What is Dry Etching?Any plasma treatment performed without the use of chemicals is commonly referred to as dry etching.
All Plasma Etch systems are designed to dry etch. This process has the following advantages compared to traditional wet etching methods:
Plasma Dry Etching:
- Processes are easily controllable through RF power, pressure, time, and gas selection
- Less sensitive to atmospheric changes such as temperature, humidity, and pressure
- No residues remain
- Minimal amount of raw materials consumed
- Waste products are mostly gaseous and are liberated directly into the atmosphere
- Most gases used are not toxic, although some can be hazardous
- Footprint is small
- Operator training is minimal
- Systems can be programmed to guarantee consistent, repeatable results
- Process can be started and stopped nearly instantaneously
- Can be used to etch patterns into glass or stone with the use of a photoresist
Chemical Wet Etching:
- Processes are sensitive to time and chemical concentrations
- Must remove or neutralize residue requiring multiple washing steps
- Large amounts of raw (liquid) materials required
- High volumes of liquid waste to dispose of; expensive government permits required
- Most solvents or acids used are toxic or hazardous
- Requires a large amount of floor space
- For safety's sake, extensive training is mandatory
- More susceptible to operator error
- Process can't be quickly started and stopped
Plasma is AnisotropicAnother advantage of a plasma etching process is the directional or anisotropic nature of plasma technology. This means that since the etching process will be performed in one direction, under etching is much less likely to occur using plasma than other etching methods. Under etching occurs when the etchant is able to etch under the photoresist, resulting in sloppy etching and possibly poor electrical reliability.
Dry Etching Printed Circuit BoardsDry etching is often used to manufacture printed circuit boards (PCBs).
The ions in the plasma bombard and etch away at the material of any exposed surface. The photoresist protects the material and allows the unprotected areas to be etched away by the plasma.
This process allows for the most effective plasma desmear solutions available today as the sludge left behind by drilling is removed from drill holes, allowing for a superior solder connection.
Chemical etching is multi-directional, allowing the chemicals to potentially etch under the photoresist from the side. This results in a higher error rate than plasma.
Reactive Ion EtchingOne of the most popular types of dry etching we build systems for is reactive ion etching. During this process, electrons are deposited onto a platter which creates a negative charge due to the platter's electrical isolation. This negative charge causes a negative voltage to develop as well. The voltage is usually a few hundred volts, creating plasma with a positive charge. The plasma created with a positive charge is a result of the additional positive ions compared to free electrons in the chamber.
The difference in voltage causes the positive ions to drift toward the wafer platter. They collide with the samples to be etched and react chemically with any organic material on the surface of the samples. This reaction strips all of the organic matter from the material, which is then removed from the chamber by the vacuum pump.
Etching conditions in any of our systems are fully adjustable. Gas flow, pressure, and RF power settings may be adjusted manually or automatically by allowing the etching equipment to follow a pre-programmed recipe.
Metal EtchingPlasma is able to etch very small amounts of metal along with plastic and glass. Etching metal is time consuming but for some applications the benefits of plasma still hold true. By heating the chamber, we can speed up the etching process.
When etching metal, if only a small amount of metal needs to be removed, plasma may be a viable solution.
Copper cleaning is not recommended as copper is highly resistant to plasma.
Plasma does an excellent job of removing organic contaminants and activating the surface of most metals.
Next: Plasma Descum