<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">Etching: cut the pattern into the wafer, straight down or all around</text><text x="20" y="50" fill="#8b949e" font-size="12.5">The resist mask protects some areas; etch removes the rest &#8212; dry etch cuts vertically, wet etch soaks in</text><!-- Panel 1: dry etch --><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; Dry (plasma / RIE)</text><text x="32" y="106" fill="#8b949e" font-size="10.5">ions bombard straight down</text><rect x="42" y="118" width="182" height="150" rx="3" fill="#111a24" stroke="#30363d"/><!-- ions falling --><g stroke="#a99cf0" stroke-width="1.3"><line x1="70" y1="126" x2="70" y2="150"/><line x1="95" y1="126" x2="95" y2="150"/><line x1="120" y1="126" x2="120" y2="150"/><line x1="145" y1="126" x2="145" y2="150"/><line x1="170" y1="126" x2="170" y2="150"/><line x1="195" y1="126" x2="195" y2="150"/></g><g fill="#a99cf0"><polygon points="67,150 73,150 70,155"/><polygon points="92,150 98,150 95,155"/><polygon points="117,150 123,150 120,155"/><polygon points="142,150 148,150 145,155"/><polygon points="167,150 173,150 170,155"/><polygon points="192,150 198,150 195,155"/></g><text x="52" y="134" fill="#a99cf0" font-size="8">energetic ions (directional)</text><!-- resist mask --><rect x="60" y="160" width="34" height="14" fill="#e0b13a"/><rect x="132" y="160" width="34" height="14" fill="#e0b13a"/><text x="113" y="170" fill="#0d1117" font-size="7" text-anchor="middle">resist</text><!-- material with vertical trench --><rect x="60" y="174" width="34" height="46" fill="#38506a"/><rect x="132" y="174" width="34" height="46" fill="#38506a"/><rect x="94" y="174" width="38" height="46" fill="#111a24" stroke="#233041"/><!-- vertical walls emphasis --><line x1="94" y1="174" x2="94" y2="220" stroke="#34d399" stroke-width="1.5"/><line x1="132" y1="174" x2="132" y2="220" stroke="#34d399" stroke-width="1.5"/><text x="113" y="236" fill="#34d399" font-size="8" text-anchor="middle">vertical, anisotropic profile</text><text x="52" y="256" fill="#8b949e" font-size="7.5">reactive gas + plasma; walls stay straight</text><text x="32" y="286" fill="#adb5bd" font-size="9.5">A plasma makes reactive ions and</text><text x="32" y="301" fill="#adb5bd" font-size="9.5">radicals; a bias pulls ions straight down</text><text x="32" y="316" fill="#adb5bd" font-size="9.5">so they etch vertically, not sideways.</text><text x="32" y="331" fill="#adb5bd" font-size="9.5">That anisotropy is what lets you print</text><text x="32" y="346" fill="#adb5bd" font-size="9.5">narrow, high-aspect-ratio features.</text><!-- Panel 2: wet etch --><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; Wet (chemical bath)</text><text x="279" y="106" fill="#8b949e" font-size="10.5">acid dissolves in all directions</text><rect x="287" y="118" width="196" height="150" rx="3" fill="#111a24" stroke="#30363d"/><!-- liquid --><rect x="295" y="126" width="180" height="20" fill="#1c2733"/><text x="385" y="140" fill="#38bdf8" font-size="8" text-anchor="middle">liquid etchant (e.g. HF, KOH)</text><!-- resist --><rect x="305" y="160" width="34" height="12" fill="#e0b13a"/><rect x="431" y="160" width="34" height="12" fill="#e0b13a"/><!-- material with undercut (isotropic) --><rect x="305" y="172" width="34" height="46" fill="#38506a"/><rect x="431" y="172" width="34" height="46" fill="#38506a"/><path d="M339,172 Q356,172 356,190 Q356,210 375,210 L395,210 Q414,210 414,190 Q414,172 431,172 Z" fill="#111a24" stroke="#233041"/><!-- undercut arrows --><path d="M339,178 Q348,178 350,186" fill="none" stroke="#f87171" stroke-width="1.2"/><path d="M431,178 Q422,178 420,186" fill="none" stroke="#f87171" stroke-width="1.2"/><text x="385" y="234" fill="#f87171" font-size="8" text-anchor="middle">undercut: etches under the mask</text><text x="299" y="254" fill="#8b949e" font-size="7.5">isotropic &#8212; same rate in every direction</text><text x="279" y="286" fill="#adb5bd" font-size="9.5">Dipping the wafer in a chemical bath</text><text x="279" y="301" fill="#adb5bd" font-size="9.5">dissolves the exposed material, but the</text><text x="279" y="316" fill="#adb5bd" font-size="9.5">acid eats sideways too, rounding and</text><text x="279" y="331" fill="#adb5bd" font-size="9.5">undercutting the mask. Cheap and gentle,</text><text x="279" y="346" fill="#adb5bd" font-size="9.5">but too blurry for fine features.</text><!-- Panel 3: what matters --><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 etch must control</text><text x="526" y="106" fill="#8b949e" font-size="10.5">the knobs that set the profile</text><circle cx="532" cy="126" r="2.4" fill="#34d399"/><text x="542" y="129" fill="#e6edf3" font-size="10" font-weight="700">Selectivity</text><text x="542" y="143" fill="#8b949e" font-size="9">etch the target fast but the mask and</text><text x="542" y="156" fill="#8b949e" font-size="9">underlying layer slowly &#8212; so you stop clean.</text><circle cx="532" cy="176" r="2.4" fill="#38bdf8"/><text x="542" y="179" fill="#e6edf3" font-size="10" font-weight="700">Anisotropy</text><text x="542" y="193" fill="#8b949e" font-size="9">vertical sidewalls hold the drawn width;</text><text x="542" y="206" fill="#8b949e" font-size="9">sideways etch blurs and shrinks features.</text><circle cx="532" cy="226" r="2.4" fill="#e0b13a"/><text x="542" y="229" fill="#e6edf3" font-size="10" font-weight="700">Endpoint &amp; uniformity</text><text x="542" y="243" fill="#8b949e" font-size="9">detect when the layer clears; etch the</text><text x="542" y="256" fill="#8b949e" font-size="9">same depth everywhere on the wafer.</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">Why dry etch dominates</text><text x="536" y="306" fill="#adb5bd" font-size="9">Fine geometry needs straight walls, so</text><text x="536" y="320" fill="#adb5bd" font-size="9">plasma etch does the critical patterning.</text><text x="536" y="334" fill="#adb5bd" font-size="9">Wet etch survives for cleaning, stripping</text><text x="536" y="348" fill="#adb5bd" font-size="9">and gentle, non-critical removal.</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">Dry etch = vertical</text><text x="32" y="424" fill="#adb5bd" font-size="9.5">Directional ions cut straight down &#8212;</text><text x="32" y="440" fill="#adb5bd" font-size="9.5">the workhorse for fine patterning.</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">Wet etch = all around</text><text x="279" y="424" fill="#adb5bd" font-size="9.5">A chemical bath dissolves evenly &#8212;</text><text x="279" y="440" fill="#adb5bd" font-size="9.5">cheap, but it undercuts the mask.</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">Selectivity &amp; profile</text><text x="526" y="424" fill="#adb5bd" font-size="9.5">Etch the target, spare the rest, and</text><text x="526" y="440" fill="#adb5bd" font-size="9.5">hold the sidewall the layout demands.</text></svg>

Dry Etch (Reactive Ion Etching) is the primary pattern transfer technique in semiconductor manufacturing that uses chemically reactive plasma to selectively remove material — providing the anisotropic (vertical) etch profiles essential for sub-10nm feature patterning, where the interplay between chemical etching (reactive species) and physical bombardment (ion energy) determines the etch rate, selectivity, and profile quality.

Dry Etch Mechanisms

• RIE synergy: Ion bombardment enhances chemical reaction rate on horizontal surfaces (where ions strike) → vertical etching 10-50x faster than lateral → anisotropic profile.

Etch Tool Types

Common Etch Chemistries

Key Etch Parameters

• Etch Rate: nm/min of material removed.
• Selectivity: Ratio of target etch rate to mask/underlayer etch rate. Target: > 10:1.
• Uniformity: Etch rate variation across wafer. Target: < 2% 3σ.
• CD Bias: Difference between mask CD and etched feature CD.
• Profile Angle: 88-90° = vertical (ideal anisotropic). < 85° = tapered.

Etch Endpoint Detection

• Optical Emission Spectroscopy (OES): Monitor plasma emission wavelengths — intensity change signals layer transition.
• Interferometry: Monitor reflected laser intensity — periodic oscillations track film thickness.
• Mass Spectrometry: Detect etch byproduct species in exhaust.

Dry etching is the critical pattern transfer step that defines every feature on a chip — from transistor gates at 3nm width to via holes with 50:1 aspect ratio, the precision of the etch process directly determines whether the designed patterns are faithfully reproduced in silicon.