Fundamentals Of Pulsed Bias Arc Ion Plating

Arc Ion Plating(AIP)is one of the most common PVD coating techniques(together with magnetron sputtering and evaporation coating)widely applied in industries.As the main method for synthesizing TiN-type hard coatings,it has produced a profound revolution in cutting tool technology in the last 80's.However,conventional AIP suffers from problems such as droplet contamination,high deposition temperature and microarc breakdown,which have imposed limitations on its applications in fine coatings like functional films.The solutions to these problems have always been the hot issues for the AIP researchers as well as in the whole coating community.Emerged in the late 20th century,Pulsed Bias Arc Ion Plating(PBAIP)is an advanced ion plating technique which brings hopes to solving the many problems of conventional AIP. Despite of its many unique advantages,this technique has not been applied in industries widely and quickly as expected,principally due to insufficient understanding about its fundamentals.Therefore the present thesis focuses on a few key issues in relation to the PBAIP fundamentals,with the objective of expanding the capability and application range of this technique.The conclusions are important not only to PBAIP itself but also to the development of ion plating techniques as a whole.1.Plasma load characteristics of PBAIPComplex non-linear behavior is observed in measuredâ… -â…¤curves in the plasma load loop, which reflects a mixed capacitance and resistance nature for the pulsed bias case according to plasma sheath theory and to simulated electrical circuit analogous analysis,in sharp contrast to nearly linear relationship for the DC bias case.A plasma load macro circuit model is thus established,where the PBAIP plasma load is represented by electrical circuit unit consisting of parallel capacitor and resistor,where the relevant capacitance and resistance can be quantitatively described by plasma sheath theory.Via such a model,the relationships between plasma load,pulse electric parameters and plasma micro parameters are established.Using Langrnuir probe,plasma mciro parameters are obtained for normal working conditions: electron temperature in plasma T_e=2.51～6.64eV,plasma density n_e～10¹⁸m^-3,plasma space potential V_p=+5～+15V.Plasma load capacitance is in the range of 10^-2～10^-1μF and the resistance is about a few hundred ohms using plasma mciro parameters.The determination of the plasma load characteristics is an important guide towards further investigations of the PBAIP fundamentals and of the design of pulse bias power sources.By applying the above-mentioned plasma load characteristics,the differences induced by DC and pulse biases are explained such as the failure of pulse bias power source unit,substrate deposition temperature prediction,working process repeatability,as well as power source design.Effective measures can then be put t0rward in practice tor enhancing the stability of working process control.2.Deposition temperature predictionOur new pulse power source generates regular pulse profiles so that bombarding energy of the ions can be fitted out.Using this input energy,it is then possible to calculate the substrate deposition temperature under different conditions using an energy balance equation.The measured temperatures match satisfactorily with the calculation,within an error of 50K.Such a calculation would play an important role in prediction of deposition temperature and the realization of widely demanded low-temperature depositions.3.Droplet particle elimination mechanismAs proved by our own experiments,the droplet particle elimination is not due to ion bombardment.A droplet particle cleaning mechanism is established using an analysis of particle movement in plasma space and in plasma sheath:the elimination is due to Coulomb repulsion force between negatively charged particles and the negatively biased substrate. Orthogonal experiments as well as force analysis have been performed,proving that,in the mode of pulsed biases,the oscillating plasmas sheath induces more negative charging in the particles so that the repulsive effect is more pronounced.The particle cleaning mechanism contributes an important guide to process optimization aiming at improved surface quality.Even without filtering,PBAIP can deposit multi-layers, achieving a substantial extension of AIP towards fine coatings.4.Feasibility of depositing insulation filmsA series of TiO2 films are obtained in self-designed PBAIP facility equipped with magnet-enhanced arc sources.The deposited TiO2 films show high density and their structure and properties are sensitively dependent on pulsed biases.The results are explained using a pulsed bias plasma sheath model on an insulating substrate and the necessary conditions for obtaining insulating films using PBAIP are revealed:(1).Micro-arcing suppression condition,i.e.the substrate surface charging should not exceed the substrate breakdown limitation(2).The condition to control deposition,i.e.the effective ion acceleration potential should be above zero.After the above two conditions are met,assisted by droplet particle elimination,PBAIP will have a great potential for the synthesis of insulating functional films.Since the differences of ion plating techniques lie in the modes of ion generation and the ions are all controlled by bias in similar manners,the above results may equally apply in other types of ion plating techniques such as unbalanced magnetron sputtering,hollow cathode ion plating and varieties of plasma-enhanced vapor deposition processes.