A capacitively coupled plasma (CCP) is one of the most common types of industrial plasma sources. It essentially consists of two metal

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s separated by a small distance, placed in a reactor. The gas pressure in the reactor can be lower than atmosphere or it can be

atmospheric An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...

Description

A typical CCP system is driven by a single

radio-frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the ...

(RF) power supply, typically at 13.56 MHz.UK Wireless Telegraphy (Short Range Devices) (Exemption) Regulations 199

/ref> One of two electrodes is connected to the power supply, and the other one is ground (electricity), grounded. As this configuration is similar in principle to a

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

in an electric circuit, the plasma formed in this configuration is called a capacitively coupled plasma. When an

electric field An electric field (sometimes called E-field) is a field (physics), physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) descri ...

is generated between electrodes, atoms are ionized and release electrons. The

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s in the gas are accelerated by the RF field and can ionize the gas directly or indirectly by

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great for ...

s, producing

secondary electrons Secondary electrons are electrons generated as ionization products. They are called 'secondary' because they are generated by other radiation In physics, radiation is the emission or transmission of energy in the form of waves or particle ...

. When the electric field is strong enough, it can lead to what is known as

electron avalanche An electron avalanche is a process in which a number of free electrons in a transmission medium are subjected to strong acceleration by an electric field and subsequently collide with other atoms of the medium, thereby ionizing them ( impact ioniz ...

. After

avalanche breakdown Avalanche breakdown (or the avalanche effect) is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwis ...

, the gas becomes electrically

conductive In physics and electrical engineering, a conductor is an object or type of material that allows the flow of Electric charge, charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. The flow ...

due to abundant free electrons. Often it accompanies light emission from excited atoms or molecules in the gas. When visible light is produced, plasma generation can be indirectly observed even with the naked eye. A variation on capacitively coupled plasma involves isolating one of the electrodes, usually with a

. The capacitor acts like a

short circuit A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit ...

to the high frequency RF field, but like an

open circuit Open circuit may refer to: * Open circuit breathing apparatus, any type of breathing apparatus where the exhaled gas is discharged to the surroundings without recycling any of it ** Open-circuit scuba, a type of Scuba-diving equipment where the user ...

direct current Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow throug ...

(DC) field. Electrons impinge on the electrode in the sheath, and the electrode quickly acquires a negative charge (or self-bias) because the capacitor does not allow it to discharge to ground. This sets up a secondary, DC field across the plasma in addition to the

alternating current Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction. Alternating current is the form in w ...

(AC) field. Massive

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s are unable to react to the quickly changing AC field, but the strong, persistent DC field accelerates them toward the self-biased electrode. These energetic ions are exploited in many

microfabrication Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known as "semiconductor manufacturing" ...

processes (see

reactive-ion etching Reactive-ion etching (RIE) is an etching (microfabrication), etching technology used in microfabrication. RIE is a type of dry etching which has different characteristics than Isotropic etching, wet etching. RIE uses chemical reaction, chemically ...

(RIE)) by placing a substrate on the isolated (self-biased) electrode. Capacitively coupled plasmas have wide applications in the semiconductor processing industry for thin film deposition (see

sputtering In physics, sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface, after the material is itself bombarded by energetic particles of a plasma or gas. It occurs naturally in outer space, and c ...

, plasma-enhanced chemical vapor deposition (PECVD)) and

etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other type ...

References

{{DEFAULTSORT:Capacitively Coupled Plasma Plasma types Electronics manufacturing

Description

See also

References