DUV (Deep Ultraviolet) lithography uses short-wavelength ultraviolet light — primarily 193nm (ArF) and 248nm (KrF) — to pattern semiconductor wafers, and has been the workhorse lithography technology for the majority of semiconductor manufacturing history, enabling feature sizes from 250nm down to approximately 38nm through resolution enhancement techniques. DUV lithography operates on the principle of photochemical reactions: the short-wavelength UV light passes through a patterned photomask, is focused by a projection lens system onto the wafer coated with photoresist, and the exposed resist undergoes chemical changes that allow selective removal during development. The fundamental resolution limit is governed by the Rayleigh criterion: Resolution = k₁ × λ / NA, where λ is the wavelength, NA is the numerical aperture of the projection lens, and k₁ is a process-dependent factor (theoretical minimum 0.25, practical minimum ~0.28-0.35). For 193nm immersion (193i) with NA = 1.35, the single-exposure resolution limit is approximately 38nm — pushing below this requires multiple patterning techniques (LELF, SADP, SAQP) that use 2-4 exposure steps per layer. Resolution enhancement techniques that extended DUV capability far beyond its natural resolution include: optical proximity correction (OPC — modifying mask patterns to compensate for optical distortion), phase-shift masks (PSM — using phase differences to improve contrast), off-axis illumination (OAI — tilting the illumination to optimize the diffraction pattern for specific feature types), source-mask optimization (SMO — jointly optimizing the illumination source shape and mask pattern), and immersion lithography (using water between the lens and wafer to increase the effective NA from 0.93 to 1.35 by replacing air with a higher refractive index medium). DUV lithography remains extensively used even in advanced fabs alongside EUV — many non-critical layers at 5nm and 3nm nodes are still printed with 193i DUV because it is more mature, higher throughput, and lower cost than EUV.

<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">Immersion lithography (193i): water under the lens to print smaller</text><text x="20" y="50" fill="#8b949e" font-size="12.5">A water film raises the 193 nm ArF numerical aperture from 0.93 to 1.35 &#8212; the DUV workhorse beside EUV</text><!-- ============ PANEL 1: the water trick ============ --><rect x="20" y="66" width="226" height="298" rx="7" fill="#0c141d" stroke="#30363d"/><text x="32" y="88" fill="#38bdf8" font-size="12" font-weight="700">1 &#183; The water trick: raise NA</text><text x="133" y="106" fill="#8b949e" font-size="8.5" text-anchor="middle">final projection lens</text><path d="M80 118 Q133 102 186 118 Q133 130 80 118 Z" fill="#38bdf8" fill-opacity="0.25" stroke="#38bdf8"/><path d="M84 122 L182 122 L133 236 Z" fill="#38bdf8" fill-opacity="0.09"/><line x1="84" y1="122" x2="133" y2="236" stroke="#38bdf8" stroke-width="1.2"/><line x1="182" y1="122" x2="133" y2="236" stroke="#38bdf8" stroke-width="1.2"/><path d="M123 210 A 13 13 0 0 0 143 210" fill="none" stroke="#e6edf3" stroke-width="1"/><text x="133" y="206" fill="#e6edf3" font-size="9" text-anchor="middle">&#952;</text><rect x="62" y="210" width="142" height="26" fill="#16465e" fill-opacity="0.65" stroke="#2b6f8c"/><text x="133" y="227" fill="#9fd8ef" font-size="8" text-anchor="middle">ultra-pure water &#183; n = 1.44</text><rect x="62" y="236" width="142" height="9" fill="#30363d"/><rect x="62" y="233" width="142" height="3" fill="#a99cf0"/><text x="133" y="258" fill="#8b949e" font-size="8" text-anchor="middle">wafer + resist</text><text x="32" y="282" fill="#e6edf3" font-size="11" font-weight="700">NA = n &#183; sin &#952;</text><text x="32" y="298" fill="#adb5bd" font-size="8.7">Water lets the lens collect a wider</text><text x="32" y="310" fill="#adb5bd" font-size="8.7">cone &#8594; NA 1.35 (vs 0.93 in air).</text><text x="32" y="330" fill="#34d399" font-size="8.7" font-weight="600">CD = k&#8321;&#955;/NA:  ~65 nm &#8594; ~38 nm</text><!-- ============ PANEL 2: fluid-control machine ============ --><rect x="267" y="66" width="226" height="298" rx="7" fill="#0c141d" stroke="#30363d"/><text x="279" y="88" fill="#e0b13a" font-size="12" font-weight="700">2 &#183; A fluid-control machine</text><line x1="287" y1="150" x2="473" y2="150" stroke="#30363d" stroke-width="2"/><rect x="356" y="106" width="48" height="18" rx="3" fill="#30363d" stroke="#6f6f6a"/><text x="380" y="119" fill="#8b949e" font-size="8" text-anchor="middle">lens</text><path d="M352 150 Q348 138 356 124 L404 124 Q412 138 408 150 Z" fill="#16465e" fill-opacity="0.75" stroke="#38bdf8"/><text x="380" y="144" fill="#9fd8ef" font-size="7.5" text-anchor="middle">water</text><line x1="416" y1="134" x2="452" y2="134" stroke="#e6edf3" stroke-width="1.5"/><path d="M456 134 l-8 -4 l0 8 Z" fill="#e6edf3"/><text x="434" y="128" fill="#adb5bd" font-size="8" text-anchor="middle">scan</text><circle cx="306" cy="147" r="3" fill="#f87171"/><text x="306" y="138" fill="#f87171" font-size="7.5" text-anchor="middle">watermark</text><circle cx="284" cy="178.5" r="2.4" fill="#e0b13a"/><text x="293" y="182" fill="#adb5bd" font-size="8.5">23.000 &#177; 0.001 &#176;C sets the index n</text><circle cx="284" cy="193.5" r="2.4" fill="#38bdf8"/><text x="293" y="197" fill="#adb5bd" font-size="8.5">degassed &#8212; bubbles print as defects</text><circle cx="284" cy="208.5" r="2.4" fill="#38bdf8"/><text x="293" y="212" fill="#adb5bd" font-size="8.5">1&#8211;3 L/min flush &#183; ultra-pure loop</text><circle cx="284" cy="223.5" r="2.4" fill="#34d399"/><text x="293" y="227" fill="#adb5bd" font-size="8.5">topcoat / hydrophobic resist stop leach</text><circle cx="284" cy="238.5" r="2.4" fill="#f87171"/><text x="293" y="242" fill="#adb5bd" font-size="8.5">receding angle &gt; 70&#176; or watermarks</text><line x1="279" y1="258" x2="481" y2="258" stroke="#30363d" stroke-width="1"/><text x="279" y="278" fill="#e0b13a" font-size="8.7" font-weight="600">As much a fluid machine as an optic.</text><!-- ============ PANEL 3: where it sits ============ --><rect x="514" y="66" width="226" height="298" rx="7" fill="#0c141d" stroke="#30363d"/><text x="526" y="88" fill="#a99cf0" font-size="12" font-weight="700">3 &#183; Where it sits</text><text x="526" y="108" fill="#adb5bd" font-size="8.7">One 193i exposure: ~38 nm half-pitch.</text><text x="526" y="121" fill="#adb5bd" font-size="8.7">Multi-patterning shrinks it:</text><text x="526" y="142" fill="#adb5bd" font-size="8.5">single</text><rect x="570" y="133" width="110" height="12" rx="2" fill="#38bdf8" fill-opacity="0.75"/><text x="686" y="143" fill="#9fd8ef" font-size="8">38 nm</text><text x="526" y="162" fill="#adb5bd" font-size="8.5">SADP</text><rect x="570" y="153" width="55" height="12" rx="2" fill="#a99cf0" fill-opacity="0.8"/><text x="631" y="163" fill="#c4b5fd" font-size="8">19 nm</text><text x="526" y="182" fill="#adb5bd" font-size="8.5">SAQP</text><rect x="570" y="173" width="28" height="12" rx="2" fill="#34d399" fill-opacity="0.85"/><text x="604" y="183" fill="#7ee6c0" font-size="8">9.5 nm</text><text x="526" y="200" fill="#8b949e" font-size="7.7">half-pitch &#183; ArFi + multi-patterning</text><line x1="526" y1="214" x2="728" y2="214" stroke="#30363d" stroke-width="1"/><text x="526" y="232" fill="#a99cf0" font-size="10" font-weight="700">ArFi + MP vs EUV</text><text x="526" y="248" fill="#adb5bd" font-size="8.5">EUV prints the hardest layers, but most</text><text x="526" y="260" fill="#adb5bd" font-size="8.5">layers still use DUV/immersion &#8212; faster,</text><text x="526" y="272" fill="#adb5bd" font-size="8.5">cheaper, mature.</text><text x="526" y="292" fill="#34d399" font-size="8.5" font-weight="600">A leading fab = EUV plus a large</text><text x="526" y="304" fill="#34d399" font-size="8.5" font-weight="600">installed base of immersion scanners.</text><!-- ============ BOTTOM CARDS ============ --><rect x="20" y="384" width="226" height="70" rx="7" fill="#111a24" stroke="#30363d"/><text x="32" y="404" fill="#38bdf8" font-size="10.5" font-weight="700">The water trick</text><text x="32" y="421" fill="#adb5bd" font-size="8.7">A 193 nm ArF beam through water</text><text x="32" y="434" fill="#adb5bd" font-size="8.7">(n=1.44) collects a wider cone &#8212;</text><text x="32" y="447" fill="#adb5bd" font-size="8.7">NA 0.93&#8594;1.35, ~35% smaller CD.</text><rect x="267" y="384" width="226" height="70" rx="7" fill="#111a24" stroke="#30363d"/><text x="279" y="404" fill="#e0b13a" font-size="10.5" font-weight="700">Fluid-control machine</text><text x="279" y="421" fill="#adb5bd" font-size="8.7">Degassed, 23.000&#177;0.001&#176;C water;</text><text x="279" y="434" fill="#adb5bd" font-size="8.7">topcoat + high contact angle beat</text><text x="279" y="447" fill="#adb5bd" font-size="8.7">bubbles and watermark defects.</text><rect x="514" y="384" width="226" height="70" rx="7" fill="#111a24" stroke="#30363d"/><text x="526" y="404" fill="#34d399" font-size="10.5" font-weight="700">Still the workhorse</text><text x="526" y="421" fill="#adb5bd" font-size="8.7">With SADP/SAQP it reaches ~9.5 nm</text><text x="526" y="434" fill="#adb5bd" font-size="8.7">half-pitch; most layers in an EUV fab</text><text x="526" y="447" fill="#adb5bd" font-size="8.7">still run on immersion scanners.</text></svg>