and the cycle repeats &#8212; dozens</text><text x="32" y="352" fill="#adb5bd" font-size="9.5">of times to build the full chip.</text><!-- Panel 2: the resist chemistry --><rect x="267" y="66" width="226" height="298" rx="7" fill="#0c141d" stroke="#30363d"/><text x="279" y="88" fill="#9fd8ef" font-size="13" font-weight="700">2 &#183; How resist responds</text><text x="279" y="106" fill="#8b949e" font-size="10.5">light flips solubility</text><rect x="287" y="118" width="196" height="60" rx="3" fill="#111a24" stroke="#30363d"/><text x="297" y="134" fill="#34d399" font-size="9.5" font-weight="700">Positive resist</text><text x="297" y="150" fill="#8b949e" font-size="8.5">exposed areas become soluble and wash</text><text x="297" y="163" fill="#8b949e" font-size="8.5">away &#8212; the mask pattern is copied.</text><rect x="287" y="184" width="196" height="60" rx="3" fill="#111a24" stroke="#30363d"/><text x="297" y="200" fill="#c4b5fd" font-size="9.5" font-weight="700">Chemically-amplified (CAR)</text><text x="297" y="216" fill="#8b949e" font-size="8.5">light releases an acid; a bake makes it</text><text x="297" y="229" fill="#8b949e" font-size="8.5">catalyze many reactions &#8212; high sensitivity</text><text x="297" y="242" fill="#8b949e" font-size="8.5">for DUV and EUV exposure.</text><rect x="287" y="250" width="196" height="60" rx="3" fill="#111a24" stroke="#30363d"/><text x="297" y="266" fill="#e0b13a" font-size="9.5" font-weight="700">The resolution triangle</text><text x="297" y="282" fill="#8b949e" font-size="8.5">resolution, line-edge roughness and</text><text x="297" y="295" fill="#8b949e" font-size="8.5">sensitivity trade off &#8212; you can&#8217;t max</text><text x="297" y="308" fill="#8b949e" font-size="8.5">all three at once (the RLS tradeoff).</text><text x="279" y="330" fill="#adb5bd" font-size="9.5">The resist is the recording medium; its</text><text x="279" y="345" fill="#adb5bd" font-size="9.5">chemistry sets how fine a line can print.</text><!-- Panel 3: what sets resolution --><rect x="514" y="66" width="226" height="298" rx="7" fill="#0c141d" stroke="#30363d"/><text x="526" y="88" fill="#c4b5fd" font-size="13" font-weight="700">3 &#183; What sets the smallest line</text><text x="526" y="106" fill="#8b949e" font-size="10.5">the Rayleigh equation, k1&#183;&#955;/NA</text><circle cx="532" cy="126" r="2.4" fill="#38bdf8"/><text x="542" y="129" fill="#e6edf3" font-size="10" font-weight="700">Wavelength &#955;</text><text x="542" y="143" fill="#8b949e" font-size="9">shorter light prints finer &#8212; 193nm DUV,</text><text x="542" y="156" fill="#8b949e" font-size="9">then 13.5nm EUV for the tightest nodes.</text><circle cx="532" cy="176" r="2.4" fill="#34d399"/><text x="542" y="179" fill="#e6edf3" font-size="10" font-weight="700">Numerical aperture NA</text><text x="542" y="193" fill="#8b949e" font-size="9">a wider lens captures more diffraction</text><text x="542" y="206" fill="#8b949e" font-size="9">orders &#8212; sharper image, shallower focus.</text><circle cx="532" cy="226" r="2.4" fill="#e0b13a"/><text x="542" y="229" fill="#e6edf3" font-size="10" font-weight="700">Process factor k1</text><text x="542" y="243" fill="#8b949e" font-size="9">RET, OPC and multi-patterning push k1</text><text x="542" y="256" fill="#8b949e" font-size="9">down toward its physical limit of 0.25.</text><rect x="526" y="272" width="202" height="82" rx="5" fill="#111a24" stroke="#30363d"/><text x="536" y="290" fill="#f87171" font-size="10" font-weight="700">The step that defines the node</text><text x="536" y="306" fill="#adb5bd" font-size="9">Lithography sets the smallest feature a</text><text x="536" y="320" fill="#adb5bd" font-size="9">process can print &#8212; and therefore the</text><text x="536" y="334" fill="#adb5bd" font-size="9">density, speed and cost of the chip. It&#8217;s</text><text x="536" y="348" fill="#adb5bd" font-size="9">the most expensive tool in the fab.</text><!-- bottom cards --><rect x="20" y="384" width="226" height="70" rx="7" fill="#111a24" stroke="#30363d"/><text x="32" y="406" fill="#7ee6c0" font-size="11" font-weight="700">Coat, expose, develop</text><text x="32" y="424" fill="#adb5bd" font-size="9.5">The three-step cycle that copies a</text><text x="32" y="440" fill="#adb5bd" font-size="9.5">mask pattern into resist on the wafer.</text><rect x="267" y="384" width="226" height="70" rx="7" fill="#111a24" stroke="#30363d"/><text x="279" y="406" fill="#9fd8ef" font-size="11" font-weight="700">Resist = recording medium</text><text x="279" y="424" fill="#adb5bd" font-size="9.5">Light flips its solubility; its chemistry</text><text x="279" y="440" fill="#adb5bd" font-size="9.5">sets how fine a line can be printed.</text><rect x="514" y="384" width="226" height="70" rx="7" fill="#111a24" stroke="#30363d"/><text x="526" y="406" fill="#e0b13a" font-size="11" font-weight="700">&#955;, NA and k1</text><text x="526" y="424" fill="#adb5bd" font-size="9.5">Resolution shrinks with shorter light,</text><text x="526" y="440" fill="#adb5bd" font-size="9.5">bigger lenses and cleverer processing.</text></svg>

Lithography is how a chip design becomes a physical pattern: light is projected through a patterned mask onto photoresist on the wafer, printing one circuit layer at a time. A leading-edge chip is built from dozens of these patterned layers stacked in tight registration, so the smallest feature a fab can print sets the practical limit for the node.

Resolution comes down to wavelength and numerical aperture. The Rayleigh relation is $\text{CD} = k_1 \cdot \lambda / \text{NA}$: critical dimension shrinks when the exposure wavelength gets shorter, the optics collect a wider cone of light, or the process pushes the empirical $k_1$ factor lower. The industry rode mercury i-line, then 248 nm KrF and 193 nm ArF deep-ultraviolet light for decades, stretched 193 nm with water immersion, and then moved the tightest layers to extreme ultraviolet at 13.5 nm.

EUV is the marvel and the bottleneck. At 13.5 nm, ordinary lenses do not work because EUV light is absorbed by almost everything, so the scanner operates in vacuum with reflective molybdenum-silicon multilayer mirrors. The light source fires a high-power laser at tin droplets tens of thousands of times per second to create plasma bright enough for production. ASML is the only company shipping these scanners at scale; current EUV tools are well over 150 million dollars, and High-NA systems are commonly discussed as several-hundred-million-dollar tools.

Computation makes sub-wavelength printing manufacturable. A mask is not a simple one-to-one drawing of the desired wafer pattern. Diffraction rounds corners, shortens line ends, and shifts edges, so computational lithography pre-distorts the mask with OPC, source-mask optimization, and inverse lithography. GPU-accelerated tools such as NVIDIA cuLitho matter because mask synthesis is now one of the most compute-heavy steps in the manufacturing flow.

Below the resolution limit, patterning gets split. Before EUV was production-ready, fabs printed the tightest layers by decomposing one design layer into multiple exposures or by using self-aligned spacers such as SADP and SAQP. EUV collapses many of those multi-mask sequences back into one exposure, reducing overlay risk and cycle time even though the scanner itself is extremely expensive.

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That is why lithography sits at the center of chip geopolitics and AI supply. Access to the best scanners gates access to leading-edge patterning, export controls target exactly these tools, and every advanced AI accelerator depends on a small number of EUV systems running in a small number of fabs.