Plasma Processes for Manufacturing Matthew Sargeant, University of Wisconsin Stout

1. Plasma Processes for Manufacturing Matthew Sargeant, University of Wisconsin Stout History Types of Plasma Processes BACKGROUND Plasma activation – is a method of functionalizing a surface by means of plasma processing. Is used with the intent to improve adhesive properties of surfaces prior to coating, painting, etc. often times a weakly ionizing oxygen plasma is used. Works by removing weak boundary layers. The plasma removes surfaces with the lowest molecular weight and simultaneously oxidizes the uppermost atomic layer of the polymer. Plasma etching – Is a form of plasma processing used to fabricate integrated circuits. Uses high-speed stream of plasma in an appropriate mixture of gases being shot at the sample. The shot atom’s elements embed themselves at or just below the surface of the target, thus modifying the physical properties of the target. Plasma etching systems ionise a variety of gases in a vacuum system by using RF excitations, the frequency used is most often 13.56 MHz which is on of the frequencies reserved worldwide for industrial, scientific, and medical uses (ISM). Plasma functionalization – is a method of functionalizing a surface by means of plasma processing. Is done with the intent to alter or improve adhesion properties of surfaces prior to coating, painting, etc. Plasma polymerization – uses plasma sources to generate a gas discharge that provides energy to activate or fragment gaseous or liquid monomer, often containing a vinyl group, in order to initiate polymerization. Polymers formed with this process have many benefits first of all they are highly branched and highly cross-linked, also they adhere to solid surfaces well, another major advantage of this process is that polymers can be directly attached to a desired surface while the chains are growing, which reduces steps necessary for other coating processes such as grafting. Creates pinhole free coatings of 100 Pico meters to 1 micrometer thick. A green aspect of this plasma process is that there are no preparation chemicals and no clean-up chemicals involved. A disadvantage of this process is that it is costly to set up due to the fact that it requires vacuum conditions to operate. Another disadvantage is the complexity of the plasma process, because there is a zoo of new particles/molecules made during the process that it is difficult to discover the optimal operating conditions without a lot of trial and error. Which also makes it impossible to predict what the resulting polymer will look like. Some applications of this technology range form adhesion, composite materials, protective coatings, printing, membranes, biomedical applications, water purification and so on. Plasma cleaning – involves the removal of impurities and contaminants from surfaces through the use of an energetic plasma or Dielectric barrier discharge (DBD) plasma created from gaseous species. The plasma is created by using high frequency voltages to ionize the low pressure gas. Great for reacting with organic compounds. Plasma electrolytic oxidation – also known as micro arc oxidation (MAO), is an electrochemical surface treatment process for generating oxide coatings on metals. This process can be used to grow thick largely crystalline, oxide coatings on metals such as aluminum, magnesium and titanium. And because they can present high hardness and a continuous barrier, these coatings can offer protection against wear, corrosion or heat as well as electrical insulation. In the plasma electrolytic oxidation of aluminum, at least 200 V must be applied. This locally exceeds the dielectric breakdown potential of the growing oxide film, and plasma discharges occur. The most significant effects, is that the oxide is partially converted from amorphous alumina into crystalline forms such as corundum which is much harder. As a result, mechanical properties such as wear resistance and toughness are enhanced. A plasma is a source of ions that can be accelerated under an electric field to high kinetic energies, and those ion can be used to apply a thin coating to a surface. Plasma chemistry is becoming more complex and is being used more to create innovative and functional surfaces for a wide variety use of applications. When blood is cleared of its various corpuscles there remains a clear liquid, named “plasma” by the great Czech medical scientist, Johannes Purkinje (1787-1869). Irving Langmuir (1881-1957), an American started referring to plasma as an phenomena that occurred when gasses became ionized because the way that electric fields carried high velocity electrons, ions and impurities reminded him of the way blood plasma carried red and white corpuscles and germs. Later the development of radio led to the discovery of the ionosphere, the natural “plasma roof” above the atmosphere. Also the realization by astronomer that most of the universe appeared to be made up of plasma, which was particularly true of the sun. The idea eventually came along that if high temperature plasma could be trapped within a powerful magnetic field that perhaps a controlled nuclear fusion reaction could controlled and maintains for cheap abundant energy. The surface of a MEMS device is cleaned with bright, blue oxygen plasma in a plasma etcher to rid it of carbon contaminants. (100mTorr, 50W RF) Schematic representation of basic internal electrode glow discharge polymerization apparatus. References Wikipedia contributors. "Plasma processing." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 11 Jun. 2013. Web. 10 Nov. 2013. Wikipedia contributors. "Plasma activation." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 12 May. 2013. Web. 10 Nov. 2013. Wikipedia contributors. "Plasma etching." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 19 Mar. 2013. Web. 10 Nov. 2013. Wikipedia contributors. "Plasma activation." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 12 May. 2013. Web. 10 Nov. 2013 Wikipedia contributors. "Plasma polymerization." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 19 Oct. 2013. Web. 10 Nov. 2013. Wikipedia contributors. "Plasma cleaning." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 15 Aug. 2013. Web. 10 Nov. 2013. Wikipedia contributors. "Plasma electrolytic oxidation." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 11 Apr. 2013. Web. 10 Nov. 2013 http://www-spof.gsfc.nasa.gov/Education/whplasma.html Walton, Scott G. “An Overview of Plasma Processes” Bulletin. Spring 2012: 46-53. Print Hypothesized model of plasma-polymerized ethylene film. Plasma Properties Is an ionized gas where the number of positively charged species are equal to the number of positively charged species. A plasma has a plasma density which is the number of negative or positive charges per unit volume. Most commonly the plasma density refers to the negatively charged portion of the plasma otherwise known as the number of electrons per unit volume the density is related to the pressure conditions the plasma is under and the average electron energy is expressed in terms of electron temperature (Te) and is measured in electron volts (eV).