Study of Plasma System by OES (Optical Emission Spectroscopy)

Low-temperature and low-pressure plasma was investigated by OES (optical emission spectroscopy) in the range 200–1100 nm. For displaying measured emission spectra and identification of spectrum lines the software Spectrum Analyzer was used. Two modes of glow discharge present in the DC cylindrical magnetron apparatus which were previously researched by a mass spectrometer were studied by OES. The changes in the spectral range 300–600 nm during the transition between discharge modes are contributed to the emission of metal particles sputtered from the cathode material. Introduction At the present time magnetron sputtering systems are widely used for deposition of thin films with unique physical or chemical characteristics in a variety of industry branches e.g. in microelectronics, cutting tools or reflecting layers manufacture. In the cylindrical magnetron the dc discharge is created by the radial electric field and discharge plasma is confined by a magnetic field applied parallel to the axis. Crossed electric and magnetic fields cause E×B drift of charged particles. Study of electron drift velocity was described in work [Borah et al., 2010]. High-energy electrons are confined in the vicinity of the cathode in E×B drift loops. These electrons help to ionize neutral noble gas atoms. Created positive ions are accelerated towards the cathode with high energy and they bombard of cathode causes secondary electron emission and sputtering atoms from the cathode. Sputtered material of the cathode deposits thin films on the substrate placed near the anode. By injection reactive gas (e.g. oxygen, nitrogen) to the discharge chamber, it is possible to fabricate extremely hard layers of oxides and nitrides of the sputtered material for a various applications (e.g. solar cells, flat panel display). Reactive magnetron sputtering allows obtain a large composition range of layers by controlling the injected reactive gas. The demand to create high quality thin films increases and it requires to make systematic experimental studies of the spatial and temporal plasma parameters and to investigate correlation between the properties of the processing plasma and the characteristics of the deposited films during the deposition in the magnetron sputtering system. The most common plasma diagnostic method is Langmuir probe [Pfau et al., 2000], which is widely used to estimate plasma parameters. This method is comparatively cheap and easily technically practicable. Optical emission spectroscopy can be used as a mutually complementary method to the probe diagnostic. The technique of the optical emission spectroscopy is non-invasive, easy to implement and measurements are fast. Method of OES is passive and based on recording light emitted from the plasma. Through collisions of plasma particles with electrons, plasma particles are excited to higher electronic states. Relaxation of excited particles, which are present in the chamber, to lower energy states is the origin of emitted photons of light. Energy of released photon is equal to the difference between excited and lower energy state and corresponding with wavelength of spectral line described by relation: