Silicon nitride (Si3N4) is a semiconductor material with excellent physical and chemical properties. It is often used as an insulation layer, surface passivation layer, final protective film, and structural functional layer in micro machining processes. The etching process of silicon nitride thin film is one of the key processes in the chip manufacturing industry. The etching process is the process of etching a wafer with an IC circuit pattern on the surface of a substrate after a development process. The unwanted material is removed by chemical etching or physical impact, or a combination of both methods, leaving behind the desired IC circuit structure. In other words, during the process of making circuits, it is necessary to transfer the photoresist pattern onto the thin film layer of the device. The process of selectively removing the exposed portion of the pattern on the thin film layer during pattern transfer is called etching. There are generally two types of etching processes: dry etching and wet etching. Reactive ion etching is currently the most advanced technology in dry etching because it has the advantages of both chemical and physical etching methods. Reactive ion etching is the use of charged active particles to bombard the surface, so that under the action of momentum, a portion of the molecules are bombarded out, accompanied by chemical reactions. Reactive ion etching is a dry etching technique that has many advantages compared to ion beam etching, such as a large reaction area, good targeting, convenient operation, and fast energy saving, making it more popular.

There are many gases that can etch silicon nitride, including gases that can produce fluorine and chlorine active groups such as CHF3, CF4, SF6, NF3, etc. Fluorocarbon compounds are commonly used gases for etching silicon nitride, such as using CHF3 and CF4 as etching gases. The main process for etching silicon nitride is:

CHF3→CHF2*，CF3*，F*，‚H*

CF4→CF3*＋CF2*＋CF*＋F*

F*＋H*→HF↑

Si＋F*→SiF4↑

Si3N4＋F*→SiF4↑＋N2↑

CF3 *, CF2 *, CF *, and F * with superscript asterisks in the formula represent active groups with strong chemical reactivity. The volatile gases such as SiF4 ↑, HF ↑, N2 ↑ generated by the reaction are evacuated from the reaction chamber by the vacuum system to complete the etching of silicon nitride. It can be seen that etching silicon nitride is mainly due to the active role of fluorine atoms. A higher proportion of fluorine active atoms in the reaction gas is advantageous for etching.