Flow & Pressure control for plasma reactors

April 13, 2021 Dion Oudejans

Besides plasma as a natural phenomenon, this fascinating physical effect also takes place in manufacturing processes of products that we use in our daily lives. Such as: mobile phones, computers, solar panels and glass windows.

In plasma processes, plasma reactors are used. In plasma reactors gas flow, vapor flow and pressure play an important role. The flow and pressure control of these gases into the reactor is regulated by flow controllers and pressure controllers. Flow controllers control the gas flow to the reactor chamber, where the gases are ignited into a plasma, and the pressure controller diverts the excess gas out of the reactor chamber, while maintaining the pressure. 

As product manager of MEMS-based instruments at Bronkhorst, I recognize the importance of these products within plasma applications. The fact that I often get questions about plasma applications, inspired me to write this blog.

Flow and Pressure control for plasma reactors

What is a plasma?

According to the Cambridge dictionary ‘plasma’ in physics is: "a highly ionised gas consisting of positive ions and free electrons". Because ionization and recombination of ions and electrons take place continuously, the plasma emits a beautiful light. Plasma is therefore also called the fourth state of matter, next to solid, liquid and gas.

Natural occurring plasma: Northern light
Natural occurring plasma: Northern light

Examples of naturally occurring plasmas are: lightning, the northern lights and the nuclear activity in the sun and other stars. Man has learned from the natural occurrence of plasma and has turned it into technology that is used today for many technological processes.

Man-made examples are: plasma lamps, nuclear fusion reactors and ordinary fluorescent lamps. Last but not least, plasma reactors should be mentioned.

Flow and pressure control for plasma reactors

Plasma enables applying coatings onto surfaces of silicon chips, glass and metal pieces. For instance, a thin coating on a chip can be structured by an etching process involving plasma. It can also clean and activate a surface to enhance a bonding process between two pieces of material before gluing them together. 

The gases introduced into a reactor form an ionized plasma by applying electrical power. A well-balanced adjustment of different gas flows, reactor pressure, temperature and electrical power turn the gases into a nice colourful light that spreads its magic on the materials inside the reactor, an ionized plasma. These balanced settings of gas flows and reactor pressure are obtained by mass flow controllers and electronic pressure controllers.

Glass coating; example of physical vapour deposition
Glass coating; example of physical vapour deposition – PVD

Vapor/Layer Deposition & Etching techniques

CVD, PVD, ALD, RIE, IBE, SAB are abbreviations for manufacturing processes in the semiconductor, solar and other industries that involve surface treatment. These processed are often performed in plasma reactors, using a plasma of gas mixtures or vapour. 

Deposition techniques

  • CVD: Chemical Vapor Deposition
  • PVD: Physical Vapor Deposition 
  • ALD: Atomic Layer Deposition

Laptop screen; example of chemical vapour deposition – CVD
Laptop screen; example of chemical vapour deposition – CVD

These vapor and layer desposition processes are designed to apply a really thin coating with thicknesses of nanometres to micrometres. Most glass windows have a thin anti-reflection coating applied by physical vapor deposition - PVD.

Your computer monitor, you are now probably looking at, contains millions of pixels made by chemical vapor deposition - CVD.

You can read more about these surface treatment techniques on our website

Etching techniques

  • RIE means Reactive Ion Etching
  • IBE means Ion Beam Etching
These etching techniques are used for removing selected areas in the surface of a semiconductor chip or sensor chip.

Surface Activated Bonding - SAB

Surface Activated Bonding technique is applied in the manufacturing of sensors and electronic circuit boards. 

Flow system for plasma reactor

In cooperation with system builders, Bronkhorst serves end-users by supplying complete flow & pressure control systems. A possible construction of a flow & pressure control system for plasma processes is shown in the flow diagram. 

Flow controllers add gases to the reactor chamber, where the gases are ignited into a plasma and used in the desired reaction with the inserted material. The pressure regulator plays an important role. It diverts the excess gases out of the reactor chamber, while maintaining on optimal process pressure. 

In this setup an evaporating system - Controlled Evaporator Module (CEM) - in combination with liquid flow controller and gas flow controller, supplies a vapor to a plasma reactor. Together with the gas flow controller below the CEM, which can add an extra gas, they create the perfect process conditions for the reactor chamber where the gases are ignited by a plasma.

The lower gas flow controller is used for the purge gas, usually nitrogen, which is used to flush out any unwanted gases from the reactor chamber after the process. An electronic pressure regulator directs the excess gas mixture away from the reactor chamber while maintaining the pressure in the process.

Setup Evaporation system with liquid- and gas flow controllers
Setup Evaporation system with liquid- and gas flow controllers

Would you like more information about controllers for plasma?

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