plasmaetching

Plasma etching is a dry etching process that removes material from a solid substrate by exposing it to a plasma, a partially ionized gas containing ions, radicals, and electrons. The removal occurs through chemical reactions between reactive species and the surface, often aided by physical sputtering from energetic ions. The combination can produce controlled material removal with directionality and high aspect ratios, reducing or avoiding the need for liquid chemicals.

Common implementations include reactive ion etching (RIE), where ions are accelerated toward the surface by an RF or DC bias, leading to anisotropic etching. Magnetically enhanced variants confine plasma with magnetic fields to increase density. Inductively coupled plasma (ICP) etching uses high-density plasma for fast rates with fine control of ion energy, improving anisotropy and selectivity. Deep reactive ion etching (DRIE) achieves very high aspect ratios, frequently used for infrared microstructures and MEMS. Cryogenic etching uses low temperatures to enhance anisotropy and selectivity for certain materials, notably silicon.

Chemistries depend on the material to be etched. Fluorine- or chlorine-containing gases are common for silicon-based materials, while oxygen-containing plasmas can etch polymers. Typical gases include SF6, CF4, CHF3, Cl2, BCl3, O2, and mixtures with argon as a physical sputter component. Process parameters—pressure, RF power, substrate temperature, gas flow rates—control the etch rate, directionality, and selectivity relative to masking layers. Endpoints may be monitored optically or via etch-rate measurements.

Advantages of plasma etching include precise, anisotropic pattern transfer and compatibility with wafer-scale fabrication. Limitations include potential plasma-induced damage, charging effects on insulators, surface roughness, and limited selectivity between certain materials. Process optimization requires careful choice of gas chemistry and operating conditions.