Plasma in dry etching
The dry etching process uses the plasma after the dissociation of anion and anion particles in a gas to perform etching. The so-called plasma, 99% of the matter in the universe, is in the isoton state. It contains neutral particles, ions, and electrons, which mix together to appear electrically neutral. In dry etching, the molecules and atoms in the gas are excited by external energy to form oscillations, so that the electrons with lighter mass are separated from the orbits of atoms and collide with adjacent molecules or atoms, releasing other electrons. In the repeated process, gas ions and free exciters are finally formed. Dry etching uses free active exciters and ions in the gas plasma to react with the etched surface to form the final feature pattern.
Features of dry etching
Dry etching and wet etching process are different in the principle of using chemical solution. When dry etching is etching surface materials, there are both chemical reactions and physical reactions. Therefore, it exhibits both chemical isotropy and physical anisotropy in etching characteristics. The so-called isotropic means that there is etching in both vertical and horizontal directions. Anisotropy, on the other hand, refers to etching in a single longitudinal direction.
Dry etching process
We can understand the main process of dry etching. The ions in the gas plasma in the reaction chamber bombard the etched surface under the action of the flattening of the reaction chamber to form a damaged layer, thereby accelerating the reaction of free active groups in the plasma on its surface. A part of the reaction product produced after the reaction is discharged from the exhaust port of the cavity by the molecular pump, and a part forms a deposition layer on the etched sidewall. Dry etching is completed in the process of the reaction between free active exciters and the surface and the continuous deposition of reaction products. Ion bombardment reflects the anisotropy of dry etching, and due to the deposition of the sidewall, the etching of the sidewall due to the isotropic effect of the free active excimer reaction is well suppressed . Because of the unique combination of physical and chemical reactions in dry etching, the size and shape of the pattern can be precisely controlled under the interaction of anisotropy and isotropy, reflecting the incomparable performance of wet etching. It has become one of the main process technologies for sub-micron pattern etching. With the in-depth development of microfabrication, the dry etching process technology has run through the entire product process and participated in each key process. From device isolation region, device gate, LDD sidewall protection, contact hole and through hole, hole plug, upper and lower wiring formation, to metal passivation and photoresist peeling and bottom damage layer repair, all involve Dry etching technology.