File Name: wet etching and dry etching .zip
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Etching is used in microfabrication to chemically remove layers from the surface of a wafer during manufacturing. Etching is a critically important process module, and every wafer undergoes many etching steps before it is complete. For many etch steps, part of the wafer is protected from the etchant by a "masking" material which resists etching.
The etch process removes selected areas from the surface of the wafer so that other materials may be deposited. Typically, part of the wafer is protected during the etch by an etch-resistant "masking" material, such as photoresist or a hard mask such as silicon nitride. Etch processes are referred to as dielectric etch or conductor etch to indicate the types of films that are removed from the wafer. For example, dielectric etch is employed to etch via holes and trenches for metal conductive paths; conductor etch removes polysilicon to create the gate in a transistor , or aluminum and tungsten to reveal the pattern of circuitry in the device structure. A plasma containing oxygen is used to oxidize "ash" photoresist and facilitate its removal. The plasma releases positively charged ions that bombard the wafer to remove etch materials and chemically reactive free radicals that react with the etched material to form volatile or nonvolatile byproducts.
Dry etching refers to the removal of material, typically a masked pattern of semiconductor material, by exposing the material to a bombardment of ions usually a plasma of reactive gases such as fluorocarbons , oxygen , chlorine , boron trichloride ; sometimes with addition of nitrogen , argon , helium and other gases that dislodge portions of the material from the exposed surface. A common type of dry etching is reactive-ion etching. Unlike with many but not all, see isotropic etching of the wet chemical etchants used in wet etching , the dry etching process typically etches directionally or anisotropically. Dry etching is used in conjunction with photolithographic techniques to attack certain areas of a semiconductor surface in order to form recesses in material, such as contact holes which are contacts to the underlying semiconductor substrate or via holes which are holes that are formed to provide an interconnect path between conductive layers in the layered semiconductor device or to otherwise remove portions of semiconductor layers where predominantly vertical sides are desired. Along with semiconductor manufacturing, micromachining and display production, the removal of organic residues by oxygen plasmas is sometimes correctly described as a dry etch process.
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The advantages of wet etching processes are relatively fast with high etch rates. The simple equipment baths or spraying of wet chemistry can have high selectivity. The wet process typical etching agent are liquid solvents, corrosive leeches and acids.
Metrics details. Wet anisotropic etching is extensively employed in silicon bulk micromachining to fabricate microstructures for various applications in the field of microelectromechanical systems MEMS. In addition, it is most widely used for surface texturing to minimize the reflectance of light to improve the efficiency of crystalline silicon solar cells. In wet bulk micromachining, the etch rate is a major factor that affects the throughput. Slower etch rate increases the fabrication time and therefore is of great concern in MEMS industry where wet anisotropic etching is employed to perform the silicon bulk micromachining, especially to fabricate deep cavities and freestanding microstructures by removal of underneath material through undercutting process.
If directionality is very important for high-resolution pattern transfer, wet chemical etching is normally not used. Dry Etch: Synonyms: plasma etching, gas etching.
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