Etching is a process of removing surface layers from a material (known as substrate/wafer). This process uses a reactive liquid (conditioner) or gas that removes the desired layers while a layer mask protects the desired layers. Furthermore, there are mainly two types in this process, known as wet etching and dry etching.
This article will explain both types, explain the difference between dry engraving and wet engraving, the factors to consider when deciding between the two types, and everything else you need to know about these engraving methods.
Factors to Consider When Choosing the Recording Method
Selecting the etching method for removing surfaces of a given material is a process that must be carefully considered. Therefore, there are some parameters that machinists must consider before choosing a specific method. Below we highlight three of them.
1. Selectivity
Selectivity compares the corrosion rate of the reactive gas or liquid and the wafer/substrate. It is the ratio of the corrosion rates of both materials. Furthermore, the affinity of the reactive gas or liquid may mean attacking only the unwanted layer or both the unwanted layer and the desired layers. This parameter is very important because it helps determine whether the mask will outlast the etching material to prevent the reactive liquid or gas from attacking the desired part.
2. Recording rate
The corrosion rate is the thickness of material that is etched per unit of time. A synonym for this is write speed. Users measure this in nanometers per minute (nm/min) or micrometers per minute (µm/min).
3. Recording uniformity
This is important when the recording process involves processing a large batch of material. It can also be used to compare the corrosion rates of different parts of a single material. This parameter is determined by subtracting the highest write rate of a batch from the lowest write rate and dividing by the sum of both rates.
Additional considerations
After selecting the etching process, machinists also consider the effects that the etching agent (etching gas or liquid) would have. There are two possible effects:
Isotropic engraving
This type of engraving removes layers from the surface of the material in multiple directions. The result is not really accurate and can lead to cuts in the layers that should not be removed.
Anisotropic engraving
Anisotropic etching removes material in only one direction. It is the preferred method among train drivers. It is a more precise form of engraving and is used to create circular patterns on the substrate.
Overview of Engraving Types: Dry vs. Dry Engraving wet recording
Now that we've explained the different recording parameters and results, we can move on to the different types. As mentioned earlier, there are two main types of recording. However, there are different subtypes between these two. This section looks at both types, their subtypes, and the advantages and disadvantages of both types.
Dry engraving process
Dry engraving is the most commonly used engraving method today. This process uses high-energy, neutrally charged ions to etch the target surface of a substrate. The process creates these ions by using a radiofrequency field to convert reactive gases into plasma. This is where the synonym plasma recording comes from.
However, it should be noted that there are dry etching processes that do not use the plasma process.
For this process to work, there must be a continuous gas supply system so that the RF field can constantly convert these reactive gases into plasma. Examples of reactive gases used in the process are argon, oxygen, helium, nitrogen, etc.
This process is preferable to wet etching because it produces less waste and uses fewer chemicals. Furthermore, the process can be isotropic or anisotropic, providing the machinist with greater control over the degree of attack.
Types of dry engraving
There are basically three types of dry engraving. They are
1. Reactive Ion Etching (RIE)
This method utilizes a setup that utilizes two electrodes, a radiofrequency field, and a gas-filled vacuum container. The operator places the substrate/wafer on one of the electrodes in a vacuum filled with reactive gas that acts as a corrosive agent. The two electrodes form an electric field to accelerate the ions toward the substrate. This electric field is responsible for the anisotropic property of this process.
A high-frequency field is then applied to split the recording gas into a neutrally charged plasma jet. This beam attacks the wafer surface and reacts with the material on the substrate surface, producing byproducts.
2. Sputter engraving/ion milling
This process uses low pressure (10 mPa) in a vacuum to direct gas (in most cases argon) to the substrate. The gas molecules use their kinetic energy to repel the molecules grafted onto the surface of the substrate. So this mode uses more of a physical aspect to remove the unwanted layers.
3. Deep Reactive Ion Etching (DRIE)
This recording technique uses the chemical RIE process as explained above. However, it also uses a physical aspect where plasma ions can expel atoms from the material if they have enough kinetic energy.
Advantages and Disadvantages of Dry Engraving
| Benefits | Disadvantages |
| Does not use many chemicals. | Some of the gases used are corrosive. |
| The process is less chaotic. | The equipment needed to do this is expensive. |
| It is a more precise recording process. | Operating special equipment requires a higher level of specialized knowledge. |
| Byproducts are easier to dispose of. | |
| Operators can automate the process, reducing operational risks. |
Wet embossing process
As the name suggests, this process uses liquid solutions as a means of attack. These liquids are commonly called caustic. To carry out the process, large quantities of these liquids are needed to create a chemical bath.
Some of these liquids are highly corrosive and therefore penetrate underground. Examples of liquids used are hydrofluoric acid, hydrochloric acid, etc.
To protect the desired layers after using chemical baths, operators use materials that are resistant to the corrosive properties of conditioners. Examples of these masks are oxides, chrome, gold, etc.
The process is quite simple. When the masked substrate comes into contact with the liquid, the liquid dissolves the unwanted layers. After sufficient exposure, only the masked parts of the substrate remain.
Due to the isotropic properties of this technique, it has lost popularity among engraving experts. However, some users have found ways to make the process somewhat anisotropic.
Types of wet recording
There are only two modes of operation for wet etching technology. These are:
1. The diving method
This is the common wet etching method that uses a chemical bath. The operator dips the substrate into the chemical bath and waits until the unwanted layers are completely removed.
2. The centrifuge and spray method
In this method, the substrate is sprayed with the conditioner while being rotated and connected to an absorption source. However, rotation of the substrate may have no real effect because the reaction depends on the atomic arrangement of the exposed part of the substrate.
Advantages and Disadvantages of Wet Etching
| Benefits | Disadvantages |
| Does not use many chemicals. | Some of the gases used are corrosive. |
| The process is less chaotic. | The equipment needed to do this is expensive. |
| It is a more precise recording process. | Operating special equipment requires a higher level of specialized knowledge. |
| Byproducts are easier to dispose of. | |
| Operators can automate the process, reducing operational risks. |
What is the difference between dry etching and wet etching?
Although both processes aim for the same result, the approach is different and the result is also slightly different. In this section, we will highlight the differences between these two processes in a diagram.
| Dry engraving | wet recording |
| This process uses reactive gases for recording. | Wet etching uses liquid components (conditioners) for etching. |
| Dry engraving is more accurate (i.e. smaller or no undercuts) | The wet etching technique presents greater selectivity. |
| The chemicals used can be easily discarded. | Disposing of large quantities of liquid chemicals is more difficult. |
| The process can be easily automated. | The process requires constant input from the operator. |
| Dry engraving has a higher level of security. | Wet recording can pose hazards to the operator. Therefore, the security level is lower. |
Dry etching and wet etching applications
Dry etching and wet etching are used in some industries, with the electronics industry being one of the best known. They are also used in the machinery industry. Many machine shops use these technologies to process logos. Examples of these applications are:
1. Semiconductor manufacturing
The dry etching process (particularly the subtypes of reactive ion etching and deep reactive ion etching) is widely used to treat semiconductor materials. Etching of semiconductor materials is a process used to etch certain necessary characteristics into the electrical devices in which they are used.
2. PCB Etching
The wet etching process is similar to the process used in manufacturing printed circuit boards (PCB). These plates often have unwanted copper residue and this technique is used to remove them. Although the actual name of the process used is photolithography, it has similar operational characteristics to the wet etching process.
3. Manufacturing of optical instruments
Engraving is a technique used to produce various optical instruments such as cameras, shutters, apertures, etc.
4. Manufacturing of measuring instruments
The process also plays a role in manufacturing measuring devices such as strain gauges, galvanometer mirror frames, electrical contacts and connectors, etc.
University Degree
Wet and dry etching are two processes that play an important role in electronics manufacturing and are useful in a variety of applications. Although they both aim for the same result, they differ in how they work and the different chemicals used in the process.
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Common questions
Which engraving process is the best choice: dry engraving or wet engraving?
Dry etching is better because it is safer and uses fewer chemicals. Furthermore, it is the best choice if you want to engrave deep into the substrate and need vertical walls. However, the procedure is expensive and not recommended if your budget is tight.
Which of the two recording processes is more economical?
The wet etching process is more economical because it mainly requires a chemical bath.
What is the difference between laser engraving and laser engraving?
The difference between the two methods lies in the way they work and the results. Laser engraving involves melting the surface of the substrate to create raised characters. Laser engraving involves removing material from the surface to create characters embedded in the material.
