MECHANISM OF TIN FILM DEPOSITION BY REACTIVE EVAPORATION MEASURED BY A QUARTZ-CRYSTAL MICROBALANCE

Three quantities must be known for investigation of the reaction mecha nism of reactive evaporated TiN coatings: the impingement of nitrogen molecules and of titanium atoms on the surface of the TiN film and the rate of TiN formation. The nitrogen impingement can be easily determi ned by measuring the nitrogen partial pressure in the reactor. The tot al rate of reacted TIN can be measured very accurately by a quartz cry stal microbalance (QCM). Determination of the third quantity, the tita nium impingement, faces some difficulties. The titanium flux to the su rface of the film cannot simply be extrapolated by measuring the evapo ration rate of the source in vacuum because nitrogen gas changes the s ituation in two ways, The titanium atoms are scattered on their way fr om the evaporation source to the TiN film surface by collisions with n itrogen gas molecules, and the evaporation source itself is poisoned b y nitrogen reactions and changes its evaporation characteristics. Thre e possibilities for measurement of the titanium flux were tested in th e present work. (1) Experiments with low nitrogen partial pressure and low titanium evaporation rates were performed in order to avoid scatt ering. The evaporation rate was measured by the QCM under vacuum condi tions. (2) The titanium flux was determined by an optical spectrometer . (3) The titanium flux was determined by a quadrupole mass analyser. Advantages and disadvantages of the three methods are discussed and re sults of the reaction rates are presented. The measurements show that below an impingement ratio [N]/[Ti]=1 no detectable nitrogen is incorp orated in the film. At higher impingement ratios the composition of th e him is changed and at an impingement ratio [N]/[Ti]=20 a stoichiomet ric TiN film is formed. The experimental results are compared with mod el calculations.