Plasma Scrubber

Green house effect and global warming are the critical issues in this new aera. These issues have some influence not only on the environment, but also on the economy and on the national safety. The main part of relevant gases, PFCs and SF6, the GHGs (Green House Gases) defined in the Kyoto Protocol are generated from the semiconductor and optical electronics industries. In dry etching procedures these gases are accumulated and mixed with CVD gas for chamber cleaning processes. The special PFCs gases from these tools such as SF6, CF4, C2F6, C3F8, CHF3 and NF3 have to be treated before emission.

A plasma scrubber system was developed and tested as a point of use abatement system for the treatment of PFC loaded gases coming from a production line in the semiconductor industry. The system consists of an arc heated water steam plasma unit followed by a combustion chamber and a quench-scrubber-system.

For chemical destrucion of PFC material, a water plasma is favourable because both, the oxygen and the hydrogen (which are necessary to produce the desired products after the high temperature zone: CO, CO2, HF and HCl) are supplied by the heat carrier itself.  Therefore a new plasma torch system using water as plasma gas was developed and tested under the specification to achieve a long lifetime of the electrodes.

The system was developed and tested under industrial conditions at a process line in semiconductor industry factories. It was demonstrated that with this process a reduction of PFC in the exhaust gas of > 99.9% can be achieved.

The Plasma Scrubber System

Plasma cracking is a non-incineration thermal process using temperatures above 2000°C by cracking highly stable materials like fluorinated compounds into smaller molecules.

The process gas is mixed into a steam plasma jet. Through the high temperatures and the available radical the PFC is cracked and reacts with the oxygen and the hydrogen coming from the water plasma to CO2 and HF. The exhaust gases from the high temperature reactors are cooled and cleaned in a specially developed quench and water scrubber stage.

In the first stage, the gas stream is quenched down by a injected water stream. In parallel to the quench effect one gets a first cleaning of the gas stream from the acid components. Temperature of the stream can be cooled to 40°C after quenching.

After the first stage, additional cleaning stages are followed by using recycling water for gases scrubbering. For achieving the required clean gas concentration, the last fine cleaning stage is done with clean city water.

Schematic of the POU process

Chemical scrubbers

Absorption Scrubbing

The absorption scrubbers are used to reduce gaseous contaminants.

Absorbable contaminants are usually inorganic compounds, such as:

  • Ammoniac NH3
  • Hydrogen Sulphide H2S
  • Hydrogen Chloride HCl
  • Sulphur dioxide SO2 etc
  • Amines

Application Areas:

  • Exhaust gas from galvanic systems – contaminants: HCl, NH3
  • Exhaust gas from core shooters – contaminants: Amines, SO3
  • Exhaust gas from semi-conductor production – contaminants: HCl, NH3, SiH4
  • Exhaus gas from sewage works – contaminants: H2S, NH3

The exhaust gas streams from the production processes are decontaminated in absorption scrubbers. The principle of the absorption lies in the solubility of the contaminated gases in scrubbing liquids. If the contaminated gases are separated out exclusively due to their solubility in the scrubbing liquid, it is a physical absorption. The degree of separation is largely determined by the solubility equilibrium of the contaminated gas. If this equilibrium is reached, the physical absorption stops. The chemical absorption is not limited by the solubility, since in this case, the gas dissolved in the scrubbing liquid is chemically converted. Both the absorption capacity of the scrubbing liquid and also the reaction speed are therefore higher. In very fast chemical absorption processes, the absorption capacity is principally determined by the extent of the boundary layer gas/liquid.

The choice of which scrubbing liquids are used to achieve the optimum effectiveness depends on the contaminant. The absorption scrubbers are either spray scrubbers (jet scrubbers) or packed tower scrubbers. They can be constructed in horizontal or vertical design.

PlasmaAir AG has vertical packed tower scrubbers as the standard design. Each scrubber and each exhaust gas system is designed to suit the process.