CORRELATION BETWEEN STRUCTURE AND PROPERTIES OF REACTIVELY DEPOSITED AL2O3 COATINGS BY PULSED MAGNETRON SPUTTERING

It has already been shown that substrate temperature and plasma densit y have a pronounced influence on the formation of crystalline Al2O3 ph ases. This paper deals with the correlation between structure and prop erties of reactively sputtered Al2O3 layers. The layers were deposited at substrate temperatures between 300 and 800 degrees C. The structur e was investigated by XRD and cross-section TEM. With increasing subst rate temperature, a phase transition from amorphous into alpha Al2O3 v ia gamma Al2O3 is observed. An enhancement of the plasma density shift s the formation of crystalline phases to lower substrate temperatures. It would appear that the growth of the crystalline layers starts with the formation of globulitic gamma crystallites. With increasing layer thickness, columnar gamma crystallites with a lateral grain size of a bout 60 to 100 nm and a pronounced (110) fiber texture occur. In addit ion, wedge-shaped alpha crystallites are present. With increasing laye r thickness these alpha crystallites reach a lateral grain size of abo ut 1 mu m. The SAD investigations indicate that a grain epitaxy betwee n the gamma and the alpha phase is present. The properties of the laye rs, e.g. hardness and chemical stability, depend strongly on the occur rence of crystalline phases. (C) 1997 Elsevier Science S.A.