Etching is the process of using chemical and physical methods to selectively remove unwanted materials from the surface of a silicon wafer. The purpose of etching is to correctly reproduce the mask pattern on the coated silicon wafer. Etching is divided into wet etching and dry etching. Wet etching is the use of liquid chemical reagents or solutions through chemical reactions to etch. Dry etching uses ions or free groups in the plasma generated by low voltage discharge to chemically react with the material, or through physical effects such as bombardment to achieve the purpose of etching. The main medium is gas. The advantages of dry etching are obvious anisotropy (that is, the vertical etching rate is much higher than the horizontal rate), good feature size control, low chemical use and treatment costs, high etching rate, good uniformity, and high yield. The common dry etching method is plasma etching.

The etching gases (special gases) of silicon wafers are mainly fluorinated gases, including carbon tetrafluoride, carbon tetrafluoride/oxygen, sulfur hexafluoride, hexafluoroethane/oxygen, nitrogen trifluoride, etc. However, due to their isotropy and poor selectivity, the improved etching gases usually include chlorine (Cl2) and bromine (Br2, HBr) gases. The products after the reaction include silicon tetrafluoride, tetrachlorosilane and SiBr4. The etching of aluminum and metal composite layers usually uses chlorine-based gases, such as CCl4, Cl2, BCl3, etc. The products mainly include AlCl3 etc

Etching is to etch away the non-photoresist masked processing surface on the substrate, such as silicon oxide film, metal film, etc., so that the photoresist masked area is preserved, so that the required imaging pattern is obtained on the surface of the substrate. The basic requirements of etching are that the edges of the pattern are neat, the lines are clear, the pattern transformation difference is small, and there is no damage and drilling to the surface of the photoresist film and its masking protection. The etching methods are wet chemical etching and dry chemical etching. The gases used in dry etching are called etching gases, which are usually fluoride gases, such as carbon tetrafluoride, nitrogen trifluoride, hexafluoroethane, perfluoropropane, trifluoromethane, etc. Dry etching is widely used because of its strong direction, precise process control, convenience, no degumming phenomenon, no substrate damage and contamination.