Main Difference – Dry vs Wet Etching

Etching is basically the removal of substances from surfaces. Different etching processes have been invented depending on the material that is going to be removed. Wet etching and dry etching are such processes. Wet etching can be called isotropic etching. Dry etching can be called anisotropic etching. These wet and dry etching processes can be further divided according to the technique and other factors that affect etching. The main difference between dry and wet etching is that dry etching is done at a liquid phase whereas wet etching is done at a plasma phase.

Key Areas Covered

1. What is Dry Etching
      – Definition, Technique, Applications, Advantages and Disadvantages
2. What is Wet Etching
      – Definition, Technique, Applications, Advantages and Disadvantages
3. What is the Difference Between Dry and Wet Etching
      – Comparison of Key Differences

Key Terms: Anisotropic, Dry Etching, Etching, Isotropic, Liquid Phase, Plasma Etching, Plasma Phase, Wet Etching

What is Dry Etching

Dry etching is the process of etching done at plasma phase. Here, the material removal reactions occur in the gas phase. Dry etching is also called plasma etching. This process can be used to create designed patterns on surfaces. Dry etching can be used on printed circuit boards. There are two types of dry etching.

Non-plasma based etching uses a spontaneous reaction of an appropriate reactive gas mixture. The plasma-based etching uses radio frequency power to drive the chemical reaction. In the plasma formation, the chamber is evacuated and filled with gas or gases. Radio frequency is applied. This applied frequency can accelerate the electrons. This results in increasing the kinetic energy inside the chamber. Electrons will colloid with neutral gas molecules. This results in the formation of ions and more electrons. This ionization finally results in the formation of a plasma. (A plasma is a system composed of equal numbers of cations and electrons along with neutral molecules.)

Figure 1: Hydrogen Plasma Etching Process

Advantages and Disadvantages

There are many advantages of dry etching process. It eliminates the need for handling dangerous chemicals. It uses small amounts of chemicals for etching. A major advantage is the high resolution and cleanliness that can be obtained from dry etching. The process is also easy to control and handle. Apart from that, dry etching can easily be automated.

But there are some disadvantages as well. For example, some gases that are used in dry etching are toxic and corrosive. The re-deposition of volatile compounds is a major problem that arises when volatile compounds are used. This method is quite expensive because specialized equipment is needed.

What is Wet Etching

Wet etching is the process of etching done at liquid phase. The chemicals used for etching process are called etchants. Wet etching uses a bath of etchants for etching. But this method is not very precise. However, it is easy to handle than the dry etching process. What basically happens in wet etching is that the material that is to be removed is dissolved by immersing it in a chemical bath.

Figure 2: Copper Sulfate Etching Bath

Advantages and Disadvantages

This is the simplest process that can be used for etching. Because it only requires a bath of chemicals as a liquid solution. However, a drawback of this method is that a chemical bath can dissolve the needed materials on the surface as well. Therefore, a suitable masking agent should be used. Or else, chemicals that slowly dissolves the surface materials (slower than the materials that have to be removed) should be used.

Difference Between Dry and Wet Etching

Definition

Dry Etching: Dry etching is the process of etching done at plasma phase.

Wet Etching: Wet etching is the process of etching done at liquid phase.

Phase

Dry Etching: Dry etching uses gaseous phase chemicals.

Wet Etching: Wet etching uses liquid phase chemicals.

Safety

Dry Etching: Dry etching is much safer than wet etching.

Wet Etching: Wet etching is not safe since disposing of hazardous chemicals can cause water contamination.

Precision

Dry Etching: The dry etching process is more precise.

Wet Etching: The wet etching process is less precise.

Chemical Usage

Dry Etching: Dry etching uses few chemicals.

Wet Etching: Wet etching uses many chemicals.

Cost

Dry Etching: Dry etching is expensive because specialized equipment is required.

Wet Etching: Wet etching is not very expensive because it needs only a chemical bath.

Conclusion

Dry and wet etching are two major types of etching processes. These processes are useful for the removal of surface materials and creation of patterns on the surfaces. The main difference between dry etching and wet etching is that dry etching is done at a liquid phase whereas wet etching is done at a plasma phase.

References:

 1. “Plasma Knowledge: Dry Etching.” Dry Etching & Dry Etching vs. Wet Etching, 12 Feb. 2016, Available here. Accessed 27 Sept. 2017.
2. “Etching Processes.” Memsnet, Available here. Accessed 27 Sept. 2017.
3. “Etching (Microfabrication).” Wikipedia, Wikimedia Foundation, 23 July 2017, Available here. Accessed 27 Sept. 2017.

Image Courtesy:

1. “Hydrogen plasma etching” By Pepinpeterkapichler – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Copper sulfate etching bath” By Ck517 – Own work (Public Domain) via Commons Wikimedia

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