Reactive ion etching or dry etching is a different process than wet etching that utilises a plasma in contrast to a liquid solvent. A plasma is a partially ionized gas that is quasi-neutral. It is created when some electrons are initially stripped from gas atoms by an application of a large voltage, at the required frequency MHZ or GHz range. They are subsequently excited by an external power supply and heated to a temperature of few electron volts (eV). When these electrons collide with neutral species, they can dissociate molecules, ionize the neutral species or excite the species to a higher energy level. Excited species emit photons when they go back to their fundamental level. As a result, a plasma is a complex mixture of ions and electrons (with an equal quantity of negative and positive charges), reactive radicals, stable molecules and energetic photons. Owing to the presence of free charge carriers, a plasma reacts to electromagnetic fields, conducts electrical current, and possesses a well-defined plasma potential.

How does the Diener Tetra 45 work?

The Tetra 45 is a capacitively coupled plasma system (CCP).

In the CCP etch system, parallel plate electrodes are excited by a continuous radio frequency (RF, 13.56 MHz) power supply. This creates an alternating electric field perpendicular to the electrodes. This electric field accelerates apart from electrons, also the ions that have been generated, towards the electrodes, which makes plasma formation (dissociation and ionization) and ion acceleration (sheath potential) directly coupled. Increasing the power not only increases the plasma density, but also the self-bias voltage and thus the ions’ energy. As a result, plasma density and ion energy are coupled and cannot be changed independently. In CCP, the ion energy can reach several hundred eV. The operating gas pressure of the system is between 0.01 – 0.6 mbar. In the range 0,01 – 0,03 mbar reactive ion etching (RIE) of Si or SiO2 by SF6 or mixtures SF6/O2 and CF4/O2 can be achieved. Etching of Si3N4 by CHF3/Omixtures can be achieved. In the same pressure range Ar processing can also take place. In the range of 0,2 – 0,6 mbar the etching of Si3N4 is possible by using CF4.

Gasses that can be used with the Diener Tetra 45 plasma etcher:

Recommended gasses are: H2, He, N2, O2, Ar, Air, CF3, CF4, CHF3, NF3, SF6 and mixtures of CF4/H2.

Most Flourine containing gasses can potentially be used.

Additional requirements must be discussed with the manufacturer.

Chamber cleaning is recommended to be carried out once a month using a mixture of CF4/O2 (10%/90%) for a few hours at low power (3-50%) and at 0.2-0.3 mbar pressure.

Gasses that are prohibited to us with the Diener Tetra 45 plasma etcher:

Gasses containing chlorine, bromine or iodine are strictly prohibited due to the risk of degradation of the valves in the vacuum pumps.

Al is usually etched by gasses containing Chlorine and thus materials containing Al cannot be processed by this system.

Typical processing gasses for various materials can be found in the book: Etching in Microsystem Technology by Michael Köhler  ISBN: 978-3-527-61378-6 (https://www.wiley.com/en-