SEM IMAGE-ANALYSIS OF DROPLET FORMATION DURING METAL-ION ETCHING BY ASTEERED ARE DISCHARGE

During cathodic are metal ion etching a pronounced influence of the me lting point of the target material on droplet formation was found. Low melting point materials showed quite an enhanced tendency to generate droplets with respect to number and size. Under the process parameter s used the TiAl alloy target showed the highest number of droplets gen erated (100 x 10(3) mm(-2)). Even using target materials with high mel ting points such as Zr (MP: 1850 degrees C), Cr (MP: 1870 degrees C) a nd Nb (MP: 2450 degrees C) severe differences were observed. Cr played a special role as 90% of its droplets were smaller than 0.5 mu m. For Zr with a melting point close to Cr the same percentage of droplets w ere less than 0.80 mu m in diameter, clearly indicating a larger avera ge droplet diameter. On the other hand, among the high melting materia ls the number of Cr droplets was 5 times higher than that of Nb and tw ice as high as that of Zr. Metals with melting points greater than 200 0 degrees C showed very similar effects of droplet generation, with me an droplet densities of 3-5 x 10(3) mm(-2) A comparison between the as -etched and UBM coated samples indicates that the number of droplets d eposited during the etching phase with TiAl and Mo formed an identical number of growth defects in the coating. In the case of Cr the number of defects on top of the coated surface was less than the number of d roplets deposited during the etching phase. (C) 1997 Elsevier Science S.A.