Titre de la dissertation: « A study on hot-target magnetron sputtering assisted by intense thermionic emission

Promoteurs de thèse: Monsieur Rony Snyders et Monsieur Stéphanos Konstantinidis

Résumé de la dissertation: Magnetron sputtering is a widespread technique to synthesize thin films for numerous applications. However, to keep up with ongoing technological progress, it calls for various improvements, particularly in the deposition rate, to increase the process productivity. In this pursuit, the concept of hot-target magnetron sputtering (HMS) discharge has emerged. In the HMS case, the sputter target is thermally insulated from a water-cooled cathode. This configuration allows applying higher power densities to the cathode, resulting in enhanced erosion and thereby deposition rates. Simultaneously, the ion bombardment leads to target heating, which may induce sublimation of the target atoms and/or amplify thermal electron emission.The HMS discharges have been studied over decades, but the research has primarily focused on sputter materials like copper (Cu) or chromium (Cr), where evaporation is the main mechanism defining high sputtering rate. Meanwhile, the HMS of refractory metals, such as niobium (Nb), represents a rather special case, when sublimation of surface atoms is barely achievable and the deposition rate can be increased only proportionally to the applied power. Nevertheless, Nb target heating beyond 1700 K, which typically cannot be attained with Cu or Cr, can amplify thermal electron emission from its surface, which may alter plasma properties and affect coating growth mechanisms.This PhD thesis is focused on studying the plasma dynamics during a direct current (DC) hot-target magnetron sputtering discharge with a Nb target and correlating the found plasma properties with the obtained coating structure. The plasma behaviour has been analysed by non-intrusive spectroscopic methods. Meanwhile, the target temperature, a key parameter in the HMS discharges, has been measured by three different approaches. The results have shown that when target temperatures exceed 1900 K, thermionic emission becomes prominent, facilitating the ionization of sputtered metal atoms. In addition, an attempt has been made to unravel the relationship between working parameters, plasma behaviour, and coating structure for gaining better control over the sputtering process with a hot target.