What is Dry Etching with Plasma?

Dry Etching is the removal of plastic or other semiconductor material using plasma as opposed to chemical treatment. The excited ions in the plasma collide with the material and remove it without any chemicals. This is the most enviromentally friendly method available.

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

Printed Circuit Boards

Dry 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.

Another advantage of a plasma etching process is the directional or anisotropic nature of plasma technology when using a reactive ion etching system. The etching process will be performed in one direction so 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.

Chemical etching is multi-directional, allowing the chemicals to potentially etch under the photoresist from the side. This results in more under etching and a higher error rate than plasma.

Reactive Ion Etching

One 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 Etching

Plasma does an excellent job of removing organic contaminants and activating the surface of most metals.

Plasma is generally not considered a viable technique to remove metal. Etching metal is technically possible, but very time consuming. By heating the chamber, we can speed up the etching process.

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