Etchants
Introduction
Etching technology is widely used in various electronic components because of its simplicity, ease of operation and low cost. In the whole etching process, the choice of etchant is crucial, because it directly affects the etching rate and device surface finish. According to the etching processes, it can be divided into wet etching and dry etching.
Wet Etching
Wet etching process is widely used to produce micro components for various industrial applications, such as microelectromechanical systems and semiconductor industry. These processes involve the removal of unwanted portions of the workpiece material by exposure to strong acid or alkaline etchants. The wet etching process mainly refers to the etching of copper and its alloys on the circuit board. The most widely used copper etchant in the wet etching process is ferric chloride (FeCl3). The advantages of this etchant are high etching rate and easy regeneration. When FeCl3 attacks the copper surface, iron ions will oxidize copper to cuprous chloride to generate green ferric chloride. In addition, copper chloride (CuCl2) is also commonly used in the wet etching process of copper because it has only one reaction product and can be easily regenerated. The stable etching rate of acidic CuCl2 allows for high production, regeneration, and recovery of etched copper from used etchants, which will reduce environmental pollution.
Alkaline etchants are widely used in copper etching due to their high etching rate, high solubility of copper and compatibility with most metal and organic corrosion inhibitors (especially solder). Hydrogen peroxide/sulfuric acid etchant [H2O2-H2SO4] is also a relatively new etchant. Although it was designed for immersion etching method due to exothermic reaction, they can now be used for spray etching by using new stabilizers. The spray etching solution has a high sulfuric acid concentration. The etchant is compatible with metal resist and high dissolved copper capacity.
Dry Etching
Dry etching uses a fluorine-containing etchant that can effectively overcome the fatal defects of wet etching. It has become the most important method for etching devices in submicron size, and is widely used in semiconductor or liquid crystal display (LCD) front-end processing. Fluorine-containing etchants mainly include CF4, CHF3, CH2F2, CH3F, C2F6, c-C4F8, C4F6, C5F8, etc. Fluorine-containing organics are often used together with other inorganic gases. For example, when fluorine-containing organics and Ar2 are used together as etchants, Ar2 is often in large quantities. On the one hand, the inert gas Ar2 can dilute the reaction gas, on the other hand, a large amount of Ar2 bombarding the surface of the etched body can accelerate the etching rate. In addition, a large number of (C-H)n polymers during the etching process, and O2 can help to remove them.
Application
Etchants have been widely used to manufacture various industrial micro components. It is a very important micro machining process in the electronic industry. In the etching of integrated circuits and semiconductors, the selection of the right etchant is critical. . This choice not only depends on the etching performance of the etchant, but the regeneration of used etchants is also a key factor. Etchants are indispensable basic support source materials in the development of integrated circuits, optoelectronics, microelectronics, especially LCD devices, semiconductor light-emitting devices and semiconductor materials manufacturing process, which fundamentally determines the accuracy and accuracy of circuits and devices.
Reference
- Çakır, Orhan. Review of etchants for copper and its alloys in wet etching processes. In: Key Engineering Materials. Trans Tech Publications Ltd, 2008. p. 460-465.