Etching (photolithography)

Etching in lithography ( etching in lithography ) is a stage of the photolithographic process, which consists in the complete or partial removal of a layer of material of a microcircuit (oxide, metal, semiconductor) in areas not protected by a photoresist mask.

Liquid etching is highly selective, but is isotropic and occurs not only in the direction perpendicular to the substrate surface, but also horizontally, under the resist layer. As a result of this, the details of the etched pattern are larger in size than the corresponding details of the mask .

Installation diagram for reactive ion etching

Reactive ion etching is most commonly used, in which a mask coated substrate is exposed to a plasma excited by a high-frequency electric field. Radicals and neutral plasma particles participate in chemical reactions on the surface, forming volatile products, and positive plasma ions bombard the surface and knock out atoms from unprotected sections of the substrate. For each material subjected to dry etching, the corresponding reactive gas is selected. For example, organic resists etch in an oxygen-containing plasma (CF ₄ + O ₂ ), aluminum in a chlorine-containing plasma (Cl ₂ , CCl ₄ , BCl ₃ , BCl ₃ + Cl ₂ , BCl ₃ + CCl ₄ + O ₂ ), silicon and its compounds are etched with chlorine and fluorine-containing plasma (CCl ₄ + Cl ₂ + Ar, ClF ₃ + Cl ₂ , CHF ₃ , CF ₄ + H ₂ , C ₂ F ₆ ). The disadvantage of dry etching is less selectivity compared to liquid etching. A variant of dry anisotropic etching is ion beam etching. Unlike reactive ion etching, which combines physical and chemical mechanisms, ion beam etching is determined only by the physical process of momentum transfer. Ion beam etching is universal, suitable for any material or combination of materials and has the highest resolution among all etching methods, making it possible to obtain elements with a size of less than 10 nm.